summaryrefslogtreecommitdiff
path: root/compiler/GHC/Tc/Module.hs
blob: 42f0a3fddc1aadad874c6aae22b6fe59c22a02fc (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
{-# LANGUAGE CPP #-}
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE NondecreasingIndentation #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE FlexibleContexts #-}

{-# OPTIONS_GHC -Wno-incomplete-record-updates #-}

{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

-}

-- | Typechecking a whole module
--
-- https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/type-checker
module GHC.Tc.Module (
        tcRnStmt, tcRnExpr, TcRnExprMode(..), tcRnType,
        tcRnImportDecls,
        tcRnLookupRdrName,
        getModuleInterface,
        tcRnDeclsi,
        isGHCiMonad,
        runTcInteractive,    -- Used by GHC API clients (#8878)
        tcRnLookupName,
        tcRnGetInfo,
        tcRnModule, tcRnModuleTcRnM,
        tcTopSrcDecls,
        rnTopSrcDecls,
        checkBootDecl, checkHiBootIface',
        findExtraSigImports,
        implicitRequirements,
        checkUnit,
        mergeSignatures,
        tcRnMergeSignatures,
        instantiateSignature,
        tcRnInstantiateSignature,
        loadUnqualIfaces,
        -- More private...
        badReexportedBootThing,
        checkBootDeclM,
        missingBootThing,
        getRenamedStuff, RenamedStuff
    ) where

import GHC.Prelude

import GHC.Driver.Env
import GHC.Driver.Plugins
import GHC.Driver.Session

import GHC.Tc.Errors.Hole.FitTypes ( HoleFitPluginR (..) )
import {-# SOURCE #-} GHC.Tc.Gen.Splice ( finishTH, runRemoteModFinalizers )
import GHC.Tc.Gen.HsType
import GHC.Tc.Validity( checkValidType )
import GHC.Tc.Gen.Match
import GHC.Tc.Utils.Unify( checkConstraints )
import GHC.Tc.Utils.Zonk
import GHC.Tc.Gen.Expr
import GHC.Tc.Gen.App( tcInferSigma )
import GHC.Tc.Utils.Monad
import GHC.Tc.Gen.Export
import GHC.Tc.Types.Evidence
import GHC.Tc.Types.Constraint
import GHC.Tc.Types.Origin
import GHC.Tc.Instance.Family
import GHC.Tc.Gen.Annotation
import GHC.Tc.Gen.Bind
import GHC.Tc.Gen.Default
import GHC.Tc.Utils.Env
import GHC.Tc.Gen.Rule
import GHC.Tc.Gen.Foreign
import GHC.Tc.TyCl.Instance
import GHC.Tc.Utils.TcMType
import GHC.Tc.Utils.TcType
import GHC.Tc.Utils.Instantiate (tcGetInsts)
import GHC.Tc.Solver
import GHC.Tc.TyCl
import GHC.Tc.Instance.Typeable ( mkTypeableBinds )
import GHC.Tc.Utils.Backpack

import GHC.Rename.Splice ( rnTopSpliceDecls, traceSplice, SpliceInfo(..) )
import GHC.Rename.HsType
import GHC.Rename.Expr
import GHC.Rename.Utils  ( HsDocContext(..) )
import GHC.Rename.Fixity ( lookupFixityRn )
import GHC.Rename.Names
import GHC.Rename.Env
import GHC.Rename.Module

import GHC.Iface.Syntax   ( ShowSub(..), showToHeader )
import GHC.Iface.Type     ( ShowForAllFlag(..) )
import GHC.Iface.Env     ( externaliseName )
import GHC.Iface.Make   ( coAxiomToIfaceDecl )
import GHC.Iface.Load

import GHC.Builtin.Types ( unitTy, mkListTy )
import GHC.Builtin.Names
import GHC.Builtin.Utils

import GHC.Hs
import GHC.Hs.Dump

import GHC.Core.PatSyn    ( pprPatSynType )
import GHC.Core.Predicate ( classMethodTy )
import GHC.Core.FVs         ( orphNamesOfFamInst )
import GHC.Core.InstEnv
import GHC.Core.TyCon
import GHC.Core.ConLike
import GHC.Core.DataCon
import GHC.Core.Type
import GHC.Core.Class
import GHC.Core.Coercion.Axiom
import GHC.Core.Unify( RoughMatchTc(..) )
import GHC.Core.FamInstEnv
   ( FamInst, pprFamInst, famInstsRepTyCons
   , famInstEnvElts, extendFamInstEnvList, normaliseType )

import GHC.Parser.Header       ( mkPrelImports )

import GHC.IfaceToCore

import GHC.Runtime.Context

import GHC.Utils.Error
import GHC.Utils.Outputable as Outputable
import GHC.Utils.Panic
import GHC.Utils.Misc
import GHC.Utils.Logger

import GHC.Types.Error
import GHC.Types.Name.Reader
import GHC.Types.Fixity.Env
import GHC.Types.Id as Id
import GHC.Types.Id.Info( IdDetails(..) )
import GHC.Types.Var.Env
import GHC.Types.TypeEnv
import GHC.Types.Unique.FM
import GHC.Types.Name
import GHC.Types.Name.Env
import GHC.Types.Name.Set
import GHC.Types.Avail
import GHC.Types.Basic hiding( SuccessFlag(..) )
import GHC.Types.Annotations
import GHC.Types.SrcLoc
import GHC.Types.SourceText
import GHC.Types.SourceFile
import GHC.Types.TyThing.Ppr ( pprTyThingInContext )
import qualified GHC.LanguageExtensions as LangExt

import GHC.Unit.External
import GHC.Unit.Types
import GHC.Unit.State
import GHC.Unit.Home
import GHC.Unit.Module
import GHC.Unit.Module.Warnings
import GHC.Unit.Module.ModSummary
import GHC.Unit.Module.ModIface
import GHC.Unit.Module.ModDetails
import GHC.Unit.Module.Deps

import GHC.Data.FastString
import GHC.Data.Maybe
import GHC.Data.List.SetOps
import GHC.Data.Bag
import qualified GHC.Data.BooleanFormula as BF

import Data.List ( find, sortBy, sort )
import Data.Ord
import Data.Data ( Data )
import qualified Data.Set as S
import Control.DeepSeq
import Control.Monad

#include "HsVersions.h"

{-
************************************************************************
*                                                                      *
        Typecheck and rename a module
*                                                                      *
************************************************************************
-}

-- | Top level entry point for typechecker and renamer
tcRnModule :: HscEnv
           -> ModSummary
           -> Bool              -- True <=> save renamed syntax
           -> HsParsedModule
           -> IO (Messages DecoratedSDoc, Maybe TcGblEnv)

tcRnModule hsc_env mod_sum save_rn_syntax
   parsedModule@HsParsedModule {hpm_module= L loc this_module}
 | RealSrcSpan real_loc _ <- loc
 = withTiming logger dflags
              (text "Renamer/typechecker"<+>brackets (ppr this_mod))
              (const ()) $
   initTc hsc_env hsc_src save_rn_syntax this_mod real_loc $
          withTcPlugins hsc_env $ withHoleFitPlugins hsc_env $

          tcRnModuleTcRnM hsc_env mod_sum parsedModule pair

  | otherwise
  = return (err_msg `addMessage` emptyMessages, Nothing)

  where
    hsc_src = ms_hsc_src mod_sum
    dflags  = hsc_dflags hsc_env
    logger  = hsc_logger hsc_env
    home_unit = hsc_home_unit hsc_env
    err_msg = mkPlainMsgEnvelope loc $
              text "Module does not have a RealSrcSpan:" <+> ppr this_mod

    pair :: (Module, SrcSpan)
    pair@(this_mod,_)
      | Just (L mod_loc mod) <- hsmodName this_module
      = (mkHomeModule home_unit mod, mod_loc)

      | otherwise   -- 'module M where' is omitted
      = (mkHomeModule home_unit mAIN_NAME, srcLocSpan (srcSpanStart loc))




tcRnModuleTcRnM :: HscEnv
                -> ModSummary
                -> HsParsedModule
                -> (Module, SrcSpan)
                -> TcRn TcGblEnv
-- Factored out separately from tcRnModule so that a Core plugin can
-- call the type checker directly
tcRnModuleTcRnM hsc_env mod_sum
                (HsParsedModule {
                   hpm_module =
                      (L loc (HsModule _ maybe_mod export_ies
                                       import_decls local_decls mod_deprec
                                       maybe_doc_hdr)),
                   hpm_src_files = src_files
                })
                (this_mod, prel_imp_loc)
 = setSrcSpan loc $
   do { let { explicit_mod_hdr = isJust maybe_mod
            ; hsc_src          = ms_hsc_src mod_sum }
      ; -- Load the hi-boot interface for this module, if any
        -- We do this now so that the boot_names can be passed
        -- to tcTyAndClassDecls, because the boot_names are
        -- automatically considered to be loop breakers
        tcg_env <- getGblEnv
      ; boot_info <- tcHiBootIface hsc_src this_mod
      ; setGblEnv (tcg_env { tcg_self_boot = boot_info })
        $ do
        { -- Deal with imports; first add implicit prelude
          implicit_prelude <- xoptM LangExt.ImplicitPrelude
        ; let { prel_imports = mkPrelImports (moduleName this_mod) prel_imp_loc
                               implicit_prelude import_decls }

        ; whenWOptM Opt_WarnImplicitPrelude $
             when (notNull prel_imports) $
                addWarn (Reason Opt_WarnImplicitPrelude) (implicitPreludeWarn)

        ; -- TODO This is a little skeevy; maybe handle a bit more directly
          let { simplifyImport (L _ idecl) =
                  ( fmap sl_fs (ideclPkgQual idecl) , ideclName idecl)
              }
        ; raw_sig_imports <- liftIO
                             $ findExtraSigImports hsc_env hsc_src
                                 (moduleName this_mod)
        ; raw_req_imports <- liftIO
                             $ implicitRequirements hsc_env
                                (map simplifyImport (prel_imports
                                                     ++ import_decls))
        ; let { mkImport (Nothing, L _ mod_name) = noLoc
                $ (simpleImportDecl mod_name)
                  { ideclHiding = Just (False, noLoc [])}
              ; mkImport _ = panic "mkImport" }
        ; let { all_imports = prel_imports ++ import_decls
                       ++ map mkImport (raw_sig_imports ++ raw_req_imports) }
        ; -- OK now finally rename the imports
          tcg_env <- {-# SCC "tcRnImports" #-}
                     tcRnImports hsc_env all_imports

        ; -- If the whole module is warned about or deprecated
          -- (via mod_deprec) record that in tcg_warns. If we do thereby add
          -- a WarnAll, it will override any subsequent deprecations added to tcg_warns
          let { tcg_env1 = case mod_deprec of
                             Just (L _ txt) ->
                               tcg_env {tcg_warns = WarnAll txt}
                             Nothing            -> tcg_env
              }
        ; setGblEnv tcg_env1
          $ do { -- Rename and type check the declarations
                 traceRn "rn1a" empty
               ; tcg_env <- if isHsBootOrSig hsc_src
                            then tcRnHsBootDecls hsc_src local_decls
                            else {-# SCC "tcRnSrcDecls" #-}
                                 tcRnSrcDecls explicit_mod_hdr local_decls export_ies

               ; whenM (goptM Opt_DoCoreLinting) $
                 lintGblEnv (hsc_logger hsc_env) (hsc_dflags hsc_env) tcg_env

               ; setGblEnv tcg_env
                 $ do { -- Process the export list
                        traceRn "rn4a: before exports" empty
                      ; tcg_env <- tcRnExports explicit_mod_hdr export_ies
                                     tcg_env
                      ; traceRn "rn4b: after exports" empty
                      ; -- Compare hi-boot iface (if any) with the real thing
                        -- Must be done after processing the exports
                        tcg_env <- checkHiBootIface tcg_env boot_info
                      ; -- The new type env is already available to stuff
                        -- slurped from interface files, via
                        -- GHC.Tc.Utils.Env.setGlobalTypeEnv. It's important that this
                        -- includes the stuff in checkHiBootIface,
                        -- because the latter might add new bindings for
                        -- boot_dfuns, which may be mentioned in imported
                        -- unfoldings.

                        -- Don't need to rename the Haddock documentation,
                        -- it's not parsed by GHC anymore.
                        tcg_env <- return (tcg_env
                                           { tcg_doc_hdr = maybe_doc_hdr })
                      ; -- Report unused names
                        -- Do this /after/ type inference, so that when reporting
                        -- a function with no type signature we can give the
                        -- inferred type
                        reportUnusedNames tcg_env hsc_src
                      ; -- add extra source files to tcg_dependent_files
                        addDependentFiles src_files
                      ; tcg_env <- runTypecheckerPlugin mod_sum tcg_env
                      ; -- Dump output and return
                        tcDump tcg_env
                      ; return tcg_env }
               }
        }
      }

implicitPreludeWarn :: SDoc
implicitPreludeWarn
  = text "Module `Prelude' implicitly imported"

{-
************************************************************************
*                                                                      *
                Import declarations
*                                                                      *
************************************************************************
-}

tcRnImports :: HscEnv -> [LImportDecl GhcPs] -> TcM TcGblEnv
tcRnImports hsc_env import_decls
  = do  { (rn_imports, rdr_env, imports, hpc_info) <- rnImports import_decls ;

        ; this_mod <- getModule
        ; let { dep_mods :: ModuleNameEnv ModuleNameWithIsBoot
              ; dep_mods = imp_dep_mods imports

                -- We want instance declarations from all home-package
                -- modules below this one, including boot modules, except
                -- ourselves.  The 'except ourselves' is so that we don't
                -- get the instances from this module's hs-boot file.  This
                -- filtering also ensures that we don't see instances from
                -- modules batch (@--make@) compiled before this one, but
                -- which are not below this one.
              ; want_instances :: ModuleName -> Bool
              ; want_instances mod = mod `elemUFM` dep_mods
                                   && mod /= moduleName this_mod
              ; (home_insts, home_fam_insts) = hptInstances hsc_env
                                                            want_instances
              } ;

                -- Record boot-file info in the EPS, so that it's
                -- visible to loadHiBootInterface in tcRnSrcDecls,
                -- and any other incrementally-performed imports
        ; updateEps_ (\eps -> eps { eps_is_boot = dep_mods }) ;

                -- Update the gbl env
        ; updGblEnv ( \ gbl ->
            gbl {
              tcg_rdr_env      = tcg_rdr_env gbl `plusGlobalRdrEnv` rdr_env,
              tcg_imports      = tcg_imports gbl `plusImportAvails` imports,
              tcg_rn_imports   = rn_imports,
              tcg_inst_env     = extendInstEnvList (tcg_inst_env gbl) home_insts,
              tcg_fam_inst_env = extendFamInstEnvList (tcg_fam_inst_env gbl)
                                                      home_fam_insts,
              tcg_hpc          = hpc_info
            }) $ do {

        ; traceRn "rn1" (ppr (imp_dep_mods imports))
                -- Fail if there are any errors so far
                -- The error printing (if needed) takes advantage
                -- of the tcg_env we have now set
--      ; traceIf (text "rdr_env: " <+> ppr rdr_env)
        ; failIfErrsM

                -- Load any orphan-module (including orphan family
                -- instance-module) interfaces, so that their rules and
                -- instance decls will be found.  But filter out a
                -- self hs-boot: these instances will be checked when
                -- we define them locally.
                -- (We don't need to load non-orphan family instance
                -- modules until we either try to use the instances they
                -- define, or define our own family instances, at which
                -- point we need to check them for consistency.)
        ; loadModuleInterfaces (text "Loading orphan modules")
                               (filter (/= this_mod) (imp_orphs imports))

                -- Check type-family consistency between imports.
                -- See Note [The type family instance consistency story]
        ; traceRn "rn1: checking family instance consistency {" empty
        ; let { dir_imp_mods = moduleEnvKeys
                             . imp_mods
                             $ imports }
        ; checkFamInstConsistency dir_imp_mods
        ; traceRn "rn1: } checking family instance consistency" empty

        ; getGblEnv } }

{-
************************************************************************
*                                                                      *
        Type-checking the top level of a module
*                                                                      *
************************************************************************
-}

tcRnSrcDecls :: Bool  -- False => no 'module M(..) where' header at all
             -> [LHsDecl GhcPs]               -- Declarations
             -> Maybe (Located [LIE GhcPs])
             -> TcM TcGblEnv
tcRnSrcDecls explicit_mod_hdr decls export_ies
 = do { -- Do all the declarations
      ; (tcg_env, tcl_env, lie) <- tc_rn_src_decls decls

