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
|
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements instantiation of generic types
// through substitution of type parameters by actual
// types.
package types
import (
"bytes"
"fmt"
"go/token"
)
// TODO(rFindley) decide error codes for the errors in this file, and check
// if error spans can be improved
type substMap struct {
// The targs field is currently needed for *Named type substitution.
// TODO(gri) rewrite that code, get rid of this field, and make this
// struct just the map (proj)
targs []Type
proj map[*_TypeParam]Type
}
// makeSubstMap creates a new substitution map mapping tpars[i] to targs[i].
// If targs[i] is nil, tpars[i] is not substituted.
func makeSubstMap(tpars []*TypeName, targs []Type) *substMap {
assert(len(tpars) == len(targs))
proj := make(map[*_TypeParam]Type, len(tpars))
for i, tpar := range tpars {
// We must expand type arguments otherwise *instance
// types end up as components in composite types.
// TODO(gri) explain why this causes problems, if it does
targ := expand(targs[i]) // possibly nil
targs[i] = targ
proj[tpar.typ.(*_TypeParam)] = targ
}
return &substMap{targs, proj}
}
func (m *substMap) String() string {
return fmt.Sprintf("%s", m.proj)
}
func (m *substMap) empty() bool {
return len(m.proj) == 0
}
func (m *substMap) lookup(tpar *_TypeParam) Type {
if t := m.proj[tpar]; t != nil {
return t
}
return tpar
}
func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist []token.Pos) (res Type) {
if trace {
check.trace(pos, "-- instantiating %s with %s", typ, typeListString(targs))
check.indent++
defer func() {
check.indent--
var under Type
if res != nil {
// Calling under() here may lead to endless instantiations.
// Test case: type T[P any] T[P]
// TODO(gri) investigate if that's a bug or to be expected.
under = res.Underlying()
}
check.trace(pos, "=> %s (under = %s)", res, under)
}()
}
assert(len(poslist) <= len(targs))
// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
var tparams []*TypeName
switch t := typ.(type) {
case *Named:
tparams = t.tparams
case *Signature:
tparams = t.tparams
defer func() {
// If we had an unexpected failure somewhere don't panic below when
// asserting res.(*Signature). Check for *Signature in case Typ[Invalid]
// is returned.
if _, ok := res.(*Signature); !ok {
return
}
// If the signature doesn't use its type parameters, subst
// will not make a copy. In that case, make a copy now (so
// we can set tparams to nil w/o causing side-effects).
if t == res {
copy := *t
res = ©
}
// After instantiating a generic signature, it is not generic
// anymore; we need to set tparams to nil.
res.(*Signature).tparams = nil
}()
default:
check.dump("%v: cannot instantiate %v", pos, typ)
unreachable() // only defined types and (defined) functions can be generic
}
// the number of supplied types must match the number of type parameters
if len(targs) != len(tparams) {
// TODO(gri) provide better error message
check.errorf(atPos(pos), _Todo, "got %d arguments but %d type parameters", len(targs), len(tparams))
return Typ[Invalid]
}
if len(tparams) == 0 {
return typ // nothing to do (minor optimization)
}
smap := makeSubstMap(tparams, targs)
// check bounds
for i, tname := range tparams {
tpar := tname.typ.(*_TypeParam)
iface := tpar.Bound()
if iface.Empty() {
continue // no type bound
}
targ := targs[i]
// best position for error reporting
pos := pos
if i < len(poslist) {
pos = poslist[i]
}
// The type parameter bound is parameterized with the same type parameters
// as the instantiated type; before we can use it for bounds checking we
// need to instantiate it with the type arguments with which we instantiate
// the parameterized type.
iface = check.subst(pos, iface, smap).(*Interface)
// targ must implement iface (methods)
// - check only if we have methods
check.completeInterface(token.NoPos, iface)
if len(iface.allMethods) > 0 {
// If the type argument is a pointer to a type parameter, the type argument's
// method set is empty.
// TODO(gri) is this what we want? (spec question)
if base, isPtr := deref(targ); isPtr && asTypeParam(base) != nil {
check.errorf(atPos(pos), 0, "%s has no methods", targ)
break
}
if m, wrong := check.missingMethod(targ, iface, true); m != nil {
// TODO(gri) needs to print updated name to avoid major confusion in error message!
// (print warning for now)
// Old warning:
// check.softErrorf(pos, "%s does not satisfy %s (warning: name not updated) = %s (missing method %s)", targ, tpar.bound, iface, m)
if m.name == "==" {
// We don't want to report "missing method ==".
check.softErrorf(atPos(pos), 0, "%s does not satisfy comparable", targ)
} else if wrong != nil {
// TODO(gri) This can still report uninstantiated types which makes the error message
// more difficult to read then necessary.
