cmd/viewer: add flag to support Clone generation without Views

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

cmd/viewer/tests/tests.go

@@ -10,7 +10,7 @@
 	"net/netip"
 )
 
-//go:generate go run tailscale.com/cmd/viewer --type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices
+//go:generate go run tailscale.com/cmd/viewer --type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone --clone-only-type=OnlyGetClone
 
 type StructWithoutPtrs struct {
 	Int int
@@ -58,3 +58,7 @@ type StructWithSlices struct {
 	Prefixes []netip.Prefix
 	Data     []byte
 }
+
+type OnlyGetClone struct {
+	SinViewerPorFavor bool
+}

cmd/viewer/tests/tests_clone.go

@@ -196,3 +196,19 @@ func (src *StructWithSlices) Clone() *StructWithSlices {
 	Prefixes       []netip.Prefix
 	Data           []byte
 }{})
+
+// Clone makes a deep copy of OnlyGetClone.
+// The result aliases no memory with the original.
+func (src *OnlyGetClone) Clone() *OnlyGetClone {
+	if src == nil {
+		return nil
+	}
+	dst := new(OnlyGetClone)
+	*dst = *src
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _OnlyGetCloneCloneNeedsRegeneration = OnlyGetClone(struct {
+	SinViewerPorFavor bool
+}{})

cmd/viewer/tests/tests_view.go

@@ -15,7 +15,7 @@
 	"tailscale.com/types/views"
 )
 
-//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices
+//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=StructWithPtrs,StructWithoutPtrs,Map,StructWithSlices,OnlyGetClone
 
 // View returns a readonly view of StructWithPtrs.
 func (p *StructWithPtrs) View() StructWithPtrsView {

cmd/viewer/viewer.go

@@ -327,6 +327,8 @@ func genView(buf *bytes.Buffer, it *codegen.ImportTracker, typ *types.Named, thi
 	flagTypes     = flag.String("type", "", "comma-separated list of types; required")
 	flagBuildTags = flag.String("tags", "", "compiler build tags to apply")
 	flagCloneFunc = flag.Bool("clonefunc", false, "add a top-level Clone func")
+
+	flagCloneOnlyTypes = flag.String("clone-only-type", "", "comma-separated list of types (a subset of --type) that should only generate a go:generate clone line and not actual views")
 )
 
 func main() {
@@ -353,10 +355,18 @@ func main() {
 	}
 	it := codegen.NewImportTracker(pkg.Types)
 
+	cloneOnlyType := map[string]bool{}
+	for _, t := range strings.Split(*flagCloneOnlyTypes, ",") {
+		cloneOnlyType[t] = true
+	}
+
 	buf := new(bytes.Buffer)
 	fmt.Fprintf(buf, "//go:generate go run tailscale.com/cmd/cloner  %s\n\n", strings.Join(flagArgs, " "))
 	runCloner := false
 	for _, typeName := range typeNames {
+		if cloneOnlyType[typeName] {
+			continue
+		}
 		typ, ok := namedTypes[typeName]
 		if !ok {
 			log.Fatalf("could not find type %s", typeName)