go/ast/astutil/imports.go - tools - Git at Google

 // Copyright 2013 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.

 // Package astutil contains common utilities for working with the Go AST.
 package astutil // import "golang.org/x/tools/go/ast/astutil"

 import (
 	"fmt"
 	"go/ast"
 	"go/token"
 	"strconv"
 	"strings"
 )

 // AddImport adds the import path to the file f, if absent.
 func AddImport(fset *token.FileSet, f *ast.File, path string) (added bool) {
 	return AddNamedImport(fset, f, "", path)
 }

 // AddNamedImport adds the import with the given name and path to the file f, if absent.
 // If name is not empty, it is used to rename the import.
 //
 // For example, calling
 //
 //	AddNamedImport(fset, f, "pathpkg", "path")
 //
 // adds
 //
 //	import pathpkg "path"
 func AddNamedImport(fset *token.FileSet, f *ast.File, name, path string) (added bool) {
 	if imports(f, name, path) {
 		return false
 	}

 	newImport := &ast.ImportSpec{
 		Path: &ast.BasicLit{
 			Kind:  token.STRING,
 			Value: strconv.Quote(path),
 		},
 	}
 	if name != "" {
 		newImport.Name = &ast.Ident{Name: name}
 	}

 	// Find an import decl to add to.
 	// The goal is to find an existing import
 	// whose import path has the longest shared
 	// prefix with path.
 	var (
 		bestMatch  = -1         // length of longest shared prefix
 		lastImport = -1         // index in f.Decls of the file's final import decl
 		impDecl    *ast.GenDecl // import decl containing the best match
 		impIndex   = -1         // spec index in impDecl containing the best match

 		isThirdPartyPath = isThirdParty(path)
 	)
 	for i, decl := range f.Decls {
 		gen, ok := decl.(*ast.GenDecl)
 		if ok && gen.Tok == token.IMPORT {
 			lastImport = i
 			// Do not add to import "C", to avoid disrupting the
 			// association with its doc comment, breaking cgo.
 			if declImports(gen, "C") {
 				continue
 			}

 			// Match an empty import decl if that's all that is available.
 			if len(gen.Specs) == 0 && bestMatch == -1 {
 				impDecl = gen
 			}

 			// Compute longest shared prefix with imports in this group and find best
 			// matched import spec.
 			// 1. Always prefer import spec with longest shared prefix.
 			// 2. While match length is 0,
 			// - for stdlib package: prefer first import spec.
 			// - for third party package: prefer first third party import spec.
 			// We cannot use last import spec as best match for third party package
 			// because grouped imports are usually placed last by goimports -local
 			// flag.
 			// See issue #19190.
 			seenAnyThirdParty := false
 			for j, spec := range gen.Specs {
 				impspec := spec.(*ast.ImportSpec)
 				p := importPath(impspec)
 				n := matchLen(p, path)
 				if n > bestMatch || (bestMatch == 0 && !seenAnyThirdParty && isThirdPartyPath) {
 					bestMatch = n
 					impDecl = gen
 					impIndex = j
 				}
 				seenAnyThirdParty = seenAnyThirdParty || isThirdParty(p)
 			}
 		}
 	}

 	// If no import decl found, add one after the last import.
 	if impDecl == nil {
 		impDecl = &ast.GenDecl{
 			Tok: token.IMPORT,
 		}
 		if lastImport >= 0 {
 			impDecl.TokPos = f.Decls[lastImport].End()
 		} else {
 			// There are no existing imports.
 			// Our new import, preceded by a blank line,  goes after the package declaration
 			// and after the comment, if any, that starts on the same line as the
 			// package declaration.
 			impDecl.TokPos = f.Package

 			file := fset.File(f.Package)
 			pkgLine := file.Line(f.Package)
 			for _, c := range f.Comments {
 				if file.Line(c.Pos()) > pkgLine {
 					break
 				}
 				// +2 for a blank line
 				impDecl.TokPos = c.End() + 2
 			}
 		}
 		f.Decls = append(f.Decls, nil)
 		copy(f.Decls[lastImport+2:], f.Decls[lastImport+1:])
 		f.Decls[lastImport+1] = impDecl
 	}

