diff --git a/astutil/imports.go b/astutil/imports.go
new file mode 100644
index 00000000..2fa7a518
--- /dev/null
+++ b/astutil/imports.go
@@ -0,0 +1,327 @@
+// Package astutil contains common utilities for working with the Go AST.
+package astutil
+
+import (
+	"go/ast"
+	"go/token"
+	"path"
+	"strconv"
+	"strings"
+)
+
+// AddImport adds the import path to the file f, if absent.
+func AddImport(f *ast.File, ipath string) (added bool) {
+	if imports(f, ipath) {
+		return false
+	}
+
+	// Determine name of import.
+	// Assume added imports follow convention of using last element.
+	_, name := path.Split(ipath)
+
+	// Rename any conflicting top-level references from name to name_.
+	renameTop(f, name, name+"_")
+
+	newImport := &ast.ImportSpec{
+		Path: &ast.BasicLit{
+			Kind:  token.STRING,
+			Value: strconv.Quote(ipath),
+		},
+	}
+
+	// Find an import decl to add to.
+	var (
+		bestMatch  = -1
+		lastImport = -1
+		impDecl    *ast.GenDecl
+		impIndex   = -1
+	)
+	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
+			}
+
+			// Compute longest shared prefix with imports in this block.
+			for j, spec := range gen.Specs {
+				impspec := spec.(*ast.ImportSpec)
+				n := matchLen(importPath(impspec), ipath)
+				if n > bestMatch {
+					bestMatch = n
+					impDecl = gen
+					impIndex = j
+				}
+			}
+		}
+	}
+
+	// If no import decl found, add one after the last import.
+	if impDecl == nil {
+		impDecl = &ast.GenDecl{
+			Tok: token.IMPORT,
+		}
+		f.Decls = append(f.Decls, nil)
+		copy(f.Decls[lastImport+2:], f.Decls[lastImport+1:])
+		f.Decls[lastImport+1] = impDecl
+	}
+
+	// Ensure the import decl has parentheses, if needed.
+	if len(impDecl.Specs) > 0 && !impDecl.Lparen.IsValid() {
+		impDecl.Lparen = impDecl.Pos()
+	}
+
+	insertAt := impIndex + 1
+	if insertAt == 0 {
+		insertAt = len(impDecl.Specs)
+	}
+	impDecl.Specs = append(impDecl.Specs, nil)
+	copy(impDecl.Specs[insertAt+1:], impDecl.Specs[insertAt:])
+	impDecl.Specs[insertAt] = newImport
+	if insertAt > 0 {
+		// Assign same position as the previous import,
+		// so that the sorter sees it as being in the same block.
+		prev := impDecl.Specs[insertAt-1]
+		newImport.Path.ValuePos = prev.Pos()
+		newImport.EndPos = prev.Pos()
+	}
+
+	f.Imports = append(f.Imports, newImport)
+	return true
+}
+
+// DeleteImport deletes the import path from the file f, if present.
+func DeleteImport(f *ast.File, path string) (deleted bool) {
+	oldImport := importSpec(f, path)
+
+	// Find the import node that imports path, if any.
+	for i, decl := range f.Decls {
+		gen, ok := decl.(*ast.GenDecl)
+		if !ok || gen.Tok != token.IMPORT {
+			continue
+		}
+		for j, spec := range gen.Specs {
+			impspec := spec.(*ast.ImportSpec)
+			if oldImport != impspec {
+				continue
+			}
+
+			// We found an import spec that imports path.
+			// Delete it.
+			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]
+			} else if len(gen.Specs) == 1 {
+				gen.Lparen = token.NoPos // drop parens
+			}
+			if j > 0 {
+				// We deleted an entry but now there will be
+				// a blank line-sized hole where the import was.
+				// Close the hole by making the previous
+				// import appear to "end" where this one did.
+				gen.Specs[j-1].(*ast.ImportSpec).EndPos = impspec.End()
+			}
+			break
+		}
+	}
+
+	// Delete it from f.Imports.
+	for i, imp := range f.Imports {
+		if imp == oldImport {
+			copy(f.Imports[i:], f.Imports[i+1:])
+			f.Imports = f.Imports[:len(f.Imports)-1]
+			break
+		}
+	}
+
+	return
+}
+
+// RewriteImport rewrites any import of path oldPath to path newPath.
+func RewriteImport(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 returns true if f imports path.
+func imports(f *ast.File, path string) bool {
+	return importSpec(f, path) != nil
+}
+
+// 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
+}
+
+// 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 t
+	}
+	return ""
+}
+
+// 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
+}
+
+// renameTop renames all references to the top-level name old.
+// It returns true if it makes any changes.
