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// 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].(*types.Named)
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"
if *flagBuildTags == "test" {
cloneOutput += "_test"
}
cloneOutput += ".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()
typeParams := typ.Origin().TypeParams()
_, typeParamNames := codegen.FormatTypeParams(typeParams, it)
nameWithParams := name + typeParamNames
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", nameWithParams, nameWithParams)
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)", nameWithParams)
writef("*dst = *src")
for i := range t.NumFields() {
fname := t.Field(i).Name()
ft := t.Field(i).Type()
if !codegen.ContainsPointers(ft) || codegen.HasNoClone(t.Tag(i)) {
continue
}
if named, _ := codegen.NamedTypeOf(ft); 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("if src.%s != nil {", fname)
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 {
writef("if src.%s[i] == nil { dst.%s[i] = nil } else {", fname, fname)
if codegen.ContainsPointers(ptr.Elem()) {
if _, isIface := ptr.Elem().Underlying().(*types.Interface); isIface {
it.Import("", "tailscale.com/types/ptr")
writef("\tdst.%s[i] = ptr.To((*src.%s[i]).Clone())", fname, fname)
} else {
writef("\tdst.%s[i] = src.%s[i].Clone()", fname, fname)
}
} else {
it.Import("", "tailscale.com/types/ptr")
writef("\tdst.%s[i] = ptr.To(*src.%s[i])", fname, fname)
}
writef("}")
} else if ft.Elem().String() == "encoding/json.RawMessage" {
writef("\tdst.%s[i] = append(src.%s[i][:0:0], src.%s[i]...)", fname, fname, fname)
} else if _, isIface := ft.Elem().Underlying().(*types.Interface); isIface {
writef("\tdst.%s[i] = src.%s[i].Clone()", fname, fname)
} else {
writef("\tdst.%s[i] = *src.%s[i].Clone()", fname, fname)
}
writef("}")
writef("}")
} else {
writef("dst.%s = append(src.%s[:0:0], src.%s...)", fname, fname, fname)
}
case *types.Pointer:
base := ft.Elem()
hasPtrs := codegen.ContainsPointers(base)
if named, _ := codegen.NamedTypeOf(base); named != nil && hasPtrs {
writef("dst.%s = src.%s.Clone()", fname, fname)
continue
}
it.Import("", "tailscale.com/types/ptr")
writef("if dst.%s != nil {", fname)
if _, isIface := base.Underlying().(*types.Interface); isIface && hasPtrs {
writef("\tdst.%s = ptr.To((*src.%s).Clone())", fname, fname)
} else if !hasPtrs {
writef("\tdst.%s = ptr.To(*src.%s)", fname, fname)
} else {
writef("\t" + `panic("TODO pointers in pointers")`)
}
writef("}")
case *types.Map:
elem := ft.Elem()
if sliceType, isSlice := elem.(*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))
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}")
writef("}")
} else if codegen.ContainsPointers(elem) {
writef("if dst.%s != nil {", fname)
writef("\tdst.%s = map[%s]%s{}", fname, it.QualifiedName(ft.Key()), it.QualifiedName(elem))
writef("\tfor k, v := range src.%s {", fname)
switch elem := elem.Underlying().(type) {
case *types.Pointer:
writef("\t\tif v == nil { dst.%s[k] = nil } else {", fname)
if base := elem.Elem().Underlying(); codegen.ContainsPointers(base) {
if _, isIface := base.(*types.Interface); isIface {
it.Import("", "tailscale.com/types/ptr")
writef("\t\t\tdst.%s[k] = ptr.To((*v).Clone())", fname)
} else {
writef("\t\t\tdst.%s[k] = v.Clone()", fname)
}
} else {
it.Import("", "tailscale.com/types/ptr")
writef("\t\t\tdst.%s[k] = ptr.To(*v)", fname)
}
writef("}")
case *types.Interface:
if cloneResultType := methodResultType(elem, "Clone"); cloneResultType != nil {
if _, isPtr := cloneResultType.(*types.Pointer); isPtr {
writef("\t\tdst.%s[k] = *(v.Clone())", fname)
} else {
writef("\t\tdst.%s[k] = v.Clone()", fname)
}
} else {
writef(`panic("%s (%v) does not have a Clone method")`, fname, elem)
}
default:
writef("\t\tdst.%s[k] = *(v.Clone())", fname)
}
writef("\t}")
writef("}")
} else {
it.Import("", "maps")
writef("\tdst.%s = maps.Clone(src.%s)", fname, fname)
}
case *types.Interface:
// If ft is an interface with a "Clone() ft" method, it can be used to clone the field.
// This includes scenarios where ft is a constrained type parameter.
if cloneResultType := methodResultType(ft, "Clone"); cloneResultType.Underlying() == ft {
writef("dst.%s = src.%s.Clone()", fname, fname)
continue
}
writef(`panic("%s (%v) does not have a compatible Clone method")`, fname, ft)
default:
writef(`panic("TODO: %s (%T)")`, fname, ft)
}
}
writef("return dst")
fmt.Fprintf(buf, "}\n\n")
buf.Write(codegen.AssertStructUnchanged(t, name, typeParams, "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
}
}
func methodResultType(typ types.Type, method string) types.Type {
viewMethod := codegen.LookupMethod(typ, method)
if viewMethod == nil {
return nil
}
sig, ok := viewMethod.Type().(*types.Signature)
if !ok || sig.Results().Len() != 1 {
return nil
}
return sig.Results().At(0).Type()
}
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