cmd/compile: use more lenient type inference for untyped arguments for go1.21

This CL permanently enables the new behavior for -lang=go1.21 and
newer, and keeps the existing behavior if -lang=go1.20 or older.

To be submitted once #58671 is accepted.

For #58671.

Change-Id: I83a1d393f0ce7871be8f38ec35742d393946c55f
Reviewed-on: https://go-review.googlesource.com/c/go/+/496035
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

12 files changed, 33 insertions, 27 deletions

diff --git a/src/cmd/compile/internal/noder/irgen.go b/src/cmd/compile/internal/noder/irgen.go
index baccd0323b..3adf9e5d11 100644
--- a/src/cmd/compile/internal/noder/irgen.go
+++ b/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{},
-		InferMaxDefaultType: true, // #58671
+		Importer: &importer,
+		Sizes:    &gcSizes{},
 	}
 	info := &types2.Info{
 		StoreTypesInSyntax: true,
diff --git a/src/cmd/compile/internal/types2/api.go b/src/cmd/compile/internal/types2/api.go
index 5860c3a92c..b798f2c888 100644
--- a/src/cmd/compile/internal/types2/api.go
+++ b/src/cmd/compile/internal/types2/api.go
@@ -169,11 +169,6 @@ type Config struct {
 	// If DisableUnusedImportCheck is set, packages are not checked
 	// for unused imports.
 	DisableUnusedImportCheck bool
-
-	// If InferMaxDefaultType is set, the minimum (smallest) default
-	// type that fits all untyped constant arguments for the same type
-	// parameter is selected in type inference. (go.dev/issue/58671)
-	InferMaxDefaultType bool
 }
 
 func srcimporter_setUsesCgo(conf *Config) {
diff --git a/src/cmd/compile/internal/types2/check_test.go b/src/cmd/compile/internal/types2/check_test.go
index 357ca7cf50..26bb1aed9e 100644
--- a/src/cmd/compile/internal/types2/check_test.go
+++ b/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.InferMaxDefaultType, "inferMaxDefaultType", false, "")
 	if err := parseFlags(filenames[0], nil, flags); err != nil {
 		t.Fatal(err)
 	}
diff --git a/src/cmd/compile/internal/types2/infer.go b/src/cmd/compile/internal/types2/infer.go
index d8c81820f8..77c594a722 100644
--- a/src/cmd/compile/internal/types2/infer.go
+++ b/src/cmd/compile/internal/types2/infer.go
@@ -273,7 +273,19 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type,
 		u.tracef("== untyped arguments: %v", untyped)
 	}
 
-	if check.conf.InferMaxDefaultType {
+	// We need a poser/positioner for check.allowVersion below.
+	// We should really use pos (argument to infer) but currently
+	// the generator that generates go/types/infer.go has trouble
+	// with that. For now, do a little dance to get a position if
+	// we need one. (If we don't have untyped arguments left, it
+	// doesn't matter which branch we take below.)
+	// TODO(gri) adjust infer signature or adjust the rewriter.
+	var at syntax.Pos
+	if len(untyped) > 0 {
+		at = params.At(untyped[0]).pos
+	}
+
+	if check.allowVersion(check.pkg, atPos(at), go1_21) {
 		// Some generic parameters with untyped arguments may have been given a type by now.
 		// Collect all remaining parameters that don't have a type yet and determine the
 		// maximum untyped type for each of those parameters, if possible.
diff --git a/src/cmd/compile/internal/types2/stdlib_test.go b/src/cmd/compile/internal/types2/stdlib_test.go
index 80a05b7491..404e1636ae 100644
--- a/src/cmd/compile/internal/types2/stdlib_test.go
+++ b/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,
-				InferMaxDefaultType: true,
+				GoVersion: goVersion,
+				Importer:  stdLibImporter,
 			}
 			_, err = conf.Check(filename, []*syntax.File{file}, nil)
 		}
diff --git a/src/go/types/api.go b/src/go/types/api.go
index 3f83a8088a..08430c9e7a 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -170,11 +170,6 @@ type Config struct {
 	// If DisableUnusedImportCheck is set, packages are not checked
 	// for unused imports.
 	DisableUnusedImportCheck bool
-
-	// If _InferMaxDefaultType is set, the minimum (smallest) default
-	// type that fits all untyped constant arguments for the same type
-	// parameter is selected in type inference. (go.dev/issue/58671)
-	_InferMaxDefaultType bool
 }
 
