util/codegen: support embedded fields

I noticed cmd/{cloner,viewer} didn't support structs with embedded
fields while working on a change in another repo. This adds support.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/viewer/tests/tests.go

@@ -9,7 +9,7 @@ import (
 	"net/netip"
 )
 
-//go:generate go run tailscale.com/cmd/viewer --type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone --clone-only-type=OnlyGetClone
+//go:generate go run tailscale.com/cmd/viewer --type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone,StructWithEmbedded --clone-only-type=OnlyGetClone
 
 type StructWithoutPtrs struct {
 	Int int
@@ -61,3 +61,8 @@ type StructWithSlices struct {
 type OnlyGetClone struct {
 	SinViewerPorFavor bool
 }
+
+type StructWithEmbedded struct {
+	A *StructWithPtrs
+	StructWithSlices
+}

cmd/viewer/tests/tests_clone.go

@@ -211,3 +211,22 @@ func (src *OnlyGetClone) Clone() *OnlyGetClone {
 var _OnlyGetCloneCloneNeedsRegeneration = OnlyGetClone(struct {
 	SinViewerPorFavor bool
 }{})
+
+// Clone makes a deep copy of StructWithEmbedded.
+// The result aliases no memory with the original.
+func (src *StructWithEmbedded) Clone() *StructWithEmbedded {
+	if src == nil {
+		return nil
+	}
+	dst := new(StructWithEmbedded)
+	*dst = *src
+	dst.A = src.A.Clone()
+	dst.StructWithSlices = *src.StructWithSlices.Clone()
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _StructWithEmbeddedCloneNeedsRegeneration = StructWithEmbedded(struct {
+	A *StructWithPtrs
+	StructWithSlices
+}{})

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
+//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone,StructWithEmbedded
 
 // View returns a readonly view of StructWithPtrs.
 func (p *StructWithPtrs) View() StructWithPtrsView {
@@ -325,3 +325,59 @@ var _StructWithSlicesViewNeedsRegeneration = StructWithSlices(struct {
 	Prefixes       []netip.Prefix
 	Data           []byte
 }{})
+
+// View returns a readonly view of StructWithEmbedded.
+func (p *StructWithEmbedded) View() StructWithEmbeddedView {
+	return StructWithEmbeddedView{ж: p}
+}
+
+// StructWithEmbeddedView provides a read-only view over StructWithEmbedded.
+//
+// Its methods should only be called if `Valid()` returns true.
+type StructWithEmbeddedView 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 *StructWithEmbedded
+}
+
+// Valid reports whether underlying value is non-nil.
+func (v StructWithEmbeddedView) Valid() bool { return v.ж != nil }
+
+// AsStruct returns a clone of the underlying value which aliases no memory with
+// the original.
+func (v StructWithEmbeddedView) AsStruct() *StructWithEmbedded {
+	if v.ж == nil {
+		return nil
+	}
+	return v.ж.Clone()
+}
+
+func (v StructWithEmbeddedView) MarshalJSON() ([]byte, error) { return json.Marshal(v.ж) }
+
+func (v *StructWithEmbeddedView) UnmarshalJSON(b []byte) error {
+	if v.ж != nil {
+		return errors.New("already initialized")
+	}
+	if len(b) == 0 {
+		return nil
+	}
+	var x StructWithEmbedded
+	if err := json.Unmarshal(b, &x); err != nil {
+		return err
+	}
+	v.ж = &x
+	return nil
+}
+
+func (v StructWithEmbeddedView) A() StructWithPtrsView { return v.ж.A.View() }
+func (v StructWithEmbeddedView) StructWithSlices() StructWithSlicesView {
+	return v.ж.StructWithSlices.View()
+}
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _StructWithEmbeddedViewNeedsRegeneration = StructWithEmbedded(struct {
+	A *StructWithPtrs
+	StructWithSlices
+}{})

util/codegen/codegen.go

@@ -202,14 +202,19 @@ func AssertStructUnchanged(t *types.Struct, tname, ctx string, it *ImportTracker
 	w("var _%s%sNeedsRegeneration = %s(struct {", tname, ctx, tname)
 
 	for i := 0; i < t.NumFields(); i++ {
-		fname := t.Field(i).Name()
+		st := t.Field(i)
+		fname := st.Name()
 		ft := t.Field(i).Type()
 		if IsInvalid(ft) {
 			continue
 		}
 		qname := it.QualifiedName(ft)
+		if st.Anonymous() {
+			w("\t%s ", fname)
+		} else {
 			w("\t%s %s", fname, qname)
 		}
+	}
 
 	w("}{})\n")
 	return buf.Bytes()