Revert "go/types, types2: make the new comparable semantics the default"

The CL below was accidentally submitted, while waiting for the freeze
exception. Reverting.

This reverts commit 15e705ea96.

Change-Id: I4dbf92dcb01fa9245a6e6a2d1514d8aa898d0048
Reviewed-on: https://go-review.googlesource.com/c/go/+/454476
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Auto-Submit: Robert Griesemer <gri@google.com>

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

@@ -122,8 +122,8 @@ type CmdFlags struct {
 	SymABIs            string       "help:\"read symbol ABIs from `file`\""
 	TraceProfile       string       "help:\"write an execution trace to `file`\""
 	TrimPath           string       "help:\"remove `prefix` from recorded source file paths\""
-	WB                 bool         "help:\"enable write barrier\""            // TODO: remove
-	OldComparable      bool         "help:\"enable old comparable semantics\"" // TODO: remove for Go 1.21
+	WB                 bool         "help:\"enable write barrier\""                    // TODO: remove
+	AltComparable      bool         "help:\"enable alternative comparable semantics\"" // experiment - remove eventually
 	PgoProfile         string       "help:\"read profile from `file`\""
 
 	// Configuration derived from flags; not a flag itself.

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

@@ -57,7 +57,7 @@ func checkFiles(noders []*noder) (posMap, *types2.Package, *types2.Info) {
 		},
 		Importer:               &importer,
 		Sizes:                  &gcSizes{},
-		OldComparableSemantics: base.Flag.OldComparable, // default is new comparable semantics
+		AltComparableSemantics: base.Flag.AltComparable, // experiment - remove eventually
 	}
 	info := &types2.Info{
 		StoreTypesInSyntax: true,

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

@@ -168,10 +168,9 @@ type Config struct {
 	// for unused imports.
 	DisableUnusedImportCheck bool
 
-	// If OldComparableSemantics is set, ordinary (non-type parameter)
-	// interfaces do not satisfy the comparable constraint.
-	// TODO(gri) remove this flag for Go 1.21
-	OldComparableSemantics bool
+	// If AltComparableSemantics is set, ordinary (non-type parameter)
+	// interfaces satisfy the comparable constraint.
+	AltComparableSemantics bool
 }
 
 func srcimporter_setUsesCgo(conf *Config) {

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

@@ -130,7 +130,7 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 	flags := flag.NewFlagSet("", flag.PanicOnError)
 	flags.StringVar(&conf.GoVersion, "lang", "", "")
 	flags.BoolVar(&conf.FakeImportC, "fakeImportC", false, "")
-	flags.BoolVar(&conf.OldComparableSemantics, "oldComparableSemantics", false, "")
+	flags.BoolVar(&conf.AltComparableSemantics, "altComparableSemantics", false, "")
 	if err := parseFlags(filenames[0], nil, flags); err != nil {
 		t.Fatal(err)
 	}

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

@@ -245,39 +245,18 @@ func (check *Checker) implements(V, T Type, constraint bool, cause *string) bool
 
 	// Only check comparability if we don't have a more specific error.
 	checkComparability := func() bool {
-		if !Ti.IsComparable() {
-			return true
-		}
 		// If T is comparable, V must be comparable.
-		// If V is strictly comparable, we're done.
-		if comparable(V, false /* strict comparability */, nil, nil) {
-			return true
-		}
-		// If check.conf.OldComparableSemantics is set (by the compiler or
-		// a test), we only consider strict comparability and we're done.
-		// TODO(gri) remove this check for Go 1.21
-		if check != nil && check.conf.OldComparableSemantics {
+		// For constraint satisfaction, use dynamic comparability for the
+		// alternative comparable semantics such that ordinary, non-type
+		// parameter interfaces implement comparable.
+		dynamic := constraint && check != nil && check.conf.AltComparableSemantics
+		if Ti.IsComparable() && !comparable(V, dynamic, nil, nil) {
 			if cause != nil {
 				*cause = check.sprintf("%s does not implement comparable", V)
 			}
 			return false
 		}
-		// For constraint satisfaction, use dynamic (spec) comparability
-		// so that ordinary, non-type parameter interfaces implement comparable.
-		if constraint && comparable(V, true /* spec comparability */, nil, nil) {
-			// V is comparable if we are at Go 1.20 or higher.
-			if check == nil || check.allowVersion(check.pkg, 1, 20) {
-				return true
-			}
-			if cause != nil {
-				*cause = check.sprintf("%s to implement comparable requires go1.20 or later", V)
-			}
-			return false
-		}
-		if cause != nil {
-			*cause = check.sprintf("%s does not implement comparable", V)
-		}
-		return false
+		return true
 	}
 
 	// V must also be in the set of types of T, if any.

src/go/types/api.go

@@ -168,10 +168,9 @@ type Config struct {
 	// for unused imports.
 	DisableUnusedImportCheck bool
 
