From 3872880617733ca92d8d698dcc692ad0fd63e1f6 Mon Sep 17 00:00:00 2001
From: Andrew Lytvynov <awly@tailscale.com>
Date: Fri, 10 Jul 2026 08:56:49 -0700
Subject: [PATCH] cmd/cloner: handle named slices as map values (#20387)

Previously cloner only handled literal slices for values, like
`map[string][]int`. This adds support for named types with an underlying
type of slice, like `map[string]IntSlice` with `type IntSlice []int`.

Updates tailscale/corp#44077

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
---
 cmd/cloner/cloner.go                  |  2 +-
 cmd/cloner/cloner_test.go             | 10 ++++++++
 cmd/cloner/clonerex/clonerex.go       | 11 ++++++++-
 cmd/cloner/clonerex/clonerex_clone.go | 33 ++++++++++++++++++++++++++-
 4 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/cmd/cloner/cloner.go b/cmd/cloner/cloner.go
index 8b4cacf7a..2894c862d 100644
--- a/cmd/cloner/cloner.go
+++ b/cmd/cloner/cloner.go
@@ -169,7 +169,7 @@ func gen(buf *bytes.Buffer, it *codegen.ImportTracker, typ *types.Named) {
 			writef("}")
 		case *types.Map:
 			elem := ft.Elem()
-			if sliceType, isSlice := elem.(*types.Slice); isSlice {
+			if sliceType, isSlice := elem.Underlying().(*types.Slice); isSlice {
 				n := it.QualifiedName(sliceType.Elem())
 				writef("if dst.%s != nil {", fname)
 				writef("\tdst.%s = map[%s]%s{}", fname, it.QualifiedName(ft.Key()), it.QualifiedName(elem))
diff --git a/cmd/cloner/cloner_test.go b/cmd/cloner/cloner_test.go
index f8beb4a88..04670e1f5 100644
--- a/cmd/cloner/cloner_test.go
+++ b/cmd/cloner/cloner_test.go
@@ -283,3 +283,13 @@ func TestDeeplyNestedMap(t *testing.T) {
 		t.Errorf("Clone() aliased FourLevels map: new nested key appeared in original")
 	}
 }
+
+func TestMapWithNamedSliceValues(t *testing.T) {
+	orig := &clonerex.MapWithNamedSliceValues{
+		M: map[string]clonerex.NamedSlice{"k": {"foo", "bar"}},
+	}
+	cloned := orig.Clone()
+	if diff := cmp.Diff(orig, cloned); diff != "" {
+		t.Errorf("Clone() mismatch (-orig +cloned):\n%s", diff)
+	}
+}
diff --git a/cmd/cloner/clonerex/clonerex.go b/cmd/cloner/clonerex/clonerex.go
index 41626d3ae..e38aec199 100644
--- a/cmd/cloner/clonerex/clonerex.go
+++ b/cmd/cloner/clonerex/clonerex.go
@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & contributors
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:generate go run tailscale.com/cmd/cloner  -clonefunc=true -type SliceContainer,InterfaceContainer,MapWithPointers,DeeplyNestedMap,NamedMapContainer,MapSlicePointerContainer
+//go:generate go run tailscale.com/cmd/cloner  -clonefunc=true -type SliceContainer,InterfaceContainer,MapWithPointers,DeeplyNestedMap,NamedMapContainer,MapSlicePointerContainer,MapWithNamedSliceValues
 
 // Package clonerex is an example package for the cloner tool.
 package clonerex
@@ -72,3 +72,12 @@ type DeeplyNestedMap struct {
 	ThreeLevels map[string]map[string]map[string]int
 	FourLevels  map[string]map[string]map[string]map[string]*SliceContainer
 }
+
+// MapWithNamedSliceValues has a map with a named slice type for values. This
+// tests that the generator treats these values like any other slice and not a
+// struct.
+type MapWithNamedSliceValues struct {
+	M map[string]NamedSlice
+}
+
+type NamedSlice []string
diff --git a/cmd/cloner/clonerex/clonerex_clone.go b/cmd/cloner/clonerex/clonerex_clone.go
index 9a4413177..dbe9f5387 100644
--- a/cmd/cloner/clonerex/clonerex_clone.go
+++ b/cmd/cloner/clonerex/clonerex_clone.go
@@ -209,9 +209,31 @@ func (src *MapSlicePointerContainer) Clone() *MapSlicePointerContainer {
 	Routes map[string][]*SliceContainer
 }{})
 
+// Clone makes a deep copy of MapWithNamedSliceValues.
+// The result aliases no memory with the original.
+func (src *MapWithNamedSliceValues) Clone() *MapWithNamedSliceValues {
+	if src == nil {
+		return nil
+	}
+	dst := new(MapWithNamedSliceValues)
+	*dst = *src
+	if dst.M != nil {
+		dst.M = map[string]NamedSlice{}
+		for k := range src.M {
+			dst.M[k] = append([]string{}, src.M[k]...)
+		}
+	}
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _MapWithNamedSliceValuesCloneNeedsRegeneration = MapWithNamedSliceValues(struct {
+	M map[string]NamedSlice
+}{})
+
 // Clone duplicates src into dst and reports whether it succeeded.
 // To succeed, <src, dst> must be of types <*T, *T> or <*T, **T>,
-// where T is one of SliceContainer,InterfaceContainer,MapWithPointers,DeeplyNestedMap,NamedMapContainer,MapSlicePointerContainer.
+// where T is one of SliceContainer,InterfaceContainer,MapWithPointers,DeeplyNestedMap,NamedMapContainer,MapSlicePointerContainer,MapWithNamedSliceValues.
 func Clone(dst, src any) bool {
 	switch src := src.(type) {
 	case *SliceContainer:
@@ -268,6 +290,15 @@ func Clone(dst, src any) bool {
 			*dst = src.Clone()
 			return true
 		}
+	case *MapWithNamedSliceValues:
+		switch dst := dst.(type) {
+		case *MapWithNamedSliceValues:
+			*dst = *src.Clone()
+			return true
+		case **MapWithNamedSliceValues:
+			*dst = src.Clone()
+			return true
+		}
 	}
 	return false
 }