diff --git a/src/cmd/godoc/index.go b/src/cmd/godoc/index.go
new file mode 100644
index 00000000000..1cd6c5ca5db
--- /dev/null
+++ b/src/cmd/godoc/index.go
@@ -0,0 +1,664 @@
+// Copyright 2009 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.
+
+// This file contains the infrastructure to create an
+// (identifier) index for a set of Go files.
+//
+// Basic indexing algorithm:
+// - traverse all .go files of the file tree specified by root
+// - for each word (identifier) encountered, collect all occurences (spots)
+//   into a list; this produces a list of spots for each word
+// - reduce the lists: from a list of spots to a list of FileRuns,
+//   and from a list of FileRuns into a list of PakRuns
+// - make a HitList from the PakRuns
+//
+// Details:
+// - keep two lists per word: one containing package-level declarations
+//   that have snippets, and one containing all other spots
+// - keep the snippets in a separate table indexed by snippet index
+//   and store the snippet index in place of the line number in a SpotInfo
+//   (the line number for spots with snippets is stored in the snippet)
+// - at the end, create lists of alternative spellings for a given
+//   word
+
+package main
+
+import (
+	"container/vector";
+	"go/ast";
+	"go/parser";
+	"go/token";
+	"os";
+	pathutil "path";
+	"sort";
+	"strings";
+)
+
+
+// ----------------------------------------------------------------------------
+// Data structures used during indexing
+
+// A RunList is a vector of entries that can be sorted according to some
+// criteria. A RunList may be compressed by grouping "runs" of entries
+// which are equal (according to the sort critera) into a new RunList of
+// runs. For instance, a RunList containing pairs (x, y) may be compressed
+// into a RunList containing pair runs (x, {y}) where each run consists of
+// a list of y's with the same x.
+type RunList struct {
+	vector.Vector;
+	less	func(x, y interface{}) bool;
+}
+
+func (h *RunList) Less(i, j int) bool {
+	return h.less(h.At(i), h.At(j));
+}
+
+
+func (h *RunList) sort(less func(x, y interface{}) bool) {
+	h.less = less;
+	sort.Sort(h);
+}
+
+
+// Compress entries which are the same according to a sort criteria
+// (specified by less) into "runs".
+func (h *RunList) reduce(less func(x, y interface{}) bool, newRun func(h *RunList, i, j int) interface{}) *RunList {
+	// create runs of entries with equal values
+	h.sort(less);
+
+	// for each run, make a new run object and collect them in a new RunList
+	var hh RunList;
+	i := 0;
+	for j := 0; j < h.Len(); j++ {
+		if less(h.At(i), h.At(j)) {
+			hh.Push(newRun(h, i, j));
+			i = j;	// start a new run
+		}
+	}
+	// add final run, if any
+	if i < h.Len() {
+		hh.Push(newRun(h, i, h.Len()));
+	}
+
+	return &hh;
+}
+
+
+// A SpotInfo value describes a particular identifier spot in a given file;
+// It encodes three values: the SpotKind (declaration or use), a line or
+// snippet index "lori", and whether it's a line or index.
+//
+// The following encoding is used:
+//
+//   bits    32   4    1       0
+//   value    [lori|kind|isIndex]
+//
+type SpotInfo uint32
+
+// SpotKind describes whether an identifier is declared (and what kind of
+// declaration) or used.
+type SpotKind uint32
+
+const (
+	ImportDecl	SpotKind	= iota;
+	ConstDecl;
+	TypeDecl;
+	VarDecl;
+	FuncDecl;
+	MethodDecl;
+	Use;
+	nKinds;
+)
+
+
+// makeSpotInfo makes a SpotInfo.