+func renameTop(f *ast.File, old, new string) bool {
+	var fixed bool
+
+	// Rename any conflicting imports
+	// (assuming package name is last element of path).
+	for _, s := range f.Imports {
+		if s.Name != nil {
+			if s.Name.Name == old {
+				s.Name.Name = new
+				fixed = true
+			}
+		} else {
+			_, thisName := path.Split(importPath(s))
+			if thisName == old {
+				s.Name = ast.NewIdent(new)
+				fixed = true
+			}
+		}
+	}
+
+	// Rename any top-level declarations.
+	for _, d := range f.Decls {
+		switch d := d.(type) {
+		case *ast.FuncDecl:
+			if d.Recv == nil && d.Name.Name == old {
+				d.Name.Name = new
+				d.Name.Obj.Name = new
+				fixed = true
+			}
+		case *ast.GenDecl:
+			for _, s := range d.Specs {
+				switch s := s.(type) {
+				case *ast.TypeSpec:
+					if s.Name.Name == old {
+						s.Name.Name = new
+						s.Name.Obj.Name = new
+						fixed = true
+					}
+				case *ast.ValueSpec:
+					for _, n := range s.Names {
+						if n.Name == old {
+							n.Name = new
+							n.Obj.Name = new
+							fixed = true
+						}
+					}
+				}
+			}
+		}
+	}
+
+	// Rename top-level old to new, both unresolved names
+	// (probably defined in another file) and names that resolve
+	// to a declaration we renamed.
+	ast.Walk(visitFn(func(n ast.Node) {
+		id, ok := n.(*ast.Ident)
+		if ok && isTopName(id, old) {
+			id.Name = new
+			fixed = true
+		}
+		if ok && id.Obj != nil && id.Name == old && id.Obj.Name == new {
+			id.Name = id.Obj.Name
+			fixed = true
+		}
+	}), f)
+
+	return fixed
+}
+
+// matchLen returns the length of the longest prefix shared by x and y.
+func matchLen(x, y string) int {
+	i := 0
+	for i < len(x) && i < len(y) && x[i] == y[i] {
+		i++
+	}
+	return i
+}
+
+// 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
+}
diff --git a/astutil/imports_test.go b/astutil/imports_test.go
new file mode 100644
index 00000000..86d6775d
--- /dev/null
+++ b/astutil/imports_test.go
@@ -0,0 +1,459 @@
+package astutil
+
+import (
+	"bytes"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+
+	"testing"
+)
+
+var fset = token.NewFileSet()
+
+func parse(t *testing.T, name, in string) *ast.File {
+	file, err := parser.ParseFile(fset, name, in, parser.ParseComments)
+	if err != nil {
+		t.Fatalf("%s parse: %v", name, err)
+	}
+	return file
+}
+
+func print(t *testing.T, name string, f *ast.File) string {
+	var buf bytes.Buffer
+	if err := format.Node(&buf, fset, f); err != nil {
+		t.Fatalf("%s gofmt: %v", name, err)
+	}
+	return string(buf.Bytes())
+}
+
+type test struct {
+	name string
+	pkg  string
+	in   string
+	out  string
+}
+
+var addTests = []test{
+	{
+		name: "leave os alone",
+		pkg:  "os",
+		in: `package main
+
+import (
+	"os"
+)
+`,
+		out: `package main
+
+import (
+	"os"
+)
+`,
+	},
+	{
+		name: "import.1",
+		pkg:  "os",
+		in: `package main
+`,
+		out: `package main
+
+import "os"
+`,
+	},
+	{
+		name: "import.2",
+		pkg:  "os",
+		in: `package main
+
+// Comment
+import "C"
+`,
+		out: `package main
+
+// Comment
+import "C"
+import "os"
+`,
+	},
+	{
+		name: "import.3",
+		pkg:  "os",
+		in: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"utf8"
+)
+`,
+		out: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+	},
+	{
+		name: "import.17",
+		pkg:  "x/y/z",
+		in: `package main
+
+// Comment
+import "C"
+
+import (
+	"a"
+	"b"
+
+	"x/w"
+
+	"d/f"
+)
+`,
+		out: `package main
+
+// Comment
+import "C"
+
+import (
+	"a"
+	"b"
+
+	"x/w"
+	"x/y/z"
+
+	"d/f"
+)
+`,
+	},
+}
+
+func TestAddImport(t *testing.T) {
+	for _, test := range addTests {
+		file := parse(t, test.name, test.in)
+		AddImport(file, test.pkg)
+		if got := print(t, test.name, file); got != test.out {
+			t.Errorf("%s:\ngot: %s\nwant: %s", test.name, got, test.out)