 	// Insert new import at insertAt.
 	insertAt := 0
 	if impIndex >= 0 {
 		// insert after the found import
 		insertAt = impIndex + 1
 	}
 	impDecl.Specs = append(impDecl.Specs, nil)
 	copy(impDecl.Specs[insertAt+1:], impDecl.Specs[insertAt:])
 	impDecl.Specs[insertAt] = newImport
 	pos := impDecl.Pos()
 	if insertAt > 0 {
 		// If there is a comment after an existing import, preserve the comment
 		// position by adding the new import after the comment.
 		if spec, ok := impDecl.Specs[insertAt-1].(*ast.ImportSpec); ok && spec.Comment != nil {
 			pos = spec.Comment.End()
 		} else {
 			// Assign same position as the previous import,
 			// so that the sorter sees it as being in the same block.
 			pos = impDecl.Specs[insertAt-1].Pos()
 		}
 	}
 	if newImport.Name != nil {
 		newImport.Name.NamePos = pos
 	}
 	newImport.Path.ValuePos = pos
 	newImport.EndPos = pos

 	// Clean up parens. impDecl contains at least one spec.
 	if len(impDecl.Specs) == 1 {
 		// Remove unneeded parens.
 		impDecl.Lparen = token.NoPos
 	} else if !impDecl.Lparen.IsValid() {
 		// impDecl needs parens added.
 		impDecl.Lparen = impDecl.Specs[0].Pos()
 	}

 	f.Imports = append(f.Imports, newImport)

 	if len(f.Decls) <= 1 {
 		return true
 	}

 	// Merge all the import declarations into the first one.
 	var first *ast.GenDecl
 	for i := 0; i < len(f.Decls); i++ {
 		decl := f.Decls[i]
 		gen, ok := decl.(*ast.GenDecl)
 		if !ok || gen.Tok != token.IMPORT || declImports(gen, "C") {
 			continue
 		}
 		if first == nil {
 			first = gen
 			continue // Don't touch the first one.
 		}
 		// We now know there is more than one package in this import
 		// declaration. Ensure that it ends up parenthesized.
 		first.Lparen = first.Pos()
 		// Move the imports of the other import declaration to the first one.
 		for _, spec := range gen.Specs {
 			spec.(*ast.ImportSpec).Path.ValuePos = first.Pos()
 			first.Specs = append(first.Specs, spec)
 		}
 		f.Decls = append(f.Decls[:i], f.Decls[i+1:]...)
 		i--
 	}

 	return true
 }

 func isThirdParty(importPath string) bool {
 	// Third party package import path usually contains "." (".com", ".org", ...)
 	// This logic is taken from golang.org/x/tools/imports package.
 	return strings.Contains(importPath, ".")
 }

 // DeleteImport deletes the import path from the file f, if present.
 // If there are duplicate import declarations, all matching ones are deleted.
 func DeleteImport(fset *token.FileSet, f *ast.File, path string) (deleted bool) {
 	return DeleteNamedImport(fset, f, "", path)
 }

 // DeleteNamedImport deletes the import with the given name and path from the file f, if present.
 // If there are duplicate import declarations, all matching ones are deleted.
 func DeleteNamedImport(fset *token.FileSet, f *ast.File, name, path string) (deleted bool) {
 	var delspecs []*ast.ImportSpec
 	var delcomments []*ast.CommentGroup

 	// Find the import nodes that import path, if any.
 	for i := 0; i < len(f.Decls); i++ {
 		decl := f.Decls[i]
 		gen, ok := decl.(*ast.GenDecl)
 		if !ok || gen.Tok != token.IMPORT {
 			continue
 		}
 		for j := 0; j < len(gen.Specs); j++ {
 			spec := gen.Specs[j]
 			impspec := spec.(*ast.ImportSpec)
 			if importName(impspec) != name || importPath(impspec) != path {
 				continue
 			}

