cmd/bundle/main.go - tools - Git at Google

 // Copyright 2015 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Bundle creates a single-source-file version of a source package
 // suitable for inclusion in a particular target package.
 //
 // Usage:
 //
 //	bundle [-o file] [-dst path] [-pkg name] [-prefix p] [-import old=new] [-tags build_constraints] <src>
 //
 // The src argument specifies the import path of the package to bundle.
 // The bundling of a directory of source files into a single source file
 // necessarily imposes a number of constraints.
 // The package being bundled must not use cgo; must not use conditional
 // file compilation, whether with build tags or system-specific file names
 // like code_amd64.go; must not depend on any special comments, which
 // may not be preserved; must not use any assembly sources;
 // must not use renaming imports; and must not use reflection-based APIs
 // that depend on the specific names of types or struct fields.
 //
 // By default, bundle writes the bundled code to standard output.
 // If the -o argument is given, bundle writes to the named file
 // and also includes a ``//go:generate'' comment giving the exact
 // command line used, for regenerating the file with ``go generate.''
 //
 // Bundle customizes its output for inclusion in a particular package, the destination package.
 // By default bundle assumes the destination is the package in the current directory,
 // but the destination package can be specified explicitly using the -dst option,
 // which takes an import path as its argument.
 // If the source package imports the destination package, bundle will remove
 // those imports and rewrite any references to use direct references to the
 // corresponding symbols.
 // Bundle also must write a package declaration in the output and must
 // choose a name to use in that declaration.
 // If the -pkg option is given, bundle uses that name.
 // Otherwise, the name of the destination package is used.
 // Build constraints for the generated file can be specified using the -tags option.
 //
 // To avoid collisions, bundle inserts a prefix at the beginning of
 // every package-level const, func, type, and var identifier in src's code,
 // updating references accordingly. The default prefix is the package name
 // of the source package followed by an underscore. The -prefix option
 // specifies an alternate prefix.
 //
 // Occasionally it is necessary to rewrite imports during the bundling
 // process. The -import option, which may be repeated, specifies that
 // an import of "old" should be rewritten to import "new" instead.
 //
 // Example
 //
 // Bundle archive/zip for inclusion in cmd/dist:
 //
 //	cd $GOROOT/src/cmd/dist
 //	bundle -o zip.go archive/zip
 //
 // Bundle golang.org/x/net/http2 for inclusion in net/http,
 // prefixing all identifiers by "http2" instead of "http2_", and
 // including a "!nethttpomithttp2" build constraint:
 //
 //	cd $GOROOT/src/net/http
 //	bundle -o h2_bundle.go -prefix http2 -tags '!nethttpomithttp2' golang.org/x/net/http2
 //
 // Update the http2 bundle in net/http:
 //
 //	go generate net/http
 //
 // Update all bundles in the standard library:
 //
 //	go generate -run bundle std
 //
 package main

 import (
 	"bytes"
 	"flag"
 	"fmt"
 	"go/ast"
 	"go/format"
 	"go/printer"
 	"go/token"
 	"go/types"
 	"io/ioutil"
 	"log"
 	"os"
 	"strconv"
 	"strings"

 	"golang.org/x/tools/go/packages"
 )

 var (
 	outputFile = flag.String("o", "", "write output to `file` (default standard output)")
 	dstPath    = flag.String("dst", ".", "set destination import `path`")
 	pkgName    = flag.String("pkg", "", "set destination package `name`")
 	prefix     = flag.String("prefix", "&_", "set bundled identifier prefix to `p` (default is \"&_\", where & stands for the original name)")
 	buildTags  = flag.String("tags", "", "the build constraints to be inserted into the generated file")

 	importMap = map[string]string{}
 )

 func init() {
 	flag.Var(flagFunc(addImportMap), "import", "rewrite import using `map`, of form old=new (can be repeated)")
 }

 func addImportMap(s string) {
 	if strings.Count(s, "=") != 1 {
 		log.Fatal("-import argument must be of the form old=new")
 	}
 	i := strings.Index(s, "=")
 	old, new := s[:i], s[i+1:]
 	if old == "" || new == "" {
 		log.Fatal("-import argument must be of the form old=new; old and new must be non-empty")
 	}
 	importMap[old] = new
 }

