cmd/cloner, tailcfg: fix nil vs len 0 issues, add tests, use for Hostinfoclone

Also use go:generate and https://golang.org/s/generatedcode header style.

1 files changed, 3 insertions, 3 deletions

diff --git a/cmd/cloner/cloner.go b/cmd/cloner/cloner.go
index a0bd04e6a..c7463b0f8 100644
--- a/cmd/cloner/cloner.go
+++ b/cmd/cloner/cloner.go
@@ -123,7 +123,7 @@ const header = `// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserve
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// AUTO-GENERATED by: tailscale.com/cmd/cloner -type %s
+// Code generated by tailscale.com/cmd/cloner -type %s; DO NOT EDIT.
 
 package %s
 
@@ -168,8 +168,8 @@ func gen(buf *bytes.Buffer, imports map[string]struct{}, name string, typ *types
 			}
 			switch ft := ft.Underlying().(type) {
 			case *types.Slice:
-				n := importedName(ft.Elem())
 				if containsPointers(ft.Elem()) {
+					n := importedName(ft.Elem())
 					writef("dst.%s = make([]%s, len(src.%s))", fname, n, fname)
 					writef("for i := range dst.%s {", fname)
 					if _, isPtr := ft.Elem().(*types.Pointer); isPtr {
@@ -179,7 +179,7 @@ func gen(buf *bytes.Buffer, imports map[string]struct{}, name string, typ *types
 					}
 					writef("}")
 				} else {
-					writef("dst.%s = append([]%s(nil), src.%s...)", fname, n, fname)
+					writef("dst.%s = append(src.%s[:0:0], src.%s...)", fname, fname, fname)
 				}
 			case *types.Pointer:
 				if named, _ := ft.Elem().(*types.Named); named != nil && containsPointers(ft.Elem()) {