 			// We found an import spec that imports path.
 			// Delete it.
 			delspecs = append(delspecs, impspec)
 			deleted = true
 			copy(gen.Specs[j:], gen.Specs[j+1:])
 			gen.Specs = gen.Specs[:len(gen.Specs)-1]

 			// If this was the last import spec in this decl,
 			// delete the decl, too.
 			if len(gen.Specs) == 0 {
 				copy(f.Decls[i:], f.Decls[i+1:])
 				f.Decls = f.Decls[:len(f.Decls)-1]
 				i--
 				break
 			} else if len(gen.Specs) == 1 {
 				if impspec.Doc != nil {
 					delcomments = append(delcomments, impspec.Doc)
 				}
 				if impspec.Comment != nil {
 					delcomments = append(delcomments, impspec.Comment)
 				}
 				for _, cg := range f.Comments {
 					// Found comment on the same line as the import spec.
 					if cg.End() < impspec.Pos() && fset.Position(cg.End()).Line == fset.Position(impspec.Pos()).Line {
 						delcomments = append(delcomments, cg)
 						break
 					}
 				}

 				spec := gen.Specs[0].(*ast.ImportSpec)

 				// Move the documentation right after the import decl.
 				if spec.Doc != nil {
 					for fset.Position(gen.TokPos).Line+1 < fset.Position(spec.Doc.Pos()).Line {
 						fset.File(gen.TokPos).MergeLine(fset.Position(gen.TokPos).Line)
 					}
 				}
 				for _, cg := range f.Comments {
 					if cg.End() < spec.Pos() && fset.Position(cg.End()).Line == fset.Position(spec.Pos()).Line {
 						for fset.Position(gen.TokPos).Line+1 < fset.Position(spec.Pos()).Line {
 							fset.File(gen.TokPos).MergeLine(fset.Position(gen.TokPos).Line)
 						}
 						break
 					}
 				}
 			}
 			if j > 0 {
 				lastImpspec := gen.Specs[j-1].(*ast.ImportSpec)
 				lastLine := fset.PositionFor(lastImpspec.Path.ValuePos, false).Line
 				line := fset.PositionFor(impspec.Path.ValuePos, false).Line

 				// We deleted an entry but now there may be
 				// a blank line-sized hole where the import was.
 				if line-lastLine > 1 || !gen.Rparen.IsValid() {
 					// There was a blank line immediately preceding the deleted import,
 					// so there's no need to close the hole. The right parenthesis is
 					// invalid after AddImport to an import statement without parenthesis.
 					// Do nothing.
 				} else if line != fset.File(gen.Rparen).LineCount() {
 					// There was no blank line. Close the hole.
 					fset.File(gen.Rparen).MergeLine(line)
 				}
 			}
 			j--
 		}
 	}

 	// Delete imports from f.Imports.
 	for i := 0; i < len(f.Imports); i++ {
 		imp := f.Imports[i]
 		for j, del := range delspecs {
 			if imp == del {
 				copy(f.Imports[i:], f.Imports[i+1:])
 				f.Imports = f.Imports[:len(f.Imports)-1]
 				copy(delspecs[j:], delspecs[j+1:])
 				delspecs = delspecs[:len(delspecs)-1]
 				i--
 				break
 			}
 		}
 	}

 	// Delete comments from f.Comments.
 	for i := 0; i < len(f.Comments); i++ {
 		cg := f.Comments[i]
 		for j, del := range delcomments {
 			if cg == del {
 				copy(f.Comments[i:], f.Comments[i+1:])
 				f.Comments = f.Comments[:len(f.Comments)-1]
 				copy(delcomments[j:], delcomments[j+1:])
 				delcomments = delcomments[:len(delcomments)-1]
 				i--
 				break
 			}
 		}
 	}

 	if len(delspecs) > 0 {
 		panic(fmt.Sprintf("deleted specs from Decls but not Imports: %v", delspecs))
 	}

 	return
 }

 // RewriteImport rewrites any import of path oldPath to path newPath.
 func RewriteImport(fset *token.FileSet, f *ast.File, oldPath, newPath string) (rewrote bool) {
 	for _, imp := range f.Imports {
 		if importPath(imp) == oldPath {
 			rewrote = true
 			// record old End, because the default is to compute
 			// it using the length of imp.Path.Value.
 			imp.EndPos = imp.End()
 			imp.Path.Value = strconv.Quote(newPath)
 		}
 	}
 	return
 }

