Add test cases for immutable to verify pointers

The code was correct, but the test case was bad at proving it.

Author: thockin

staging/src/k8s.io/code-generator/cmd/validation-gen/output_tests/tags/immutable/doc_test.go

@@ -38,6 +38,13 @@ func Test(t *testing.T) {
 		ImmutableField:              "fff",
 		ImmutablePtrField:           ptr.To(ImmutableType("fff")),
 	}
+
+	structA2 := structA // dup of A but with different pointer values
+	structA2.StringPtrField = ptr.To(*structA2.StringPtrField)
+	structA2.StructPtrField = ptr.To(*structA2.StructPtrField)
+	structA2.NonComparableStructPtrField = ptr.To(*structA2.NonComparableStructPtrField)
+	structA2.ImmutablePtrField = ptr.To(*structA2.ImmutablePtrField)
+
 	structB := Struct{
 		StringField:                 "uuu",
 		StringPtrField:              ptr.To("uuu"),
@@ -52,6 +59,8 @@ func Test(t *testing.T) {
 	}
 
 	st.Value(&structA).OldValue(&structA).ExpectValid()
+	st.Value(&structA).OldValue(&structA2).ExpectValid()
+	st.Value(&structA2).OldValue(&structA).ExpectValid()
 
 	st.Value(&structA).OldValue(&structB).ExpectInvalid(
 		field.Forbidden(field.NewPath("stringField"), "field is immutable"),

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/common.go

@@ -50,6 +50,8 @@ func isNilableType(t *types.Type) bool {
 	return false
 }
 
+// realType returns the underlying type of a type, unwrapping aliases and
+// dropping pointerness.
 func realType(t *types.Type) *types.Type {
 	for {
 		if t.Kind == types.Alias {

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/immutable.go

@@ -51,15 +51,8 @@ var (
 func (immutableTagValidator) GetValidations(context Context, _ []string, payload string) (Validations, error) {
 	var result Validations
 
-	t := context.Type
-	for t.Kind == types.Pointer || t.Kind == types.Alias {
-		if t.Kind == types.Pointer {
-			t = t.Elem
-		} else if t.Kind == types.Alias {
-			t = t.Underlying
-		}
-	}
-	if t.IsComparable() {
+	if realType(context.Type).IsComparable() {
+		// Note: This compares the pointee, not the pointer itself.
 		result.AddFunction(Function(immutableTagName, DefaultFlags, immutableValidator))
 	} else {
 		result.AddFunction(Function(immutableTagName, DefaultFlags, immutableNonComparableValidator))