tailscale/cmd/cloner/cloner.go

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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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"
"golang.org/x/tools/go/packages"
"tailscale.com/util/codegen"
)
var (
flagTypes = flag.String("type", "", "comma-separated list of types; required")
flagOutput = flag.String("output", "", "output file; 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, ",")
cfg := &packages.Config{
Mode: packages.NeedTypes | packages.NeedTypesInfo | packages.NeedSyntax | packages.NeedName,
Tests: false,
}
if *flagBuildTags != "" {
cfg.BuildFlags = []string{"-tags=" + *flagBuildTags}
}
pkgs, err := packages.Load(cfg, ".")
if err != nil {
log.Fatal(err)
}
if len(pkgs) != 1 {
log.Fatalf("wrong number of packages: %d", len(pkgs))
}
pkg := pkgs[0]
buf := new(bytes.Buffer)
imports := make(map[string]struct{})
namedTypes := codegen.NamedTypes(pkg)
for _, typeName := range typeNames {
typ, ok := namedTypes[typeName]
if !ok {
log.Fatalf("could not find type %s", typeName)
}
gen(buf, imports, typ, pkg.Types)
}
w := func(format string, args ...interface{}) {
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 interface{}) 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("}")
}
contents := new(bytes.Buffer)
var flagArgs []string
if *flagTypes != "" {
flagArgs = append(flagArgs, "-type="+*flagTypes)
}
if *flagOutput != "" {
flagArgs = append(flagArgs, "-output="+*flagOutput)
}
if *flagBuildTags != "" {
flagArgs = append(flagArgs, "-tags="+*flagBuildTags)
}
if *flagCloneFunc {
flagArgs = append(flagArgs, "-clonefunc")
}
fmt.Fprintf(contents, header, strings.Join(flagArgs, " "), pkg.Name)
fmt.Fprintf(contents, "import (\n")
for s := range imports {
fmt.Fprintf(contents, "\t%q\n", s)
}
fmt.Fprintf(contents, ")\n\n")
contents.Write(buf.Bytes())
output := *flagOutput
if output == "" {
flag.Usage()
os.Exit(2)
}
if err := codegen.WriteFormatted(contents.Bytes(), output); err != nil {
log.Fatal(err)
}
}
const header = `// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Code generated by tailscale.com/cmd/cloner; DO NOT EDIT.
//` + `go:generate` + ` go run tailscale.com/cmd/cloner %s
package %s
`
func gen(buf *bytes.Buffer, imports map[string]struct{}, typ *types.Named, thisPkg *types.Package) {
pkgQual := func(pkg *types.Package) string {
if thisPkg == pkg {
return ""
}
imports[pkg.Path()] = struct{}{}
return pkg.Name()
}
importedName := func(t types.Type) string {
return types.TypeString(t, pkgQual)
}
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 ...interface{}) {
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) {
continue
}
if named, _ := ft.(*types.Named); named != nil && !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 := 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 {
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 := importedName(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:
writef("if dst.%s != nil {", fname)
writef("\tdst.%s = map[%s]%s{}", fname, importedName(ft.Key()), importedName(ft.Elem()))
if sliceType, isSlice := ft.Elem().(*types.Slice); isSlice {
n := importedName(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(ft.Elem()) {
writef("\tfor k, v := range src.%s {", fname)
writef("\t\tdst.%s[k] = v.Clone()", 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, thisPkg, name, "Clone", imports))
}
func hasBasicUnderlying(typ types.Type) bool {
switch typ.Underlying().(type) {
case *types.Slice, *types.Map:
return true
default:
return false
}
}