        -- Check for the 'main' declaration
        -- Must do this inside the captureTopConstraints
        -- NB: always set envs *before* captureTopConstraints
      ; (tcg_env, lie_main) <- setEnvs (tcg_env, tcl_env) $
                               captureTopConstraints $
                               checkMain explicit_mod_hdr export_ies

      ; setEnvs (tcg_env, tcl_env) $ do {

             --         Simplify constraints
             --
             -- We do this after checkMain, so that we use the type info
             -- that checkMain adds
             --
             -- We do it with both global and local env in scope:
             --  * the global env exposes the instances to simplifyTop
             --  * the local env exposes the local Ids to simplifyTop,
             --    so that we get better error messages (monomorphism restriction)
      ; new_ev_binds <- {-# SCC "simplifyTop" #-}
                        simplifyTop (lie `andWC` lie_main)

        -- Emit Typeable bindings
      ; tcg_env <- mkTypeableBinds


      ; traceTc "Tc9" empty

      ; failIfErrsM     -- Don't zonk if there have been errors
                        -- It's a waste of time; and we may get debug warnings
                        -- about strangely-typed TyCons!
      ; traceTc "Tc10" empty

        -- Zonk the final code.  This must be done last.
        -- Even simplifyTop may do some unification.
        -- This pass also warns about missing type signatures
      ; (bind_env, ev_binds', binds', fords', imp_specs', rules')
            <- zonkTcGblEnv new_ev_binds tcg_env

        -- Finalizers must run after constraints are simplified, or some types
        -- might not be complete when using reify (see #12777).
        -- and also after we zonk the first time because we run typed splices
        -- in the zonker which gives rise to the finalisers.
      ; (tcg_env_mf, _) <- setGblEnv (clearTcGblEnv tcg_env)
                                     run_th_modfinalizers
      ; finishTH
      ; traceTc "Tc11" empty

      ; -- zonk the new bindings arising from running the finalisers.
        -- This won't give rise to any more finalisers as you can't nest
        -- finalisers inside finalisers.
      ; (bind_env_mf, ev_binds_mf, binds_mf, fords_mf, imp_specs_mf, rules_mf)
            <- zonkTcGblEnv emptyBag tcg_env_mf


      ; let { final_type_env = plusTypeEnv (tcg_type_env tcg_env)
                                (plusTypeEnv bind_env_mf bind_env)
            ; tcg_env' = tcg_env_mf
                          { tcg_binds    = binds' `unionBags` binds_mf,
                            tcg_ev_binds = ev_binds' `unionBags` ev_binds_mf ,
                            tcg_imp_specs = imp_specs' ++ imp_specs_mf ,
                            tcg_rules    = rules' ++ rules_mf ,
                            tcg_fords    = fords' ++ fords_mf } } ;

      ; setGlobalTypeEnv tcg_env' final_type_env

   } }

zonkTcGblEnv :: Bag EvBind -> TcGblEnv
             -> TcM (TypeEnv, Bag EvBind, LHsBinds GhcTc,
                       [LForeignDecl GhcTc], [LTcSpecPrag], [LRuleDecl GhcTc])
zonkTcGblEnv new_ev_binds tcg_env =
  let TcGblEnv {   tcg_binds     = binds,
                   tcg_ev_binds  = cur_ev_binds,
                   tcg_imp_specs = imp_specs,
                   tcg_rules     = rules,
                   tcg_fords     = fords } = tcg_env

      all_ev_binds = cur_ev_binds `unionBags` new_ev_binds

  in {-# SCC "zonkTopDecls" #-}
      zonkTopDecls all_ev_binds binds rules imp_specs fords


-- | Remove accumulated bindings, rules and so on from TcGblEnv
clearTcGblEnv :: TcGblEnv -> TcGblEnv
clearTcGblEnv tcg_env
  = tcg_env { tcg_binds    = emptyBag,
              tcg_ev_binds = emptyBag ,
              tcg_imp_specs = [],
              tcg_rules    = [],
              tcg_fords    = [] }

-- | Runs TH finalizers and renames and typechecks the top-level declarations
-- that they could introduce.
run_th_modfinalizers :: TcM (TcGblEnv, TcLclEnv)
run_th_modfinalizers = do
  th_modfinalizers_var <- fmap tcg_th_modfinalizers getGblEnv
  th_modfinalizers <- readTcRef th_modfinalizers_var
  if null th_modfinalizers
  then getEnvs
  else do
    writeTcRef th_modfinalizers_var []
    let run_finalizer (lcl_env, f) =
            setLclEnv lcl_env (runRemoteModFinalizers f)

    (_, lie_th) <- captureTopConstraints $
                   mapM_ run_finalizer th_modfinalizers

      -- Finalizers can add top-level declarations with addTopDecls, so
      -- we have to run tc_rn_src_decls to get them
    (tcg_env, tcl_env, lie_top_decls) <- tc_rn_src_decls []

    setEnvs (tcg_env, tcl_env) $ do
      -- Subsequent rounds of finalizers run after any new constraints are
      -- simplified, or some types might not be complete when using reify
      -- (see #12777).
      new_ev_binds <- {-# SCC "simplifyTop2" #-}
                      simplifyTop (lie_th `andWC` lie_top_decls)
      addTopEvBinds new_ev_binds run_th_modfinalizers
        -- addTopDecls can add declarations which add new finalizers.

tc_rn_src_decls :: [LHsDecl GhcPs]
                -> TcM (TcGblEnv, TcLclEnv, WantedConstraints)
-- Loops around dealing with each top level inter-splice group
-- in turn, until it's dealt with the entire module
-- Never emits constraints; calls captureTopConstraints internally
tc_rn_src_decls ds
 = {-# SCC "tc_rn_src_decls" #-}
   do { (first_group, group_tail) <- findSplice ds
                -- If ds is [] we get ([], Nothing)

        -- Deal with decls up to, but not including, the first splice
      ; (tcg_env, rn_decls) <- rnTopSrcDecls first_group
                -- rnTopSrcDecls fails if there are any errors

        -- Get TH-generated top-level declarations and make sure they don't
        -- contain any splices since we don't handle that at the moment
        --
        -- The plumbing here is a bit odd: see #10853
      ; th_topdecls_var <- fmap tcg_th_topdecls getGblEnv
      ; th_ds <- readTcRef th_topdecls_var
      ; writeTcRef th_topdecls_var []

      ; (tcg_env, rn_decls) <-
            if null th_ds
            then return (tcg_env, rn_decls)
            else do { (th_group, th_group_tail) <- findSplice th_ds
                    ; case th_group_tail of
                        { Nothing -> return ()
                        ; Just (SpliceDecl _ (L loc _) _, _) ->
                            setSrcSpan loc
                            $ addErr (text
                                ("Declaration splices are not "
                                  ++ "permitted inside top-level "
                                  ++ "declarations added with addTopDecls"))
                        }
                      -- Rename TH-generated top-level declarations
                    ; (tcg_env, th_rn_decls) <- setGblEnv tcg_env
                        $ rnTopSrcDecls th_group

                      -- Dump generated top-level declarations
                    ; let msg = "top-level declarations added with addTopDecls"
                    ; traceSplice
                        $ SpliceInfo { spliceDescription = msg
                                     , spliceIsDecl    = True
                                     , spliceSource    = Nothing
                                     , spliceGenerated = ppr th_rn_decls }
                    ; return (tcg_env, appendGroups rn_decls th_rn_decls)
                    }

      -- Type check all declarations
      -- NB: set the env **before** captureTopConstraints so that error messages
      -- get reported w.r.t. the right GlobalRdrEnv. It is for this reason that
      -- the captureTopConstraints must go here, not in tcRnSrcDecls.
      ; ((tcg_env, tcl_env), lie1) <- setGblEnv tcg_env $
                                      captureTopConstraints $
                                      tcTopSrcDecls rn_decls

        -- If there is no splice, we're nearly done
      ; setEnvs (tcg_env, tcl_env) $
        case group_tail of
          { Nothing -> return (tcg_env, tcl_env, lie1)

            -- If there's a splice, we must carry on
          ; Just (SpliceDecl _ (L _ splice) _, rest_ds) ->
            do {
                 -- We need to simplify any constraints from the previous declaration
                 -- group, or else we might reify metavariables, as in #16980.
               ; ev_binds1 <- simplifyTop lie1

                 -- Rename the splice expression, and get its supporting decls
               ; (spliced_decls, splice_fvs) <- rnTopSpliceDecls splice

                 -- Glue them on the front of the remaining decls and loop
               ; (tcg_env, tcl_env, lie2) <-
                   setGblEnv (tcg_env `addTcgDUs` usesOnly splice_fvs) $
                   addTopEvBinds ev_binds1 $
                   tc_rn_src_decls (spliced_decls ++ rest_ds)

               ; return (tcg_env, tcl_env, lie2)
               }
          }
      }

{-
************************************************************************
*                                                                      *
        Compiling hs-boot source files, and
        comparing the hi-boot interface with the real thing
*                                                                      *
************************************************************************
-}

tcRnHsBootDecls :: HscSource -> [LHsDecl GhcPs] -> TcM TcGblEnv
tcRnHsBootDecls hsc_src decls
   = do { (first_group, group_tail) <- findSplice decls

                -- Rename the declarations
        ; (tcg_env, HsGroup { hs_tyclds = tycl_decls
                            , hs_derivds = deriv_decls
                            , hs_fords  = for_decls
                            , hs_defds  = def_decls
                            , hs_ruleds = rule_decls
                            , hs_annds  = _
                            , hs_valds  = XValBindsLR (NValBinds val_binds val_sigs) })
              <- rnTopSrcDecls first_group

        -- The empty list is for extra dependencies coming from .hs-boot files
        -- See Note [Extra dependencies from .hs-boot files] in GHC.Rename.Module

        ; (gbl_env, lie) <- setGblEnv tcg_env $ captureTopConstraints $ do {
              -- NB: setGblEnv **before** captureTopConstraints so that
              -- if the latter reports errors, it knows what's in scope

                -- Check for illegal declarations
        ; case group_tail of
             Just (SpliceDecl _ d _, _) -> badBootDecl hsc_src "splice" d
             Nothing                    -> return ()
        ; mapM_ (badBootDecl hsc_src "foreign") for_decls
        ; mapM_ (badBootDecl hsc_src "default") def_decls
        ; mapM_ (badBootDecl hsc_src "rule")    rule_decls

                -- Typecheck type/class/instance decls
        ; traceTc "Tc2 (boot)" empty
        ; (tcg_env, inst_infos, _deriv_binds)
             <- tcTyClsInstDecls tycl_decls deriv_decls val_binds
        ; setGblEnv tcg_env     $ do {

        -- Emit Typeable bindings
        ; tcg_env <- mkTypeableBinds
        ; setGblEnv tcg_env $ do {

                -- Typecheck value declarations
        ; traceTc "Tc5" empty
        ; val_ids <- tcHsBootSigs val_binds val_sigs

                -- Wrap up
                -- No simplification or zonking to do
        ; traceTc "Tc7a" empty
        ; gbl_env <- getGblEnv

                -- Make the final type-env
                -- Include the dfun_ids so that their type sigs
                -- are written into the interface file.
        ; let { type_env0 = tcg_type_env gbl_env
              ; type_env1 = extendTypeEnvWithIds type_env0 val_ids
              ; type_env2 = extendTypeEnvWithIds type_env1 dfun_ids
              ; dfun_ids = map iDFunId inst_infos
              }

        ; setGlobalTypeEnv gbl_env type_env2
   }}}
   ; traceTc "boot" (ppr lie); return gbl_env }

badBootDecl :: HscSource -> String -> Located decl -> TcM ()
badBootDecl hsc_src what (L loc _)
  = addErrAt loc (char 'A' <+> text what
      <+> text "declaration is not (currently) allowed in a"
      <+> (case hsc_src of
            HsBootFile -> text "hs-boot"
            HsigFile -> text "hsig"
            _ -> panic "badBootDecl: should be an hsig or hs-boot file")
      <+> text "file")

{-
Once we've typechecked the body of the module, we want to compare what
we've found (gathered in a TypeEnv) with the hi-boot details (if any).
-}

checkHiBootIface :: TcGblEnv -> SelfBootInfo -> TcM TcGblEnv
-- Compare the hi-boot file for this module (if there is one)
-- with the type environment we've just come up with
-- In the common case where there is no hi-boot file, the list
-- of boot_names is empty.

checkHiBootIface tcg_env boot_info
  | NoSelfBoot <- boot_info  -- Common case
  = return tcg_env

  | HsBootFile <- tcg_src tcg_env   -- Current module is already a hs-boot file!
  = return tcg_env

  | SelfBoot { sb_mds = boot_details } <- boot_info
  , TcGblEnv { tcg_binds    = binds
             , tcg_insts    = local_insts
             , tcg_type_env = local_type_env
             , tcg_exports  = local_exports } <- tcg_env
  = do  { -- This code is tricky, see Note [DFun knot-tying]
        ; dfun_prs <- checkHiBootIface' local_insts local_type_env
                                        local_exports boot_details

        -- Now add the boot-dfun bindings  $fxblah = $fblah
        -- to (a) the type envt, and (b) the top-level bindings
        ; let boot_dfuns = map fst dfun_prs
              type_env'  = extendTypeEnvWithIds local_type_env boot_dfuns
              dfun_binds = listToBag [ mkVarBind boot_dfun (nlHsVar dfun)
                                     | (boot_dfun, dfun) <- dfun_prs ]
              tcg_env_w_binds
                = tcg_env { tcg_binds = binds `unionBags` dfun_binds }

        ; type_env' `seq`
             -- Why the seq?  Without, we will put a TypeEnv thunk in
             -- tcg_type_env_var.  That thunk will eventually get
             -- forced if we are typechecking interfaces, but that
             -- is no good if we are trying to typecheck the very
             -- DFun we were going to put in.
             -- TODO: Maybe setGlobalTypeEnv should be strict.
          setGlobalTypeEnv tcg_env_w_binds type_env' }

#if __GLASGOW_HASKELL__ <= 810
  | otherwise = panic "checkHiBootIface: unreachable code"
#endif

{- Note [DFun impedance matching]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We return a list of "impedance-matching" bindings for the dfuns
defined in the hs-boot file, such as
          $fxEqT = $fEqT
We need these because the module and hi-boot file might differ in
the name it chose for the dfun: the name of a dfun is not
uniquely determined by its type; there might be multiple dfuns
which, individually, would map to the same name (in which case
we have to disambiguate them.)  There's no way for the hi file
to know exactly what disambiguation to use... without looking
at the hi-boot file itself.

In fact, the names will always differ because we always pick names
prefixed with "$fx" for boot dfuns, and "$f" for real dfuns
(so that this impedance matching is always possible).