 // UsesImport reports whether a given import is used.
 func UsesImport(f *ast.File, path string) (used bool) {
 	spec := importSpec(f, path)
 	if spec == nil {
 		return
 	}

 	name := spec.Name.String()
 	switch name {
 	case "<nil>":
 		// If the package name is not explicitly specified,
 		// make an educated guess. This is not guaranteed to be correct.
 		lastSlash := strings.LastIndex(path, "/")
 		if lastSlash == -1 {
 			name = path
 		} else {
 			name = path[lastSlash+1:]
 		}
 	case "_", ".":
 		// Not sure if this import is used - err on the side of caution.
 		return true
 	}

 	ast.Walk(visitFn(func(n ast.Node) {
 		sel, ok := n.(*ast.SelectorExpr)
 		if ok && isTopName(sel.X, name) {
 			used = true
 		}
 	}), f)

 	return
 }

 type visitFn func(node ast.Node)

 func (fn visitFn) Visit(node ast.Node) ast.Visitor {
 	fn(node)
 	return fn
 }

 // imports reports whether f has an import with the specified name and path.
 func imports(f *ast.File, name, path string) bool {
 	for _, s := range f.Imports {
 		if importName(s) == name && importPath(s) == path {
 			return true
 		}
 	}
 	return false
 }

 // importSpec returns the import spec if f imports path,
 // or nil otherwise.
 func importSpec(f *ast.File, path string) *ast.ImportSpec {
 	for _, s := range f.Imports {
 		if importPath(s) == path {
 			return s
 		}
 	}
 	return nil
 }

 // importName returns the name of s,
 // or "" if the import is not named.
 func importName(s *ast.ImportSpec) string {
 	if s.Name == nil {
 		return ""
 	}
 	return s.Name.Name
 }

 // importPath returns the unquoted import path of s,
 // or "" if the path is not properly quoted.
 func importPath(s *ast.ImportSpec) string {
 	t, err := strconv.Unquote(s.Path.Value)
 	if err != nil {
 		return ""
 	}
 	return t
 }

 // declImports reports whether gen contains an import of path.
 func declImports(gen *ast.GenDecl, path string) bool {
 	if gen.Tok != token.IMPORT {
 		return false
 	}
 	for _, spec := range gen.Specs {
 		impspec := spec.(*ast.ImportSpec)
 		if importPath(impspec) == path {
 			return true
 		}
 	}
 	return false
 }

 // matchLen returns the length of the longest path segment prefix shared by x and y.
 func matchLen(x, y string) int {
 	n := 0
 	for i := 0; i < len(x) && i < len(y) && x[i] == y[i]; i++ {
 		if x[i] == '/' {
 			n++
 		}
 	}
 	return n
 }

 // isTopName returns true if n is a top-level unresolved identifier with the given name.
 func isTopName(n ast.Expr, name string) bool {
 	id, ok := n.(*ast.Ident)
 	return ok && id.Name == name && id.Obj == nil
 }

 // Imports returns the file imports grouped by paragraph.
 func Imports(fset *token.FileSet, f *ast.File) [][]*ast.ImportSpec {
 	var groups [][]*ast.ImportSpec

 	for _, decl := range f.Decls {
 		genDecl, ok := decl.(*ast.GenDecl)
 		if !ok || genDecl.Tok != token.IMPORT {
 			break
 		}

 		group := []*ast.ImportSpec{}

 		var lastLine int
 		for _, spec := range genDecl.Specs {
 			importSpec := spec.(*ast.ImportSpec)
 			pos := importSpec.Path.ValuePos
 			line := fset.Position(pos).Line
 			if lastLine > 0 && pos > 0 && line-lastLine > 1 {
 				groups = append(groups, group)
 				group = []*ast.ImportSpec{}
 			}
 			group = append(group, importSpec)
 			lastLine = line
 		}
 		groups = append(groups, group)
 	}

 	return groups
 }
	// Copyright 2013 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.

