go/types, types2: disallow new methods on (aliases to) cgo-generated types

This makes methods on aliases of cgo-generated types a new compiler error.
That is ok because cgo-behavior is not covered by the G1 compatibility
guarantee.

Background: In 2023 we fixed a gopls issue related to this by actually
enabling methods on cgo-generated types in the first place (#59944).
See the discussion in #60725 and this CL for why we believe it is ok
to make this an error now.

Based on a variation of CL 503596 (by Xie Cui).

Fixes #60725.
For #59944.

Change-Id: I7e9e6e1a76447167483a282b268f5183214027c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/629715
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/cmd/compile/internal/types2/issues_test.go b/src/cmd/compile/internal/types2/issues_test.go
index 317a5f80c83a6652a14828d73c51c8043eb5b708..a856fcc790854eddea7d01a12d8a0cf4e836356a 100644 (file)
--- a/src/cmd/compile/internal/types2/issues_test.go
+++ b/src/cmd/compile/internal/types2/issues_test.go
@@ -839,7 +839,8 @@ func TestIssue59944(t *testing.T) {
        testenv.MustHaveCGO(t)
 
        // The typechecker should resolve methods declared on aliases of cgo types.
-       const src = `
+       const src = `// -gotypesalias=1
+
 package p
 
 /*
@@ -851,7 +852,7 @@ import "C"
 
 type Layout = C.struct_layout
 
-func (l *Layout) Binding() {}
+func (l /* ERROR "cannot define new methods on non-local type Layout" */ *Layout) Binding() {}
 
 func _() {
        _ = (*Layout).Binding

diff --git a/src/cmd/compile/internal/types2/signature.go b/src/cmd/compile/internal/types2/signature.go
index 43233aeb5ab4b30b1674c9fb38afa3e263d20bcc..7199e9c0e4859070e2ca97a8c235a0cda1466410 100644 (file)
--- a/src/cmd/compile/internal/types2/signature.go
+++ b/src/cmd/compile/internal/types2/signature.go
@@ -8,6 +8,8 @@ import (
        "cmd/compile/internal/syntax"
        "fmt"
        . "internal/types/errors"
+       "path/filepath"
+       "strings"
 )
 
 // ----------------------------------------------------------------------------
@@ -410,7 +412,7 @@ func (check *Checker) validRecv(recv *Var) {
        // as the method."
        switch T := atyp.(type) {
        case *Named:
-               if T.obj.pkg != check.pkg {
+               if T.obj.pkg != check.pkg || isCGoTypeObj(T.obj) {
                        check.errorf(recv, InvalidRecv, "cannot define new methods on non-local type %s", rtyp)
                        break
                }
@@ -437,3 +439,9 @@ func (check *Checker) validRecv(recv *Var) {
                check.errorf(recv, InvalidRecv, "invalid receiver type %s", recv.typ)
        }
 }
+
+// isCGoTypeObj reports whether the given type name was created by cgo.
+func isCGoTypeObj(obj *TypeName) bool {
+       return strings.HasPrefix(obj.name, "_Ctype_") ||
+               strings.HasPrefix(filepath.Base(obj.pos.FileBase().Filename()), "_cgo_")
+}

diff --git a/src/cmd/go/testdata/script/cgo_badmethod_issue60725.txt b/src/cmd/go/testdata/script/cgo_badmethod_issue60725.txt
new file mode 100644 (file)
index 0000000..1ed087a
--- /dev/null
+++ b/src/cmd/go/testdata/script/cgo_badmethod_issue60725.txt
@@ -0,0 +1,26 @@
+[short] skip
+[!cgo] skip
+
+# Test that cgo rejects attempts to declare methods
+# on the types A or *A; see issue #60725.
+
+! go build ./a
+stderr 'cannot define new methods on non-local type A'
+stderr 'cannot define new methods on non-local type A'
+
+-- go.mod --
+module example.com
+go 1.24
+
+-- a/a.go --
+package a
+
+/*
+typedef int T;
+*/
+import "C"
+
+type A = C.T
+
+func (A) m1() {}
+func (*A) m2() {}

diff --git a/src/go/types/issues_test.go b/src/go/types/issues_test.go
index 5a55822abad5f3aa5ee67e3dedd153f3fb8f4311..925ca0ebfa9626b77ef52a58037a21bbf395d323 100644 (file)
--- a/src/go/types/issues_test.go
+++ b/src/go/types/issues_test.go
@@ -848,7 +848,8 @@ func TestIssue59944(t *testing.T) {
        testenv.MustHaveCGO(t)
 
        // The typechecker should resolve methods declared on aliases of cgo types.
-       const src = `
+       const src = `// -gotypesalias=1
+
 package p
 
 /*
@@ -860,7 +861,7 @@ import "C"
 
 type Layout = C.struct_layout
 
-func (l *Layout) Binding() {}
+func (l /* ERROR "cannot define new methods on non-local type Layout" */ *Layout) Binding() {}
 
 func _() {
        _ = (*Layout).Binding

diff --git a/src/go/types/signature.go b/src/go/types/signature.go
index 384389c8f4692fb90e6e32a4c1452804c2814a9d..c0f2e611203de806dd6cfd0e904bd31c14fd136c 100644 (file)
--- a/src/go/types/signature.go
+++ b/src/go/types/signature.go
@@ -9,6 +9,8 @@ import (
        "go/ast"
        "go/token"
        . "internal/types/errors"
+       "path/filepath"
+       "strings"
 )
 
 // ----------------------------------------------------------------------------
@@ -430,7 +432,7 @@ func (check *Checker) validRecv(recv *Var) {
        // as the method."
        switch T := atyp.(type) {
        case *Named:
-               if T.obj.pkg != check.pkg {
+               if T.obj.pkg != check.pkg || isCGoTypeObj(check.fset, T.obj) {
                        check.errorf(recv, InvalidRecv, "cannot define new methods on non-local type %s", rtyp)
                        break
                }
@@ -457,3 +459,9 @@ func (check *Checker) validRecv(recv *Var) {
                check.errorf(recv, InvalidRecv, "invalid receiver type %s", recv.typ)
        }
 }
+
+// isCGoTypeObj reports whether the given type name was created by cgo.
+func isCGoTypeObj(fset *token.FileSet, obj *TypeName) bool {
+       return strings.HasPrefix(obj.name, "_Ctype_") ||
+               strings.HasPrefix(filepath.Base(fset.File(obj.pos).Name()), "_cgo_")
+}