Note [DFun knot-tying]
~~~~~~~~~~~~~~~~~~~~~~
The 'SelfBootInfo' that is fed into 'checkHiBootIface' comes from
typechecking the hi-boot file that we are presently implementing.
Suppose we are typechecking the module A: when we typecheck the
hi-boot file, whenever we see an identifier A.T, we knot-tie this
identifier to the *local* type environment (via if_rec_types.)  The
contract then is that we don't *look* at 'SelfBootInfo' until we've
finished typechecking the module and updated the type environment with
the new tycons and ids.

This most works well, but there is one problem: DFuns!  We do not want
to look at the mb_insts of the ModDetails in SelfBootInfo, because a
dfun in one of those ClsInsts is gotten (in GHC.IfaceToCore.tcIfaceInst) by a
(lazily evaluated) lookup in the if_rec_types.  We could extend the
type env, do a setGloblaTypeEnv etc; but that all seems very indirect.
It is much more directly simply to extract the DFunIds from the
md_types of the SelfBootInfo.

See #4003, #16038 for why we need to take care here.
-}

checkHiBootIface' :: [ClsInst] -> TypeEnv -> [AvailInfo]
                  -> ModDetails -> TcM [(Id, Id)]
-- Variant which doesn't require a full TcGblEnv; you could get the
-- local components from another ModDetails.
checkHiBootIface'
        local_insts local_type_env local_exports
        (ModDetails { md_types = boot_type_env
                    , md_fam_insts = boot_fam_insts
                    , md_exports = boot_exports })
  = do  { traceTc "checkHiBootIface" $ vcat
             [ ppr boot_type_env, ppr boot_exports]

                -- Check the exports of the boot module, one by one
        ; mapM_ check_export boot_exports

                -- Check for no family instances
        ; unless (null boot_fam_insts) $
            panic ("GHC.Tc.Module.checkHiBootIface: Cannot handle family " ++
                   "instances in boot files yet...")
            -- FIXME: Why?  The actual comparison is not hard, but what would
            --        be the equivalent to the dfun bindings returned for class
            --        instances?  We can't easily equate tycons...

                -- Check instance declarations
                -- and generate an impedance-matching binding
        ; mb_dfun_prs <- mapM check_cls_inst boot_dfuns

        ; failIfErrsM

        ; return (catMaybes mb_dfun_prs) }

  where
    boot_dfun_names = map idName boot_dfuns
    boot_dfuns      = filter isDFunId $ typeEnvIds boot_type_env
       -- NB: boot_dfuns is /not/ defined thus: map instanceDFunId md_insts
       --     We don't want to look at md_insts!
       --     Why not?  See Note [DFun knot-tying]

    check_export boot_avail     -- boot_avail is exported by the boot iface
      | name `elem` boot_dfun_names = return ()
      | isWiredInName name          = return () -- No checking for wired-in names.  In particular,
                                                -- 'error' is handled by a rather gross hack
                                                -- (see comments in GHC.Err.hs-boot)

        -- Check that the actual module exports the same thing
      | not (null missing_names)
      = addErrAt (nameSrcSpan (head missing_names))
                 (missingBootThing True (head missing_names) "exported by")

        -- If the boot module does not *define* the thing, we are done
        -- (it simply re-exports it, and names match, so nothing further to do)
      | isNothing mb_boot_thing = return ()

        -- Check that the actual module also defines the thing, and
        -- then compare the definitions
      | Just real_thing <- lookupTypeEnv local_type_env name,
        Just boot_thing <- mb_boot_thing
      = checkBootDeclM True boot_thing real_thing

      | otherwise
      = addErrTc (missingBootThing True name "defined in")
      where
        name          = availName boot_avail
        mb_boot_thing = lookupTypeEnv boot_type_env name
        missing_names = case lookupNameEnv local_export_env name of
                          Nothing    -> [name]
                          Just avail -> availNames boot_avail `minusList` availNames avail

    local_export_env :: NameEnv AvailInfo
    local_export_env = availsToNameEnv local_exports

    check_cls_inst :: DFunId -> TcM (Maybe (Id, Id))
        -- Returns a pair of the boot dfun in terms of the equivalent
        -- real dfun. Delicate (like checkBootDecl) because it depends
        -- on the types lining up precisely even to the ordering of
        -- the type variables in the foralls.
    check_cls_inst boot_dfun
      | (real_dfun : _) <- find_real_dfun boot_dfun
      , let local_boot_dfun = Id.mkExportedVanillaId
                                  (idName boot_dfun) (idType real_dfun)
      = return (Just (local_boot_dfun, real_dfun))
          -- Two tricky points here:
          --
          --  * The local_boot_fun should have a Name from the /boot-file/,
          --    but type from the dfun defined in /this module/.
          --    That ensures that the TyCon etc inside the type are
          --    the ones defined in this module, not the ones gotten
          --    from the hi-boot file, which may have a lot less info
          --    (#8743, comment:10).
          --
          --  * The DFunIds from boot_details are /GlobalIds/, because
          --    they come from typechecking M.hi-boot.
          --    But all bindings in this module should be for /LocalIds/,
          --    otherwise dependency analysis fails (#16038). This
          --    is another reason for using mkExportedVanillaId, rather
          --    that modifying boot_dfun, to make local_boot_fun.

      | otherwise
      = setSrcSpan (nameSrcSpan (getName boot_dfun)) $
        do { traceTc "check_cls_inst" $ vcat
                [ text "local_insts"  <+>
                     vcat (map (ppr . idType . instanceDFunId) local_insts)
                , text "boot_dfun_ty" <+> ppr (idType boot_dfun) ]

           ; addErrTc (instMisMatch boot_dfun)
           ; return Nothing }

    find_real_dfun :: DFunId -> [DFunId]
    find_real_dfun boot_dfun
       = [dfun | inst <- local_insts
               , let dfun = instanceDFunId inst
               , idType dfun `eqType` boot_dfun_ty ]
       where
          boot_dfun_ty   = idType boot_dfun


-- In general, to perform these checks we have to
-- compare the TyThing from the .hi-boot file to the TyThing
-- in the current source file.  We must be careful to allow alpha-renaming
-- where appropriate, and also the boot declaration is allowed to omit
-- constructors and class methods.
--
-- See rnfail055 for a good test of this stuff.

-- | Compares two things for equivalence between boot-file and normal code,
-- reporting an error if they don't match up.
checkBootDeclM :: Bool  -- ^ True <=> an hs-boot file (could also be a sig)
               -> TyThing -> TyThing -> TcM ()
checkBootDeclM is_boot boot_thing real_thing
  = whenIsJust (checkBootDecl is_boot boot_thing real_thing) $ \ err ->
       addErrAt span
                (bootMisMatch is_boot err real_thing boot_thing)
  where
    -- Here we use the span of the boot thing or, if it doesn't have a sensible
    -- span, that of the real thing,
    span
      | let span = nameSrcSpan (getName boot_thing)
      , isGoodSrcSpan span
      = span
      | otherwise
      = nameSrcSpan (getName real_thing)

-- | Compares the two things for equivalence between boot-file and normal
-- code. Returns @Nothing@ on success or @Just "some helpful info for user"@
-- failure. If the difference will be apparent to the user, @Just empty@ is
-- perfectly suitable.
checkBootDecl :: Bool -> TyThing -> TyThing -> Maybe SDoc

checkBootDecl _ (AnId id1) (AnId id2)
  = ASSERT(id1 == id2)
    check (idType id1 `eqType` idType id2)
          (text "The two types are different")

checkBootDecl is_boot (ATyCon tc1) (ATyCon tc2)
  = checkBootTyCon is_boot tc1 tc2

checkBootDecl _ (AConLike (RealDataCon dc1)) (AConLike (RealDataCon _))
  = pprPanic "checkBootDecl" (ppr dc1)

checkBootDecl _ _ _ = Just empty -- probably shouldn't happen

-- | Combines two potential error messages
andThenCheck :: Maybe SDoc -> Maybe SDoc -> Maybe SDoc
Nothing `andThenCheck` msg     = msg
msg     `andThenCheck` Nothing = msg
Just d1 `andThenCheck` Just d2 = Just (d1 $$ d2)
infixr 0 `andThenCheck`

-- | If the test in the first parameter is True, succeed with @Nothing@;
-- otherwise, return the provided check
checkUnless :: Bool -> Maybe SDoc -> Maybe SDoc
checkUnless True  _ = Nothing
checkUnless False k = k

-- | Run the check provided for every pair of elements in the lists.
-- The provided SDoc should name the element type, in the plural.
checkListBy :: (a -> a -> Maybe SDoc) -> [a] -> [a] -> SDoc
            -> Maybe SDoc
checkListBy check_fun as bs whats = go [] as bs
  where
    herald = text "The" <+> whats <+> text "do not match"

    go []   [] [] = Nothing
    go docs [] [] = Just (hang (herald <> colon) 2 (vcat $ reverse docs))
    go docs (x:xs) (y:ys) = case check_fun x y of
      Just doc -> go (doc:docs) xs ys
      Nothing  -> go docs       xs ys
    go _    _  _ = Just (hang (herald <> colon)
                            2 (text "There are different numbers of" <+> whats))

-- | If the test in the first parameter is True, succeed with @Nothing@;
-- otherwise, fail with the given SDoc.
check :: Bool -> SDoc -> Maybe SDoc
check True  _   = Nothing
check False doc = Just doc

-- | A more perspicuous name for @Nothing@, for @checkBootDecl@ and friends.
checkSuccess :: Maybe SDoc
checkSuccess = Nothing

----------------
checkBootTyCon :: Bool -> TyCon -> TyCon -> Maybe SDoc
checkBootTyCon is_boot tc1 tc2
  | not (eqType (tyConKind tc1) (tyConKind tc2))
  = Just $ text "The types have different kinds"    -- First off, check the kind

  | Just c1 <- tyConClass_maybe tc1
  , Just c2 <- tyConClass_maybe tc2
  , let (clas_tvs1, clas_fds1, sc_theta1, _, ats1, op_stuff1)
          = classExtraBigSig c1
        (clas_tvs2, clas_fds2, sc_theta2, _, ats2, op_stuff2)
          = classExtraBigSig c2
  , Just env <- eqVarBndrs emptyRnEnv2 clas_tvs1 clas_tvs2
  = let
       eqSig (id1, def_meth1) (id2, def_meth2)
         = check (name1 == name2)
                 (text "The names" <+> pname1 <+> text "and" <+> pname2 <+>
                  text "are different") `andThenCheck`
           check (eqTypeX env op_ty1 op_ty2)
                 (text "The types of" <+> pname1 <+>
                  text "are different") `andThenCheck`
           if is_boot
               then check (eqMaybeBy eqDM def_meth1 def_meth2)
                          (text "The default methods associated with" <+> pname1 <+>
                           text "are different")
               else check (subDM op_ty1 def_meth1 def_meth2)
                          (text "The default methods associated with" <+> pname1 <+>
                           text "are not compatible")
         where
          name1 = idName id1
          name2 = idName id2
          pname1 = quotes (ppr name1)
          pname2 = quotes (ppr name2)
          op_ty1 = classMethodTy id1
          op_ty2 = classMethodTy id2

       eqAT (ATI tc1 def_ats1) (ATI tc2 def_ats2)
         = checkBootTyCon is_boot tc1 tc2 `andThenCheck`
           check (eqATDef def_ats1 def_ats2)
                 (text "The associated type defaults differ")

       eqDM (_, VanillaDM)    (_, VanillaDM)    = True
       eqDM (_, GenericDM t1) (_, GenericDM t2) = eqTypeX env t1 t2
       eqDM _ _ = False

       -- NB: first argument is from hsig, second is from real impl.
       -- Order of pattern matching matters.
       subDM _ Nothing _ = True
       subDM _ _ Nothing = False
       -- If the hsig wrote:
       --
       --   f :: a -> a
       --   default f :: a -> a
       --
       -- this should be validly implementable using an old-fashioned
       -- vanilla default method.
       subDM t1 (Just (_, GenericDM t2)) (Just (_, VanillaDM))
        = eqTypeX env t1 t2
       -- This case can occur when merging signatures
       subDM t1 (Just (_, VanillaDM)) (Just (_, GenericDM t2))
        = eqTypeX env t1 t2
       subDM _ (Just (_, VanillaDM)) (Just (_, VanillaDM)) = True
       subDM _ (Just (_, GenericDM t1)) (Just (_, GenericDM t2))
        = eqTypeX env t1 t2

       -- Ignore the location of the defaults
       eqATDef Nothing             Nothing             = True
       eqATDef (Just (ty1, _loc1)) (Just (ty2, _loc2)) = eqTypeX env ty1 ty2
       eqATDef _ _ = False

       eqFD (as1,bs1) (as2,bs2) =
         eqListBy (eqTypeX env) (mkTyVarTys as1) (mkTyVarTys as2) &&
         eqListBy (eqTypeX env) (mkTyVarTys bs1) (mkTyVarTys bs2)
    in
    checkRoles roles1 roles2 `andThenCheck`
          -- Checks kind of class
    check (eqListBy eqFD clas_fds1 clas_fds2)
          (text "The functional dependencies do not match") `andThenCheck`
    checkUnless (isAbstractTyCon tc1) $
    check (eqListBy (eqTypeX env) sc_theta1 sc_theta2)
          (text "The class constraints do not match") `andThenCheck`
    checkListBy eqSig op_stuff1 op_stuff2 (text "methods") `andThenCheck`
    checkListBy eqAT ats1 ats2 (text "associated types") `andThenCheck`
    check (classMinimalDef c1 `BF.implies` classMinimalDef c2)
        (text "The MINIMAL pragmas are not compatible")

  | Just syn_rhs1 <- synTyConRhs_maybe tc1
  , Just syn_rhs2 <- synTyConRhs_maybe tc2
  , Just env <- eqVarBndrs emptyRnEnv2 (tyConTyVars tc1) (tyConTyVars tc2)
  = ASSERT(tc1 == tc2)
    checkRoles roles1 roles2 `andThenCheck`
    check (eqTypeX env syn_rhs1 syn_rhs2) empty   -- nothing interesting to say
  -- This allows abstract 'data T a' to be implemented using 'type T = ...'
  -- and abstract 'class K a' to be implement using 'type K = ...'
  -- See Note [Synonyms implement abstract data]
  | not is_boot -- don't support for hs-boot yet
  , isAbstractTyCon tc1
  , Just (tvs, ty) <- synTyConDefn_maybe tc2
  , Just (tc2', args) <- tcSplitTyConApp_maybe ty
  = checkSynAbsData tvs ty tc2' args
    -- TODO: When it's a synonym implementing a class, we really
    -- should check if the fundeps are satisfied, but
    -- there is not an obvious way to do this for a constraint synonym.
    -- So for now, let it all through (it won't cause segfaults, anyway).
    -- Tracked at #12704.

  -- This allows abstract 'data T :: Nat' to be implemented using
  -- 'type T = 42' Since the kinds already match (we have checked this
  -- upfront) all we need to check is that the implementation 'type T
  -- = ...' defined an actual literal.  See #15138 for the case this
  -- handles.
  | not is_boot
  , isAbstractTyCon tc1
  , Just (_,ty2) <- synTyConDefn_maybe tc2
  , isJust (isLitTy ty2)
  = Nothing

  | Just fam_flav1 <- famTyConFlav_maybe tc1
  , Just fam_flav2 <- famTyConFlav_maybe tc2
  = ASSERT(tc1 == tc2)
    let eqFamFlav OpenSynFamilyTyCon   OpenSynFamilyTyCon = True
        eqFamFlav (DataFamilyTyCon {}) (DataFamilyTyCon {}) = True
        -- This case only happens for hsig merging:
        eqFamFlav AbstractClosedSynFamilyTyCon AbstractClosedSynFamilyTyCon = True
        eqFamFlav AbstractClosedSynFamilyTyCon (ClosedSynFamilyTyCon {}) = True
        eqFamFlav (ClosedSynFamilyTyCon {}) AbstractClosedSynFamilyTyCon = True
        eqFamFlav (ClosedSynFamilyTyCon ax1) (ClosedSynFamilyTyCon ax2)
            = eqClosedFamilyAx ax1 ax2
        eqFamFlav (BuiltInSynFamTyCon {}) (BuiltInSynFamTyCon {}) = tc1 == tc2
        eqFamFlav _ _ = False
        injInfo1 = tyConInjectivityInfo tc1
        injInfo2 = tyConInjectivityInfo tc2
    in
    -- check equality of roles, family flavours and injectivity annotations
    -- (NB: Type family roles are always nominal. But the check is
    -- harmless enough.)
    checkRoles roles1 roles2 `andThenCheck`
    check (eqFamFlav fam_flav1 fam_flav2)
        (whenPprDebug $
            text "Family flavours" <+> ppr fam_flav1 <+> text "and" <+> ppr fam_flav2 <+>
            text "do not match") `andThenCheck`
    check (injInfo1 == injInfo2) (text "Injectivities do not match")

  | isAlgTyCon tc1 && isAlgTyCon tc2
  , Just env <- eqVarBndrs emptyRnEnv2 (tyConTyVars tc1) (tyConTyVars tc2)
  = ASSERT(tc1 == tc2)
    checkRoles roles1 roles2 `andThenCheck`
    check (eqListBy (eqTypeX env)
                     (tyConStupidTheta tc1) (tyConStupidTheta tc2))
          (text "The datatype contexts do not match") `andThenCheck`
    eqAlgRhs tc1 (algTyConRhs tc1) (algTyConRhs tc2)

  | otherwise = Just empty   -- two very different types -- should be obvious
  where
    roles1 = tyConRoles tc1 -- the abstract one
    roles2 = tyConRoles tc2
    roles_msg = text "The roles do not match." $$
                (text "Roles on abstract types default to" <+>
                 quotes (text "representational") <+> text "in boot files.")

    roles_subtype_msg = text "The roles are not compatible:" $$
                        text "Main module:" <+> ppr roles2 $$
                        text "Hsig file:" <+> ppr roles1

    checkRoles r1 r2
      | is_boot || isInjectiveTyCon tc1 Representational -- See Note [Role subtyping]
      = check (r1 == r2) roles_msg
      | otherwise = check (r2 `rolesSubtypeOf` r1) roles_subtype_msg

    -- Note [Role subtyping]
    -- ~~~~~~~~~~~~~~~~~~~~~
