go/types, types2: remove Config.EnableReverseTypeInference flag

Proposal #59338 has been accepted and we expect this feature to
be available starting with Go 1.21. Remove the flag to explicitly
enable it through the API and enable by default.

For now keep an internal constant enableReverseTypeInference to
guard and mark the respective code, so we can disable it for
debugging purposes.

For #59338.

Change-Id: Ia1bf3032483ae603017a0f459417ec73837e2891
Reviewed-on: https://go-review.googlesource.com/c/go/+/491798
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

@@ -50,9 +50,8 @@ func checkFiles(m posMap, noders []*noder) (*types2.Package, *types2.Info) {
 			}
 			base.ErrorfAt(m.makeXPos(terr.Pos), terr.Code, "%s", msg)
 		},
-		Importer:                   &importer,
-		Sizes:                      &gcSizes{},
-		EnableReverseTypeInference: true,
+		Importer: &importer,
+		Sizes:    &gcSizes{},
 	}
 	info := &types2.Info{
 		StoreTypesInSyntax: true,

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

@@ -169,13 +169,6 @@ type Config struct {
 	// If DisableUnusedImportCheck is set, packages are not checked
 	// for unused imports.
 	DisableUnusedImportCheck bool
-
-	// If EnableReverseTypeInference is set, uninstantiated and
-	// partially instantiated generic functions may be assigned
-	// (incl. returned) to variables of function type and type
-	// inference will attempt to infer the missing type arguments.
-	// See proposal go.dev/issue/59338.
-	EnableReverseTypeInference bool
 }
 
 func srcimporter_setUsesCgo(conf *Config) {

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

@@ -594,10 +594,7 @@ type T[P any] []P
 
 	for _, test := range tests {
 		imports := make(testImporter)
-		conf := Config{
-			Importer:                   imports,
-			EnableReverseTypeInference: true,
-		}
+		conf := Config{Importer: imports}
 		instMap := make(map[*syntax.Name]Instance)
 		useMap := make(map[*syntax.Name]Object)
 		makePkg := func(src string) *Package {

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

@@ -496,7 +496,7 @@ func (check *Checker) arguments(call *syntax.CallExpr, sig *Signature, targs []T
 
 	// collect type parameters from generic function arguments
 	var genericArgs []int // indices of generic function arguments
-	if check.conf.EnableReverseTypeInference {
+	if enableReverseTypeInference {
 		for i, arg := range args {
 			// generic arguments cannot have a defined (*Named) type - no need for underlying type below
 			if asig, _ := arg.typ.(*Signature); asig != nil && asig.TypeParams().Len() > 0 {

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

@@ -133,7 +133,6 @@ 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.EnableReverseTypeInference, "reverseTypeInference", false, "")
 	if err := parseFlags(filenames[0], nil, flags); err != nil {
 		t.Fatal(err)
 	}

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

@@ -1291,7 +1291,7 @@ func (check *Checker) nonGeneric(T Type, x *operand) {
 		}
 	case *Signature:
 		if t.tparams != nil {
-			if check.conf.EnableReverseTypeInference && T != nil {
+			if enableReverseTypeInference && T != nil {
 				if tsig, _ := under(T).(*Signature); tsig != nil {
 					check.funcInst(tsig, x.Pos(), x, nil)
 					return
@@ -1617,7 +1617,7 @@ func (check *Checker) exprInternal(T Type, x *operand, e syntax.Expr, hint Type)
 	case *syntax.IndexExpr:
 		if check.indexExpr(x, e) {
 			var tsig *Signature
-			if check.conf.EnableReverseTypeInference && T != nil {
+			if enableReverseTypeInference && T != nil {
 				tsig, _ = under(T).(*Signature)
 			}
 			check.funcInst(tsig, e.Pos(), x, e)

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

@@ -13,6 +13,13 @@ import (
 	"strings"
 )
 
+// If enableReverseTypeInference is set, uninstantiated and
+// partially instantiated generic functions may be assigned
+// (incl. returned) to variables of function type and type
+// inference will attempt to infer the missing type arguments.
+// Available with go1.21.
+const enableReverseTypeInference = true // disable for debugging
+
 // infer attempts to infer the complete set of type arguments for generic function instantiation/call
 // based on the given type parameters tparams, type arguments targs, function parameters params, and
 // function arguments args, if any. There must be at least one type parameter, no more type arguments

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

@@ -139,9 +139,8 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 		file, err := syntax.ParseFile(filename, nil, nil, 0)
 		if err == nil {
 			conf := Config{
-				GoVersion:                  goVersion,
-				Importer:                   stdLibImporter,
-				EnableReverseTypeInference: true,
+				GoVersion: goVersion,
+				Importer:  stdLibImporter,
 			}
 			_, err = conf.Check(filename, []*syntax.File{file}, nil)
 		}
@@ -254,9 +253,8 @@ func typecheckFiles(t *testing.T, path string, filenames []string) {
 
