go/types,types2: avoid data race to object.color_ through dot imports

As described in issue #69912, type checking dot-imported identifiers can
result in a call to objDecl on an imported object, which leads to a data
race to the color_ field.

There are multiple potential fixes for this race. Opt for avoiding the
call to objDecl altogether, rather than setting color_ during import.
The color_ field is an internal property of objects that should only be
valid during the type checking of their package. We should not be
calling objDecl on imported objects.

Fixes #69912

Change-Id: I55eb652479715f2a7ac84104db2f448091c4e7ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/621637
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

src/cmd/compile/internal/importer/gcimporter_test.go

@@ -6,6 +6,7 @@ package importer
 
 import (
 	"bytes"
+	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/types2"
 	"fmt"
 	"go/build"
@@ -16,6 +17,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
@@ -593,3 +595,66 @@ func lookupObj(t *testing.T, scope *types2.Scope, name string) types2.Object {
 	t.Fatalf("%s not found", name)
 	return nil
 }
+
+// importMap implements the types2.Importer interface.
+type importMap map[string]*types2.Package
+
+func (m importMap) Import(path string) (*types2.Package, error) { return m[path], nil }
+
+func TestIssue69912(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	tmpdir := t.TempDir()
+	testoutdir := filepath.Join(tmpdir, "testdata")
+	if err := os.Mkdir(testoutdir, 0700); err != nil {
+		t.Fatalf("making output dir: %v", err)
+	}
+
+	compile(t, "testdata", "issue69912.go", testoutdir, nil)
+
+	issue69912, err := Import(make(map[string]*types2.Package), "./testdata/issue69912", tmpdir, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	check := func(pkgname, src string, imports importMap) (*types2.Package, error) {
+		f, err := syntax.Parse(syntax.NewFileBase(pkgname), strings.NewReader(src), nil, nil, 0)
+		if err != nil {
+			return nil, err
+		}
+		config := &types2.Config{
+			Importer: imports,
+		}
+		return config.Check(pkgname, []*syntax.File{f}, nil)
+	}
+
+	// Use the resulting package concurrently, via dot-imports, to exercise the
+	// race of issue #69912.
+	const pSrc = `package p
+
+import . "issue69912"
+
+type S struct {
+	f T
+}
+`
+	importer := importMap{
+		"issue69912": issue69912,
+	}
+	var wg sync.WaitGroup
+	for range 10 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if _, err := check("p", pSrc, importer); err != nil {
+				t.Errorf("Check failed: %v", err)
+			}
+		}()
+	}
+	wg.Wait()
+}

src/cmd/compile/internal/importer/testdata/issue69912.go

@@ -0,0 +1,9 @@
+// Copyright 2024 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 issue69912
+
+// Define an arbitrary type name, which will be used to demonstrate
+// the race of issue #69912.
+type T int

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

@@ -63,13 +63,16 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
 	// Type-check the object.
 	// Only call Checker.objDecl if the object doesn't have a type yet
 	// (in which case we must actually determine it) or the object is a
-	// TypeName and we also want a type (in which case we might detect
-	// a cycle which needs to be reported). Otherwise we can skip the
-	// call and avoid a possible cycle error in favor of the more
-	// informative "not a type/value" error that this function's caller
-	// will issue (see go.dev/issue/25790).
+	// TypeName from the current package and we also want a type (in which case
+	// we might detect a cycle which needs to be reported). Otherwise we can skip
+	// the call and avoid a possible cycle error in favor of the more informative
+	// "not a type/value" error that this function's caller will issue (see
+	// go.dev/issue/25790).
+	//
+	// Note that it is important to avoid calling objDecl on objects from other
+	// packages, to avoid races: see issue #69912.
 	typ := obj.Type()
-	if typ == nil || gotType && wantType {
+	if typ == nil || (gotType && wantType && obj.Pkg() == check.pkg) {
 		check.objDecl(obj, def)
 		typ = obj.Type() // type must have been assigned by Checker.objDecl
 	}

src/go/internal/gcimporter/gcimporter_test.go

@@ -14,6 +14,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -750,3 +751,68 @@ func lookupObj(t *testing.T, scope *types.Scope, name string) types.Object {
 	t.Fatalf("%s not found", name)
 	return nil
 }
+
+// importMap implements the types.Importer interface.
+type importMap map[string]*types.Package
+
+func (m importMap) Import(path string) (*types.Package, error) { return m[path], nil }
+
+func TestIssue69912(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	tmpdir := t.TempDir()
+	testoutdir := filepath.Join(tmpdir, "testdata")
+	if err := os.Mkdir(testoutdir, 0700); err != nil {
+		t.Fatalf("making output dir: %v", err)
+	}
+
+	compile(t, "testdata", "issue69912.go", testoutdir, nil)
+
+	fset := token.NewFileSet()
+
+	issue69912, err := Import(fset, make(map[string]*types.Package), "./testdata/issue69912", tmpdir, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	check := func(pkgname, src string, imports importMap) (*types.Package, error) {
+		f, err := parser.ParseFile(fset, "a.go", src, 0)
+		if err != nil {
+			return nil, err
+		}
+		config := &types.Config{
+			Importer: imports,
+		}
+		return config.Check(pkgname, fset, []*ast.File{f}, nil)
+	}
+
+	// Use the resulting package concurrently, via dot-imports, to exercise the
+	// race of issue #69912.
+	const pSrc = `package p
+
+import . "issue69912"
+
+type S struct {
+	f T
+}
+`
+	importer := importMap{
+		"issue69912": issue69912,
+	}
+	var wg sync.WaitGroup
+	for range 10 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if _, err := check("p", pSrc, importer); err != nil {
+				t.Errorf("Check failed: %v", err)
+			}
+		}()
+	}
+	wg.Wait()
+}

src/go/internal/gcimporter/testdata/issue69912.go

@@ -0,0 +1,9 @@
+// Copyright 2024 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 issue69912
+
+// Define an arbitrary type name, which will be used to demonstrate
+// the race of issue #69912.
+type T int

src/go/types/typexpr.go

@@ -63,13 +63,16 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
 	// Type-check the object.
 	// Only call Checker.objDecl if the object doesn't have a type yet
 	// (in which case we must actually determine it) or the object is a
-	// TypeName and we also want a type (in which case we might detect
-	// a cycle which needs to be reported). Otherwise we can skip the
-	// call and avoid a possible cycle error in favor of the more
-	// informative "not a type/value" error that this function's caller
-	// will issue (see go.dev/issue/25790).
+	// TypeName from the current package and we also want a type (in which case
+	// we might detect a cycle which needs to be reported). Otherwise we can skip
+	// the call and avoid a possible cycle error in favor of the more informative
+	// "not a type/value" error that this function's caller will issue (see
+	// go.dev/issue/25790).
+	//
+	// Note that it is important to avoid calling objDecl on objects from other
+	// packages, to avoid races: see issue #69912.
 	typ := obj.Type()
-	if typ == nil || gotType && wantType {
+	if typ == nil || (gotType && wantType && obj.Pkg() == check.pkg) {
 		check.objDecl(obj, def)
 		typ = obj.Type() // type must have been assigned by Checker.objDecl
 	}