Skip to content
Permalink
main
Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
Go to file
 
 
Cannot retrieve contributors at this time
// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Cloner is a tool to automate the creation of a Clone method.
//
// The result of the Clone method aliases no memory that can be edited
// with the original.
//
// This tool makes lots of implicit assumptions about the types you feed it.
// In particular, it can only write relatively "shallow" Clone methods.
// That is, if a type contains another named struct type, cloner assumes that
// named type will also have a Clone method.
package main
import (
"bytes"
"flag"
"fmt"
"go/types"
"log"
"os"
"strings"
"tailscale.com/util/codegen"
)
var (
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")
)
func main() {
log.SetFlags(0)
log.SetPrefix("cloner: ")
flag.Parse()
if len(*flagTypes) == 0 {
flag.Usage()
os.Exit(2)
}
typeNames := strings.Split(*flagTypes, ",")
pkg, namedTypes, err := codegen.LoadTypes(*flagBuildTags, ".")
if err != nil {
log.Fatal(err)
}
it := codegen.NewImportTracker(pkg.Types)
buf := new(bytes.Buffer)
for _, typeName := range typeNames {
typ, ok := namedTypes[typeName]
if !ok {
log.Fatalf("could not find type %s", typeName)
}
gen(buf, it, typ)
}
w := func(format string, args ...any) {
fmt.Fprintf(buf, format+"\n", args...)
}
if *flagCloneFunc {
w("// Clone duplicates src into dst and reports whether it succeeded.")
w("// To succeed, <src, dst> must be of types <*T, *T> or <*T, **T>,")
w("// where T is one of %s.", *flagTypes)
w("func Clone(dst, src any) bool {")
w(" switch src := src.(type) {")
for _, typeName := range typeNames {
w(" case *%s:", typeName)
w(" switch dst := dst.(type) {")
w(" case *%s:", typeName)
w(" *dst = *src.Clone()")
w(" return true")
w(" case **%s:", typeName)
w(" *dst = src.Clone()")
w(" return true")
w(" }")
}
w(" }")
w(" return false")
w("}")
}
cloneOutput := pkg.Name + "_clone.go"
if err := codegen.WritePackageFile("tailscale.com/cmd/cloner", pkg, cloneOutput, it, buf); err != nil {
log.Fatal(err)
}
}
func gen(buf *bytes.Buffer, it *codegen.ImportTracker, typ *types.Named) {
t, ok := typ.Underlying().(*types.Struct)
if !ok {
return
}
name := typ.Obj().Name()
fmt.Fprintf(buf, "// Clone makes a deep copy of %s.\n", name)
fmt.Fprintf(buf, "// The result aliases no memory with the original.\n")
fmt.Fprintf(buf, "func (src *%s) Clone() *%s {\n", name, name)
writef := func(format string, args ...any) {
fmt.Fprintf(buf, "\t"+format+"\n", args...)
}
writef("if src == nil {")
writef("\treturn nil")
writef("}")
writef("dst := new(%s)", name)
writef("*dst = *src")
for i := 0; i < t.NumFields(); i++ {
fname := t.Field(i).Name()
ft := t.Field(i).Type()
if !codegen.ContainsPointers(ft) || codegen.HasNoClone(t.Tag(i)) {
continue
}
if named, _ := ft.(*types.Named); named != nil {
if codegen.IsViewType(ft) {
writef("dst.%s = src.%s", fname, fname)
continue
}
if !hasBasicUnderlying(ft) {
writef("dst.%s = *src.%s.Clone()", fname, fname)
continue
}
}
switch ft := ft.Underlying().(type) {
case *types.Slice:
if codegen.ContainsPointers(ft.Elem()) {
n := it.QualifiedName(ft.Elem())
writef("dst.%s = make([]%s, len(src.%s))", fname, n, fname)
writef("for i := range dst.%s {", fname)
if ptr, isPtr := ft.Elem().(*types.Pointer); isPtr {
if _, isBasic := ptr.Elem().Underlying().(*types.Basic); isBasic {
writef("\tx := *src.%s[i]", fname)
writef("\tdst.%s[i] = &x", fname)
} else {
writef("\tdst.%s[i] = src.%s[i].Clone()", fname, fname)
}
} else {
writef("\tdst.%s[i] = *src.%s[i].Clone()", fname, fname)
}
writef("}")
} else {
writef("dst.%s = append(src.%s[:0:0], src.%s...)", fname, fname, fname)
}
case *types.Pointer:
if named, _ := ft.Elem().(*types.Named); named != nil && codegen.ContainsPointers(ft.Elem()) {
writef("dst.%s = src.%s.Clone()", fname, fname)
continue
}
n := it.QualifiedName(ft.Elem())
writef("if dst.%s != nil {", fname)
writef("\tdst.%s = new(%s)", fname, n)
writef("\t*dst.%s = *src.%s", fname, fname)
if codegen.ContainsPointers(ft.Elem()) {
writef("\t" + `panic("TODO pointers in pointers")`)
}
writef("}")
case *types.Map:
elem := ft.Elem()
writef("if dst.%s != nil {", fname)
writef("\tdst.%s = map[%s]%s{}", fname, it.QualifiedName(ft.Key()), it.QualifiedName(elem))
if sliceType, isSlice := elem.(*types.Slice); isSlice {
n := it.QualifiedName(sliceType.Elem())
writef("\tfor k := range src.%s {", fname)
// use zero-length slice instead of nil to ensure
// the key is always copied.
writef("\t\tdst.%s[k] = append([]%s{}, src.%s[k]...)", fname, n, fname)
writef("\t}")
} else if codegen.ContainsPointers(elem) {
writef("\tfor k, v := range src.%s {", fname)
switch elem.(type) {
case *types.Pointer:
writef("\t\tdst.%s[k] = v.Clone()", fname)
default:
writef("\t\tv2 := v.Clone()")
writef("\t\tdst.%s[k] = *v2", fname)
}
writef("\t}")
} else {
writef("\tfor k, v := range src.%s {", fname)
writef("\t\tdst.%s[k] = v", fname)
writef("\t}")
}
writef("}")
default:
writef(`panic("TODO: %s (%T)")`, fname, ft)
}
}
writef("return dst")
fmt.Fprintf(buf, "}\n\n")
buf.Write(codegen.AssertStructUnchanged(t, name, "Clone", it))
}
// hasBasicUnderlying reports true when typ.Underlying() is a slice or a map.
func hasBasicUnderlying(typ types.Type) bool {
switch typ.Underlying().(type) {
case *types.Slice, *types.Map:
return true
default:
return false
}
}