 func usage() {
 	fmt.Fprintf(os.Stderr, "Usage: bundle [options] <src>\n")
 	flag.PrintDefaults()
 }

 func main() {
 	log.SetPrefix("bundle: ")
 	log.SetFlags(0)

 	flag.Usage = usage
 	flag.Parse()
 	args := flag.Args()
 	if len(args) != 1 {
 		usage()
 		os.Exit(2)
 	}

 	cfg := &packages.Config{Mode: packages.NeedName}
 	pkgs, err := packages.Load(cfg, *dstPath)
 	if err != nil {
 		log.Fatalf("cannot load destination package: %v", err)
 	}
 	if packages.PrintErrors(pkgs) > 0 || len(pkgs) != 1 {
 		log.Fatalf("failed to load destination package")
 	}
 	if *pkgName == "" {
 		*pkgName = pkgs[0].Name
 	}

 	code, err := bundle(args[0], pkgs[0].PkgPath, *pkgName, *prefix, *buildTags)
 	if err != nil {
 		log.Fatal(err)
 	}
 	if *outputFile != "" {
 		err := ioutil.WriteFile(*outputFile, code, 0666)
 		if err != nil {
 			log.Fatal(err)
 		}
 	} else {
 		_, err := os.Stdout.Write(code)
 		if err != nil {
 			log.Fatal(err)
 		}
 	}
 }

 // isStandardImportPath is copied from cmd/go in the standard library.
 func isStandardImportPath(path string) bool {
 	i := strings.Index(path, "/")
 	if i < 0 {
 		i = len(path)
 	}
 	elem := path[:i]
 	return !strings.Contains(elem, ".")
 }

 var testingOnlyPackagesConfig *packages.Config

 func bundle(src, dst, dstpkg, prefix, buildTags string) ([]byte, error) {
 	// Load the initial package.
 	cfg := &packages.Config{}
 	if testingOnlyPackagesConfig != nil {
 		*cfg = *testingOnlyPackagesConfig
 	} else {
 		// Bypass default vendor mode, as we need a package not available in the
 		// std module vendor folder.
 		cfg.Env = append(os.Environ(), "GOFLAGS=-mod=mod")
 	}
 	cfg.Mode = packages.NeedTypes | packages.NeedSyntax | packages.NeedTypesInfo
 	pkgs, err := packages.Load(cfg, src)
 	if err != nil {
 		return nil, err
 	}
 	if packages.PrintErrors(pkgs) > 0 || len(pkgs) != 1 {
 		return nil, fmt.Errorf("failed to load source package")
 	}
 	pkg := pkgs[0]

 	if strings.Contains(prefix, "&") {
 		prefix = strings.Replace(prefix, "&", pkg.Syntax[0].Name.Name, -1)
 	}

 	objsToUpdate := make(map[types.Object]bool)
 	var rename func(from types.Object)
 	rename = func(from types.Object) {
 		if !objsToUpdate[from] {
 			objsToUpdate[from] = true

 			// Renaming a type that is used as an embedded field
 			// requires renaming the field too. e.g.
 			// 	type T int // if we rename this to U..
 			// 	var s struct {T}
 			// 	print(s.T) // ...this must change too
 			if _, ok := from.(*types.TypeName); ok {
 				for id, obj := range pkg.TypesInfo.Uses {
 					if obj == from {
 						if field := pkg.TypesInfo.Defs[id]; field != nil {
 							rename(field)
 						}
 					}
 				}
 			}
 		}
 	}

 	// Rename each package-level object.
 	scope := pkg.Types.Scope()
 	for _, name := range scope.Names() {
 		rename(scope.Lookup(name))
 	}

 	var out bytes.Buffer
 	if buildTags != "" {
 		fmt.Fprintf(&out, "// +build %s\n\n", buildTags)
 	}

 	fmt.Fprintf(&out, "// Code generated by golang.org/x/tools/cmd/bundle. DO NOT EDIT.\n")
 	if *outputFile != "" && buildTags == "" {
 		fmt.Fprintf(&out, "//go:generate bundle %s\n", strings.Join(os.Args[1:], " "))
 	} else {
 		fmt.Fprintf(&out, "//   $ bundle %s\n", strings.Join(os.Args[1:], " "))
 	}
 	fmt.Fprintf(&out, "\n")