    -- In the current formulation of roles, role subtyping is only OK if the
    -- "abstract" TyCon was not representationally injective.  Among the most
    -- notable examples of non representationally injective TyCons are abstract
    -- data, which can be implemented via newtypes (which are not
    -- representationally injective).  The key example is
    -- in this example from #13140:
    --
    --      -- In an hsig file
    --      data T a -- abstract!
    --      type role T nominal
    --
    --      -- Elsewhere
    --      foo :: Coercible (T a) (T b) => a -> b
    --      foo x = x
    --
    -- We must NOT allow foo to typecheck, because if we instantiate
    -- T with a concrete data type with a phantom role would cause
    -- Coercible (T a) (T b) to be provable.  Fortunately, if T is not
    -- representationally injective, we cannot make the inference that a ~N b if
    -- T a ~R T b.
    --
    -- Unconditional role subtyping would be possible if we setup
    -- an extra set of roles saying when we can project out coercions
    -- (we call these proj-roles); then it would NOT be valid to instantiate T
    -- with a data type at phantom since the proj-role subtyping check
    -- would fail.  See #13140 for more details.
    --
    -- One consequence of this is we get no role subtyping for non-abstract
    -- data types in signatures. Suppose you have:
    --
    --      signature A where
    --          type role T nominal
    --          data T a = MkT
    --
    -- If you write this, we'll treat T as injective, and make inferences
    -- like T a ~R T b ==> a ~N b (mkNthCo).  But if we can
    -- subsequently replace T with one at phantom role, we would then be able to
    -- infer things like T Int ~R T Bool which is bad news.
    --
    -- We could allow role subtyping here if we didn't treat *any* data types
    -- defined in signatures as injective.  But this would be a bit surprising,
    -- replacing a data type in a module with one in a signature could cause
    -- your code to stop typechecking (whereas if you made the type abstract,
    -- it is more understandable that the type checker knows less).
    --
    -- It would have been best if this was purely a question of defaults
    -- (i.e., a user could explicitly ask for one behavior or another) but
    -- the current role system isn't expressive enough to do this.
    -- Having explicit proj-roles would solve this problem.

    rolesSubtypeOf [] [] = True
    -- NB: this relation is the OPPOSITE of the subroling relation
    rolesSubtypeOf (x:xs) (y:ys) = x >= y && rolesSubtypeOf xs ys
    rolesSubtypeOf _ _ = False

    -- Note [Synonyms implement abstract data]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- An abstract data type or class can be implemented using a type synonym,
    -- but ONLY if the type synonym is nullary and has no type family
    -- applications.  This arises from two properties of skolem abstract data:
    --
    --    For any T (with some number of paramaters),
    --
    --    1. T is a valid type (it is "curryable"), and
    --
    --    2. T is valid in an instance head (no type families).
    --
    -- See also 'HowAbstract' and Note [Skolem abstract data].

    -- | Given @type T tvs = ty@, where @ty@ decomposes into @tc2' args@,
    -- check that this synonym is an acceptable implementation of @tc1@.
    -- See Note [Synonyms implement abstract data]
    checkSynAbsData :: [TyVar] -> Type -> TyCon -> [Type] -> Maybe SDoc
    checkSynAbsData tvs ty tc2' args =
        check (null (tcTyFamInsts ty))
              (text "Illegal type family application in implementation of abstract data.")
                `andThenCheck`
        check (null tvs)
              (text "Illegal parameterized type synonym in implementation of abstract data." $$
               text "(Try eta reducing your type synonym so that it is nullary.)")
                `andThenCheck`
        -- Don't report roles errors unless the type synonym is nullary
        checkUnless (not (null tvs)) $
            ASSERT( null roles2 )
            -- If we have something like:
            --
            --  signature H where
            --      data T a
            --  module H where
            --      data K a b = ...
            --      type T = K Int
            --
            -- we need to drop the first role of K when comparing!
            checkRoles roles1 (drop (length args) (tyConRoles tc2'))
{-
        -- Hypothetically, if we were allow to non-nullary type synonyms, here
        -- is how you would check the roles
        if length tvs == length roles1
            then checkRoles roles1 roles2
            else case tcSplitTyConApp_maybe ty of
                    Just (tc2', args) ->
                        checkRoles roles1 (drop (length args) (tyConRoles tc2') ++ roles2)
                    Nothing -> Just roles_msg
-}

    eqAlgRhs _ AbstractTyCon _rhs2
      = checkSuccess -- rhs2 is guaranteed to be injective, since it's an AlgTyCon
    eqAlgRhs _  tc1@DataTyCon{} tc2@DataTyCon{} =
        checkListBy eqCon (data_cons tc1) (data_cons tc2) (text "constructors")
    eqAlgRhs _  tc1@NewTyCon{} tc2@NewTyCon{} =
        eqCon (data_con tc1) (data_con tc2)
    eqAlgRhs _ _ _ = Just (text "Cannot match a" <+> quotes (text "data") <+>
                           text "definition with a" <+> quotes (text "newtype") <+>
                           text "definition")

    eqCon c1 c2
      =  check (name1 == name2)
               (text "The names" <+> pname1 <+> text "and" <+> pname2 <+>
                text "differ") `andThenCheck`
         check (dataConIsInfix c1 == dataConIsInfix c2)
               (text "The fixities of" <+> pname1 <+>
                text "differ") `andThenCheck`
         check (eqListBy eqHsBang (dataConImplBangs c1) (dataConImplBangs c2))
               (text "The strictness annotations for" <+> pname1 <+>
                text "differ") `andThenCheck`
         check (map flSelector (dataConFieldLabels c1) == map flSelector (dataConFieldLabels c2))
               (text "The record label lists for" <+> pname1 <+>
                text "differ") `andThenCheck`
         check (eqType (dataConWrapperType c1) (dataConWrapperType c2))
               (text "The types for" <+> pname1 <+> text "differ")
      where
        name1 = dataConName c1
        name2 = dataConName c2
        pname1 = quotes (ppr name1)
        pname2 = quotes (ppr name2)

    eqClosedFamilyAx Nothing Nothing  = True
    eqClosedFamilyAx Nothing (Just _) = False
    eqClosedFamilyAx (Just _) Nothing = False
    eqClosedFamilyAx (Just (CoAxiom { co_ax_branches = branches1 }))
                     (Just (CoAxiom { co_ax_branches = branches2 }))
      =  numBranches branches1 == numBranches branches2
      && (and $ zipWith eqClosedFamilyBranch branch_list1 branch_list2)
      where
        branch_list1 = fromBranches branches1
        branch_list2 = fromBranches branches2

    eqClosedFamilyBranch (CoAxBranch { cab_tvs = tvs1, cab_cvs = cvs1
                                     , cab_lhs = lhs1, cab_rhs = rhs1 })
                         (CoAxBranch { cab_tvs = tvs2, cab_cvs = cvs2
                                     , cab_lhs = lhs2, cab_rhs = rhs2 })
      | Just env1 <- eqVarBndrs emptyRnEnv2 tvs1 tvs2
      , Just env  <- eqVarBndrs env1        cvs1 cvs2
      = eqListBy (eqTypeX env) lhs1 lhs2 &&
        eqTypeX env rhs1 rhs2

      | otherwise = False

emptyRnEnv2 :: RnEnv2
emptyRnEnv2 = mkRnEnv2 emptyInScopeSet

----------------
missingBootThing :: Bool -> Name -> String -> SDoc
missingBootThing is_boot name what
  = quotes (ppr name) <+> text "is exported by the"
    <+> (if is_boot then text "hs-boot" else text "hsig")
    <+> text "file, but not"
    <+> text what <+> text "the module"

badReexportedBootThing :: Bool -> Name -> Name -> SDoc
badReexportedBootThing is_boot name name'
  = withUserStyle alwaysQualify AllTheWay $ vcat
        [ text "The" <+> (if is_boot then text "hs-boot" else text "hsig")
           <+> text "file (re)exports" <+> quotes (ppr name)
        , text "but the implementing module exports a different identifier" <+> quotes (ppr name')
        ]

bootMisMatch :: Bool -> SDoc -> TyThing -> TyThing -> SDoc
bootMisMatch is_boot extra_info real_thing boot_thing
  = pprBootMisMatch is_boot extra_info real_thing real_doc boot_doc
  where
    to_doc
      = pprTyThingInContext $ showToHeader { ss_forall =
                                              if is_boot
                                                then ShowForAllMust
                                                else ShowForAllWhen }

    real_doc = to_doc real_thing
    boot_doc = to_doc boot_thing

    pprBootMisMatch :: Bool -> SDoc -> TyThing -> SDoc -> SDoc -> SDoc
    pprBootMisMatch is_boot extra_info real_thing real_doc boot_doc
      = vcat
          [ ppr real_thing <+>
            text "has conflicting definitions in the module",
            text "and its" <+>
              (if is_boot
                then text "hs-boot file"
                else text "hsig file"),
            text "Main module:" <+> real_doc,
              (if is_boot
                then text "Boot file:  "
                else text "Hsig file: ")
                <+> boot_doc,
            extra_info
          ]

instMisMatch :: DFunId -> SDoc
instMisMatch dfun
  = hang (text "instance" <+> ppr (idType dfun))
       2 (text "is defined in the hs-boot file, but not in the module itself")

{-
************************************************************************
*                                                                      *
        Type-checking the top level of a module (continued)
*                                                                      *
************************************************************************
-}

rnTopSrcDecls :: HsGroup GhcPs -> TcM (TcGblEnv, HsGroup GhcRn)
-- Fails if there are any errors
rnTopSrcDecls group
 = do { -- Rename the source decls
        traceRn "rn12" empty ;
        (tcg_env, rn_decls) <- checkNoErrs $ rnSrcDecls group ;
        traceRn "rn13" empty ;
        (tcg_env, rn_decls) <- runRenamerPlugin tcg_env rn_decls ;
        traceRn "rn13-plugin" empty ;

        -- save the renamed syntax, if we want it
        let { tcg_env'
                | Just grp <- tcg_rn_decls tcg_env
                  = tcg_env{ tcg_rn_decls = Just (appendGroups grp rn_decls) }
                | otherwise
                   = tcg_env };

                -- Dump trace of renaming part
        rnDump rn_decls ;
        return (tcg_env', rn_decls)
   }

tcTopSrcDecls :: HsGroup GhcRn -> TcM (TcGblEnv, TcLclEnv)
tcTopSrcDecls (HsGroup { hs_tyclds = tycl_decls,
                         hs_derivds = deriv_decls,
                         hs_fords  = foreign_decls,
                         hs_defds  = default_decls,
                         hs_annds  = annotation_decls,
                         hs_ruleds = rule_decls,
                         hs_valds  = hs_val_binds@(XValBindsLR
                                              (NValBinds val_binds val_sigs)) })
 = do {         -- Type-check the type and class decls, and all imported decls
                -- The latter come in via tycl_decls
        traceTc "Tc2 (src)" empty ;

                -- Source-language instances, including derivings,
                -- and import the supporting declarations
        traceTc "Tc3" empty ;
        (tcg_env, inst_infos, XValBindsLR (NValBinds deriv_binds deriv_sigs))
            <- tcTyClsInstDecls tycl_decls deriv_decls val_binds ;

        setGblEnv tcg_env       $ do {

                -- Generate Applicative/Monad proposal (AMP) warnings
        traceTc "Tc3b" empty ;

                -- Generate Semigroup/Monoid warnings
        traceTc "Tc3c" empty ;
        tcSemigroupWarnings ;

                -- Foreign import declarations next.
        traceTc "Tc4" empty ;
        (fi_ids, fi_decls, fi_gres) <- tcForeignImports foreign_decls ;
        tcExtendGlobalValEnv fi_ids     $ do {

                -- Default declarations
        traceTc "Tc4a" empty ;
        default_tys <- tcDefaults default_decls ;
        updGblEnv (\gbl -> gbl { tcg_default = default_tys }) $ do {

                -- Value declarations next.
                -- It is important that we check the top-level value bindings
                -- before the GHC-generated derived bindings, since the latter
                -- may be defined in terms of the former. (For instance,
                -- the bindings produced in a Data instance.)
        traceTc "Tc5" empty ;
        tc_envs <- tcTopBinds val_binds val_sigs;
        setEnvs tc_envs $ do {

                -- Now GHC-generated derived bindings, generics, and selectors
                -- Do not generate warnings from compiler-generated code;
                -- hence the use of discardWarnings
        tc_envs@(tcg_env, tcl_env)
            <- discardWarnings (tcTopBinds deriv_binds deriv_sigs) ;
        setEnvs tc_envs $ do {  -- Environment doesn't change now

                -- Second pass over class and instance declarations,
                -- now using the kind-checked decls
        traceTc "Tc6" empty ;
        inst_binds <- tcInstDecls2 (tyClGroupTyClDecls tycl_decls) inst_infos ;

                -- Foreign exports
        traceTc "Tc7" empty ;
        (foe_binds, foe_decls, foe_gres) <- tcForeignExports foreign_decls ;

                -- Annotations
        annotations <- tcAnnotations annotation_decls ;

                -- Rules
        rules <- tcRules rule_decls ;

                -- Wrap up
        traceTc "Tc7a" empty ;
        let { all_binds = inst_binds     `unionBags`
                          foe_binds

            ; fo_gres = fi_gres `unionBags` foe_gres
            ; fo_fvs = foldr (\gre fvs -> fvs `addOneFV` greMangledName gre)
                                emptyFVs fo_gres

            ; sig_names = mkNameSet (collectHsValBinders CollNoDictBinders hs_val_binds)
                          `minusNameSet` getTypeSigNames val_sigs

                -- Extend the GblEnv with the (as yet un-zonked)
                -- bindings, rules, foreign decls
            ; tcg_env' = tcg_env { tcg_binds   = tcg_binds tcg_env `unionBags` all_binds
                                 , tcg_sigs    = tcg_sigs tcg_env `unionNameSet` sig_names
                                 , tcg_rules   = tcg_rules tcg_env
                                                      ++ flattenRuleDecls rules
                                 , tcg_anns    = tcg_anns tcg_env ++ annotations
                                 , tcg_ann_env = extendAnnEnvList (tcg_ann_env tcg_env) annotations
                                 , tcg_fords   = tcg_fords tcg_env ++ foe_decls ++ fi_decls
                                 , tcg_dus     = tcg_dus tcg_env `plusDU` usesOnly fo_fvs } } ;
                                 -- tcg_dus: see Note [Newtype constructor usage in foreign declarations]

        -- See Note [Newtype constructor usage in foreign declarations]
        addUsedGREs (bagToList fo_gres) ;

        return (tcg_env', tcl_env)
    }}}}}}

tcTopSrcDecls _ = panic "tcTopSrcDecls: ValBindsIn"


tcSemigroupWarnings :: TcM ()
tcSemigroupWarnings = do
    traceTc "tcSemigroupWarnings" empty
    let warnFlag = Opt_WarnSemigroup
    tcPreludeClashWarn warnFlag sappendName
    tcMissingParentClassWarn warnFlag monoidClassName semigroupClassName


-- | Warn on local definitions of names that would clash with future Prelude
-- elements.
--
--   A name clashes if the following criteria are met:
--       1. It would is imported (unqualified) from Prelude
--       2. It is locally defined in the current module
--       3. It has the same literal name as the reference function
--       4. It is not identical to the reference function
tcPreludeClashWarn :: WarningFlag
                   -> Name
                   -> TcM ()
tcPreludeClashWarn warnFlag name = do
    { warn <- woptM warnFlag
    ; when warn $ do
    { traceTc "tcPreludeClashWarn/wouldBeImported" empty
    -- Is the name imported (unqualified) from Prelude? (Point 4 above)
    ; rnImports <- fmap (map unLoc . tcg_rn_imports) getGblEnv
    -- (Note that this automatically handles -XNoImplicitPrelude, as Prelude
    -- will not appear in rnImports automatically if it is set.)

    -- Continue only the name is imported from Prelude
    ; when (importedViaPrelude name rnImports) $ do
      -- Handle 2.-4.
    { rdrElts <- fmap (concat . occEnvElts . tcg_rdr_env) getGblEnv

    ; let clashes :: GlobalRdrElt -> Bool
          clashes x = isLocalDef && nameClashes && isNotInProperModule
            where
              isLocalDef = gre_lcl x == True
              -- Names are identical ...
              nameClashes = nameOccName (greMangledName x) == nameOccName name
              -- ... but not the actual definitions, because we don't want to
              -- warn about a bad definition of e.g. <> in Data.Semigroup, which
              -- is the (only) proper place where this should be defined
              isNotInProperModule = greMangledName x /= name

          -- List of all offending definitions
          clashingElts :: [GlobalRdrElt]
