patch sync/atomic; typepatch fix (don't change types)

internal/typepatch/patch.go

@@ -22,6 +22,17 @@ import (
 	"unsafe"
 )
 
+type typesPackage struct {
+	path      string
+	name      string
+	scope     *types.Scope
+	imports   []*types.Package
+	complete  bool
+	fake      bool   // scope lookup errors are silently dropped if package is fake (internal use only)
+	cgo       bool   // uses of this package will be rewritten into uses of declarations from _cgo_gotypes.go
+	goVersion string // minimum Go version required for package (by Config.GoVersion, typically from go.mod)
+}
+
 type typesScope struct {
 	parent   *types.Scope
 	children []*types.Scope
@@ -44,23 +55,42 @@ type iface struct {
 	data unsafe.Pointer
 }
 
+func setScope(pkg *types.Package, scope *types.Scope) {
+	p := (*typesPackage)(unsafe.Pointer(pkg))
+	p.scope = scope
+}
+
 func setPkg(o types.Object, pkg *types.Package) {
 	data := (*iface)(unsafe.Pointer(&o)).data
 	(*object)(data).pkg = pkg
 }
 
-func setObject(scope *types.Scope, name string, o types.Object) {
+func getElems(scope *types.Scope) map[string]types.Object {
 	s := (*typesScope)(unsafe.Pointer(scope))
-	s.elems[name] = o
+	return s.elems
+}
+
+func setElems(scope *types.Scope, elems map[string]types.Object) {
+	s := (*typesScope)(unsafe.Pointer(scope))
+	s.elems = elems
 }
 
 func Pkg(pkg, alt *types.Package) *types.Package {
-	scope := pkg.Scope()
-	altScope := alt.Scope()
-	for _, name := range altScope.Names() {
-		o := altScope.Lookup(name)
-		setPkg(o, pkg)
-		setObject(scope, name, o)
+	ret := *pkg
+	scope := *pkg.Scope()
+
+	old := getElems(&scope)
+	elems := make(map[string]types.Object, len(old))
+	for name, o := range old {
+		elems[name] = o
 	}
-	return pkg
+
+	altScope := alt.Scope()
+	for name, o := range getElems(altScope) {
+		setPkg(o, pkg)
+		elems[name] = o
+	}
+	setElems(&scope, elems)
+	setScope(&ret, &scope)
+	return &ret
 }