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griesemerRobert Griesemer
griesemer
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Robert Griesemer
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go/types, types2: make the new comparable semantics the default
Ordinary interface types now satisfy comparable constraints. This is a fully backward-compatible change: it simply permits additional code to be valid that wasn't valid before. This change makes the new comparable semantics the default behavior, depending on the Go -lang version. It also renames the flag types2.Config.AltComparableSemantics to types2.Config.OldComparableSemantics and inverts its meaning (or types.Config.oldComparableSemantics respectively). Add new predicate Satisfies (matching the predicate Implements but for constraint satisfaction), per the proposal description. Adjust some existing tests by setting -oldComparableSemantics and add some new tests that verify version-dependent behavior. The compiler flag -oldcomparable may be used to temporarily switch back to the Go 1.18/1.19 behavior should this change cause problems, or to identify that a problem is unrelated to this change. The flag will be removed for Go 1.21. For #52509. For #56548. For #57011. Change-Id: I8b3b3d9d492fc24b0693567055f0053ccb5aeb42 Reviewed-on: https://go-review.googlesource.com/c/go/+/454575 TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Robert Griesemer <[email protected]> Run-TryBot: Robert Griesemer <[email protected]> Reviewed-by: Robert Findley <[email protected]>
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‎api/next/56548.txt

Lines changed: 1 addition & 0 deletions
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@@ -0,0 +1 @@
1+
pkg go/types, func Satisfies(Type, *Interface) bool #56548

‎src/cmd/compile/internal/base/flag.go

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -122,8 +122,8 @@ type CmdFlags struct {
122122
SymABIs string "help:\"read symbol ABIs from `file`\""
123123
TraceProfile string "help:\"write an execution trace to `file`\""
124124
TrimPath string "help:\"remove `prefix` from recorded source file paths\""
125-
WB bool "help:\"enable write barrier\"" // TODO: remove
126-
AltComparable bool "help:\"enable alternative comparable semantics\"" // experiment - remove eventually
125+
WB bool "help:\"enable write barrier\"" // TODO: remove
126+
OldComparable bool "help:\"enable old comparable semantics\"" // TODO: remove for Go 1.21
127127
PgoProfile string "help:\"read profile from `file`\""
128128

129129
// Configuration derived from flags; not a flag itself.

‎src/cmd/compile/internal/noder/irgen.go

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -57,7 +57,7 @@ func checkFiles(noders []*noder) (posMap, *types2.Package, *types2.Info) {
5757
},
5858
Importer: &importer,
5959
Sizes: &gcSizes{},
60-
AltComparableSemantics: base.Flag.AltComparable, // experiment - remove eventually
60+
OldComparableSemantics: base.Flag.OldComparable, // default is new comparable semantics
6161
}
6262
info := &types2.Info{
6363
StoreTypesInSyntax: true,

‎src/cmd/compile/internal/types2/api.go

Lines changed: 12 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -168,9 +168,10 @@ type Config struct {
168168
// for unused imports.
169169
DisableUnusedImportCheck bool
170170

171-
// If AltComparableSemantics is set, ordinary (non-type parameter)
172-
// interfaces satisfy the comparable constraint.
173-
AltComparableSemantics bool
171+
// If OldComparableSemantics is set, ordinary (non-type parameter)
172+
// interfaces do not satisfy the comparable constraint.
173+
// TODO(gri) remove this flag for Go 1.21
174+
OldComparableSemantics bool
174175
}
175176

176177
func srcimporter_setUsesCgo(conf *Config) {
@@ -487,6 +488,14 @@ func Implements(V Type, T *Interface) bool {
487488
return (*Checker)(nil).implements(V, T, false, nil)
488489
}
489490

491+
// Satisfies reports whether type V satisfies the constraint T.
492+
//
493+
// The behavior of Satisfies is unspecified if V is Typ[Invalid] or an uninstantiated
494+
// generic type.
495+
func Satisfies(V Type, T *Interface) bool {
496+
return (*Checker)(nil).implements(V, T, true, nil)
497+
}
498+
490499
// Identical reports whether x and y are identical types.
491500
// Receivers of Signature types are ignored.
492501
func Identical(x, y Type) bool {

‎src/cmd/compile/internal/types2/check_test.go

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -130,7 +130,7 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
130130
flags := flag.NewFlagSet("", flag.PanicOnError)
131131
flags.StringVar(&conf.GoVersion, "lang", "", "")
132132
flags.BoolVar(&conf.FakeImportC, "fakeImportC", false, "")
133-
flags.BoolVar(&conf.AltComparableSemantics, "altComparableSemantics", false, "")
133+
flags.BoolVar(&conf.OldComparableSemantics, "oldComparableSemantics", false, "")
134134
if err := parseFlags(filenames[0], nil, flags); err != nil {
135135
t.Fatal(err)
136136
}

‎src/cmd/compile/internal/types2/instantiate.go

Lines changed: 27 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -245,18 +245,39 @@ func (check *Checker) implements(V, T Type, constraint bool, cause *string) bool
245245