-	// If oldComparableSemantics is set, ordinary (non-type parameter)
-	// interfaces do not satisfy the comparable constraint.
-	// TODO(gri) remove this flag for Go 1.21
-	oldComparableSemantics bool
+	// If altComparableSemantics is set, ordinary (non-type parameter)
+	// interfaces satisfy the comparable constraint.
+	altComparableSemantics bool
 }
 
 func srcimporter_setUsesCgo(conf *Config) {

src/go/types/check_test.go

@@ -217,7 +217,7 @@ func testFiles(t *testing.T, sizes Sizes, filenames []string, srcs [][]byte, man
 	flags := flag.NewFlagSet("", flag.PanicOnError)
 	flags.StringVar(&conf.GoVersion, "lang", "", "")
 	flags.BoolVar(&conf.FakeImportC, "fakeImportC", false, "")
-	flags.BoolVar(addrOldComparableSemantics(&conf), "oldComparableSemantics", false, "")
+	flags.BoolVar(addrAltComparableSemantics(&conf), "altComparableSemantics", false, "")
 	if err := parseFlags(filenames[0], srcs[0], flags); err != nil {
 		t.Fatal(err)
 	}
@@ -294,10 +294,10 @@ func readCode(err Error) int {
 	return int(v.FieldByName("go116code").Int())
 }
 
-// addrOldComparableSemantics(conf) returns &conf.oldComparableSemantics (unexported field).
-func addrOldComparableSemantics(conf *Config) *bool {
+// addrAltComparableSemantics(conf) returns &conf.altComparableSemantics (unexported field).
+func addrAltComparableSemantics(conf *Config) *bool {
 	v := reflect.Indirect(reflect.ValueOf(conf))
-	return (*bool)(v.FieldByName("oldComparableSemantics").Addr().UnsafePointer())
+	return (*bool)(v.FieldByName("altComparableSemantics").Addr().UnsafePointer())
 }
 
 // TestManual is for manual testing of a package - either provided

src/go/types/instantiate.go

@@ -245,39 +245,18 @@ func (check *Checker) implements(V, T Type, constraint bool, cause *string) bool
 
 	// Only check comparability if we don't have a more specific error.
 	checkComparability := func() bool {
-		if !Ti.IsComparable() {
-			return true
-		}
 		// If T is comparable, V must be comparable.
-		// If V is strictly comparable, we're done.
-		if comparable(V, false /* strict comparability */, nil, nil) {
-			return true
-		}
-		// If check.conf.OldComparableSemantics is set (by the compiler or
-		// a test), we only consider strict comparability and we're done.
-		// TODO(gri) remove this check for Go 1.21
-		if check != nil && check.conf.oldComparableSemantics {
+		// For constraint satisfaction, use dynamic comparability for the
+		// alternative comparable semantics such that ordinary, non-type
+		// parameter interfaces implement comparable.
+		dynamic := constraint && check != nil && check.conf.altComparableSemantics
+		if Ti.IsComparable() && !comparable(V, dynamic, nil, nil) {
 			if cause != nil {
 				*cause = check.sprintf("%s does not implement comparable", V)
 			}
 			return false
 		}
-		// For constraint satisfaction, use dynamic (spec) comparability
-		// so that ordinary, non-type parameter interfaces implement comparable.
-		if constraint && comparable(V, true /* spec comparability */, nil, nil) {
-			// V is comparable if we are at Go 1.20 or higher.
-			if check == nil || check.allowVersion(check.pkg, 1, 20) {
-				return true
-			}
-			if cause != nil {
-				*cause = check.sprintf("%s to implement comparable requires go1.20 or later", V)
-			}
-			return false
-		}
-		if cause != nil {
-			*cause = check.sprintf("%s does not implement comparable", V)
-		}
-		return false
+		return true
 	}
 
 	// V must also be in the set of types of T, if any.

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

@@ -1,5 +1,3 @@
-// -oldComparableSemantics
-
 // Copyright 2020 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.

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

@@ -1,5 +1,3 @@
-// -oldComparableSemantics
-
 // Copyright 2022 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.

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

@@ -1,5 +1,3 @@
-// -oldComparableSemantics
-
 // Copyright 2022 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.

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

@@ -1,3 +1,5 @@
+// -altComparableSemantics
+
 // Copyright 2022 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.

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

@@ -1,28 +0,0 @@
-// -lang=go1.19
-
-// Copyright 2022 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.
-
-package p
-
-func f1[_ comparable]()              {}
-func f2[_ interface{ comparable }]() {}
-
-type T interface{ m() }
-
-func _[P comparable, Q ~int, R any]() {
-	_ = f1[int]
-	_ = f1[T /* ERROR T to implement comparable requires go1\.20 or later */]
-	_ = f1[any /* ERROR any to implement comparable requires go1\.20 or later */]
-	_ = f1[P]
-	_ = f1[Q]
-	_ = f1[R /* ERROR R does not implement comparable */]
-
-	_ = f2[int]
-	_ = f2[T /* ERROR T to implement comparable requires go1\.20 or later */]
-	_ = f2[any /* ERROR any to implement comparable requires go1\.20 or later */]
-	_ = f2[P]
-	_ = f2[Q]
-	_ = f2[R /* ERROR R does not implement comparable */]
-}

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

@@ -1,28 +0,0 @@
-// -oldComparableSemantics
-
-// Copyright 2022 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.
-
-package p
-
-func f1[_ comparable]()              {}
-func f2[_ interface{ comparable }]() {}
-
-type T interface{ m() }
-
-func _[P comparable, Q ~int, R any]() {
-	_ = f1[int]
-	_ = f1[T /* ERROR T does not implement comparable */]
-	_ = f1[any /* ERROR any does not implement comparable */]
-	_ = f1[P]
-	_ = f1[Q]
-	_ = f1[R /* ERROR R does not implement comparable */]
-
-	_ = f2[int]
-	_ = f2[T /* ERROR T does not implement comparable */]
-	_ = f2[any /* ERROR any does not implement comparable */]
-	_ = f2[P]
-	_ = f2[Q]
-	_ = f2[R /* ERROR R does not implement comparable */]
-}