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 #13224
Updates #12912

Signed-off-by: Nick Khyl <nickk@tailscale.com>

cmd/viewer/tests/tests_view.go

@@ -14,7 +14,7 @@ import (
 	"tailscale.com/types/views"
 )
 
-//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone,StructWithEmbedded,GenericIntStruct,GenericNoPtrsStruct,GenericCloneableStruct,StructWithContainers
+//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone,StructWithEmbedded,GenericIntStruct,GenericNoPtrsStruct,GenericCloneableStruct,StructWithContainers,StructWithTypeAliasFields,GenericTypeAliasStruct
 
 // View returns a readonly view of StructWithPtrs.
 func (p *StructWithPtrs) View() StructWithPtrsView {
@@ -676,3 +676,115 @@ var _StructWithContainersViewNeedsRegeneration = StructWithContainers(struct {
 	CloneableMap              MapContainer[int, *StructWithPtrs]
 	CloneableGenericMap       MapContainer[int, *GenericNoPtrsStruct[int]]
 }{})
+
+// View returns a readonly view of StructWithTypeAliasFields.
+func (p *StructWithTypeAliasFields) View() StructWithTypeAliasFieldsView {
+	return StructWithTypeAliasFieldsView{ж: p}
+}
+
+// StructWithTypeAliasFieldsView provides a read-only view over StructWithTypeAliasFields.
+//
+// Its methods should only be called if `Valid()` returns true.
+type StructWithTypeAliasFieldsView struct {
+	// ж is the underlying mutable value, named with a hard-to-type
+	// character that looks pointy like a pointer.
+	// It is named distinctively to make you think of how dangerous it is to escape
+	// to callers. You must not let callers be able to mutate it.
+	ж *StructWithTypeAliasFields
+}
+
+// Valid reports whether underlying value is non-nil.
+func (v StructWithTypeAliasFieldsView) Valid() bool { return v.ж != nil }
+
+// AsStruct returns a clone of the underlying value which aliases no memory with
+// the original.
+func (v StructWithTypeAliasFieldsView) AsStruct() *StructWithTypeAliasFields {
+	if v.ж == nil {
+		return nil
+	}
+	return v.ж.Clone()
+}
+
+func (v StructWithTypeAliasFieldsView) MarshalJSON() ([]byte, error) { return json.Marshal(v.ж) }
+
+func (v *StructWithTypeAliasFieldsView) UnmarshalJSON(b []byte) error {
+	if v.ж != nil {
+		return errors.New("already initialized")
+	}
+	if len(b) == 0 {
+		return nil
+	}
+	var x StructWithTypeAliasFields
+	if err := json.Unmarshal(b, &x); err != nil {
+		return err
+	}
+	v.ж = &x
+	return nil
+}
+
+func (v StructWithTypeAliasFieldsView) WithPtr() StructWithPtrsView        { return v.ж.WithPtr.View() }
+func (v StructWithTypeAliasFieldsView) WithoutPtr() StructWithoutPtrsAlias { return v.ж.WithoutPtr }
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _StructWithTypeAliasFieldsViewNeedsRegeneration = StructWithTypeAliasFields(struct {
+	WithPtr    StructWithPtrsAlias
+	WithoutPtr StructWithoutPtrsAlias
+}{})
+
+// View returns a readonly view of GenericTypeAliasStruct.
+func (p *GenericTypeAliasStruct[T, T2, V2]) View() GenericTypeAliasStructView[T, T2, V2] {
+	return GenericTypeAliasStructView[T, T2, V2]{ж: p}
+}
+
+// GenericTypeAliasStructView[T, T2, V2] provides a read-only view over GenericTypeAliasStruct[T, T2, V2].
+//
+// Its methods should only be called if `Valid()` returns true.
+type GenericTypeAliasStructView[T integer, T2 views.ViewCloner[T2, V2], V2 views.StructView[T2]] struct {
+	// ж is the underlying mutable value, named with a hard-to-type
+	// character that looks pointy like a pointer.
+	// It is named distinctively to make you think of how dangerous it is to escape
+	// to callers. You must not let callers be able to mutate it.
+	ж *GenericTypeAliasStruct[T, T2, V2]
+}
+
+// Valid reports whether underlying value is non-nil.
+func (v GenericTypeAliasStructView[T, T2, V2]) Valid() bool { return v.ж != nil }
+
+// AsStruct returns a clone of the underlying value which aliases no memory with
+// the original.
+func (v GenericTypeAliasStructView[T, T2, V2]) AsStruct() *GenericTypeAliasStruct[T, T2, V2] {
+	if v.ж == nil {
+		return nil
+	}
+	return v.ж.Clone()
+}
+
+func (v GenericTypeAliasStructView[T, T2, V2]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(v.ж)
+}
+
+func (v *GenericTypeAliasStructView[T, T2, V2]) UnmarshalJSON(b []byte) error {
+	if v.ж != nil {
+		return errors.New("already initialized")
+	}
+	if len(b) == 0 {
+		return nil
+	}
+	var x GenericTypeAliasStruct[T, T2, V2]
+	if err := json.Unmarshal(b, &x); err != nil {
+		return err
+	}
+	v.ж = &x
+	return nil
+}
+
+func (v GenericTypeAliasStructView[T, T2, V2]) NonCloneable() T { return v.ж.NonCloneable }
+func (v GenericTypeAliasStructView[T, T2, V2]) Cloneable() V2   { return v.ж.Cloneable.View() }
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+func _GenericTypeAliasStructViewNeedsRegeneration[T integer, T2 views.ViewCloner[T2, V2], V2 views.StructView[T2]](GenericTypeAliasStruct[T, T2, V2]) {
+	_GenericTypeAliasStructViewNeedsRegeneration(struct {
+		NonCloneable T
+		Cloneable    T2
+	}{})
+}