 	// typecheck package files
 	conf := Config{
-		Error:                      func(err error) { t.Error(err) },
-		Importer:                   stdLibImporter,
-		EnableReverseTypeInference: true,
+		Error:    func(err error) { t.Error(err) },
+		Importer: stdLibImporter,
 	}
 	info := Info{Uses: make(map[*syntax.Name]Object)}
 	conf.Check(path, files, &info)

src/go/types/api.go

@@ -170,13 +170,6 @@ type Config struct {
 	// If DisableUnusedImportCheck is set, packages are not checked
 	// for unused imports.
 	DisableUnusedImportCheck bool
-
-	// If _EnableReverseTypeInference is set, uninstantiated and
-	// partially instantiated generic functions may be assigned
-	// (incl. returned) to variables of function type and type
-	// inference will attempt to infer the missing type arguments.
-	// See proposal go.dev/issue/59338.
-	_EnableReverseTypeInference bool
 }
 
 func srcimporter_setUsesCgo(conf *Config) {

src/go/types/api_test.go

@@ -594,12 +594,7 @@ type T[P any] []P
 
 	for _, test := range tests {
 		imports := make(testImporter)
-		conf := Config{
-			Importer: imports,
-			// Unexported field: set below with boolFieldAddr
-			// _EnableReverseTypeInference: true,
-		}
-		*boolFieldAddr(&conf, "_EnableReverseTypeInference") = true
+		conf := Config{Importer: imports}
 		instMap := make(map[*ast.Ident]Instance)
 		useMap := make(map[*ast.Ident]Object)
 		makePkg := func(src string) *Package {

src/go/types/call.go

@@ -499,7 +499,7 @@ func (check *Checker) arguments(call *ast.CallExpr, sig *Signature, targs []Type
 
 	// collect type parameters from generic function arguments
 	var genericArgs []int // indices of generic function arguments
-	if check.conf._EnableReverseTypeInference {
+	if enableReverseTypeInference {
 		for i, arg := range args {
 			// generic arguments cannot have a defined (*Named) type - no need for underlying type below
 			if asig, _ := arg.typ.(*Signature); asig != nil && asig.TypeParams().Len() > 0 {

src/go/types/check_test.go

@@ -146,7 +146,6 @@ 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(boolFieldAddr(&conf, "_EnableReverseTypeInference"), "reverseTypeInference", false, "")
 	if err := parseFlags(filenames[0], srcs[0], flags); err != nil {
 		t.Fatal(err)
 	}

src/go/types/expr.go

@@ -1276,7 +1276,7 @@ func (check *Checker) nonGeneric(T Type, x *operand) {
 		}
 	case *Signature:
 		if t.tparams != nil {
-			if check.conf._EnableReverseTypeInference && T != nil {
+			if enableReverseTypeInference && T != nil {
 				if tsig, _ := under(T).(*Signature); tsig != nil {
 					check.funcInst(tsig, x.Pos(), x, nil)
 					return
@@ -1600,7 +1600,7 @@ func (check *Checker) exprInternal(T Type, x *operand, e ast.Expr, hint Type) ex
 		ix := typeparams.UnpackIndexExpr(e)
 		if check.indexExpr(x, ix) {
 			var tsig *Signature
-			if check.conf._EnableReverseTypeInference && T != nil {
+			if enableReverseTypeInference && T != nil {
 				tsig, _ = under(T).(*Signature)
 			}
 			check.funcInst(tsig, e.Pos(), x, ix)

src/go/types/infer.go

@@ -15,6 +15,13 @@ import (
 	"strings"
 )
 
+// If enableReverseTypeInference is set, uninstantiated and
+// partially instantiated generic functions may be assigned
+// (incl. returned) to variables of function type and type
+// inference will attempt to infer the missing type arguments.
+// Available with go1.21.
+const enableReverseTypeInference = true // disable for debugging
+
 // infer attempts to infer the complete set of type arguments for generic function instantiation/call
 // based on the given type parameters tparams, type arguments targs, function parameters params, and
 // function arguments args, if any. There must be at least one type parameter, no more type arguments

src/go/types/stdlib_test.go

@@ -143,7 +143,6 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 				GoVersion: goVersion,
 				Importer:  stdLibImporter,
 			}
-			*boolFieldAddr(&conf, "_EnableReverseTypeInference") = true
 			_, err = conf.Check(filename, fset, []*ast.File{file}, nil)
 		}
 
@@ -271,7 +270,6 @@ func typecheckFiles(t *testing.T, path string, filenames []string) {
 		},
 		Importer: stdLibImporter,
 	}
-	*boolFieldAddr(&conf, "_EnableReverseTypeInference") = true
 	info := Info{Uses: make(map[*ast.Ident]Object)}
 	conf.Check(path, fset, files, &info)
 

src/internal/types/testdata/examples/inference.go

@@ -1,3 +1,5 @@
+// -lang=go1.20
+
 // Copyright 2021 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.
@@ -154,4 +156,4 @@ func _() {
 func f[P any](P) {}
 
 // This must not crash.
-var _ func(int) = f // ERROR "cannot use generic function f without instantiation"
+var _ func(int) = f // ERROR "implicitly instantiated function in assignment requires go1.21 or later"

src/internal/types/testdata/examples/inference2.go

@@ -1,5 +1,3 @@
-// -reverseTypeInference
-
 // Copyright 2023 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/issue59338a.go

@@ -1,4 +1,4 @@
-// -reverseTypeInference -lang=go1.20
+// -lang=go1.20
 
 // Copyright 2023 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

src/internal/types/testdata/fixedbugs/issue59338b.go

@@ -1,5 +1,3 @@
-// -reverseTypeInference
-
 // Copyright 2023 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/issue59639.go

@@ -1,4 +1,4 @@
-// -reverseTypeInference -lang=go1.17
+// -lang=go1.17
 
 // Copyright 2023 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

src/internal/types/testdata/fixedbugs/issue59953.go

@@ -1,5 +1,3 @@
-// -reverseTypeInference
-
 // Copyright 2023 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/issue59956.go

@@ -1,5 +1,3 @@
-// -reverseTypeInference
-
 // Copyright 2023 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.