 	// Concatenate package comments from all files...
 	for _, f := range pkg.Syntax {
 		if doc := f.Doc.Text(); strings.TrimSpace(doc) != "" {
 			for _, line := range strings.Split(doc, "\n") {
 				fmt.Fprintf(&out, "// %s\n", line)
 			}
 		}
 	}
 	// ...but don't let them become the actual package comment.
 	fmt.Fprintln(&out)

 	fmt.Fprintf(&out, "package %s\n\n", dstpkg)

 	// BUG(adonovan,shurcooL): bundle may generate incorrect code
 	// due to shadowing between identifiers and imported package names.
 	//
 	// The generated code will either fail to compile or
 	// (unlikely) compile successfully but have different behavior
 	// than the original package. The risk of this happening is higher
 	// when the original package has renamed imports (they're typically
 	// renamed in order to resolve a shadow inside that particular .go file).

 	// TODO(adonovan,shurcooL):
 	// - detect shadowing issues, and either return error or resolve them
 	// - preserve comments from the original import declarations.

 	// pkgStd and pkgExt are sets of printed import specs. This is done
 	// to deduplicate instances of the same import name and path.
 	var pkgStd = make(map[string]bool)
 	var pkgExt = make(map[string]bool)
 	for _, f := range pkg.Syntax {
 		for _, imp := range f.Imports {
 			path, err := strconv.Unquote(imp.Path.Value)
 			if err != nil {
 				log.Fatalf("invalid import path string: %v", err) // Shouldn't happen here since packages.Load succeeded.
 			}
 			if path == dst {
 				continue
 			}
 			if newPath, ok := importMap[path]; ok {
 				path = newPath
 			}

 			var name string
 			if imp.Name != nil {
 				name = imp.Name.Name
 			}
 			spec := fmt.Sprintf("%s %q", name, path)
 			if isStandardImportPath(path) {
 				pkgStd[spec] = true
 			} else {
 				pkgExt[spec] = true
 			}
 		}
 	}

 	// Print a single declaration that imports all necessary packages.
 	fmt.Fprintln(&out, "import (")
 	for p := range pkgStd {
 		fmt.Fprintf(&out, "\t%s\n", p)
 	}
 	if len(pkgExt) > 0 {
 		fmt.Fprintln(&out)
 	}
 	for p := range pkgExt {
 		fmt.Fprintf(&out, "\t%s\n", p)
 	}
 	fmt.Fprint(&out, ")\n\n")

 	// Modify and print each file.
 	for _, f := range pkg.Syntax {
 		// Update renamed identifiers.
 		for id, obj := range pkg.TypesInfo.Defs {
 			if objsToUpdate[obj] {
 				id.Name = prefix + obj.Name()
 			}
 		}
 		for id, obj := range pkg.TypesInfo.Uses {
 			if objsToUpdate[obj] {
 				id.Name = prefix + obj.Name()
 			}
 		}

 		// For each qualified identifier that refers to the
 		// destination package, remove the qualifier.
 		// The "@@@." strings are removed in postprocessing.
 		ast.Inspect(f, func(n ast.Node) bool {
 			if sel, ok := n.(*ast.SelectorExpr); ok {
 				if id, ok := sel.X.(*ast.Ident); ok {
 					if obj, ok := pkg.TypesInfo.Uses[id].(*types.PkgName); ok {
 						if obj.Imported().Path() == dst {
 							id.Name = "@@@"
 						}
 					}
 				}
 			}
 			return true
 		})

 		last := f.Package
 		if len(f.Imports) > 0 {
 			imp := f.Imports[len(f.Imports)-1]
 			last = imp.End()
 			if imp.Comment != nil {
 				if e := imp.Comment.End(); e > last {
 					last = e
 				}
 			}
 		}