+func makeSpotInfo(kind SpotKind, lori int, isIndex bool) SpotInfo {
+	// encode lori: bits [4..32)
+	x := SpotInfo(lori)<<4;
+	if int(x>>4) != lori {
+		// lori value doesn't fit - since snippet indices are
+		// most certainly always smaller then 1<<28, this can
+		// only happen for line numbers; give it no line number (= 0)
+		x = 0;
+	}
+	// encode kind: bits [1..4)
+	x |= SpotInfo(kind)<<1;
+	// encode isIndex: bit 0
+	if isIndex {
+		x |= 1;
+	}
+	return x;
+}
+
+
+func (x SpotInfo) less(y SpotInfo) bool {
+	return x.Lori() < y.Lori();
+}
+
+
+func (x SpotInfo) Kind() SpotKind {
+	return SpotKind(x>>1&7);
+}
+
+
+func (x SpotInfo) Lori() int {
+	return int(x>>4);
+}
+
+
+func (x SpotInfo) IsIndex() bool {
+	return x&1 != 0;
+}
+
+
+// A Pak describes a Go package.
+type Pak struct {
+	Path	string;	// directory name containing the package
+	Name	string;	// package name as declared by package clause
+}
+
+
+func (p *Pak) less(q *Pak) bool {
+	return p.Path < q.Path || p.Name < q.Name;
+}
+
+
+// A File describes a Go file.
+type File struct {
+	Path	string;	// complete file name
+	Pak	Pak;	// the package to which the file belongs
+}
+
+
+func (f *File) less(g *File) bool {
+	return f.Path < g.Path;
+}
+
+
+// A Spot describes a single occurence of a word.
+type Spot struct {
+	File	*File;
+	Info	SpotInfo;
+}
+
+
+// Spots are sorted by filename.
+func lessSpot(x, y interface{}) bool {
+	return x.(Spot).File.less(y.(Spot).File);
+}
+
+
+// A FileRun describes a run of Spots of a word in a single file.
+type FileRun struct {
+	File	*File;
+	Infos	[]SpotInfo;
+}
+
+
+// newFileRun allocates a new *FileRun from the Spot run [i, j) in h.
+func newFileRun(h *RunList, i, j int) interface{} {
+	file := h.At(i).(Spot).File;
+	lines := make([]SpotInfo, j-i);
+	prev := 0;
+	k := 0;
+	for ; i < j; i++ {
+		info := h.At(i).(Spot).Info;
+		// ignore line duplicates
+		// (if lori is a snippet index it is unique - no need to check IsIndex())
+		lori := info.Lori();
+		if lori != prev {
+			lines[k] = info;
+			prev = lori;
+			k++;
+		}
+	}
+	return &FileRun{file, lines[0:k]};
+}
+
+
+// FileRuns are sorted by package.
+func lessFileRun(x, y interface{}) bool {
+	return x.(*FileRun).File.Pak.less(&y.(*FileRun).File.Pak);
+}
+
+
+// A PakRun describes a run of *FileRuns of a package.
+type PakRun struct {
+	Pak	Pak;
+	Files	[]*FileRun;
+}
+
+// Sorting support for files within a PakRun.
+func (p *PakRun) Len() int {
+	return len(p.Files);
+}
+func (p *PakRun) Less(i, j int) bool {
+	return p.Files[i].File.less(p.Files[j].File);
+}
+func (p *PakRun) Swap(i, j int) {
+	p.Files[i], p.Files[j] = p.Files[j], p.Files[i];
+}
+
+
+// newPakRun allocates a new *PakRun from the *FileRun run [i, j) in h.
+func newPakRun(h *RunList, i, j int) interface{} {
+	pak := h.At(i).(*FileRun).File.Pak;
+	files := make([]*FileRun, j-i);
+	k := 0;
+	for ; i < j; i++ {
+		files[k] = h.At(i).(*FileRun);
+		k++;
+	}
+	run := &PakRun{pak, files};
+	sort.Sort(run);	// files were sorted by package; sort them by file now
+	return run;
+}
+
+
+// PakRuns are sorted by package.
+func lessPakRun(x, y interface{}) bool {
+	return x.(*PakRun).Pak.less(&y.(*PakRun).Pak);
+}
+
+
+// A HitList describes a list of PakRuns.
