Rework renaming of children in export lists.

The target of this patch is exports such as:

```
module Foo ( T(A, B, C) ) where
```

Essentially this patch makes sure that we use the correct lookup functions in order
to lookup the names in parent-children export lists. This change
highlighted the complexity of this small part of GHC which accounts for
the scale.

This change was motivated by wanting to
remove the `PatternSynonym` constructor from `Parent`. As with all these
things, it quickly spiraled out of control into a much larger refactor.

Reviewers: simonpj, goldfire, bgamari, austin

Subscribers: adamgundry, thomie

Differential Revision: https://phabricator.haskell.org/D2179

GHC Trac Issues: #11970

14 files changed, 82 insertions, 10 deletions

diff --git a/testsuite/tests/module/MultiExport.hs b/testsuite/tests/module/MultiExport.hs
new file mode 100644
index 0000000000..4f8079ee81
--- /dev/null
+++ b/testsuite/tests/module/MultiExport.hs
@@ -0,0 +1,6 @@
+{-# LANGUAGE PatternSynonyms #-}
+module Foo ( A(x, x) ) where
+
+data A = A  Int
+
+pattern Pattern{x} = A x
diff --git a/testsuite/tests/module/MultiExport.stderr b/testsuite/tests/module/MultiExport.stderr
new file mode 100644
index 0000000000..d117b69c8b
--- /dev/null
+++ b/testsuite/tests/module/MultiExport.stderr
@@ -0,0 +1,3 @@
+
+MultiExport.hs:2:14: warning: [-Wduplicate-exports (in -Wdefault)]
+    ‘x’ is exported by ‘A(x, x)’ and ‘A(x, x)’
diff --git a/testsuite/tests/module/T11970.hs b/testsuite/tests/module/T11970.hs
new file mode 100644
index 0000000000..3c90c6913d
--- /dev/null
+++ b/testsuite/tests/module/T11970.hs
@@ -0,0 +1,19 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE PatternSynonyms #-}
+
+module T11970(B(recSel), Foo((--.->)), C(C,P,x,Q, B, recSel)) where
+
+pattern D = Nothing
+
+newtype B = B { recSel :: Int }
+
+class Foo a where
+  type (--.->) a
+
+newtype C = C Int
+
+pattern P x = C x
+
+pattern Q{x} = C x
diff --git a/testsuite/tests/module/T11970.stderr b/testsuite/tests/module/T11970.stderr
new file mode 100644
index 0000000000..c6799a1898
--- /dev/null
+++ b/testsuite/tests/module/T11970.stderr
@@ -0,0 +1,12 @@
+
+T11970.hs:6:40: error:
+    • The type constructor ‘C’ is not the parent of the data constructor ‘B’.
+      Data constructors can only be exported with their parent type constructor.
+      Parent: B
+    • In the export: C(C, P, x, Q, B, recSel)
+
+T11970.hs:6:40: error:
+    • The type constructor ‘C’ is not the parent of the record selector ‘recSel’.
+      Record selectors can only be exported with their parent type constructor.
+      Parent: B
+    • In the export: C(C, P, x, Q, B, recSel)
diff --git a/testsuite/tests/module/T11970A.hs b/testsuite/tests/module/T11970A.hs
new file mode 100644
index 0000000000..e9d6e95568
--- /dev/null
+++ b/testsuite/tests/module/T11970A.hs
@@ -0,0 +1,3 @@
+module T11970A ( Fail(a) ) where
+
+import T11970A1 ( Fail(a, b) )
diff --git a/testsuite/tests/module/T11970A.stderr b/testsuite/tests/module/T11970A.stderr
new file mode 100644
index 0000000000..6b478a7335
--- /dev/null
+++ b/testsuite/tests/module/T11970A.stderr
@@ -0,0 +1,5 @@
+[1 of 2] Compiling T11970A1         ( T11970A1.hs, T11970A1.o )
+[2 of 2] Compiling T11970A          ( T11970A.hs, T11970A.o )
+
+T11970A.hs:3:1: warning: [-Wunused-imports (in -Wextra)]
+    The import of ‘Fail(b)’ from module ‘T11970A1’ is redundant
diff --git a/testsuite/tests/module/T11970A1.hs b/testsuite/tests/module/T11970A1.hs
new file mode 100644
index 0000000000..6c9c6d2a7a
--- /dev/null
+++ b/testsuite/tests/module/T11970A1.hs
@@ -0,0 +1,3 @@
+module T11970A1 where
+
+data Fail = Fail { a :: Int, b :: Int }
diff --git a/testsuite/tests/module/T11970B.hs b/testsuite/tests/module/T11970B.hs
new file mode 100644
index 0000000000..70a091f141
--- /dev/null
+++ b/testsuite/tests/module/T11970B.hs
@@ -0,0 +1,5 @@
+module T11970B ( A(f) ) where
+
+data A = A
+
+f = A
diff --git a/testsuite/tests/module/T11970B.stderr b/testsuite/tests/module/T11970B.stderr
new file mode 100644
index 0000000000..240a5fa5f6
--- /dev/null
+++ b/testsuite/tests/module/T11970B.stderr
@@ -0,0 +1,5 @@
+
+T11970B.hs:1:18: error:
+    • The type constructor ‘A’ is not the parent of the identifier ‘f’.
+      Identifiers can only be exported with their parent type constructor.
+    • In the export: A(f)
diff --git a/testsuite/tests/module/all.T b/testsuite/tests/module/all.T
index 89bdcc00e0..c7097b2dfc 100644
--- a/testsuite/tests/module/all.T
+++ b/testsuite/tests/module/all.T
@@ -350,3 +350,7 @@ test('T10233', extra_clean(['T01233a.hi', 'T01233a.o']),
 test('T11432', normal, compile_fail, [''])
 test('T11432a', normal, compile_fail, [''])
 test('T12026', normal, compile_fail, [''])
+test('T11970', normal, compile_fail, [''])
+test('T11970A', [], multimod_compile, ['T11970A','-Wunused-imports'])
+test('T11970B', normal, compile_fail, [''])
+test('MultiExport', normal, compile, [''])
diff --git a/testsuite/tests/module/mod10.stderr b/testsuite/tests/module/mod10.stderr
index dd08d880b3..1412b6af7d 100644
--- a/testsuite/tests/module/mod10.stderr
+++ b/testsuite/tests/module/mod10.stderr
@@ -1,2 +1,4 @@
 
