util/codegen, cmd/cloner, cmd/viewer: update codegen.LookupMethod to …

…support alias type nodes

Go 1.23 updates the go/types package to produce Alias type nodes for type aliases, unless disabled with gotypesalias=0.
This new default behavior breaks codegen.LookupMethod, which uses checked type assertions to types.Named and
types.Interface, as only named types and interfaces have methods.

In this PR, we update codegen.LookupMethod to perform method lookup on the right-hand side of the alias declaration
and clearly switch on the supported type nodes types. We also improve support for various edge cases, such as when an alias
is used as a type parameter constraint, and add tests for the LookupMethod function.

Additionally, we update cmd/viewer/tests to include types with aliases used in type fields and generic type constraints.

Updates tailscale#13224
Updates tailscale#12912

Signed-off-by: Nick Khyl <[email protected]>

cmd/cloner/cloner.go

@@ -47,7 +47,7 @@ func main() {
 	it := codegen.NewImportTracker(pkg.Types)
 	buf := new(bytes.Buffer)
 	for _, typeName := range typeNames {
-		typ, ok := namedTypes[typeName]
+		typ, ok := namedTypes[typeName].(*types.Named)
 		if !ok {
 			log.Fatalf("could not find type %s", typeName)
 		}

cmd/viewer/tests/tests.go

@@ -13,7 +13,7 @@ import (
 	"tailscale.com/types/views"
 )
 
-//go:generate go run tailscale.com/cmd/viewer --type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone,StructWithEmbedded,GenericIntStruct,GenericNoPtrsStruct,GenericCloneableStruct,StructWithContainers --clone-only-type=OnlyGetClone
+//go:generate go run tailscale.com/cmd/viewer --type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone,StructWithEmbedded,GenericIntStruct,GenericNoPtrsStruct,GenericCloneableStruct,StructWithContainers,StructWithTypeAliasFields,GenericTypeAliasStruct --clone-only-type=OnlyGetClone
 
 type StructWithoutPtrs struct {
 	Int int
@@ -202,3 +202,20 @@ type StructWithContainers struct {
 	CloneableMap              MapContainer[int, *StructWithPtrs]
 	CloneableGenericMap       MapContainer[int, *GenericNoPtrsStruct[int]]
 }
+
+type (
+	StructWithPtrsAlias    = StructWithPtrs
+	StructWithoutPtrsAlias = StructWithoutPtrs
+)
+
+type StructWithTypeAliasFields struct {
+	WithPtr    StructWithPtrsAlias
+	WithoutPtr StructWithoutPtrsAlias
+}
+
+type integer = constraints.Integer
+
+type GenericTypeAliasStruct[T integer, T2 views.ViewCloner[T2, V2], V2 views.StructView[T2]] struct {
+	NonCloneable T
+	Cloneable    T2
+}

cmd/viewer/viewer.go

@@ -567,7 +567,7 @@ func main() {
 		if cloneOnlyType[typeName] {
 			continue
 		}
-		typ, ok := namedTypes[typeName]
+		typ, ok := namedTypes[typeName].(*types.Named)
 		if !ok {
 			log.Fatalf("could not find type %s", typeName)
 		}

util/codegen/codegen.go

@@ -24,7 +24,7 @@ import (
 var flagCopyright = flag.Bool("copyright", true, "add Tailscale copyright to generated file headers")
 
 // LoadTypes returns all named types in pkgName, keyed by their type name.
-func LoadTypes(buildTags string, pkgName string) (*packages.Package, map[string]*types.Named, error) {
+func LoadTypes(buildTags string, pkgName string) (*packages.Package, map[string]types.Type, error) {
 	cfg := &packages.Config{
 		Mode:  packages.NeedTypes | packages.NeedTypesInfo | packages.NeedSyntax | packages.NeedName,
 		Tests: buildTags == "test",
@@ -181,8 +181,8 @@ func writeFormatted(code []byte, path string) error {
 }
 
 // namedTypes returns all named types in pkg, keyed by their type name.
-func namedTypes(pkg *packages.Package) map[string]*types.Named {
-	nt := make(map[string]*types.Named)
+func namedTypes(pkg *packages.Package) map[string]types.Type {
+	nt := make(map[string]types.Type)
 	for _, file := range pkg.Syntax {
 		for _, d := range file.Decls {
 			decl, ok := d.(*ast.GenDecl)
@@ -198,11 +198,10 @@ func namedTypes(pkg *packages.Package) map[string]*types.Named {
 				if !ok {
 					continue
 				}
-				typ, ok := typeNameObj.Type().(*types.Named)
-				if !ok {
-					continue
+				switch typ := typeNameObj.Type(); typ.(type) {
+				case *types.Alias, *types.Named:
+					nt[spec.Name.Name] = typ
 				}
-				nt[spec.Name.Name] = typ
 			}
 		}
 	}
@@ -356,14 +355,25 @@ func FormatTypeParams(params *types.TypeParamList, it *ImportTracker) (constrain
 
 // LookupMethod returns the method with the specified name in t, or nil if the method does not exist.
 func LookupMethod(t types.Type, name string) *types.Func {
-	if t, ok := t.(*types.Named); ok {
-		for i := 0; i < t.NumMethods(); i++ {
-			if method := t.Method(i); method.Name() == name {
-				return method
+	switch t := t.(type) {
+	case *types.Alias:
+		return LookupMethod(t.Rhs(), name)
+	case *types.TypeParam:
+		return LookupMethod(t.Constraint(), name)
+	case *types.Pointer:
+		return LookupMethod(t.Elem(), name)
+	case *types.Named:
+		switch u := t.Underlying().(type) {
+		case *types.Interface:
+			return LookupMethod(u, name)
+		default:
+			for i := 0; i < t.NumMethods(); i++ {
+				if method := t.Method(i); method.Name() == name {
+					return method
+				}
 			}
 		}
-	}
-	if t, ok := t.Underlying().(*types.Interface); ok {
+	case *types.Interface:
 		for i := 0; i < t.NumMethods(); i++ {
 			if method := t.Method(i); method.Name() == name {
 				return method