+type HitList []*PakRun
+
+
+func reduce(h0 *RunList) HitList {
+	// reduce a list of Spots into a list of FileRuns
+	h1 := h0.reduce(lessSpot, newFileRun);
+	// reduce a list of FileRuns into a list of PakRuns
+	h2 := h1.reduce(lessFileRun, newPakRun);
+	// sort the list of PakRuns by package
+	h2.sort(lessPakRun);
+	// create a HitList
+	h := make(HitList, h2.Len());
+	for i := 0; i < h2.Len(); i++ {
+		h[i] = h2.At(i).(*PakRun);
+	}
+	return h;
+}
+
+
+func (h HitList) filter(pakname string) HitList {
+	// determine number of matching packages (most of the time just one)
+	n := 0;
+	for _, p := range h {
+		if p.Pak.Name == pakname {
+			n++;
+		}
+	}
+	// create filtered HitList
+	hh := make(HitList, n);
+	i := 0;
+	for _, p := range h {
+		if p.Pak.Name == pakname {
+			hh[i] = p;
+			i++;
+		}
+	}
+	return hh;
+}
+
+
+type wordPair struct {
+	canon	string;	// canonical word spelling (all lowercase)
+	alt	string;	// alternative spelling
+}
+
+
+// An AltWords describes a list of alternative spellings for a
+// canonical (all lowercase) spelling of a word.
+type AltWords struct {
+	Canon	string;		// canonical word spelling (all lowercase)
+	Alts	[]string;	// alternative spelling for the same word
+}
+
+
+func lessWordPair(x, y interface{}) bool {
+	return x.(*wordPair).canon < y.(*wordPair).canon;
+}
+
+
+// newAltWords allocates a new *AltWords from the *wordPair run [i, j) in h.
+func newAltWords(h *RunList, i, j int) interface{} {
+	canon := h.At(i).(*wordPair).canon;
+	alts := make([]string, j-i);
+	k := 0;
+	for ; i < j; i++ {
+		alts[k] = h.At(i).(*wordPair).alt;
+		k++;
+	}
+	return &AltWords{canon, alts};
+}
+
+
+func (a *AltWords) filter(s string) *AltWords {
+	if len(a.Alts) == 1 && a.Alts[0] == s {
+		// there are no different alternatives
+		return nil;
+	}
+
+	// make a new AltWords with the current spelling removed
+	alts := make([]string, len(a.Alts));
+	i := 0;
+	for _, w := range a.Alts {
+		if w != s {
+			alts[i] = w;
+			i++;
+		}
+	}
+	return &AltWords{a.Canon, alts[0:i]};
+}
+
+
+// ----------------------------------------------------------------------------
+// Indexer
+
+type IndexResult struct {
+	Decls	RunList;	// package-level declarations (with snippets)
+	Others	RunList;	// all other occurences
+}
+
+
+// An Indexer maintains the data structures and provides the machinery
+// for indexing .go files under a file tree. It implements the path.Visitor
+// interface for walking file trees, and the ast.Visitor interface for
+// walking Go ASTs.