	// Package astutil contains common utilities for working with the Go AST.
	package astutil // import "golang.org/x/tools/go/ast/astutil"

	import (
	"fmt"
	"go/ast"
	"go/token"
	"strconv"
	"strings"
	)

	// AddImport adds the import path to the file f, if absent.
	func AddImport(fset token.FileSet, f ast.File, path string) (added bool) {
	return AddNamedImport(fset, f, "", path)
	}

	// AddNamedImport adds the import with the given name and path to the file f, if absent.
	// If name is not empty, it is used to rename the import.
	//
	// For example, calling
	//
	// AddNamedImport(fset, f, "pathpkg", "path")
	//
	// adds
	//
	// import pathpkg "path"
	func AddNamedImport(fset token.FileSet, f ast.File, name, path string) (added bool) {
	if imports(f, name, path) {
	return false
	}

	newImport := &ast.ImportSpec{
	Path: &ast.BasicLit{
	Kind: token.STRING,
	Value: strconv.Quote(path),
	},
	}
	if name != "" {
	newImport.Name = &ast.Ident{Name: name}
	}

	// Find an import decl to add to.
	// The goal is to find an existing import
	// whose import path has the longest shared
	// prefix with path.
	var (
	bestMatch = -1 // length of longest shared prefix
	lastImport = -1 // index in f.Decls of the file's final import decl
	impDecl *ast.GenDecl // import decl containing the best match
	impIndex = -1 // spec index in impDecl containing the best match

	isThirdPartyPath = isThirdParty(path)
	)
	for i, decl := range f.Decls {
	gen, ok := decl.(*ast.GenDecl)
	if ok && gen.Tok == token.IMPORT {
	lastImport = i
	// Do not add to import "C", to avoid disrupting the
	// association with its doc comment, breaking cgo.
	if declImports(gen, "C") {
	continue
	}

	// Match an empty import decl if that's all that is available.
	if len(gen.Specs) == 0 && bestMatch == -1 {
	impDecl = gen
	}

	// Compute longest shared prefix with imports in this group and find best
	// matched import spec.
	// 1. Always prefer import spec with longest shared prefix.
	// 2. While match length is 0,
	// - for stdlib package: prefer first import spec.
	// - for third party package: prefer first third party import spec.
	// We cannot use last import spec as best match for third party package
	// because grouped imports are usually placed last by goimports -local
	// flag.
	// See issue #19190.
	seenAnyThirdParty := false
	for j, spec := range gen.Specs {
	impspec := spec.(*ast.ImportSpec)
	p := importPath(impspec)
	n := matchLen(p, path)
	if n > bestMatch \|\| (bestMatch == 0 && !seenAnyThirdParty && isThirdPartyPath) {
	bestMatch = n
	impDecl = gen
	impIndex = j
	}
	seenAnyThirdParty = seenAnyThirdParty \|\| isThirdParty(p)
	}
	}
	}

	// If no import decl found, add one after the last import.
	if impDecl == nil {
	impDecl = &ast.GenDecl{
	Tok: token.IMPORT,
	}
	if lastImport >= 0 {
	impDecl.TokPos = f.Decls[lastImport].End()
	} else {
	// There are no existing imports.
	// Our new import, preceded by a blank line, goes after the package declaration
	// and after the comment, if any, that starts on the same line as the
	// package declaration.
	impDecl.TokPos = f.Package

	file := fset.File(f.Package)
	pkgLine := file.Line(f.Package)
	for _, c := range f.Comments {
	if file.Line(c.Pos()) > pkgLine {
	break
	}
	// +2 for a blank line
	impDecl.TokPos = c.End() + 2
	}
	}
	f.Decls = append(f.Decls, nil)
	copy(f.Decls[lastImport+2:], f.Decls[lastImport+1:])
	f.Decls[lastImport+1] = impDecl
	}