// TODO(rFindley) should this use parentheses rather than ':' for qualification?
check.softErrorf(atPos(pos), _Todo,
"%s does not satisfy %s: wrong method signature\n\tgot %s\n\twant %s",
targ, tpar.bound, wrong, m,
)
} else {
check.softErrorf(atPos(pos), 0, "%s does not satisfy %s (missing method %s)", targ, tpar.bound, m.name)
}
break
}
}
// targ's underlying type must also be one of the interface types listed, if any
if iface.allTypes == nil {
continue // nothing to do
}
// If targ is itself a type parameter, each of its possible types, but at least one, must be in the
// list of iface types (i.e., the targ type list must be a non-empty subset of the iface types).
if targ := asTypeParam(targ); targ != nil {
targBound := targ.Bound()
if targBound.allTypes == nil {
check.softErrorf(atPos(pos), _Todo, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
break
}
for _, t := range unpackType(targBound.allTypes) {
if !iface.isSatisfiedBy(t) {
// TODO(gri) match this error message with the one below (or vice versa)
check.softErrorf(atPos(pos), 0, "%s does not satisfy %s (%s type constraint %s not found in %s)", targ, tpar.bound, targ, t, iface.allTypes)
break
}
}
break
}
// Otherwise, targ's type or underlying type must also be one of the interface types listed, if any.
if !iface.isSatisfiedBy(targ) {
check.softErrorf(atPos(pos), _Todo, "%s does not satisfy %s (%s or %s not found in %s)", targ, tpar.bound, targ, under(targ), iface.allTypes)
break
}
}
return check.subst(pos, typ, smap)
}
// subst returns the type typ with its type parameters tpars replaced by
// the corresponding type arguments targs, recursively.
// subst is functional in the sense that it doesn't modify the incoming
// type. If a substitution took place, the result type is different from
// from the incoming type.
func (check *Checker) subst(pos token.Pos, typ Type, smap *substMap) Type {
if smap.empty() {
return typ
}
// common cases
switch t := typ.(type) {
case *Basic:
return typ // nothing to do
case *_TypeParam:
return smap.lookup(t)
}
// general case
subst := subster{check, pos, make(map[Type]Type), smap}
return subst.typ(typ)
}
type subster struct {
check *Checker
pos token.Pos
cache map[Type]Type
smap *substMap
}
func (subst *subster) typ(typ Type) Type {
switch t := typ.(type) {
case nil:
// Call typOrNil if it's possible that typ is nil.
panic("nil typ")
case *Basic, *bottom, *top:
// nothing to do
case *Array:
elem := subst.typOrNil(t.elem)
if elem != t.elem {
return &Array{len: t.len, elem: elem}
}
case *Slice:
elem := subst.typOrNil(t.elem)
if elem != t.elem {
return &Slice{elem: elem}
}
case *Struct:
if fields, copied := subst.varList(t.fields); copied {
return &Struct{fields: fields, tags: t.tags}
}
case *Pointer:
base := subst.typ(t.base)
if base != t.base {
return &Pointer{base: base}
}
case *Tuple:
return subst.tuple(t)
case *Signature:
// TODO(gri) rethink the recv situation with respect to methods on parameterized types
// recv := subst.var_(t.recv) // TODO(gri) this causes a stack overflow - explain
recv := t.recv
params := subst.tuple(t.params)
results := subst.tuple(t.results)
if recv != t.recv || params != t.params || results != t.results {
return &Signature{
rparams: t.rparams,
// TODO(rFindley) why can't we nil out tparams here, rather than in
// instantiate above?
tparams: t.tparams,
scope: t.scope,
recv: recv,
params: params,
results: results,
variadic: t.variadic,
}
}
case *_Sum:
types, copied := subst.typeList(t.types)
if copied {
// Don't do it manually, with a Sum literal: the new
// types list may not be unique and NewSum may remove
// duplicates.
return _NewSum(types)
}
case *Interface:
methods, mcopied := subst.funcList(t.methods)
types := t.types
if t.types != nil {
types = subst.typ(t.types)
}
embeddeds, ecopied := subst.typeList(t.embeddeds)
if mcopied || types != t.types || ecopied {
iface := &Interface{methods: methods, types: types, embeddeds: embeddeds}
subst.check.posMap[iface] = subst.check.posMap[t] // satisfy completeInterface requirement
subst.check.completeInterface(token.NoPos, iface)
return iface
}
case *Map:
key := subst.typ(t.key)
elem := subst.typ(t.elem)
if key != t.key || elem != t.elem {
return &Map{key: key, elem: elem}
}
case *Chan:
elem := subst.typ(t.elem)
if elem != t.elem {
return &Chan{dir: t.dir, elem: elem}
}
case *Named:
subst.check.indent++
defer func() {
subst.check.indent--
}()
dump := func(format string, args ...interface{}) {
if trace {
subst.check.trace(subst.pos, format, args...)