          clashingElts = filter clashes rdrElts

    ; traceTc "tcPreludeClashWarn/prelude_functions"
                (hang (ppr name) 4 (sep [ppr clashingElts]))

    ; let warn_msg x = addWarnAt (Reason warnFlag) (nameSrcSpan (greMangledName x)) (hsep
              [ text "Local definition of"
              , (quotes . ppr . nameOccName . greMangledName) x
              , text "clashes with a future Prelude name." ]
              $$
              text "This will become an error in a future release." )
    ; mapM_ warn_msg clashingElts
    }}}

  where

    -- Is the given name imported via Prelude?
    --
    -- Possible scenarios:
    --   a) Prelude is imported implicitly, issue warnings.
    --   b) Prelude is imported explicitly, but without mentioning the name in
    --      question. Issue no warnings.
    --   c) Prelude is imported hiding the name in question. Issue no warnings.
    --   d) Qualified import of Prelude, no warnings.
    importedViaPrelude :: Name
                       -> [ImportDecl GhcRn]
                       -> Bool
    importedViaPrelude name = any importViaPrelude
      where
        isPrelude :: ImportDecl GhcRn -> Bool
        isPrelude imp = unLoc (ideclName imp) == pRELUDE_NAME

        -- Implicit (Prelude) import?
        isImplicit :: ImportDecl GhcRn -> Bool
        isImplicit = ideclImplicit

        -- Unqualified import?
        isUnqualified :: ImportDecl GhcRn -> Bool
        isUnqualified = not . isImportDeclQualified . ideclQualified

        -- List of explicitly imported (or hidden) Names from a single import.
        --   Nothing -> No explicit imports
        --   Just (False, <names>) -> Explicit import list of <names>
        --   Just (True , <names>) -> Explicit hiding of <names>
        importListOf :: ImportDecl GhcRn -> Maybe (Bool, [Name])
        importListOf = fmap toImportList . ideclHiding
          where
            toImportList (h, loc) = (h, map (ieName . unLoc) (unLoc loc))

        isExplicit :: ImportDecl GhcRn -> Bool
        isExplicit x = case importListOf x of
            Nothing -> False
            Just (False, explicit)
                -> nameOccName name `elem`    map nameOccName explicit
            Just (True, hidden)
                -> nameOccName name `notElem` map nameOccName hidden

        -- Check whether the given name would be imported (unqualified) from
        -- an import declaration.
        importViaPrelude :: ImportDecl GhcRn -> Bool
        importViaPrelude x = isPrelude x
                          && isUnqualified x
                          && (isImplicit x || isExplicit x)


-- Notation: is* is for classes the type is an instance of, should* for those
--           that it should also be an instance of based on the corresponding
--           is*.
tcMissingParentClassWarn :: WarningFlag
                         -> Name -- ^ Instances of this ...
                         -> Name -- ^ should also be instances of this
                         -> TcM ()
tcMissingParentClassWarn warnFlag isName shouldName
  = do { warn <- woptM warnFlag
       ; when warn $ do
       { traceTc "tcMissingParentClassWarn" empty
       ; isClass'     <- tcLookupClass_maybe isName
       ; shouldClass' <- tcLookupClass_maybe shouldName
       ; case (isClass', shouldClass') of
              (Just isClass, Just shouldClass) -> do
                  { localInstances <- tcGetInsts
                  ; let isInstance m = is_cls m == isClass
                        isInsts = filter isInstance localInstances
                  ; traceTc "tcMissingParentClassWarn/isInsts" (ppr isInsts)
                  ; forM_ isInsts (checkShouldInst isClass shouldClass)
                  }
              (is',should') ->
                  traceTc "tcMissingParentClassWarn/notIsShould"
                          (hang (ppr isName <> text "/" <> ppr shouldName) 2 (
                            (hsep [ quotes (text "Is"), text "lookup for"
                                  , ppr isName
                                  , text "resulted in", ppr is' ])
                            $$
                            (hsep [ quotes (text "Should"), text "lookup for"
                                  , ppr shouldName
                                  , text "resulted in", ppr should' ])))
       }}
  where
    -- Check whether the desired superclass exists in a given environment.
    checkShouldInst :: Class   -- ^ Class of existing instance
                    -> Class   -- ^ Class there should be an instance of
                    -> ClsInst -- ^ Existing instance
                    -> TcM ()
    checkShouldInst isClass shouldClass isInst
      = do { instEnv <- tcGetInstEnvs
           ; let (instanceMatches, shouldInsts, _)
                    = lookupInstEnv False instEnv shouldClass (is_tys isInst)

           ; traceTc "tcMissingParentClassWarn/checkShouldInst"
                     (hang (ppr isInst) 4
                         (sep [ppr instanceMatches, ppr shouldInsts]))

           -- "<location>: Warning: <type> is an instance of <is> but not
           -- <should>" e.g. "Foo is an instance of Monad but not Applicative"
           ; let instLoc = srcLocSpan . nameSrcLoc $ getName isInst
                 warnMsg (KnownTc name:_) =
                      addWarnAt (Reason warnFlag) instLoc $
                           hsep [ (quotes . ppr . nameOccName) name
                                , text "is an instance of"
                                , (ppr . nameOccName . className) isClass
                                , text "but not"
                                , (ppr . nameOccName . className) shouldClass ]
                                <> text "."
                           $$
                           hsep [ text "This will become an error in"
                                , text "a future release." ]
                 warnMsg _ = pure ()
           ; when (null shouldInsts && null instanceMatches) $
                  warnMsg (is_tcs isInst)
           }

    tcLookupClass_maybe :: Name -> TcM (Maybe Class)
    tcLookupClass_maybe name = tcLookupImported_maybe name >>= \case
        Succeeded (ATyCon tc) | cls@(Just _) <- tyConClass_maybe tc -> pure cls
        _else -> pure Nothing


---------------------------
tcTyClsInstDecls :: [TyClGroup GhcRn]
                 -> [LDerivDecl GhcRn]
                 -> [(RecFlag, LHsBinds GhcRn)]
                 -> TcM (TcGblEnv,            -- The full inst env
                         [InstInfo GhcRn],    -- Source-code instance decls to
                                              -- process; contains all dfuns for
                                              -- this module
                          HsValBinds GhcRn)   -- Supporting bindings for derived
                                              -- instances

tcTyClsInstDecls tycl_decls deriv_decls binds
 = tcAddDataFamConPlaceholders (tycl_decls >>= group_instds) $
   tcAddPatSynPlaceholders (getPatSynBinds binds) $
   do { (tcg_env, inst_info, deriv_info)
          <- tcTyAndClassDecls tycl_decls ;
      ; setGblEnv tcg_env $ do {
          -- With the @TyClDecl@s and @InstDecl@s checked we're ready to
          -- process the deriving clauses, including data family deriving
          -- clauses discovered in @tcTyAndClassDecls@.
          --
          -- Careful to quit now in case there were instance errors, so that
          -- the deriving errors don't pile up as well.
          ; failIfErrsM
          ; (tcg_env', inst_info', val_binds)
              <- tcInstDeclsDeriv deriv_info deriv_decls
          ; setGblEnv tcg_env' $ do {
                failIfErrsM
              ; pure (tcg_env', inst_info' ++ inst_info, val_binds)
      }}}

{- *********************************************************************
*                                                                      *
        Checking for 'main'
*                                                                      *
************************************************************************
-}

checkMain :: Bool  -- False => no 'module M(..) where' header at all
          -> Maybe (Located [LIE GhcPs])  -- Export specs of Main module
          -> TcM TcGblEnv
-- If we are in module Main, check that 'main' is defined and exported.
checkMain explicit_mod_hdr export_ies
 = do   { hsc_env  <- getTopEnv
        ; tcg_env <- getGblEnv
        ; check_main hsc_env tcg_env explicit_mod_hdr export_ies }

check_main :: HscEnv -> TcGblEnv -> Bool -> Maybe (Located [LIE GhcPs])
           -> TcM TcGblEnv
check_main hsc_env tcg_env explicit_mod_hdr export_ies
 | mod /= main_mod
 = traceTc "checkMain not" (ppr main_mod <+> ppr mod) >>
   return tcg_env

 | otherwise
   -- Compare the list of main functions in scope with those
   --   specified in the export list.
 = do mains_all <- lookupInfoOccRn main_fn
                    -- get all 'main' functions in scope
                    -- They may also be imported from other modules!
      case exportedMains of -- check the main(s) specified in the export list
        [ ] -> do
          -- The module has no main functions in the export spec, so we must give
          -- some kind of error message. The tricky part is giving an error message
          -- that accurately characterizes what the problem is.
          -- See Note [Main module without a main function in the export spec]
          traceTc "checkMain no main module exported" ppr_mod_mainfn
          complain_no_main
          -- In order to reduce the number of potential error messages, we check
          -- to see if there are any main functions defined (but not exported)...
          case getSomeMain mains_all of
            Nothing -> return tcg_env
              -- ...if there are no such main functions, there is nothing we can do...
            Just some_main -> use_as_main some_main
                -- ...if there is such a main function, then communicate this to the
                -- typechecker. This can prevent a spurious "Ambiguous type variable"
                -- error message in certain cases, as described in
                -- Note [Main module without a main function in the export spec].
        _ -> do    -- The module has one or more main functions in the export spec
          let mains = filterInsMains exportedMains mains_all
          case mains of
            [] -> do  --
              traceTc "checkMain fail" ppr_mod_mainfn
              complain_no_main
              return tcg_env
            [main_name] -> use_as_main main_name
            _ -> do           -- multiple main functions are exported
              addAmbiguousNameErr main_fn          -- issue error msg
              return tcg_env
  where
    dflags      = hsc_dflags hsc_env
    mod         = tcg_mod tcg_env
    main_mod    = mainModIs hsc_env
    main_mod_nm = moduleName main_mod
    main_fn     = getMainFun dflags
    occ_main_fn = occName main_fn
    interactive = ghcLink dflags == LinkInMemory
    exportedMains = selExportMains export_ies
    ppr_mod_mainfn = ppr main_mod <+> ppr main_fn

    -- There is a single exported 'main' function.
    use_as_main :: Name -> TcM TcGblEnv
    use_as_main main_name = do
        { traceTc "checkMain found" (ppr main_mod <+> ppr main_fn)
        ; let loc       = srcLocSpan (getSrcLoc main_name)
        ; ioTyCon <- tcLookupTyCon ioTyConName
        ; res_ty <- newFlexiTyVarTy liftedTypeKind
        ; let io_ty = mkTyConApp ioTyCon [res_ty]
              skol_info = SigSkol (FunSigCtxt main_name False) io_ty []
              main_expr_rn = L loc (HsVar noExtField (L loc main_name))
        ; (ev_binds, main_expr)
               <- checkConstraints skol_info [] [] $
                  addErrCtxt mainCtxt    $
                  tcCheckMonoExpr main_expr_rn io_ty

                -- See Note [Root-main Id]
                -- Construct the binding
                --      :Main.main :: IO res_ty = runMainIO res_ty main
        ; run_main_id <- tcLookupId runMainIOName
        ; let { root_main_name =  mkExternalName rootMainKey rOOT_MAIN
                                   (mkVarOccFS (fsLit "main"))
                                   (getSrcSpan main_name)
              ; root_main_id = Id.mkExportedVanillaId root_main_name
                                                      (mkTyConApp ioTyCon [res_ty])
              ; co  = mkWpTyApps [res_ty]
              -- The ev_binds of the `main` function may contain deferred
              -- type error when type of `main` is not `IO a`. The `ev_binds`
              -- must be put inside `runMainIO` to ensure the deferred type
              -- error can be emitted correctly. See #13838.
              ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) $
                        mkHsDictLet ev_binds main_expr
              ; main_bind = mkVarBind root_main_id rhs }

        ; return (tcg_env { tcg_main  = Just main_name,
                            tcg_binds = tcg_binds tcg_env
                                        `snocBag` main_bind,
                            tcg_dus   = tcg_dus tcg_env
                                        `plusDU` usesOnly (unitFV main_name)
                        -- Record the use of 'main', so that we don't
                        -- complain about it being defined but not used
        })}

    complain_no_main = unless (interactive && not explicit_mod_hdr)
                              (addErrTc noMainMsg)                  -- #12906
        -- Without an explicit module header...
          -- in interactive mode, don't worry about the absence of 'main'.
          -- in other modes, add error message and go on with typechecking.

    mainCtxt  = text "When checking the type of the" <+> pp_main_fn
    noMainMsg = text "The" <+> pp_main_fn
                <+> text "is not" <+> text defOrExp <+> text "module"
                <+> quotes (ppr main_mod)
    defOrExp  = if null exportedMains then "exported by" else "defined in"

    pp_main_fn = ppMainFn main_fn

    -- Select the main functions from the export list.
    -- Only the module name is needed, the function name is fixed.
    selExportMains :: Maybe (Located [LIE GhcPs]) -> [ModuleName]    -- #16453
    selExportMains Nothing = [main_mod_nm]
        -- no main specified, but there is a header.
    selExportMains (Just exps) = fmap fst $
        filter (\(_,n) -> n == occ_main_fn ) texp
      where
        ies = fmap unLoc $ unLoc exps
        texp = mapMaybe transExportIE ies

    -- Filter all main functions in scope that match the export specs
    filterInsMains :: [ModuleName] -> [Name] -> [Name]               -- #16453
    filterInsMains export_mains inscope_mains =
      [mod | mod <- inscope_mains,
          (moduleName . nameModule) mod `elem` export_mains]

    -- Transform an export_ie to a (ModuleName, OccName) pair.
    -- 'IEVar' constructors contain exported values (functions), eg '(Main.main)'
    -- 'IEModuleContents' constructors contain fully exported modules, eg '(Main)'
    -- All other 'IE...' constructors are not used and transformed to Nothing.
    transExportIE :: IE GhcPs -> Maybe (ModuleName, OccName)         -- #16453
    transExportIE (IEVar _  var) = isQual_maybe $
         upqual $ ieWrappedName $ unLoc var
       where
         -- A module name is always needed, so qualify 'UnQual' rdr names.
         upqual (Unqual occ) = Qual main_mod_nm occ
         upqual rdr = rdr
    transExportIE (IEModuleContents _ mod) = Just (unLoc mod, occ_main_fn)
    transExportIE _ = Nothing

    -- Get a main function that is in scope.
    -- See Note [Main module without a main function in the export spec]
    getSomeMain :: [Name] -> Maybe Name                            -- #16453
    getSomeMain all_mains = case all_mains of
        []  -> Nothing                -- No main function in scope
        [m] -> Just m                 -- Just one main function in scope
        _   -> case mbMainOfMain of
          Nothing -> listToMaybe all_mains -- Take the first main function in scope or Nothing
          _       -> mbMainOfMain          -- Take the Main module's main function or Nothing
      where
        mbMainOfMain = find (\n -> (moduleName . nameModule) n == main_mod_nm )
                          all_mains         -- the main function of the Main module

-- | Get the unqualified name of the function to use as the \"main\" for the main module.
-- Either returns the default name or the one configured on the command line with -main-is
getMainFun :: DynFlags -> RdrName
getMainFun dflags = case mainFunIs dflags of
                      Just fn -> mkRdrUnqual (mkVarOccFS (mkFastString fn))
                      Nothing -> main_RDR_Unqual

ppMainFn :: RdrName -> SDoc
ppMainFn main_fn
  | rdrNameOcc main_fn == mainOcc
  = text "IO action" <+> quotes (ppr main_fn)
  | otherwise
  = text "main IO action" <+> quotes (ppr main_fn)

mainOcc :: OccName
mainOcc = mkVarOccFS (fsLit "main")

{-
Note [Root-main Id]
~~~~~~~~~~~~~~~~~~~
The function that the RTS invokes is always :Main.main, which we call
root_main_id.  (Because GHC allows the user to have a module not
called Main as the main module, we can't rely on the main function
being called "Main.main".  That's why root_main_id has a fixed module
":Main".)