246246
// Only check comparability if we don't have a more specific error.
247247
checkComparability := func() bool {
248+
if !Ti.IsComparable() {
249+
return true
250+
}
248251
// If T is comparable, V must be comparable.
249-
// For constraint satisfaction, use dynamic comparability for the
250-
// alternative comparable semantics such that ordinary, non-type
251-
// parameter interfaces implement comparable.
252-
dynamic := constraint && check != nil && check.conf.AltComparableSemantics
253-
if Ti.IsComparable() && !comparable(V, dynamic, nil, nil) {
252+
// If V is strictly comparable, we're done.
253+
if comparable(V, false /* strict comparability */, nil, nil) {
254+
return true
255+
}
256+
// If check.conf.OldComparableSemantics is set (by the compiler or
257+
// a test), we only consider strict comparability and we're done.
258+
// TODO(gri) remove this check for Go 1.21
259+
if check != nil && check.conf.OldComparableSemantics {
254260
if cause != nil {
255261
*cause = check.sprintf("%s does not implement comparable", V)
256262
}
257263
return false
258264
}
259-
return true
265+
// For constraint satisfaction, use dynamic (spec) comparability
266+
// so that ordinary, non-type parameter interfaces implement comparable.
267+
if constraint && comparable(V, true /* spec comparability */, nil, nil) {
268+
// V is comparable if we are at Go 1.20 or higher.
269+
if check == nil || check.allowVersion(check.pkg, 1, 20) {
270+
return true
271+
}
272+
if cause != nil {
273+
*cause = check.sprintf("%s to implement comparable requires go1.20 or later", V)
274+
}
275+
return false
276+
}
277+
if cause != nil {
278+
*cause = check.sprintf("%s does not implement comparable", V)
279+
}
280+
return false
260281
}
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262283
// V must also be in the set of types of T, if any.

‎src/go/types/api.go

Lines changed: 12 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -168,9 +168,10 @@ type Config struct {
168168
// for unused imports.
169169
DisableUnusedImportCheck bool
170170

171-
// If altComparableSemantics is set, ordinary (non-type parameter)
172-
// interfaces satisfy the comparable constraint.
173-
altComparableSemantics bool
171+
// If oldComparableSemantics is set, ordinary (non-type parameter)
172+
// interfaces do not satisfy the comparable constraint.
173+
// TODO(gri) remove this flag for Go 1.21
174+
oldComparableSemantics bool
174175
}
175176

176177
func srcimporter_setUsesCgo(conf *Config) {
@@ -470,6 +471,14 @@ func Implements(V Type, T *Interface) bool {
470471
return (*Checker)(nil).implements(V, T, false, nil)
471472
}
472473

474+
// Satisfies reports whether type V satisfies the constraint T.
475+
//
476+
// The behavior of Satisfies is unspecified if V is Typ[Invalid] or an uninstantiated
477+
// generic type.
478+
func Satisfies(V Type, T *Interface) bool {
479+
return (*Checker)(nil).implements(V, T, true, nil)
480+
}
481+
473482
// Identical reports whether x and y are identical types.
474483
// Receivers of Signature types are ignored.
475484
func Identical(x, y Type) bool {

‎src/go/types/check_test.go

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -217,7 +217,7 @@ func testFiles(t *testing.T, sizes Sizes, filenames []string, srcs [][]byte, man
217217
flags := flag.NewFlagSet("", flag.PanicOnError)
218218
flags.StringVar(&conf.GoVersion, "lang", "", "")
219219
flags.BoolVar(&conf.FakeImportC, "fakeImportC", false, "")
220-
flags.BoolVar(addrAltComparableSemantics(&conf), "altComparableSemantics", false, "")
220+
flags.BoolVar(addrOldComparableSemantics(&conf), "oldComparableSemantics", false, "")
221221
if err := parseFlags(filenames[0], srcs[0], flags); err != nil {
222222
t.Fatal(err)
223223
}
@@ -294,10 +294,10 @@ func readCode(err Error) int {
294294
return int(v.FieldByName("go116code").Int())
295295
}
296296

297-
// addrAltComparableSemantics(conf) returns &conf.altComparableSemantics (unexported field).
298-
func addrAltComparableSemantics(conf *Config) *bool {
297+
// addrOldComparableSemantics(conf) returns &conf.oldComparableSemantics (unexported field).
298+
func addrOldComparableSemantics(conf *Config) *bool {
299299
v := reflect.Indirect(reflect.ValueOf(conf))
300-
return (*bool)(v.FieldByName("altComparableSemantics").Addr().UnsafePointer())
300+
return (*bool)(v.FieldByName("oldComparableSemantics").Addr().UnsafePointer())
301301
}
302302

303303
// TestManual is for manual testing of a package - either provided

‎src/go/types/instantiate.go

Lines changed: 27 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -245,18 +245,39 @@ func (check *Checker) implements(V, T Type, constraint bool, cause *string) bool
245245