-mod10.hs:2:10: Not in scope: type constructor or class ‘T’
+mod10.hs:2:10: error:
+    • Not in scope: type constructor or class ‘T’
+    • In the export: T(K1)
diff --git a/testsuite/tests/module/mod17.stderr b/testsuite/tests/module/mod17.stderr
index 9dcf0e612f..91c4ff2731 100644
--- a/testsuite/tests/module/mod17.stderr
+++ b/testsuite/tests/module/mod17.stderr
@@ -1,4 +1,6 @@
 
-mod17.hs:2:10:
-    The export item ‘C(m1, m2, m3, Left)’
-    attempts to export constructors or class methods that are not visible here
+mod17.hs:2:10: error:
+    • The type constructor ‘C’ is not the parent of the data constructor ‘Left’.
+      Data constructors can only be exported with their parent type constructor.
+      Parent: Either
+    • In the export: C(m1, m2, m3, Left)
diff --git a/testsuite/tests/module/mod3.stderr b/testsuite/tests/module/mod3.stderr
index 6e7a88bd6d..c0c620e240 100644
--- a/testsuite/tests/module/mod3.stderr
+++ b/testsuite/tests/module/mod3.stderr
@@ -1,4 +1,6 @@
 
-mod3.hs:2:10:
-    The export item ‘T(K1)’
-    attempts to export constructors or class methods that are not visible here
+mod3.hs:2:10: error:
+    • The type constructor ‘T’ is not the parent of the data constructor ‘K1’.
+      Data constructors can only be exported with their parent type constructor.
+      Parent: T'
+    • In the export: T(K1)
diff --git a/testsuite/tests/module/mod4.stderr b/testsuite/tests/module/mod4.stderr
index 2391dadcdc..d9e8339740 100644
--- a/testsuite/tests/module/mod4.stderr
+++ b/testsuite/tests/module/mod4.stderr
@@ -1,4 +1,5 @@
 
-mod4.hs:2:10:
-    The export item ‘T(K1, K2)’
-    attempts to export constructors or class methods that are not visible here
+mod4.hs:2:10: error:
+    • Not in scope: data constructor ‘K2’
+      Perhaps you meant ‘K1’ (line 3)
+    • In the export: T(K1, K2)