This is unusual: it's a LocalId whose Name has a Module from another
module. Tiresomely, we must filter it out again in GHC.Iface.Make, less we
get two defns for 'main' in the interface file!


Note [Main module without a main function in the export spec]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Giving accurate error messages for a Main module that does not export a main
function is surprisingly tricky. To see why, consider a module in a file
`Foo.hs` that has no `main` function in the explicit export specs of the module
header:

    module Main () where
    foo = return ()

This does not export a main function and therefore should be rejected, per
chapter 5 of the Haskell Report 2010:

   A Haskell program is a collection of modules, one of which, by convention,
   must be called Main and must export the value main. The value of the
   program is the value of the identifier main in module Main, which must be
   a computation of type IO τ for some type τ.

In fact, when you compile the program above using `ghc Foo.hs`, you will
actually get *two* errors:

 - The IO action ‘main’ is not defined in module ‘Main’

 - Ambiguous type variable ‘m0’ arising from a use of ‘return’
   prevents the constraint ‘(Monad m0)’ from being solved.

The first error is self-explanatory, while the second error message occurs
due to the monomorphism restriction.

Now consider what would happen if the program above were compiled with
`ghc -main-is foo Foo`. The has the effect of `foo` being designated as the
main function. The program will still be rejected since it does not export
`foo` (and therefore does not export its main function), but there is one
important difference: `foo` will be checked against the type `IO τ`. As a
result, we would *not* expect the monomorphism restriction error message
to occur, since the typechecker should have no trouble figuring out the type
of `foo`. In other words, we should only throw the former error message,
not the latter.

The implementation uses the function `getSomeMain` to find a potential main
function that is defined but not exported. If one is found, it is passed to
`use_as_main` to inform the typechecker that the main function should be of
type `IO τ`. See also the `T414` and `T17171a` test cases for similar examples
of programs whose error messages are influenced by the situation described in
this Note.


*********************************************************
*                                                       *
                GHCi stuff
*                                                       *
*********************************************************
-}

runTcInteractive :: HscEnv -> TcRn a -> IO (Messages DecoratedSDoc, Maybe a)
-- Initialise the tcg_inst_env with instances from all home modules.
-- This mimics the more selective call to hptInstances in tcRnImports
runTcInteractive hsc_env thing_inside
  = initTcInteractive hsc_env $ withTcPlugins hsc_env $ withHoleFitPlugins hsc_env $
    do { traceTc "setInteractiveContext" $
            vcat [ text "ic_tythings:" <+> vcat (map ppr (ic_tythings icxt))
                 , text "ic_insts:" <+> vcat (map (pprBndr LetBind . instanceDFunId) ic_insts)
                 , text "ic_rn_gbl_env (LocalDef)" <+>
                      vcat (map ppr [ local_gres | gres <- occEnvElts (ic_rn_gbl_env icxt)
                                                 , let local_gres = filter isLocalGRE gres
                                                 , not (null local_gres) ]) ]

       ; let getOrphans m mb_pkg = fmap (\iface -> mi_module iface
                                          : dep_orphs (mi_deps iface))
                                 (loadSrcInterface (text "runTcInteractive") m
                                                   NotBoot mb_pkg)

       ; !orphs <- fmap (force . concat) . forM (ic_imports icxt) $ \i ->
            case i of                   -- force above: see #15111
                IIModule n -> getOrphans n Nothing
                IIDecl i ->
                  let mb_pkg = sl_fs <$> ideclPkgQual i in
                  getOrphans (unLoc (ideclName i)) mb_pkg

       ; let imports = emptyImportAvails {
                            imp_orphs = orphs
                        }

       ; (gbl_env, lcl_env) <- getEnvs
       ; let gbl_env' = gbl_env {
                           tcg_rdr_env      = ic_rn_gbl_env icxt
                         , tcg_type_env     = type_env
                         , tcg_inst_env     = extendInstEnvList
                                               (extendInstEnvList (tcg_inst_env gbl_env) ic_insts)
                                               home_insts
                         , tcg_fam_inst_env = extendFamInstEnvList
                                               (extendFamInstEnvList (tcg_fam_inst_env gbl_env)
                                                                     ic_finsts)
                                               home_fam_insts
                         , tcg_field_env    = mkNameEnv con_fields
                              -- setting tcg_field_env is necessary
                              -- to make RecordWildCards work (test: ghci049)
                         , tcg_fix_env      = ic_fix_env icxt
                         , tcg_default      = ic_default icxt
                              -- must calculate imp_orphs of the ImportAvails
                              -- so that instance visibility is done correctly
                         , tcg_imports      = imports
                         }

             lcl_env' = tcExtendLocalTypeEnv lcl_env lcl_ids

       ; setEnvs (gbl_env', lcl_env') thing_inside }
  where
    (home_insts, home_fam_insts) = hptInstances hsc_env (\_ -> True)

    icxt                     = hsc_IC hsc_env
    (ic_insts, ic_finsts)    = ic_instances icxt
    (lcl_ids, top_ty_things) = partitionWith is_closed (ic_tythings icxt)

    is_closed :: TyThing -> Either (Name, TcTyThing) TyThing
    -- Put Ids with free type variables (always RuntimeUnks)
    -- in the *local* type environment
    -- See Note [Initialising the type environment for GHCi]
    is_closed thing
      | AnId id <- thing
      , not (isTypeClosedLetBndr id)
      = Left (idName id, ATcId { tct_id = id
                               , tct_info = NotLetBound })
      | otherwise
      = Right thing

    type_env1 = mkTypeEnvWithImplicits top_ty_things
    type_env  = extendTypeEnvWithIds type_env1 (map instanceDFunId ic_insts)
                -- Putting the dfuns in the type_env
                -- is just to keep Core Lint happy

    con_fields = [ (dataConName c, dataConFieldLabels c)
                 | ATyCon t <- top_ty_things
                 , c <- tyConDataCons t ]


{- Note [Initialising the type environment for GHCi]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Most of the Ids in ic_things, defined by the user in 'let' stmts,
have closed types. E.g.
   ghci> let foo x y = x && not y

However the GHCi debugger creates top-level bindings for Ids whose
types have free RuntimeUnk skolem variables, standing for unknown
types.  If we don't register these free TyVars as global TyVars then
the typechecker will try to quantify over them and fall over in
skolemiseQuantifiedTyVar. so we must add any free TyVars to the
typechecker's global TyVar set.  That is done by using
tcExtendLocalTypeEnv.

We do this by splitting out the Ids with open types, using 'is_closed'
to do the partition.  The top-level things go in the global TypeEnv;
the open, NotTopLevel, Ids, with free RuntimeUnk tyvars, go in the
local TypeEnv.

Note that we don't extend the local RdrEnv (tcl_rdr); all the in-scope
things are already in the interactive context's GlobalRdrEnv.
Extending the local RdrEnv isn't terrible, but it means there is an
entry for the same Name in both global and local RdrEnvs, and that
lead to duplicate "perhaps you meant..." suggestions (e.g. T5564).

We don't bother with the tcl_th_bndrs environment either.
-}

-- | The returned [Id] is the list of new Ids bound by this statement. It can
-- be used to extend the InteractiveContext via extendInteractiveContext.
--
-- The returned TypecheckedHsExpr is of type IO [ () ], a list of the bound
-- values, coerced to ().
tcRnStmt :: HscEnv -> GhciLStmt GhcPs
         -> IO (Messages DecoratedSDoc, Maybe ([Id], LHsExpr GhcTc, FixityEnv))
tcRnStmt hsc_env rdr_stmt
  = runTcInteractive hsc_env $ do {

    -- The real work is done here
    ((bound_ids, tc_expr), fix_env) <- tcUserStmt rdr_stmt ;
    zonked_expr <- zonkTopLExpr tc_expr ;
    zonked_ids  <- zonkTopBndrs bound_ids ;

    failIfErrsM ;  -- we can't do the next step if there are levity polymorphism errors
                   -- test case: ghci/scripts/T13202{,a}

        -- None of the Ids should be of unboxed type, because we
        -- cast them all to HValues in the end!
    mapM_ bad_unboxed (filter (isUnliftedType . idType) zonked_ids) ;

    traceTc "tcs 1" empty ;
    this_mod <- getModule ;
    global_ids <- mapM (externaliseAndTidyId this_mod) zonked_ids ;
        -- Note [Interactively-bound Ids in GHCi] in GHC.Driver.Env

{- ---------------------------------------------
   At one stage I removed any shadowed bindings from the type_env;
   they are inaccessible but might, I suppose, cause a space leak if we leave them there.
   However, with Template Haskell they aren't necessarily inaccessible.  Consider this
   GHCi session
         Prelude> let f n = n * 2 :: Int
         Prelude> fName <- runQ [| f |]
         Prelude> $(return $ AppE fName (LitE (IntegerL 7)))
         14
         Prelude> let f n = n * 3 :: Int
         Prelude> $(return $ AppE fName (LitE (IntegerL 7)))
   In the last line we use 'fName', which resolves to the *first* 'f'
   in scope. If we delete it from the type env, GHCi crashes because
   it doesn't expect that.

   Hence this code is commented out

-------------------------------------------------- -}

    traceOptTcRn Opt_D_dump_tc
        (vcat [text "Bound Ids" <+> pprWithCommas ppr global_ids,
               text "Typechecked expr" <+> ppr zonked_expr]) ;

    return (global_ids, zonked_expr, fix_env)
    }
  where
    bad_unboxed id = addErr (sep [text "GHCi can't bind a variable of unlifted type:",
                                  nest 2 (pprPrefixOcc id <+> dcolon <+> ppr (idType id))])

{-
--------------------------------------------------------------------------
                Typechecking Stmts in GHCi

Here is the grand plan, implemented in tcUserStmt

        What you type                   The IO [HValue] that hscStmt returns
        -------------                   ------------------------------------
        let pat = expr          ==>     let pat = expr in return [coerce HVal x, coerce HVal y, ...]
                                        bindings: [x,y,...]

        pat <- expr             ==>     expr >>= \ pat -> return [coerce HVal x, coerce HVal y, ...]
                                        bindings: [x,y,...]

        expr (of IO type)       ==>     expr >>= \ it -> return [coerce HVal it]
          [NB: result not printed]      bindings: [it]

        expr (of non-IO type,   ==>     let it = expr in print it >> return [coerce HVal it]
          result showable)              bindings: [it]

        expr (of non-IO type,
          result not showable)  ==>     error
-}

-- | A plan is an attempt to lift some code into the IO monad.
type PlanResult = ([Id], LHsExpr GhcTc)
type Plan = TcM PlanResult

-- | Try the plans in order. If one fails (by raising an exn), try the next.
-- If one succeeds, take it.
runPlans :: [Plan] -> TcM PlanResult
runPlans []     = panic "runPlans"
runPlans [p]    = p
runPlans (p:ps) = tryTcDiscardingErrs (runPlans ps) p

-- | Typecheck (and 'lift') a stmt entered by the user in GHCi into the
-- GHCi 'environment'.
--
-- By 'lift' and 'environment we mean that the code is changed to
-- execute properly in an IO monad. See Note [Interactively-bound Ids
-- in GHCi] in GHC.Driver.Env for more details. We do this lifting by trying
-- different ways ('plans') of lifting the code into the IO monad and
-- type checking each plan until one succeeds.
tcUserStmt :: GhciLStmt GhcPs -> TcM (PlanResult, FixityEnv)

-- An expression typed at the prompt is treated very specially
tcUserStmt (L loc (BodyStmt _ expr _ _))
  = do  { (rn_expr, fvs) <- checkNoErrs (rnLExpr expr)
               -- Don't try to typecheck if the renamer fails!
        ; ghciStep <- getGhciStepIO
        ; uniq <- newUnique
        ; interPrintName <- getInteractivePrintName
        ; let fresh_it  = itName uniq loc
              matches   = [mkMatch (mkPrefixFunRhs (L loc fresh_it)) [] rn_expr
                                   (noLoc emptyLocalBinds)]
              -- [it = expr]
              the_bind  = L loc $ (mkTopFunBind FromSource
                                     (L loc fresh_it) matches)
                                         { fun_ext = fvs }
              -- Care here!  In GHCi the expression might have
              -- free variables, and they in turn may have free type variables
              -- (if we are at a breakpoint, say).  We must put those free vars

              -- [let it = expr]
              let_stmt  = L loc $ LetStmt noExtField $ noLoc $ HsValBinds noExtField
                           $ XValBindsLR
                               (NValBinds [(NonRecursive,unitBag the_bind)] [])

              -- [it <- e]
              bind_stmt = L loc $ BindStmt
                                       (XBindStmtRn
                                          { xbsrn_bindOp = mkRnSyntaxExpr bindIOName
                                          , xbsrn_failOp = Nothing
                                          })
                                       (L loc (VarPat noExtField (L loc fresh_it)))
                                       (nlHsApp ghciStep rn_expr)

              -- [; print it]
              print_it  = L loc $ BodyStmt noExtField
                                           (nlHsApp (nlHsVar interPrintName)
                                           (nlHsVar fresh_it))
                                           (mkRnSyntaxExpr thenIOName)
                                                  noSyntaxExpr

              -- NewA
              no_it_a = L loc $ BodyStmt noExtField (nlHsApps bindIOName
                                       [rn_expr , nlHsVar interPrintName])
                                       (mkRnSyntaxExpr thenIOName)
                                       noSyntaxExpr

              no_it_b = L loc $ BodyStmt noExtField (rn_expr)
                                       (mkRnSyntaxExpr thenIOName)
                                       noSyntaxExpr

              no_it_c = L loc $ BodyStmt noExtField
                                      (nlHsApp (nlHsVar interPrintName) rn_expr)
                                      (mkRnSyntaxExpr thenIOName)
                                      noSyntaxExpr

              -- See Note [GHCi Plans]

              it_plans = [
                    -- Plan A
                    do { stuff@([it_id], _) <- tcGhciStmts [bind_stmt, print_it]
                       ; it_ty <- zonkTcType (idType it_id)
                       ; when (isUnitTy $ it_ty) failM
                       ; return stuff },

                        -- Plan B; a naked bind statement
                    tcGhciStmts [bind_stmt],

                        -- Plan C; check that the let-binding is typeable all by itself.
                        -- If not, fail; if so, try to print it.
                        -- The two-step process avoids getting two errors: one from
                        -- the expression itself, and one from the 'print it' part
                        -- This two-step story is very clunky, alas
                    do { _ <- checkNoErrs (tcGhciStmts [let_stmt])
                                --- checkNoErrs defeats the error recovery of let-bindings
                       ; tcGhciStmts [let_stmt, print_it] } ]

              -- Plans where we don't bind "it"
              no_it_plans = [
                    tcGhciStmts [no_it_a] ,
                    tcGhciStmts [no_it_b] ,
                    tcGhciStmts [no_it_c] ]

        ; generate_it <- goptM Opt_NoIt

        -- We disable `-fdefer-type-errors` in GHCi for naked expressions.
        -- See Note [Deferred type errors in GHCi]

        -- NB: The flag `-fdefer-type-errors` implies `-fdefer-type-holes`
        -- and `-fdefer-out-of-scope-variables`. However the flag
        -- `-fno-defer-type-errors` doesn't imply `-fdefer-type-holes` and
        -- `-fno-defer-out-of-scope-variables`. Thus the later two flags
        -- also need to be unset here.
        ; plan <- unsetGOptM Opt_DeferTypeErrors $
                  unsetGOptM Opt_DeferTypedHoles $
                  unsetGOptM Opt_DeferOutOfScopeVariables $
                    runPlans $ if generate_it
                                 then no_it_plans
                                 else it_plans

        ; fix_env <- getFixityEnv
        ; return (plan, fix_env) }

{- Note [Deferred type errors in GHCi]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In GHCi, we ensure that type errors don't get deferred when type checking the
naked expressions. Deferring type errors here is unhelpful because the
expression gets evaluated right away anyway. It also would potentially emit
two redundant type-error warnings, one from each plan.

#14963 reveals another bug that when deferred type errors is enabled
in GHCi, any reference of imported/loaded variables (directly or indirectly)
in interactively issued naked expressions will cause ghc panic. See more
detailed discussion in #14963.