246246
// Only check comparability if we don't have a more specific error.
247247
checkComparability := func() bool {
248+
if !Ti.IsComparable() {
249+
return true
250+
}
248251
// If T is comparable, V must be comparable.
249-
// For constraint satisfaction, use dynamic comparability for the
250-
// alternative comparable semantics such that ordinary, non-type
251-
// parameter interfaces implement comparable.
252-
dynamic := constraint && check != nil && check.conf.altComparableSemantics
253-
if Ti.IsComparable() && !comparable(V, dynamic, nil, nil) {
252+
// If V is strictly comparable, we're done.
253+
if comparable(V, false /* strict comparability */, nil, nil) {
254+
return true
255+
}
256+
// If check.conf.OldComparableSemantics is set (by the compiler or
257+
// a test), we only consider strict comparability and we're done.
258+
// TODO(gri) remove this check for Go 1.21
259+
if check != nil && check.conf.oldComparableSemantics {
254260
if cause != nil {
255261
*cause = check.sprintf("%s does not implement comparable", V)
256262
}
257263
return false
258264
}
259-
return true
265+
// For constraint satisfaction, use dynamic (spec) comparability
266+
// so that ordinary, non-type parameter interfaces implement comparable.
267+
if constraint && comparable(V, true /* spec comparability */, nil, nil) {
268+
// V is comparable if we are at Go 1.20 or higher.
269+
if check == nil || check.allowVersion(check.pkg, 1, 20) {
270+
return true
271+
}
272+
if cause != nil {
273+
*cause = check.sprintf("%s to implement comparable requires go1.20 or later", V)
274+
}
275+
return false
276+
}
277+
if cause != nil {
278+
*cause = check.sprintf("%s does not implement comparable", V)
279+
}
280+
return false
260281
}
261282

262283
// V must also be in the set of types of T, if any.

‎src/internal/types/testdata/check/issues1.go

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,5 @@
1+
// -oldComparableSemantics
2+
13
// Copyright 2020 The Go Authors. All rights reserved.
24
// Use of this source code is governed by a BSD-style
35
// license that can be found in the LICENSE file.

‎src/internal/types/testdata/fixedbugs/issue50646.go

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,5 @@
1+
// -oldComparableSemantics
2+
13
// Copyright 2022 The Go Authors. All rights reserved.
24
// Use of this source code is governed by a BSD-style
35
// license that can be found in the LICENSE file.

‎src/internal/types/testdata/fixedbugs/issue51257.go

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,5 @@
1+
// -oldComparableSemantics
2+
13
// Copyright 2022 The Go Authors. All rights reserved.
24
// Use of this source code is governed by a BSD-style
35
// license that can be found in the LICENSE file.

‎src/internal/types/testdata/spec/comparable.go

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Original file line numberDiff line numberDiff line change
@@ -1,5 +1,3 @@
1-
// -altComparableSemantics
2-
31
// Copyright 2022 The Go Authors. All rights reserved.
42
// Use of this source code is governed by a BSD-style
53
// license that can be found in the LICENSE file.

‎src/internal/types/testdata/spec/comparable1.19.go

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,28 @@
1+
// -lang=go1.19
2+
3+
// Copyright 2022 The Go Authors. All rights reserved.
4+
// Use of this source code is governed by a BSD-style
5+
// license that can be found in the LICENSE file.
6+
7+
package p
8+
9+
func f1[_ comparable]() {}
10+
func f2[_ interface{ comparable }]() {}
11+
12+
type T interface{ m() }
13+
14+
func _[P comparable, Q ~int, R any]() {
15+
_ = f1[int]
16+
_ = f1[T /* ERROR T to implement comparable requires go1\.20 or later */]
17+
_ = f1[any /* ERROR any to implement comparable requires go1\.20 or later */]
18+
_ = f1[P]
19+
_ = f1[Q]
20+
_ = f1[R /* ERROR R does not implement comparable */]
21+
22+
_ = f2[int]
23+
_ = f2[T /* ERROR T to implement comparable requires go1\.20 or later */]
24+
_ = f2[any /* ERROR any to implement comparable requires go1\.20 or later */]
25+
_ = f2[P]
26+
_ = f2[Q]
27+
_ = f2[R /* ERROR R does not implement comparable */]
28+
}

‎src/internal/types/testdata/spec/oldcomparable.go

Lines changed: 28 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,28 @@
1+
// -oldComparableSemantics
2+
3+
// Copyright 2022 The Go Authors. All rights reserved.
4+
// Use of this source code is governed by a BSD-style
5+
// license that can be found in the LICENSE file.
6+
7+
package p
8+
9+
func f1[_ comparable]() {}
10+
func f2[_ interface{ comparable }]() {}
11+
12+
type T interface{ m() }
13+
14+
func _[P comparable, Q ~int, R any]() {
15+
_ = f1[int]
16+
_ = f1[T /* ERROR T does not implement comparable */]
17+
_ = f1[any /* ERROR any does not implement comparable */]
18+
_ = f1[P]
19+
_ = f1[Q]
20+
_ = f1[R /* ERROR R does not implement comparable */]
21+
22+
_ = f2[int]
23+
_ = f2[T /* ERROR T does not implement comparable */]
24+
_ = f2[any /* ERROR any does not implement comparable */]
25+
_ = f2[P]
26+
_ = f2[Q]
27+
_ = f2[R /* ERROR R does not implement comparable */]
28+
}

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