 		// Pretty-print package-level declarations.
 		// but no package or import declarations.
 		var buf bytes.Buffer
 		for _, decl := range f.Decls {
 			if decl, ok := decl.(*ast.GenDecl); ok && decl.Tok == token.IMPORT {
 				continue
 			}

 			beg, end := sourceRange(decl)

 			printComments(&out, f.Comments, last, beg)

 			buf.Reset()
 			format.Node(&buf, pkg.Fset, &printer.CommentedNode{Node: decl, Comments: f.Comments})
 			// Remove each "@@@." in the output.
 			// TODO(adonovan): not hygienic.
 			out.Write(bytes.Replace(buf.Bytes(), []byte("@@@."), nil, -1))

 			last = printSameLineComment(&out, f.Comments, pkg.Fset, end)

 			out.WriteString("\n\n")
 		}

 		printLastComments(&out, f.Comments, last)
 	}

 	// Now format the entire thing.
 	result, err := format.Source(out.Bytes())
 	if err != nil {
 		log.Fatalf("formatting failed: %v", err)
 	}

 	return result, nil
 }

 // sourceRange returns the [beg, end) interval of source code
 // belonging to decl (incl. associated comments).
 func sourceRange(decl ast.Decl) (beg, end token.Pos) {
 	beg = decl.Pos()
 	end = decl.End()

 	var doc, com *ast.CommentGroup

 	switch d := decl.(type) {
 	case *ast.GenDecl:
 		doc = d.Doc
 		if len(d.Specs) > 0 {
 			switch spec := d.Specs[len(d.Specs)-1].(type) {
 			case *ast.ValueSpec:
 				com = spec.Comment
 			case *ast.TypeSpec:
 				com = spec.Comment
 			}
 		}
 	case *ast.FuncDecl:
 		doc = d.Doc
 	}

 	if doc != nil {
 		beg = doc.Pos()
 	}
 	if com != nil && com.End() > end {
 		end = com.End()
 	}

 	return beg, end
 }

 func printComments(out *bytes.Buffer, comments []*ast.CommentGroup, pos, end token.Pos) {
 	for _, cg := range comments {
 		if pos <= cg.Pos() && cg.Pos() < end {
 			for _, c := range cg.List {
 				fmt.Fprintln(out, c.Text)
 			}
 			fmt.Fprintln(out)
 		}
 	}
 }

 const infinity = 1 << 30

 func printLastComments(out *bytes.Buffer, comments []*ast.CommentGroup, pos token.Pos) {
 	printComments(out, comments, pos, infinity)
 }

 func printSameLineComment(out *bytes.Buffer, comments []*ast.CommentGroup, fset *token.FileSet, pos token.Pos) token.Pos {
 	tf := fset.File(pos)
 	for _, cg := range comments {
 		if pos <= cg.Pos() && tf.Line(cg.Pos()) == tf.Line(pos) {
 			for _, c := range cg.List {
 				fmt.Fprintln(out, c.Text)
 			}
 			return cg.End()
 		}
 	}
 	return pos
 }

 type flagFunc func(string)

 func (f flagFunc) Set(s string) error {
 	f(s)
 	return nil
 }

 func (f flagFunc) String() string { return "" }
	// Copyright 2015 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Bundle creates a single-source-file version of a source package
	// suitable for inclusion in a particular target package.
	//
	// Usage:
	//
	// bundle [-o file] [-dst path] [-pkg name] [-prefix p] [-import old=new] [-tags build_constraints] <src>
	//
	// The src argument specifies the import path of the package to bundle.
	// The bundling of a directory of source files into a single source file
	// necessarily imposes a number of constraints.
	// The package being bundled must not use cgo; must not use conditional
	// file compilation, whether with build tags or system-specific file names
	// like code_amd64.go; must not depend on any special comments, which
	// may not be preserved; must not use any assembly sources;
	// must not use renaming imports; and must not use reflection-based APIs
	// that depend on the specific names of types or struct fields.
	//
	// By default, bundle writes the bundled code to standard output.
	// If the -o argument is given, bundle writes to the named file
	// and also includes a ``//go:generate'' comment giving the exact
	// command line used, for regenerating the file with ``go generate.''
	//
	// Bundle customizes its output for inclusion in a particular package, the destination package.
	// By default bundle assumes the destination is the package in the current directory,
	// but the destination package can be specified explicitly using the -dst option,
	// which takes an import path as its argument.
	// If the source package imports the destination package, bundle will remove
	// those imports and rewrite any references to use direct references to the
	// corresponding symbols.
	// Bundle also must write a package declaration in the output and must
	// choose a name to use in that declaration.
	// If the -pkg option is given, bundle uses that name.
	// Otherwise, the name of the destination package is used.
	// Build constraints for the generated file can be specified using the -tags option.
	//
	// To avoid collisions, bundle inserts a prefix at the beginning of
	// every package-level const, func, type, and var identifier in src's code,
	// updating references accordingly. The default prefix is the package name
	// of the source package followed by an underscore. The -prefix option
	// specifies an alternate prefix.
	//
	// Occasionally it is necessary to rewrite imports during the bundling
	// process. The -import option, which may be repeated, specifies that
	// an import of "old" should be rewritten to import "new" instead.
	//
	// Example
	//
	// Bundle archive/zip for inclusion in cmd/dist:
	//
	// cd $GOROOT/src/cmd/dist
	// bundle -o zip.go archive/zip
	//
	// Bundle golang.org/x/net/http2 for inclusion in net/http,
	// prefixing all identifiers by "http2" instead of "http2_", and
	// including a "!nethttpomithttp2" build constraint:
	//
	// cd $GOROOT/src/net/http
	// bundle -o h2_bundle.go -prefix http2 -tags '!nethttpomithttp2' golang.org/x/net/http2
	//
	// Update the http2 bundle in net/http:
	//
	// go generate net/http
	//
	// Update all bundles in the standard library:
	//
	// go generate -run bundle std
	//
	package main