}
}
if t.tparams == nil {
dump(">>> %s is not parameterized", t)
return t // type is not parameterized
}
var newTargs []Type
if len(t.targs) > 0 {
// already instantiated
dump(">>> %s already instantiated", t)
assert(len(t.targs) == len(t.tparams))
// For each (existing) type argument targ, determine if it needs
// to be substituted; i.e., if it is or contains a type parameter
// that has a type argument for it.
for i, targ := range t.targs {
dump(">>> %d targ = %s", i, targ)
newTarg := subst.typ(targ)
if newTarg != targ {
dump(">>> substituted %d targ %s => %s", i, targ, newTarg)
if newTargs == nil {
newTargs = make([]Type, len(t.tparams))
copy(newTargs, t.targs)
}
newTargs[i] = newTarg
}
}
if newTargs == nil {
dump(">>> nothing to substitute in %s", t)
return t // nothing to substitute
}
} else {
// not yet instantiated
dump(">>> first instantiation of %s", t)
// TODO(rFindley) can we instead subst the tparam types here?
newTargs = subst.smap.targs
}
// before creating a new named type, check if we have this one already
h := instantiatedHash(t, newTargs)
dump(">>> new type hash: %s", h)
if named, found := subst.check.typMap[h]; found {
dump(">>> found %s", named)
subst.cache[t] = named
return named
}
// create a new named type and populate caches to avoid endless recursion
tname := NewTypeName(subst.pos, t.obj.pkg, t.obj.name, nil)
named := subst.check.newNamed(tname, t.underlying, t.methods) // method signatures are updated lazily
named.tparams = t.tparams // new type is still parameterized
named.targs = newTargs
subst.check.typMap[h] = named
subst.cache[t] = named
// do the substitution
dump(">>> subst %s with %s (new: %s)", t.underlying, subst.smap, newTargs)
named.underlying = subst.typOrNil(t.underlying)
named.orig = named.underlying // for cycle detection (Checker.validType)
return named
case *_TypeParam:
return subst.smap.lookup(t)
case *instance:
// TODO(gri) can we avoid the expansion here and just substitute the type parameters?
return subst.typ(t.expand())
default:
panic("unimplemented")
}
return typ
}
// TODO(gri) Eventually, this should be more sophisticated.
// It won't work correctly for locally declared types.
func instantiatedHash(typ *Named, targs []Type) string {
var buf bytes.Buffer
writeTypeName(&buf, typ.obj, nil)
buf.WriteByte('[')
writeTypeList(&buf, targs, nil, nil)
buf.WriteByte(']')
// With respect to the represented type, whether a
// type is fully expanded or stored as instance
// does not matter - they are the same types.
// Remove the instanceMarkers printed for instances.
res := buf.Bytes()
i := 0
for _, b := range res {
if b != instanceMarker {
res[i] = b
i++
}
}
return string(res[:i])
}
func typeListString(list []Type) string {
var buf bytes.Buffer
writeTypeList(&buf, list, nil, nil)
return buf.String()
}
// typOrNil is like typ but if the argument is nil it is replaced with Typ[Invalid].
// A nil type may appear in pathological cases such as type T[P any] []func(_ T([]_))
// where an array/slice element is accessed before it is set up.
func (subst *subster) typOrNil(typ Type) Type {
if typ == nil {
return Typ[Invalid]
}
return subst.typ(typ)
}
func (subst *subster) var_(v *Var) *Var {
if v != nil {
if typ := subst.typ(v.typ); typ != v.typ {
copy := *v
copy.typ = typ
return ©
}
}
return v
}
func (subst *subster) tuple(t *Tuple) *Tuple {
if t != nil {
if vars, copied := subst.varList(t.vars); copied {
return &Tuple{vars: vars}
}
}
return t
}
func (subst *subster) varList(in []*Var) (out []*Var, copied bool) {
out = in
for i, v := range in {
if w := subst.var_(v); w != v {
if !copied {
// first variable that got substituted => allocate new out slice
// and copy all variables
new := make([]*Var, len(in))
copy(new, out)
out = new
copied = true
}
out[i] = w
}
}
return
}
func (subst *subster) func_(f *Func) *Func {
if f != nil {
if typ := subst.typ(f.typ); typ != f.typ {
copy := *f
copy.typ = typ
return ©
}
}
return f
}
func (subst *subster) funcList(in []*Func) (out []*Func, copied bool) {
out = in
for i, f := range in {
if g := subst.func_(f); g != f {
if !copied {
// first function that got substituted => allocate new out slice
// and copy all functions
new := make([]*Func, len(in))
copy(new, out)
out = new
copied = true
}
out[i] = g
}
}
return
}
func (subst *subster) typeList(in []Type) (out []Type, copied bool) {
out = in
for i, t := range in {
if u := subst.typ(t); u != t {
if !copied {
// first function that got substituted => allocate new out slice
// and copy all functions
new := make([]Type, len(in))
copy(new, out)
out = new
copied = true
}
out[i] = u
}
}
return
}
|