The interactively issued declarations, statements, as well as the modules
loaded into GHCi, are not affected. That means, for declaration, you could
have

    Prelude> :set -fdefer-type-errors
    Prelude> x :: IO (); x = putStrLn True
    <interactive>:14:26: warning: [-Wdeferred-type-errors]
        ? Couldn't match type ‘Bool’ with ‘[Char]’
          Expected type: String
            Actual type: Bool
        ? In the first argument of ‘putStrLn’, namely ‘True’
          In the expression: putStrLn True
          In an equation for ‘x’: x = putStrLn True

But for naked expressions, you will have

    Prelude> :set -fdefer-type-errors
    Prelude> putStrLn True
    <interactive>:2:10: error:
        ? Couldn't match type ‘Bool’ with ‘[Char]’
          Expected type: String
            Actual type: Bool
        ? In the first argument of ‘putStrLn’, namely ‘True’
          In the expression: putStrLn True
          In an equation for ‘it’: it = putStrLn True

    Prelude> let x = putStrLn True
    <interactive>:2:18: warning: [-Wdeferred-type-errors]
        ? Couldn't match type ‘Bool’ with ‘[Char]’
          Expected type: String
            Actual type: Bool
        ? In the first argument of ‘putStrLn’, namely ‘True’
          In the expression: putStrLn True
          In an equation for ‘x’: x = putStrLn True
-}

tcUserStmt rdr_stmt@(L loc _)
  = do { (([rn_stmt], fix_env), fvs) <- checkNoErrs $
           rnStmts GhciStmtCtxt rnLExpr [rdr_stmt] $ \_ -> do
             fix_env <- getFixityEnv
             return (fix_env, emptyFVs)
            -- Don't try to typecheck if the renamer fails!
       ; traceRn "tcRnStmt" (vcat [ppr rdr_stmt, ppr rn_stmt, ppr fvs])
       ; rnDump rn_stmt ;

       ; ghciStep <- getGhciStepIO
       ; let gi_stmt
               | (L loc (BindStmt x pat expr)) <- rn_stmt
                     = L loc $ BindStmt x pat (nlHsApp ghciStep expr)
               | otherwise = rn_stmt

       ; opt_pr_flag <- goptM Opt_PrintBindResult
       ; let print_result_plan
               | opt_pr_flag                         -- The flag says "print result"
               , [v] <- collectLStmtBinders CollNoDictBinders gi_stmt  -- One binder
               = [mk_print_result_plan gi_stmt v]
               | otherwise = []

        -- The plans are:
        --      [stmt; print v]         if one binder and not v::()
        --      [stmt]                  otherwise
       ; plan <- runPlans (print_result_plan ++ [tcGhciStmts [gi_stmt]])
       ; return (plan, fix_env) }
  where
    mk_print_result_plan stmt v
      = do { stuff@([v_id], _) <- tcGhciStmts [stmt, print_v]
           ; v_ty <- zonkTcType (idType v_id)
           ; when (isUnitTy v_ty || not (isTauTy v_ty)) failM
           ; return stuff }
      where
        print_v  = L loc $ BodyStmt noExtField (nlHsApp (nlHsVar printName)
                                    (nlHsVar v))
                                    (mkRnSyntaxExpr thenIOName) noSyntaxExpr

{-
Note [GHCi Plans]
~~~~~~~~~~~~~~~~~
When a user types an expression in the repl we try to print it in three different
ways. Also, depending on whether -fno-it is set, we bind a variable called `it`
which can be used to refer to the result of the expression subsequently in the repl.

The normal plans are :
  A. [it <- e; print e]     but not if it::()
  B. [it <- e]
  C. [let it = e; print it]

When -fno-it is set, the plans are:
  A. [e >>= print]
  B. [e]
  C. [let it = e in print it]

The reason for -fno-it is explained in #14336. `it` can lead to the repl
leaking memory as it is repeatedly queried.
-}

-- | Typecheck the statements given and then return the results of the
-- statement in the form 'IO [()]'.
tcGhciStmts :: [GhciLStmt GhcRn] -> TcM PlanResult
tcGhciStmts stmts
 = do { ioTyCon <- tcLookupTyCon ioTyConName
      ; ret_id  <- tcLookupId returnIOName             -- return @ IO
      ; let ret_ty      = mkListTy unitTy
            io_ret_ty   = mkTyConApp ioTyCon [ret_ty]
            tc_io_stmts = tcStmtsAndThen GhciStmtCtxt tcDoStmt stmts
                                         (mkCheckExpType io_ret_ty)
            names = collectLStmtsBinders CollNoDictBinders stmts

        -- OK, we're ready to typecheck the stmts
      ; traceTc "GHC.Tc.Module.tcGhciStmts: tc stmts" empty
      ; ((tc_stmts, ids), lie) <- captureTopConstraints $
                                  tc_io_stmts $ \ _ ->
                                  mapM tcLookupId names
                        -- Look up the names right in the middle,
                        -- where they will all be in scope

        -- Simplify the context
      ; traceTc "GHC.Tc.Module.tcGhciStmts: simplify ctxt" empty
      ; const_binds <- checkNoErrs (simplifyInteractive lie)
                -- checkNoErrs ensures that the plan fails if context redn fails


      ; traceTc "GHC.Tc.Module.tcGhciStmts: done" empty

      -- rec_expr is the expression
      --      returnIO @ [()] [unsafeCoerce# () x, ..,  unsafeCorece# () z]
      --
      -- Despite the inconvenience of building the type applications etc,
      -- this *has* to be done in type-annotated post-typecheck form
      -- because we are going to return a list of *polymorphic* values
      -- coerced to type (). If we built a *source* stmt
      --      return [coerce x, ..., coerce z]
      -- then the type checker would instantiate x..z, and we wouldn't
      -- get their *polymorphic* values.  (And we'd get ambiguity errs
      -- if they were overloaded, since they aren't applied to anything.)

      ; AnId unsafe_coerce_id <- tcLookupGlobal unsafeCoercePrimName
           -- We use unsafeCoerce# here because of (U11) in
           -- Note [Implementing unsafeCoerce] in base:Unsafe.Coerce

      ; let ret_expr = nlHsApp (nlHsTyApp ret_id [ret_ty]) $
                       noLoc $ ExplicitList unitTy Nothing $
                       map mk_item ids

            mk_item id = unsafe_coerce_id `nlHsTyApp` [ getRuntimeRep (idType id)
                                                      , getRuntimeRep unitTy
                                                      , idType id, unitTy]
                                          `nlHsApp` nlHsVar id
            stmts = tc_stmts ++ [noLoc (mkLastStmt ret_expr)]

      ; return (ids, mkHsDictLet (EvBinds const_binds) $
                     noLoc (HsDo io_ret_ty GhciStmtCtxt (noLoc stmts)))
    }

-- | Generate a typed ghciStepIO expression (ghciStep :: Ty a -> IO a)
getGhciStepIO :: TcM (LHsExpr GhcRn)
getGhciStepIO = do
    ghciTy <- getGHCiMonad
    a_tv <- newName (mkTyVarOccFS (fsLit "a"))
    let ghciM   = nlHsAppTy (nlHsTyVar ghciTy) (nlHsTyVar a_tv)
        ioM     = nlHsAppTy (nlHsTyVar ioTyConName) (nlHsTyVar a_tv)

        step_ty :: LHsSigType GhcRn
        step_ty = noLoc $ HsSig
                     { sig_bndrs = HsOuterImplicit{hso_ximplicit = [a_tv]}
                     , sig_ext = noExtField
                     , sig_body = nlHsFunTy ghciM ioM }

        stepTy :: LHsSigWcType GhcRn
        stepTy = mkEmptyWildCardBndrs step_ty

    return (noLoc $ ExprWithTySig noExtField (nlHsVar ghciStepIoMName) stepTy)

isGHCiMonad :: HscEnv -> String -> IO (Messages DecoratedSDoc, Maybe Name)
isGHCiMonad hsc_env ty
  = runTcInteractive hsc_env $ do
        rdrEnv <- getGlobalRdrEnv
        let occIO = lookupOccEnv rdrEnv (mkOccName tcName ty)
        case occIO of
            Just [n] -> do
                let name = greMangledName n
                ghciClass <- tcLookupClass ghciIoClassName
                userTyCon <- tcLookupTyCon name
                let userTy = mkTyConApp userTyCon []
                _ <- tcLookupInstance ghciClass [userTy]
                return name

            Just _  -> failWithTc $ text "Ambiguous type!"
            Nothing -> failWithTc $ text ("Can't find type:" ++ ty)

-- | How should we infer a type? See Note [TcRnExprMode]
data TcRnExprMode = TM_Inst     -- ^ Instantiate inferred quantifiers only (:type)
                  | TM_Default  -- ^ Instantiate all quantifiers,
                                --   and do eager defaulting (:type +d)

-- | tcRnExpr just finds the type of an expression
--   for :type
tcRnExpr :: HscEnv
         -> TcRnExprMode
         -> LHsExpr GhcPs
         -> IO (Messages DecoratedSDoc, Maybe Type)
tcRnExpr hsc_env mode rdr_expr
  = runTcInteractive hsc_env $
    do {

    (rn_expr, _fvs) <- rnLExpr rdr_expr ;
    failIfErrsM ;

    -- Typecheck the expression
    ((tclvl, res_ty), lie)
          <- captureTopConstraints $
             pushTcLevelM          $
             tcInferSigma inst rn_expr ;

    -- Generalise
    uniq <- newUnique ;
    let { fresh_it = itName uniq (getLoc rdr_expr) } ;
    ((qtvs, dicts, _, _), residual)
         <- captureConstraints $
            simplifyInfer tclvl infer_mode
                          []    {- No sig vars -}
                          [(fresh_it, res_ty)]
                          lie ;

    -- Ignore the dictionary bindings
    _ <- perhaps_disable_default_warnings $
         simplifyInteractive residual ;

    let { all_expr_ty = mkInfForAllTys qtvs $
                        mkPhiTy (map idType dicts) res_ty } ;
    ty <- zonkTcType all_expr_ty ;

    -- We normalise type families, so that the type of an expression is the
    -- same as of a bound expression (GHC.Tc.Gen.Bind.mkInferredPolyId). See Trac
    -- #10321 for further discussion.
    fam_envs <- tcGetFamInstEnvs ;
    -- normaliseType returns a coercion which we discard, so the Role is
    -- irrelevant
    return (snd (normaliseType fam_envs Nominal ty))
    }
  where
    -- Optionally instantiate the type of the expression
    -- See Note [TcRnExprMode]
    (inst, infer_mode, perhaps_disable_default_warnings) = case mode of
      TM_Inst    -> (False, NoRestrictions,  id)
      TM_Default -> (True,  EagerDefaulting, unsetWOptM Opt_WarnTypeDefaults)

{- Note [Implementing :type]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider   :type const

We want    forall a b. a -> b -> a
and not    forall {a}{b}. a -> b -> a

The latter is what we'd get if we eagerly instantiated and then
re-generalised with Inferred binders.  It makes a difference, because
it tells us we where we can use Visible Type Application (VTA).

And also for   :type const @Int
we want        forall b. Int -> b -> Int
and not        forall {b}. Int -> b -> Int

Solution: use tcInferSigma, which in turn uses tcInferApp, which
has a special case for application chains.
-}

--------------------------
tcRnImportDecls :: HscEnv
                -> [LImportDecl GhcPs]
                -> IO (Messages DecoratedSDoc, Maybe GlobalRdrEnv)
-- Find the new chunk of GlobalRdrEnv created by this list of import
-- decls.  In contract tcRnImports *extends* the TcGblEnv.
tcRnImportDecls hsc_env import_decls
 =  runTcInteractive hsc_env $
    do { gbl_env <- updGblEnv zap_rdr_env $
                    tcRnImports hsc_env import_decls
       ; return (tcg_rdr_env gbl_env) }
  where
    zap_rdr_env gbl_env = gbl_env { tcg_rdr_env = emptyGlobalRdrEnv }

-- tcRnType just finds the kind of a type
tcRnType :: HscEnv
         -> ZonkFlexi
         -> Bool        -- Normalise the returned type
         -> LHsType GhcPs
         -> IO (Messages DecoratedSDoc, Maybe (Type, Kind))
tcRnType hsc_env flexi normalise rdr_type
  = runTcInteractive hsc_env $
    setXOptM LangExt.PolyKinds $   -- See Note [Kind-generalise in tcRnType]
    do { (HsWC { hswc_ext = wcs, hswc_body = rn_type }, _fvs)
               <- rnHsWcType GHCiCtx (mkHsWildCardBndrs rdr_type)
                  -- The type can have wild cards, but no implicit
                  -- generalisation; e.g.   :kind (T _)
       ; failIfErrsM

        -- We follow Note [Recipe for checking a signature] in GHC.Tc.Gen.HsType here

        -- Now kind-check the type
        -- It can have any rank or kind
        -- First bring into scope any wildcards
       ; traceTc "tcRnType" (vcat [ppr wcs, ppr rn_type])
       ; ((ty, kind), wanted)
               <- captureTopConstraints $
                  pushTcLevelM_         $
                  bindNamedWildCardBinders wcs $ \ wcs' ->
                  do { mapM_ emitNamedTypeHole wcs'
                     ; tcInferLHsTypeUnsaturated rn_type }

       -- Since all the wanteds are equalities, the returned bindings will be empty
       ; empty_binds <- simplifyTop wanted
       ; MASSERT2( isEmptyBag empty_binds, ppr empty_binds )

       -- Do kind generalisation; see Note [Kind-generalise in tcRnType]
       ; kvs <- kindGeneralizeAll kind

       ; e <- mkEmptyZonkEnv flexi
       ; ty  <- zonkTcTypeToTypeX e ty

       -- Do validity checking on type
       ; checkValidType (GhciCtxt True) ty

       -- Optionally (:k vs :k!) normalise the type. Does two things:
       --   normaliseType: expand type-family applications
       --   expandTypeSynonyms: expand type synonyms (#18828)
       ; fam_envs <- tcGetFamInstEnvs
       ; let ty' | normalise = expandTypeSynonyms $ snd $
                               normaliseType fam_envs Nominal ty
                 | otherwise = ty

       ; return (ty', mkInfForAllTys kvs (tcTypeKind ty')) }


{- Note [TcRnExprMode]
~~~~~~~~~~~~~~~~~~~~~~
How should we infer a type when a user asks for the type of an expression e
at the GHCi prompt? We offer 2 different possibilities, described below. Each
considers this example, with -fprint-explicit-foralls enabled.  See also
https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0179-printing-foralls.rst

:type / TM_Inst

  In this mode, we report the type obained by instantiating only the
  /inferred/ quantifiers of e's type, solving constraints, and
  re-generalising, as discussed in #11376.

  > :type reverse
  reverse :: forall a. [a] -> [a]

  -- foo :: forall a f b. (Show a, Num b, Foldable f) => a -> f b -> String
  > :type +v foo @Int
  forall f b. (Show Int, Num b, Foldable f) => Int -> f b -> String

  Note that Show Int is still reported, because the solver never got a chance
  to see it.

:type +d / TM_Default

  This mode is for the benefit of users who wish to see instantiations
  of generalized types, and in particular to instantiate Foldable and
  Traversable.  In this mode, all type variables (inferred or
  specified) are instantiated.  Because GHCi uses
  -XExtendedDefaultRules, this means that Foldable and Traversable are
  defaulted.

  > :type +d reverse
  reverse :: forall {a}. [a] -> [a]

  -- foo :: forall a f b. (Show a, Num b, Foldable f) => a -> f b -> String
  > :type +d foo @Int
  Int -> [Integer] -> String

  Note that this mode can sometimes lead to a type error, if a type variable is
  used with a defaultable class but cannot actually be defaulted:

  bar :: (Num a, Monoid a) => a -> a
  > :type +d bar
  ** error **

  The error arises because GHC tries to default a but cannot find a concrete
  type in the defaulting list that is both Num and Monoid. (If this list is
  modified to include an element that is both Num and Monoid, the defaulting
  would succeed, of course.)

  Note that the variables and constraints are reordered here, because this
  is possible during regeneralization. Also note that the variables are
  reported as Inferred instead of Specified.

Note [Kind-generalise in tcRnType]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We switch on PolyKinds when kind-checking a user type, so that we will
kind-generalise the type, even when PolyKinds is not otherwise on.
This gives the right default behaviour at the GHCi prompt, where if
you say ":k T", and T has a polymorphic kind, you'd like to see that
polymorphism. Of course.  If T isn't kind-polymorphic you won't get
anything unexpected, but the apparent *loss* of polymorphism, for
types that you know are polymorphic, is quite surprising.  See Trac
#7688 for a discussion.

Note that the goal is to generalise the *kind of the type*, not
the type itself! Example:
  ghci> data SameKind :: k -> k -> Type
  ghci> :k SameKind _

We want to get `k -> Type`, not `Any -> Type`, which is what we would
get without kind-generalisation. Note that `:k SameKind` is OK, as
GHC will not instantiate SameKind here, and so we see its full kind
of `forall k. k -> k -> Type`.