+type Indexer struct {
+	words		map[string]*IndexResult;	// RunLists of Spots
+	snippets	vector.Vector;			// vector of *Snippets, indexed by snippet indices
+	file		*File;				// current file
+	decl		ast.Decl;			// current decl
+	nspots		int;				// number of spots encountered
+}
+
+
+func (x *Indexer) addSnippet(s *Snippet) int {
+	index := x.snippets.Len();
+	x.snippets.Push(s);
+	return index;
+}
+
+
+func (x *Indexer) visitComment(c *ast.CommentGroup) {
+	if c != nil {
+		ast.Walk(x, c);
+	}
+}
+
+
+func (x *Indexer) visitIdent(kind SpotKind, id *ast.Ident) {
+	if id != nil {
+		lists, found := x.words[id.Value];
+		if !found {
+			lists = new(IndexResult);
+			x.words[id.Value] = lists;
+		}
+
+		if kind == Use || x.decl == nil {
+			// not a declaration or no snippet required
+			info := makeSpotInfo(kind, id.Pos().Line, false);
+			lists.Others.Push(Spot{x.file, info});
+		} else {
+			// a declaration with snippet
+			index := x.addSnippet(NewSnippet(x.decl, id));
+			info := makeSpotInfo(kind, index, true);
+			lists.Decls.Push(Spot{x.file, info});
+		}
+
+		x.nspots++;
+	}
+}
+
+
+func (x *Indexer) visitSpec(spec ast.Spec, isVarDecl bool) {
+	switch n := spec.(type) {
+	case *ast.ImportSpec:
+		x.visitComment(n.Doc);
+		x.visitIdent(ImportDecl, n.Name);
+		for _, s := range n.Path {
+			ast.Walk(x, s);
+		}
+		x.visitComment(n.Comment);
+
+	case *ast.ValueSpec:
+		x.visitComment(n.Doc);
+		kind := ConstDecl;
+		if isVarDecl {
+			kind = VarDecl;
+		}
+		for _, n := range n.Names {
+			x.visitIdent(kind, n);
+		}
+		ast.Walk(x, n.Type);
+		for _, v := range n.Values {
+			ast.Walk(x, v);
+		}
+		x.visitComment(n.Comment);
+
+	case *ast.TypeSpec:
+		x.visitComment(n.Doc);
+		x.visitIdent(TypeDecl, n.Name);
+		ast.Walk(x, n.Type);
+		x.visitComment(n.Comment);
+	}
+}
+
+
+func (x *Indexer) Visit(node interface{}) bool {
+	// TODO(gri): methods in interface types are categorized as VarDecl
+	switch n := node.(type) {
+	case *ast.Ident:
+		x.visitIdent(Use, n);
+
+	case *ast.Field:
+		x.decl = nil;	// no snippets for fields
+		x.visitComment(n.Doc);
+		for _, m := range n.Names {
+			x.visitIdent(VarDecl, m);
+		}
+		ast.Walk(x, n.Type);
+		for _, s := range n.Tag {
+			ast.Walk(x, s);
+		}
+		x.visitComment(n.Comment);
+
+	case *ast.DeclStmt:
+		if decl, ok := n.Decl.(*ast.GenDecl); ok {
+			// local declarations can only be *ast.GenDecls
+			x.decl = nil;	// no snippets for local declarations
+			x.visitComment(decl.Doc);
+			for _, s := range decl.Specs {
+				x.visitSpec(s, decl.Tok == token.VAR);
+			}
+		} else {
+			// handle error case gracefully
+			ast.Walk(x, n.Decl);
+		}
+
+	case *ast.GenDecl:
+		x.decl = n;
+		x.visitComment(n.Doc);
+		for _, s := range n.Specs {
+			x.visitSpec(s, n.Tok == token.VAR);
+		}
+
+	case *ast.FuncDecl:
+		x.visitComment(n.Doc);
+		kind := FuncDecl;
+		if n.Recv != nil {
+			kind = MethodDecl;
+			ast.Walk(x, n.Recv);
+		}
+		x.decl = n;
+		x.visitIdent(kind, n.Name);
+		ast.Walk(x, n.Type);
+		if n.Body != nil {
+			ast.Walk(x, n.Type);
+		}
+
+	default:
+		return true;
+	}
+
+	return false;
+}
+
+
+func (x *Indexer) VisitDir(path string, d *os.Dir) bool {
+	return true;
+}
+
+
+func (x *Indexer) VisitFile(path string, d *os.Dir) {
+	if !isGoFile(d) {
+		return;
+	}
+
+	file, err := parser.ParseFile(path, nil, parser.ParseComments);
+	if err != nil {
+		return;	// ignore files with (parse) errors
+	}
+
+	dir, _ := pathutil.Split(path);
+	pak := Pak{dir, file.Name.Value};
+	x.file = &File{path, pak};
+	ast.Walk(x, file);
+}
+
+
+// ----------------------------------------------------------------------------
+// Index
+
+type LookupResult struct {
+	Decls	HitList;	// package-level declarations (with snippets)
+	Others	HitList;	// all other occurences
+}
+
+
+type Index struct {
+	words		map[string]*LookupResult;	// maps words to hit lists
+	alts		map[string]*AltWords;		// maps canonical(words) to lists of alternative spellings
+	snippets	[]*Snippet;			// all snippets, indexed by snippet index
+	nspots		int;				// number of spots indexed (a measure of the index size)
+}
+
+
+func canonical(w string) string {
+	return strings.ToLower(w);
+}
+
+
+// NewIndex creates a new index for the file tree rooted at root.