	// Insert new import at insertAt.
	insertAt := 0
	if impIndex >= 0 {
	// insert after the found import
	insertAt = impIndex + 1
	}
	impDecl.Specs = append(impDecl.Specs, nil)
	copy(impDecl.Specs[insertAt+1:], impDecl.Specs[insertAt:])
	impDecl.Specs[insertAt] = newImport
	pos := impDecl.Pos()
	if insertAt > 0 {
	// If there is a comment after an existing import, preserve the comment
	// position by adding the new import after the comment.
	if spec, ok := impDecl.Specs[insertAt-1].(*ast.ImportSpec); ok && spec.Comment != nil {
	pos = spec.Comment.End()
	} else {
	// Assign same position as the previous import,
	// so that the sorter sees it as being in the same block.
	pos = impDecl.Specs[insertAt-1].Pos()
	}
	}
	if newImport.Name != nil {
	newImport.Name.NamePos = pos
	}
	newImport.Path.ValuePos = pos
	newImport.EndPos = pos

	// Clean up parens. impDecl contains at least one spec.
	if len(impDecl.Specs) == 1 {
	// Remove unneeded parens.
	impDecl.Lparen = token.NoPos
	} else if !impDecl.Lparen.IsValid() {
	// impDecl needs parens added.
	impDecl.Lparen = impDecl.Specs[0].Pos()
	}

	f.Imports = append(f.Imports, newImport)

	if len(f.Decls) <= 1 {
	return true
	}

	// Merge all the import declarations into the first one.
	var first *ast.GenDecl
	for i := 0; i < len(f.Decls); i++ {
	decl := f.Decls[i]
	gen, ok := decl.(*ast.GenDecl)
	if !ok \|\| gen.Tok != token.IMPORT \|\| declImports(gen, "C") {
	continue
	}
	if first == nil {
	first = gen
	continue // Don't touch the first one.
	}
	// We now know there is more than one package in this import
	// declaration. Ensure that it ends up parenthesized.
	first.Lparen = first.Pos()
	// Move the imports of the other import declaration to the first one.
	for _, spec := range gen.Specs {
	spec.(*ast.ImportSpec).Path.ValuePos = first.Pos()
	first.Specs = append(first.Specs, spec)
	}
	f.Decls = append(f.Decls[:i], f.Decls[i+1:]...)
	i--
	}

	return true
	}

	func isThirdParty(importPath string) bool {
	// Third party package import path usually contains "." (".com", ".org", ...)
	// This logic is taken from golang.org/x/tools/imports package.
	return strings.Contains(importPath, ".")
	}

	// DeleteImport deletes the import path from the file f, if present.
	// If there are duplicate import declarations, all matching ones are deleted.
	func DeleteImport(fset token.FileSet, f ast.File, path string) (deleted bool) {
	return DeleteNamedImport(fset, f, "", path)
	}

	// DeleteNamedImport deletes the import with the given name and path from the file f, if present.
	// If there are duplicate import declarations, all matching ones are deleted.
	func DeleteNamedImport(fset token.FileSet, f ast.File, name, path string) (deleted bool) {
	var delspecs []*ast.ImportSpec
	var delcomments []*ast.CommentGroup

	// Find the import nodes that import path, if any.
	for i := 0; i < len(f.Decls); i++ {
	decl := f.Decls[i]
	gen, ok := decl.(*ast.GenDecl)
	if !ok \|\| gen.Tok != token.IMPORT {
	continue
	}
	for j := 0; j < len(gen.Specs); j++ {
	spec := gen.Specs[j]
	impspec := spec.(*ast.ImportSpec)
	if importName(impspec) != name \|\| importPath(impspec) != path {
	continue
	}