+		}
+	}
+}
+
+var deleteTests = []test{
+	{
+		name: "import.4",
+		pkg:  "os",
+		in: `package main
+
+import (
+	"os"
+)
+`,
+		out: `package main
+`,
+	},
+	{
+		name: "import.5",
+		pkg:  "os",
+		in: `package main
+
+// Comment
+import "C"
+import "os"
+`,
+		out: `package main
+
+// Comment
+import "C"
+`,
+	},
+	{
+		name: "import.6",
+		pkg:  "os",
+		in: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		out: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"utf8"
+)
+`,
+	},
+	{
+		name: "import.7",
+		pkg:  "io",
+		in: `package main
+
+import (
+	"io"   // a
+	"os"   // b
+	"utf8" // c
+)
+`,
+		out: `package main
+
+import (
+	// a
+	"os"   // b
+	"utf8" // c
+)
+`,
+	},
+	{
+		name: "import.8",
+		pkg:  "os",
+		in: `package main
+
+import (
+	"io"   // a
+	"os"   // b
+	"utf8" // c
+)
+`,
+		out: `package main
+
+import (
+	"io" // a
+	// b
+	"utf8" // c
+)
+`,
+	},
+	{
+		name: "import.9",
+		pkg:  "utf8",
+		in: `package main
+
+import (
+	"io"   // a
+	"os"   // b
+	"utf8" // c
+)
+`,
+		out: `package main
+
+import (
+	"io" // a
+	"os" // b
+	// c
+)
+`,
+	},
+	{
+		name: "import.10",
+		pkg:  "io",
+		in: `package main
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		out: `package main
+
+import (
+	"os"
+	"utf8"
+)
+`,
+	},
+	{
+		name: "import.11",
+		pkg:  "os",
+		in: `package main
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		out: `package main
+
+import (
+	"io"
+	"utf8"
+)
+`,
+	},
+	{
+		name: "import.12",
+		pkg:  "utf8",
+		in: `package main
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		out: `package main
+
+import (
+	"io"
+	"os"
+)
+`,
+	},
+}
+
+func TestDeleteImport(t *testing.T) {
+	for _, test := range deleteTests {
+		file := parse(t, test.name, test.in)
+		DeleteImport(file, test.pkg)
+		if got := print(t, test.name, file); got != test.out {
+			t.Errorf("%s:\ngot: %s\nwant: %s", test.name, got, test.out)
+		}
+	}
+}
+
+type rewriteTest struct {
+	name   string
+	srcPkg string
+	dstPkg string
+	in     string
+	out    string
+}
+
+var rewriteTests = []rewriteTest{
+	{
+		name:   "import.13",
+		srcPkg: "utf8",
+		dstPkg: "encoding/utf8",
+		in: `package main
+
+import (
+	"io"
+	"os"
+	"utf8" // thanks ken
+)
+`,
+		out: `package main
+
+import (
+	"encoding/utf8" // thanks ken
+	"io"
+	"os"
+)
+`,
+	},
+	{
+		name:   "import.14",
+		srcPkg: "asn1",
+		dstPkg: "encoding/asn1",
+		in: `package main
+
+import (
+	"asn1"
+	"crypto"
+	"crypto/rsa"
+	_ "crypto/sha1"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"time"
+)
+
+var x = 1
+`,
+		out: `package main
+
+import (
+	"crypto"
+	"crypto/rsa"
+	_ "crypto/sha1"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"time"
+)
+
+var x = 1
+`,
+	},
+	{
+		name:   "import.15",
+		srcPkg: "url",
+		dstPkg: "net/url",
+		in: `package main
+
+import (
+	"bufio"
+	"net"
+	"path"
+	"url"
+)
+
+var x = 1 // comment on x, not on url
+`,
+		out: `package main
+
+import (
+	"bufio"
+	"net"
+	"net/url"
+	"path"
+)
+
+var x = 1 // comment on x, not on url
+`,
+	},
+	{
+		name:   "import.16",
+		srcPkg: "http",
+		dstPkg: "net/http",
+		in: `package main
+
+import (
+	"flag"
+	"http"
+	"log"
+	"text/template"
+)
+
+var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18
+`,
+		out: `package main
+
+import (
+	"flag"
+	"log"
+	"net/http"
+	"text/template"
+)
+
+var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18
+`,
+	},
+}
+
+func TestRewriteImport(t *testing.T) {
+	for _, test := range rewriteTests {
+		file := parse(t, test.name, test.in)
+		RewriteImport(file, test.srcPkg, test.dstPkg)
+		if got := print(t, test.name, file); got != test.out {
+			t.Errorf("%s:\ngot: %s\nwant: %s", test.name, got, test.out)
+		}
+	}
+}