	import (
	"bytes"
	"flag"
	"fmt"
	"go/ast"
	"go/format"
	"go/printer"
	"go/token"
	"go/types"
	"io/ioutil"
	"log"
	"os"
	"strconv"
	"strings"

	"golang.org/x/tools/go/packages"
	)

	var (
	outputFile = flag.String("o", "", "write output to `file` (default standard output)")
	dstPath = flag.String("dst", ".", "set destination import `path`")
	pkgName = flag.String("pkg", "", "set destination package `name`")
	prefix = flag.String("prefix", "&_", "set bundled identifier prefix to `p` (default is \"&_\", where & stands for the original name)")
	buildTags = flag.String("tags", "", "the build constraints to be inserted into the generated file")

	importMap = map[string]string{}
	)

	func init() {
	flag.Var(flagFunc(addImportMap), "import", "rewrite import using `map`, of form old=new (can be repeated)")
	}

	func addImportMap(s string) {
	if strings.Count(s, "=") != 1 {
	log.Fatal("-import argument must be of the form old=new")
	}
	i := strings.Index(s, "=")
	old, new := s[:i], s[i+1:]
	if old == "" \|\| new == "" {
	log.Fatal("-import argument must be of the form old=new; old and new must be non-empty")
	}
	importMap[old] = new
	}

	func usage() {
	fmt.Fprintf(os.Stderr, "Usage: bundle [options] <src>\n")
	flag.PrintDefaults()
	}

	func main() {
	log.SetPrefix("bundle: ")
	log.SetFlags(0)

	flag.Usage = usage
	flag.Parse()
	args := flag.Args()
	if len(args) != 1 {
	usage()
	os.Exit(2)
	}

	cfg := &packages.Config{Mode: packages.NeedName}
	pkgs, err := packages.Load(cfg, *dstPath)
	if err != nil {
	log.Fatalf("cannot load destination package: %v", err)
	}
	if packages.PrintErrors(pkgs) > 0 \|\| len(pkgs) != 1 {
	log.Fatalf("failed to load destination package")
	}
	if *pkgName == "" {
	*pkgName = pkgs[0].Name
	}

	code, err := bundle(args[0], pkgs[0].PkgPath, pkgName, prefix, *buildTags)
	if err != nil {
	log.Fatal(err)
	}
	if *outputFile != "" {
	err := ioutil.WriteFile(*outputFile, code, 0666)
	if err != nil {
	log.Fatal(err)
	}
	} else {
	_, err := os.Stdout.Write(code)
	if err != nil {
	log.Fatal(err)
	}
	}
	}

	// isStandardImportPath is copied from cmd/go in the standard library.
	func isStandardImportPath(path string) bool {
	i := strings.Index(path, "/")
	if i < 0 {
	i = len(path)
	}
	elem := path[:i]
	return !strings.Contains(elem, ".")
	}