	// We found an import spec that imports path.
	// Delete it.
	delspecs = append(delspecs, impspec)
	deleted = true
	copy(gen.Specs[j:], gen.Specs[j+1:])
	gen.Specs = gen.Specs[:len(gen.Specs)-1]

	// If this was the last import spec in this decl,
	// delete the decl, too.
	if len(gen.Specs) == 0 {
	copy(f.Decls[i:], f.Decls[i+1:])
	f.Decls = f.Decls[:len(f.Decls)-1]
	i--
	break
	} else if len(gen.Specs) == 1 {
	if impspec.Doc != nil {
	delcomments = append(delcomments, impspec.Doc)
	}
	if impspec.Comment != nil {
	delcomments = append(delcomments, impspec.Comment)
	}
	for _, cg := range f.Comments {
	// Found comment on the same line as the import spec.
	if cg.End() < impspec.Pos() && fset.Position(cg.End()).Line == fset.Position(impspec.Pos()).Line {
	delcomments = append(delcomments, cg)
	break
	}
	}

	spec := gen.Specs[0].(*ast.ImportSpec)

	// Move the documentation right after the import decl.
	if spec.Doc != nil {
	for fset.Position(gen.TokPos).Line+1 < fset.Position(spec.Doc.Pos()).Line {
	fset.File(gen.TokPos).MergeLine(fset.Position(gen.TokPos).Line)
	}
	}
	for _, cg := range f.Comments {
	if cg.End() < spec.Pos() && fset.Position(cg.End()).Line == fset.Position(spec.Pos()).Line {
	for fset.Position(gen.TokPos).Line+1 < fset.Position(spec.Pos()).Line {
	fset.File(gen.TokPos).MergeLine(fset.Position(gen.TokPos).Line)
	}
	break
	}
	}
	}
	if j > 0 {
	lastImpspec := gen.Specs[j-1].(*ast.ImportSpec)
	lastLine := fset.PositionFor(lastImpspec.Path.ValuePos, false).Line
	line := fset.PositionFor(impspec.Path.ValuePos, false).Line

	// We deleted an entry but now there may be
	// a blank line-sized hole where the import was.
	if line-lastLine > 1 \|\| !gen.Rparen.IsValid() {
	// There was a blank line immediately preceding the deleted import,
	// so there's no need to close the hole. The right parenthesis is
	// invalid after AddImport to an import statement without parenthesis.
	// Do nothing.
	} else if line != fset.File(gen.Rparen).LineCount() {
	// There was no blank line. Close the hole.
	fset.File(gen.Rparen).MergeLine(line)
	}
	}
	j--
	}
	}

	// Delete imports from f.Imports.
	for i := 0; i < len(f.Imports); i++ {
	imp := f.Imports[i]
	for j, del := range delspecs {
	if imp == del {
	copy(f.Imports[i:], f.Imports[i+1:])
	f.Imports = f.Imports[:len(f.Imports)-1]
	copy(delspecs[j:], delspecs[j+1:])
	delspecs = delspecs[:len(delspecs)-1]
	i--
	break
	}
	}
	}

	// Delete comments from f.Comments.
	for i := 0; i < len(f.Comments); i++ {
	cg := f.Comments[i]
	for j, del := range delcomments {
	if cg == del {
	copy(f.Comments[i:], f.Comments[i+1:])
	f.Comments = f.Comments[:len(f.Comments)-1]
	copy(delcomments[j:], delcomments[j+1:])
	delcomments = delcomments[:len(delcomments)-1]
	i--
	break
	}
	}
	}

	if len(delspecs) > 0 {
	panic(fmt.Sprintf("deleted specs from Decls but not Imports: %v", delspecs))
	}

	return
	}

	// RewriteImport rewrites any import of path oldPath to path newPath.
	func RewriteImport(fset token.FileSet, f ast.File, oldPath, newPath string) (rewrote bool) {
	for _, imp := range f.Imports {
	if importPath(imp) == oldPath {
	rewrote = true
	// record old End, because the default is to compute
	// it using the length of imp.Path.Value.
	imp.EndPos = imp.End()
	imp.Path.Value = strconv.Quote(newPath)
	}
	}
	return
	}