 func srcimporter_setUsesCgo(conf *Config) {
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 9dbcb326cf..d53aaeadc5 100644
--- a/src/go/types/check_test.go
+++ b/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, "_InferMaxDefaultType"), "inferMaxDefaultType", false, "")
 	if err := parseFlags(filenames[0], srcs[0], flags); err != nil {
 		t.Fatal(err)
 	}
diff --git a/src/go/types/generate_test.go b/src/go/types/generate_test.go
index 73ad2c5b89..6a8343c615 100644
--- a/src/go/types/generate_test.go
+++ b/src/go/types/generate_test.go
@@ -106,7 +106,6 @@ var filemap = map[string]action{
 	"infer.go": func(f *ast.File) {
 		fixTokenPos(f)
 		fixInferSig(f)
-		renameIdent(f, "InferMaxDefaultType", "_InferMaxDefaultType")
 	},
 	// "initorder.go": fixErrErrorfCall, // disabled for now due to unresolved error_ use implications for gopls
 	"instantiate.go":      func(f *ast.File) { fixTokenPos(f); fixCheckErrorfCall(f) },
diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index 9c31d6adf6..b376ce4a4a 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -275,7 +275,19 @@ func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type,
 		u.tracef("== untyped arguments: %v", untyped)
 	}
 
-	if check.conf._InferMaxDefaultType {
+	// We need a poser/positioner for check.allowVersion below.
+	// We should really use pos (argument to infer) but currently
+	// the generator that generates go/types/infer.go has trouble
+	// with that. For now, do a little dance to get a position if
+	// we need one. (If we don't have untyped arguments left, it
+	// doesn't matter which branch we take below.)
+	// TODO(gri) adjust infer signature or adjust the rewriter.
+	var at token.Pos
+	if len(untyped) > 0 {
+		at = params.At(untyped[0]).pos
+	}
+
+	if check.allowVersion(check.pkg, atPos(at), go1_21) {
 		// Some generic parameters with untyped arguments may have been given a type by now.
 		// Collect all remaining parameters that don't have a type yet and determine the
 		// maximum untyped type for each of those parameters, if possible.
diff --git a/src/go/types/stdlib_test.go b/src/go/types/stdlib_test.go
index a7c1ae2eba..82f22de836 100644
--- a/src/go/types/stdlib_test.go
+++ b/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, "_InferMaxDefaultType") = true
 			_, err = conf.Check(filename, fset, []*ast.File{file}, nil)
 		}
 
diff --git a/src/internal/types/testdata/check/typeparams.go b/src/internal/types/testdata/check/typeparams.go
index 9f06b0888d..b002377df7 100644
--- a/src/internal/types/testdata/check/typeparams.go
+++ b/src/internal/types/testdata/check/typeparams.go
@@ -307,15 +307,15 @@ var _ int = f7 /* ERROR "cannot use" */ ([]float64{}...)
 var _ float64 = f7([]float64{}...)
 var _ = f7[float64](1, 2.3)
 var _ = f7(float64(1), 2.3)
-var _ = f7(1, 2.3 /* ERROR "does not match" */ )
-var _ = f7(1.2, 3 /* ERROR "does not match" */ )
+var _ = f7(1, 2.3)
+var _ = f7(1.2, 3)
 
 func f8[A, B any](A, B, ...B) int { panic(0) }
 
 var _ = f8(1) /* ERROR "not enough arguments" */
 var _ = f8(1, 2.3)
 var _ = f8(1, 2.3, 3.4, 4.5)
-var _ = f8(1, 2.3, 3.4, 4 /* ERROR "does not match" */ )
+var _ = f8(1, 2.3, 3.4, 4)
 var _ = f8[int, float64](1, 2.3, 3.4, 4)
 
 var _ = f8[int, float64](0, 0, nil...) // test case for #18268
diff --git a/src/internal/types/testdata/fixedbugs/issue58671.go b/src/internal/types/testdata/fixedbugs/issue58671.go
index 166ffda3d9..fa964aa5fd 100644
--- a/src/internal/types/testdata/fixedbugs/issue58671.go
+++ b/src/internal/types/testdata/fixedbugs/issue58671.go
@@ -1,5 +1,3 @@
-// -inferMaxDefaultType
-
 // 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.