************************************************************************
*                                                                      *
                 tcRnDeclsi
*                                                                      *
************************************************************************

tcRnDeclsi exists to allow class, data, and other declarations in GHCi.
-}

tcRnDeclsi :: HscEnv
           -> [LHsDecl GhcPs]
           -> IO (Messages DecoratedSDoc, Maybe TcGblEnv)
tcRnDeclsi hsc_env local_decls
  = runTcInteractive hsc_env $
    tcRnSrcDecls False local_decls Nothing

externaliseAndTidyId :: Module -> Id -> TcM Id
externaliseAndTidyId this_mod id
  = do { name' <- externaliseName this_mod (idName id)
       ; return $ globaliseId id
                     `setIdName` name'
                     `setIdType` tidyTopType (idType id) }


{-
************************************************************************
*                                                                      *
        More GHCi stuff, to do with browsing and getting info
*                                                                      *
************************************************************************
-}

-- | ASSUMES that the module is either in the 'HomePackageTable' or is
-- a package module with an interface on disk.  If neither of these is
-- true, then the result will be an error indicating the interface
-- could not be found.
getModuleInterface :: HscEnv -> Module -> IO (Messages DecoratedSDoc, Maybe ModIface)
getModuleInterface hsc_env mod
  = runTcInteractive hsc_env $
    loadModuleInterface (text "getModuleInterface") mod

tcRnLookupRdrName :: HscEnv -> Located RdrName
                  -> IO (Messages DecoratedSDoc, Maybe [Name])
-- ^ Find all the Names that this RdrName could mean, in GHCi
tcRnLookupRdrName hsc_env (L loc rdr_name)
  = runTcInteractive hsc_env $
    setSrcSpan loc           $
    do {   -- If the identifier is a constructor (begins with an
           -- upper-case letter), then we need to consider both
           -- constructor and type class identifiers.
         let rdr_names = dataTcOccs rdr_name
       ; names_s <- mapM lookupInfoOccRn rdr_names
       ; let names = concat names_s
       ; when (null names) (addErrTc (text "Not in scope:" <+> quotes (ppr rdr_name)))
       ; return names }

tcRnLookupName :: HscEnv -> Name -> IO (Messages DecoratedSDoc, Maybe TyThing)
tcRnLookupName hsc_env name
  = runTcInteractive hsc_env $
    tcRnLookupName' name

-- To look up a name we have to look in the local environment (tcl_lcl)
-- as well as the global environment, which is what tcLookup does.
-- But we also want a TyThing, so we have to convert:

tcRnLookupName' :: Name -> TcRn TyThing
tcRnLookupName' name = do
   tcthing <- tcLookup name
   case tcthing of
     AGlobal thing    -> return thing
     ATcId{tct_id=id} -> return (AnId id)
     _ -> panic "tcRnLookupName'"

tcRnGetInfo :: HscEnv
            -> Name
            -> IO ( Messages DecoratedSDoc
                  , Maybe (TyThing, Fixity, [ClsInst], [FamInst], SDoc))

-- Used to implement :info in GHCi
--
-- Look up a RdrName and return all the TyThings it might be
-- A capitalised RdrName is given to us in the DataName namespace,
-- but we want to treat it as *both* a data constructor
--  *and* as a type or class constructor;
-- hence the call to dataTcOccs, and we return up to two results
tcRnGetInfo hsc_env name
  = runTcInteractive hsc_env $
    do { loadUnqualIfaces hsc_env (hsc_IC hsc_env)
           -- Load the interface for all unqualified types and classes
           -- That way we will find all the instance declarations
           -- (Packages have not orphan modules, and we assume that
           --  in the home package all relevant modules are loaded.)

       ; thing  <- tcRnLookupName' name
       ; fixity <- lookupFixityRn name
       ; (cls_insts, fam_insts) <- lookupInsts thing
       ; let info = lookupKnownNameInfo name
       ; return (thing, fixity, cls_insts, fam_insts, info) }


-- Lookup all class and family instances for a type constructor.
--
-- This function filters all instances in the type environment, so there
-- is a lot of duplicated work if it is called many times in the same
-- type environment. If this becomes a problem, the NameEnv computed
-- in GHC.getNameToInstancesIndex could be cached in TcM and both functions
-- could be changed to consult that index.
lookupInsts :: TyThing -> TcM ([ClsInst],[FamInst])
lookupInsts (ATyCon tc)
  = do  { InstEnvs { ie_global = pkg_ie, ie_local = home_ie, ie_visible = vis_mods } <- tcGetInstEnvs
        ; (pkg_fie, home_fie) <- tcGetFamInstEnvs
                -- Load all instances for all classes that are
                -- in the type environment (which are all the ones
                -- we've seen in any interface file so far)

          -- Return only the instances relevant to the given thing, i.e.
          -- the instances whose head contains the thing's name.
        ; let cls_insts =
                 [ ispec        -- Search all
                 | ispec <- instEnvElts home_ie ++ instEnvElts pkg_ie
                 , instIsVisible vis_mods ispec
                 , tc_name `elemNameSet` orphNamesOfClsInst ispec ]
        ; let fam_insts =
                 [ fispec
                 | fispec <- famInstEnvElts home_fie ++ famInstEnvElts pkg_fie
                 , tc_name `elemNameSet` orphNamesOfFamInst fispec ]
        ; return (cls_insts, fam_insts) }
  where
    tc_name     = tyConName tc

lookupInsts _ = return ([],[])

loadUnqualIfaces :: HscEnv -> InteractiveContext -> TcM ()
-- Load the interface for everything that is in scope unqualified
-- This is so that we can accurately report the instances for
-- something
loadUnqualIfaces hsc_env ictxt
  = initIfaceTcRn $
    mapM_ (loadSysInterface doc) (moduleSetElts (mkModuleSet unqual_mods))
  where
    home_unit = hsc_home_unit hsc_env

    unqual_mods = [ nameModule name
                  | gre <- globalRdrEnvElts (ic_rn_gbl_env ictxt)
                  , let name = greMangledName gre
                  , nameIsFromExternalPackage home_unit name
                  , isTcOcc (nameOccName name)   -- Types and classes only
                  , unQualOK gre ]               -- In scope unqualified
    doc = text "Need interface for module whose export(s) are in scope unqualified"



{-
************************************************************************
*                                                                      *
                Debugging output
      This is what happens when you do -ddump-types
*                                                                      *
************************************************************************
-}

-- | Dump, with a banner, if -ddump-rn
rnDump :: (Outputable a, Data a) => a -> TcRn ()
rnDump rn = dumpOptTcRn Opt_D_dump_rn "Renamer" FormatHaskell (ppr rn)

tcDump :: TcGblEnv -> TcRn ()
tcDump env
 = do { dflags <- getDynFlags ;
        unit_state <- hsc_units <$> getTopEnv ;

        -- Dump short output if -ddump-types or -ddump-tc
        when (dopt Opt_D_dump_types dflags || dopt Opt_D_dump_tc dflags)
          (dumpTcRn True Opt_D_dump_types
            "" FormatText (pprWithUnitState unit_state short_dump)) ;

        -- Dump bindings if -ddump-tc
        dumpOptTcRn Opt_D_dump_tc "Typechecker" FormatHaskell full_dump;

        -- Dump bindings as an hsSyn AST if -ddump-tc-ast
        dumpOptTcRn Opt_D_dump_tc_ast "Typechecker AST" FormatHaskell ast_dump
   }
  where
    short_dump = pprTcGblEnv env
    full_dump  = pprLHsBinds (tcg_binds env)
        -- NB: foreign x-d's have undefined's in their types;
        --     hence can't show the tc_fords
    ast_dump = showAstData NoBlankSrcSpan (tcg_binds env)

-- It's unpleasant having both pprModGuts and pprModDetails here
pprTcGblEnv :: TcGblEnv -> SDoc
pprTcGblEnv (TcGblEnv { tcg_type_env  = type_env,
                        tcg_insts     = insts,
                        tcg_fam_insts = fam_insts,
                        tcg_rules     = rules,
                        tcg_imports   = imports })
  = getPprDebug $ \debug ->
    vcat [ ppr_types debug type_env
         , ppr_tycons debug fam_insts type_env
         , ppr_datacons debug type_env
         , ppr_patsyns type_env
         , ppr_insts insts
         , ppr_fam_insts fam_insts
         , ppr_rules rules
         , text "Dependent modules:" <+>
                pprUFM (imp_dep_mods imports) (ppr . sort)
         , text "Dependent packages:" <+>
                ppr (S.toList $ imp_dep_pkgs imports)]
                -- The use of sort is just to reduce unnecessary
                -- wobbling in testsuite output

ppr_rules :: [LRuleDecl GhcTc] -> SDoc
ppr_rules rules
  = ppUnless (null rules) $
    hang (text "RULES")
       2 (vcat (map ppr rules))

ppr_types :: Bool -> TypeEnv -> SDoc
ppr_types debug type_env
  = ppr_things "TYPE SIGNATURES" ppr_sig
             (sortBy (comparing getOccName) ids)
  where
    ids = [id | id <- typeEnvIds type_env, want_sig id]
    want_sig id
      | debug     = True
      | otherwise = hasTopUserName id
                    && case idDetails id of
                         VanillaId    -> True
                         RecSelId {}  -> True
                         ClassOpId {} -> True
                         FCallId {}   -> True
                         _            -> False
             -- Data cons (workers and wrappers), pattern synonyms,
             -- etc are suppressed (unless -dppr-debug),
             -- because they appear elsewhere

    ppr_sig id = hang (pprPrefixOcc id <+> dcolon) 2 (ppr (tidyTopType (idType id)))

ppr_tycons :: Bool -> [FamInst] -> TypeEnv -> SDoc
ppr_tycons debug fam_insts type_env
  = vcat [ ppr_things "TYPE CONSTRUCTORS" ppr_tc tycons
         , ppr_things "COERCION AXIOMS" ppr_ax
                      (typeEnvCoAxioms type_env) ]
  where
    fi_tycons = famInstsRepTyCons fam_insts

    tycons = sortBy (comparing getOccName) $
             [tycon | tycon <- typeEnvTyCons type_env
                    , want_tycon tycon]
             -- Sort by OccName to reduce unnecessary changes
    want_tycon tycon | debug      = True
                     | otherwise  = isExternalName (tyConName tycon) &&
                                    not (tycon `elem` fi_tycons)
    ppr_tc tc
       = vcat [ hang (ppr (tyConFlavour tc) <+> pprPrefixOcc (tyConName tc)
                      <> braces (ppr (tyConArity tc)) <+> dcolon)
                   2 (ppr (tidyTopType (tyConKind tc)))
              , nest 2 $
                ppWhen show_roles $
                text "roles" <+> (sep (map ppr roles)) ]
       where
         show_roles = debug || not (all (== boring_role) roles)
         roles = tyConRoles tc
         boring_role | isClassTyCon tc = Nominal
                     | otherwise       = Representational
            -- Matches the choice in GHC.Iface.Syntax, calls to pprRoles

    ppr_ax ax = ppr (coAxiomToIfaceDecl ax)
      -- We go via IfaceDecl rather than using pprCoAxiom
      -- This way we get the full axiom (both LHS and RHS) with
      -- wildcard binders tidied to _1, _2, etc.

ppr_datacons :: Bool -> TypeEnv -> SDoc
ppr_datacons debug type_env
  = ppr_things "DATA CONSTRUCTORS" ppr_dc wanted_dcs
      -- The filter gets rid of class data constructors
  where
    ppr_dc dc = sdocOption sdocLinearTypes (\show_linear_types ->
                ppr dc <+> dcolon <+> ppr (dataConDisplayType show_linear_types dc))
    all_dcs    = typeEnvDataCons type_env
    wanted_dcs | debug     = all_dcs
               | otherwise = filterOut is_cls_dc all_dcs
    is_cls_dc dc = isClassTyCon (dataConTyCon dc)

ppr_patsyns :: TypeEnv -> SDoc
ppr_patsyns type_env
  = ppr_things "PATTERN SYNONYMS" ppr_ps
               (typeEnvPatSyns type_env)
  where
    ppr_ps ps = pprPrefixOcc ps <+> dcolon <+> pprPatSynType ps

ppr_insts :: [ClsInst] -> SDoc
ppr_insts ispecs
  = ppr_things "CLASS INSTANCES" pprInstance ispecs

ppr_fam_insts :: [FamInst] -> SDoc
ppr_fam_insts fam_insts
  = ppr_things "FAMILY INSTANCES" pprFamInst fam_insts

ppr_things :: String -> (a -> SDoc) -> [a] -> SDoc
ppr_things herald ppr_one things
  | null things = empty
  | otherwise   = text herald $$ nest 2 (vcat (map ppr_one things))

hasTopUserName :: NamedThing x => x -> Bool
-- A top-level thing whose name is not "derived"
-- Thus excluding things like $tcX, from Typeable boilerplate
-- and C:Coll from class-dictionary data constructors
hasTopUserName x
  = isExternalName name && not (isDerivedOccName (nameOccName name))
  where
    name = getName x

{-
********************************************************************************

Type Checker Plugins

********************************************************************************
-}

withTcPlugins :: HscEnv -> TcM a -> TcM a
withTcPlugins hsc_env m =
    case getTcPlugins hsc_env of
       []      -> m  -- Common fast case
       plugins -> do
                ev_binds_var <- newTcEvBinds
                (solvers,stops) <- unzip `fmap` mapM (startPlugin ev_binds_var) plugins
                -- This ensures that tcPluginStop is called even if a type
                -- error occurs during compilation (Fix of #10078)
                eitherRes <- tryM $
                  updGblEnv (\e -> e { tcg_tc_plugins = solvers }) m
                mapM_ (flip runTcPluginM ev_binds_var) stops
                case eitherRes of
                  Left _ -> failM
                  Right res -> return res
  where
  startPlugin ev_binds_var (TcPlugin start solve stop) =
    do s <- runTcPluginM start ev_binds_var
       return (solve s, stop s)

getTcPlugins :: HscEnv -> [GHC.Tc.Utils.Monad.TcPlugin]
getTcPlugins hsc_env = catMaybes $ mapPlugins hsc_env (\p args -> tcPlugin p args)


withHoleFitPlugins :: HscEnv -> TcM a -> TcM a
withHoleFitPlugins hsc_env m =
  case getHfPlugins hsc_env of
    [] -> m  -- Common fast case
    plugins -> do (plugins,stops) <- unzip `fmap` mapM startPlugin plugins
                  -- This ensures that hfPluginStop is called even if a type
                  -- error occurs during compilation.
                  eitherRes <- tryM $
                    updGblEnv (\e -> e { tcg_hf_plugins = plugins }) m
                  sequence_ stops
                  case eitherRes of
                    Left _ -> failM
                    Right res -> return res
  where
    startPlugin (HoleFitPluginR init plugin stop) =
      do ref <- init
         return (plugin ref, stop ref)

getHfPlugins :: HscEnv -> [HoleFitPluginR]
getHfPlugins hsc_env =
  catMaybes $ mapPlugins hsc_env (\p args -> holeFitPlugin p args)


runRenamerPlugin :: TcGblEnv
                 -> HsGroup GhcRn
                 -> TcM (TcGblEnv, HsGroup GhcRn)
runRenamerPlugin gbl_env hs_group = do
    hsc_env <- getTopEnv
    withPlugins hsc_env
      (\p opts (e, g) -> ( mark_plugin_unsafe (hsc_dflags hsc_env)
                            >> renamedResultAction p opts e g))
      (gbl_env, hs_group)


-- XXX: should this really be a Maybe X?  Check under which circumstances this
-- can become a Nothing and decide whether this should instead throw an
-- exception/signal an error.
type RenamedStuff =
        (Maybe (HsGroup GhcRn, [LImportDecl GhcRn], Maybe [(LIE GhcRn, Avails)],
                Maybe LHsDocString))

-- | Extract the renamed information from TcGblEnv.
getRenamedStuff :: TcGblEnv -> RenamedStuff
getRenamedStuff tc_result
  = fmap (\decls -> ( decls, tcg_rn_imports tc_result
                    , tcg_rn_exports tc_result, tcg_doc_hdr tc_result ) )
         (tcg_rn_decls tc_result)

runTypecheckerPlugin :: ModSummary -> TcGblEnv -> TcM TcGblEnv
runTypecheckerPlugin sum gbl_env = do
    hsc_env <- getTopEnv
    withPlugins hsc_env
      (\p opts env -> mark_plugin_unsafe (hsc_dflags hsc_env)
                        >> typeCheckResultAction p opts sum env)
      gbl_env

mark_plugin_unsafe :: DynFlags -> TcM ()
mark_plugin_unsafe dflags = unless (gopt Opt_PluginTrustworthy dflags) $
  recordUnsafeInfer pluginUnsafe
  where
    unsafeText = "Use of plugins makes the module unsafe"
    pluginUnsafe = unitBag ( mkPlainWarnMsg noSrcSpan
                                   (Outputable.text unsafeText) )