	// UsesImport reports whether a given import is used.
	func UsesImport(f *ast.File, path string) (used bool) {
	spec := importSpec(f, path)
	if spec == nil {
	return
	}

	name := spec.Name.String()
	switch name {
	case "<nil>":
	// If the package name is not explicitly specified,
	// make an educated guess. This is not guaranteed to be correct.
	lastSlash := strings.LastIndex(path, "/")
	if lastSlash == -1 {
	name = path
	} else {
	name = path[lastSlash+1:]
	}
	case "_", ".":
	// Not sure if this import is used - err on the side of caution.
	return true
	}

	ast.Walk(visitFn(func(n ast.Node) {
	sel, ok := n.(*ast.SelectorExpr)
	if ok && isTopName(sel.X, name) {
	used = true
	}
	}), f)

	return
	}

	type visitFn func(node ast.Node)

	func (fn visitFn) Visit(node ast.Node) ast.Visitor {
	fn(node)
	return fn
	}

	// imports reports whether f has an import with the specified name and path.
	func imports(f *ast.File, name, path string) bool {
	for _, s := range f.Imports {
	if importName(s) == name && importPath(s) == path {
	return true
	}
	}
	return false
	}

	// importSpec returns the import spec if f imports path,
	// or nil otherwise.
	func importSpec(f ast.File, path string) ast.ImportSpec {
	for _, s := range f.Imports {
	if importPath(s) == path {
	return s
	}
	}
	return nil
	}

	// importName returns the name of s,
	// or "" if the import is not named.
	func importName(s *ast.ImportSpec) string {
	if s.Name == nil {
	return ""
	}
	return s.Name.Name
	}

	// importPath returns the unquoted import path of s,
	// or "" if the path is not properly quoted.
	func importPath(s *ast.ImportSpec) string {
	t, err := strconv.Unquote(s.Path.Value)
	if err != nil {
	return ""
	}
	return t
	}

	// declImports reports whether gen contains an import of path.
	func declImports(gen *ast.GenDecl, path string) bool {
	if gen.Tok != token.IMPORT {
	return false
	}
	for _, spec := range gen.Specs {
	impspec := spec.(*ast.ImportSpec)
	if importPath(impspec) == path {
	return true
	}
	}
	return false
	}

	// matchLen returns the length of the longest path segment prefix shared by x and y.
	func matchLen(x, y string) int {
	n := 0
	for i := 0; i < len(x) && i < len(y) && x[i] == y[i]; i++ {
	if x[i] == '/' {
	n++
	}
	}
	return n
	}

	// isTopName returns true if n is a top-level unresolved identifier with the given name.
	func isTopName(n ast.Expr, name string) bool {
	id, ok := n.(*ast.Ident)
	return ok && id.Name == name && id.Obj == nil
	}

	// Imports returns the file imports grouped by paragraph.
	func Imports(fset token.FileSet, f ast.File) [][]*ast.ImportSpec {
	var groups [][]*ast.ImportSpec

	for _, decl := range f.Decls {
	genDecl, ok := decl.(*ast.GenDecl)
	if !ok \|\| genDecl.Tok != token.IMPORT {
	break
	}

	group := []*ast.ImportSpec{}

	var lastLine int
	for _, spec := range genDecl.Specs {
	importSpec := spec.(*ast.ImportSpec)
	pos := importSpec.Path.ValuePos
	line := fset.Position(pos).Line
	if lastLine > 0 && pos > 0 && line-lastLine > 1 {
	groups = append(groups, group)
	group = []*ast.ImportSpec{}
	}
	group = append(group, importSpec)
	lastLine = line
	}
	groups = append(groups, group)
	}

	return groups
	}