	var testingOnlyPackagesConfig *packages.Config

	func bundle(src, dst, dstpkg, prefix, buildTags string) ([]byte, error) {
	// Load the initial package.
	cfg := &packages.Config{}
	if testingOnlyPackagesConfig != nil {
	cfg = testingOnlyPackagesConfig
	} else {
	// Bypass default vendor mode, as we need a package not available in the
	// std module vendor folder.
	cfg.Env = append(os.Environ(), "GOFLAGS=-mod=mod")
	}
	cfg.Mode = packages.NeedTypes \| packages.NeedSyntax \| packages.NeedTypesInfo
	pkgs, err := packages.Load(cfg, src)
	if err != nil {
	return nil, err
	}
	if packages.PrintErrors(pkgs) > 0 \|\| len(pkgs) != 1 {
	return nil, fmt.Errorf("failed to load source package")
	}
	pkg := pkgs[0]

	if strings.Contains(prefix, "&") {
	prefix = strings.Replace(prefix, "&", pkg.Syntax[0].Name.Name, -1)
	}

	objsToUpdate := make(map[types.Object]bool)
	var rename func(from types.Object)
	rename = func(from types.Object) {
	if !objsToUpdate[from] {
	objsToUpdate[from] = true

	// Renaming a type that is used as an embedded field
	// requires renaming the field too. e.g.
	// type T int // if we rename this to U..
	// var s struct {T}
	// print(s.T) // ...this must change too
	if _, ok := from.(*types.TypeName); ok {
	for id, obj := range pkg.TypesInfo.Uses {
	if obj == from {
	if field := pkg.TypesInfo.Defs[id]; field != nil {
	rename(field)
	}
	}
	}
	}
	}
	}

	// Rename each package-level object.
	scope := pkg.Types.Scope()
	for _, name := range scope.Names() {
	rename(scope.Lookup(name))
	}

	var out bytes.Buffer
	if buildTags != "" {
	fmt.Fprintf(&out, "// +build %s\n\n", buildTags)
	}

	fmt.Fprintf(&out, "// Code generated by golang.org/x/tools/cmd/bundle. DO NOT EDIT.\n")
	if *outputFile != "" && buildTags == "" {
	fmt.Fprintf(&out, "//go:generate bundle %s\n", strings.Join(os.Args[1:], " "))
	} else {
	fmt.Fprintf(&out, "// $ bundle %s\n", strings.Join(os.Args[1:], " "))
	}
	fmt.Fprintf(&out, "\n")

	// Concatenate package comments from all files...
	for _, f := range pkg.Syntax {
	if doc := f.Doc.Text(); strings.TrimSpace(doc) != "" {
	for _, line := range strings.Split(doc, "\n") {
	fmt.Fprintf(&out, "// %s\n", line)
	}
	}
	}
	// ...but don't let them become the actual package comment.
	fmt.Fprintln(&out)

	fmt.Fprintf(&out, "package %s\n\n", dstpkg)

	// BUG(adonovan,shurcooL): bundle may generate incorrect code
	// due to shadowing between identifiers and imported package names.
	//
	// The generated code will either fail to compile or
	// (unlikely) compile successfully but have different behavior
	// than the original package. The risk of this happening is higher
	// when the original package has renamed imports (they're typically
	// renamed in order to resolve a shadow inside that particular .go file).

	// TODO(adonovan,shurcooL):
	// - detect shadowing issues, and either return error or resolve them
	// - preserve comments from the original import declarations.

	// pkgStd and pkgExt are sets of printed import specs. This is done
	// to deduplicate instances of the same import name and path.
	var pkgStd = make(map[string]bool)
	var pkgExt = make(map[string]bool)
	for _, f := range pkg.Syntax {
	for _, imp := range f.Imports {
	path, err := strconv.Unquote(imp.Path.Value)
	if err != nil {
	log.Fatalf("invalid import path string: %v", err) // Shouldn't happen here since packages.Load succeeded.
	}
	if path == dst {
	continue
	}
	if newPath, ok := importMap[path]; ok {
	path = newPath
	}

	var name string
	if imp.Name != nil {
	name = imp.Name.Name
	}
	spec := fmt.Sprintf("%s %q", name, path)
	if isStandardImportPath(path) {
	pkgStd[spec] = true
	} else {
	pkgExt[spec] = true
	}
	}
	}

	// Print a single declaration that imports all necessary packages.
	fmt.Fprintln(&out, "import (")
	for p := range pkgStd {
	fmt.Fprintf(&out, "\t%s\n", p)
	}
	if len(pkgExt) > 0 {
	fmt.Fprintln(&out)
	}
	for p := range pkgExt {
	fmt.Fprintf(&out, "\t%s\n", p)
	}
	fmt.Fprint(&out, ")\n\n")