+func NewIndex(root string) *Index {
+	var x Indexer;
+
+	// initialize Indexer
+	x.words = make(map[string]*IndexResult);
+
+	// collect all Spots
+	pathutil.Walk(root, &x, nil);
+
+	// for each word, reduce the RunLists into a LookupResult;
+	// also collect the word with its canonical spelling in a
+	// word list for later computation of alternative spellings
+	words := make(map[string]*LookupResult);
+	var wlist RunList;
+	for w, h := range x.words {
+		decls := reduce(&h.Decls);
+		others := reduce(&h.Others);
+		words[w] = &LookupResult{
+			Decls: decls,
+			Others: others,
+		};
+		wlist.Push(&wordPair{canonical(w), w});
+	}
+
+	// reduce the word list {canonical(w), w} into
+	// a list of AltWords runs {canonical(w), {w}}
+	alist := wlist.reduce(lessWordPair, newAltWords);
+
+	// convert alist into a map of alternative spellings
+	alts := make(map[string]*AltWords);
+	for i := 0; i < alist.Len(); i++ {
+		a := alist.At(i).(*AltWords);
+		alts[a.Canon] = a;
+	}
+
+	// convert snippet vector into a list
+	snippets := make([]*Snippet, x.snippets.Len());
+	for i := 0; i < x.snippets.Len(); i++ {
+		snippets[i] = x.snippets.At(i).(*Snippet);
+	}
+
+	return &Index{words, alts, snippets, x.nspots};
+}
+
+
+// Size returns the number of different words and
+// spots indexed as a measure for the index size.
+func (x *Index) Size() (nwords int, nspots int) {
+	return len(x.words), x.nspots;
+}
+
+
+func (x *Index) LookupWord(w string) (match *LookupResult, alt *AltWords) {
+	match, _ = x.words[w];
+	alt, _ = x.alts[canonical(w)];
+	// remove current spelling from alternatives
+	// (if there is no match, the alternatives do
+	// not contain the current spelling)
+	if match != nil && alt != nil {
+		alt = alt.filter(w);
+	}
+	return;
+}
+
+
+// For a given string s, which is either a single identifier or a qualified
+// identifier, Lookup returns a LookupResult, and a list of alternative
+// spellings, if any.
+func (x *Index) Lookup(s string) (match *LookupResult, alt *AltWords) {
+	ss := strings.Split(s, ".", 0);
+
+	switch len(ss) {
+	case 1:
+		match, alt = x.LookupWord(ss[0]);
+
+	case 2:
+		pakname := ss[0];
+		match, alt = x.LookupWord(ss[1]);
+		if match != nil {
+			// found a match - filter by package name
+			decls := match.Decls.filter(pakname);
+			others := match.Others.filter(pakname);
+			match = &LookupResult{decls, others};
+		}
+		if alt != nil {
+			// alternative spellings found - add package name
+			// TODO(gri): At the moment this is not very smart
+			// and likely will produce suggestions that have
+			// no match. Should filter incorrect alternatives.
+			canon := pakname + "." + alt.Canon;	// for completeness (currently not used)
+			alts := make([]string, len(alt.Alts));
+			for i, a := range alt.Alts {
+				alts[i] = pakname+"."+a;
+			}
+			alt = &AltWords{canon, alts};
+		}
+	}
+
+	return;
+}
+
+
+func (x *Index) Snippet(i int) *Snippet {
+	// handle illegal snippet indices gracefully
+	if 0 <= i && i < len(x.snippets) {
+		return x.snippets[i];
+	}
+	return nil;
+}