cmd/compile: enable reverse type inference

For #59338.

Change-Id: I8141d421cdc60e47ee5794fc1ca81246bd8a8a25
Reviewed-on: https://go-review.googlesource.com/c/go/+/491475
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

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

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

@@ -138,7 +138,11 @@ 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}
+			conf := Config{
+				GoVersion:                  goVersion,
+				Importer:                   stdLibImporter,
+				EnableReverseTypeInference: true,
+			}
 			_, err = conf.Check(filename, []*syntax.File{file}, nil)
 		}
 
@@ -250,8 +254,9 @@ func typecheckFiles(t *testing.T, path string, filenames []string) {
 
 	// typecheck package files
 	conf := Config{
-		Error:    func(err error) { t.Error(err) },
-		Importer: stdLibImporter,
+		Error:                      func(err error) { t.Error(err) },
+		Importer:                   stdLibImporter,
+		EnableReverseTypeInference: true,
 	}
 	info := Info{Uses: make(map[*syntax.Name]Object)}
 	conf.Check(path, files, &info)

src/go/types/stdlib_test.go

@@ -139,7 +139,11 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 		// parse and type-check file
 		file, err := parser.ParseFile(fset, filename, nil, 0)
 		if err == nil {
-			conf := Config{GoVersion: goVersion, Importer: stdLibImporter}
+			conf := Config{
+				GoVersion: goVersion,
+				Importer:  stdLibImporter,
+			}
+			*boolFieldAddr(&conf, "_EnableReverseTypeInference") = true
 			_, err = conf.Check(filename, fset, []*ast.File{file}, nil)
 		}
 
@@ -267,6 +271,7 @@ 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)
 

test/fixedbugs/issue59338.go

@@ -0,0 +1,39 @@
+// run
+
+// 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.
+
+// Smoke test for reverse type inference.
+// The type checker has more expansive tests.
+
+package main
+
+func main() {
+	var f1 func(int) int
+	f1 = g1
+	if f1(1) != g1(1) {
+		panic(1)
+	}
+
+	var f2 func(int) string = g2
+	if f2(2) != "" {
+		panic(2)
+	}
+
+	// Disabled for now - requires some noder work
+	// TODO fix this
+	// if g3(g1, 3) != g1(3) {
+	// 	panic(3)
+	// }
+
+	// if g4(g2, 4) != "" {
+	// 	panic(4)
+	// }
+}
+
+func g1[P any](x P) P    { return x }
+func g2[P, Q any](x P) Q { var q Q; return q }
+
+func g3(f1 func(int) int, x int) int       { return f1(x) }
+func g4(f2 func(int) string, x int) string { return f2(x) }