	// Modify and print each file.
	for _, f := range pkg.Syntax {
	// Update renamed identifiers.
	for id, obj := range pkg.TypesInfo.Defs {
	if objsToUpdate[obj] {
	id.Name = prefix + obj.Name()
	}
	}
	for id, obj := range pkg.TypesInfo.Uses {
	if objsToUpdate[obj] {
	id.Name = prefix + obj.Name()
	}
	}

	// For each qualified identifier that refers to the
	// destination package, remove the qualifier.
	// The "@@@." strings are removed in postprocessing.
	ast.Inspect(f, func(n ast.Node) bool {
	if sel, ok := n.(*ast.SelectorExpr); ok {
	if id, ok := sel.X.(*ast.Ident); ok {
	if obj, ok := pkg.TypesInfo.Uses[id].(*types.PkgName); ok {
	if obj.Imported().Path() == dst {
	id.Name = "@@@"
	}
	}
	}
	}
	return true
	})

	last := f.Package
	if len(f.Imports) > 0 {
	imp := f.Imports[len(f.Imports)-1]
	last = imp.End()
	if imp.Comment != nil {
	if e := imp.Comment.End(); e > last {
	last = e
	}
	}
	}

	// Pretty-print package-level declarations.
	// but no package or import declarations.
	var buf bytes.Buffer
	for _, decl := range f.Decls {
	if decl, ok := decl.(*ast.GenDecl); ok && decl.Tok == token.IMPORT {
	continue
	}

	beg, end := sourceRange(decl)

	printComments(&out, f.Comments, last, beg)

	buf.Reset()
	format.Node(&buf, pkg.Fset, &printer.CommentedNode{Node: decl, Comments: f.Comments})
	// Remove each "@@@." in the output.
	// TODO(adonovan): not hygienic.
	out.Write(bytes.Replace(buf.Bytes(), []byte("@@@."), nil, -1))

	last = printSameLineComment(&out, f.Comments, pkg.Fset, end)

	out.WriteString("\n\n")
	}

	printLastComments(&out, f.Comments, last)
	}

	// Now format the entire thing.
	result, err := format.Source(out.Bytes())
	if err != nil {
	log.Fatalf("formatting failed: %v", err)
	}

	return result, nil
	}

	// sourceRange returns the [beg, end) interval of source code
	// belonging to decl (incl. associated comments).
	func sourceRange(decl ast.Decl) (beg, end token.Pos) {
	beg = decl.Pos()
	end = decl.End()

	var doc, com *ast.CommentGroup

	switch d := decl.(type) {
	case *ast.GenDecl:
	doc = d.Doc
	if len(d.Specs) > 0 {
	switch spec := d.Specs[len(d.Specs)-1].(type) {
	case *ast.ValueSpec:
	com = spec.Comment
	case *ast.TypeSpec:
	com = spec.Comment
	}
	}
	case *ast.FuncDecl:
	doc = d.Doc
	}

	if doc != nil {
	beg = doc.Pos()
	}
	if com != nil && com.End() > end {
	end = com.End()
	}

	return beg, end
	}

	func printComments(out bytes.Buffer, comments []ast.CommentGroup, pos, end token.Pos) {
	for _, cg := range comments {
	if pos <= cg.Pos() && cg.Pos() < end {
	for _, c := range cg.List {
	fmt.Fprintln(out, c.Text)
	}
	fmt.Fprintln(out)
	}
	}
	}

	const infinity = 1 << 30

	func printLastComments(out bytes.Buffer, comments []ast.CommentGroup, pos token.Pos) {
	printComments(out, comments, pos, infinity)
	}

	func printSameLineComment(out bytes.Buffer, comments []ast.CommentGroup, fset *token.FileSet, pos token.Pos) token.Pos {
	tf := fset.File(pos)
	for _, cg := range comments {
	if pos <= cg.Pos() && tf.Line(cg.Pos()) == tf.Line(pos) {
	for _, c := range cg.List {
	fmt.Fprintln(out, c.Text)
	}
	return cg.End()
	}
	}
	return pos
	}

	type flagFunc func(string)

	func (f flagFunc) Set(s string) error {
	f(s)
	return nil
	}

	func (f flagFunc) String() string { return "" }