go/printer, gofmt: avoid exponential layout algorithm

Use memoization to avoid repeated recomputation of nested
node sizes. Speeds up testdata/slow.input by several orders
of magnitude.

- added respective test case
- added timeout to test code
- deleted some unrelated unused code

Fixes #1628.

R=rsc, r
CC=golang-dev
https://golang.org/cl/4274075

src/cmd/godoc/godoc.go

@@ -374,7 +374,7 @@ func writeNode(w io.Writer, fset *token.FileSet, x interface{}) {
 	//           with an another printer mode (which is more efficiently
 	//           implemented in the printer than here with another layer)
 	mode := printer.TabIndent | printer.UseSpaces
-	(&printer.Config{mode, *tabwidth}).Fprint(&tconv{output: w}, fset, x)
+	(&printer.Config{Mode: mode, Tabwidth: *tabwidth}).Fprint(&tconv{output: w}, fset, x)
 }
 
 

src/cmd/gofix/main.go

@@ -127,7 +127,7 @@ func processFile(filename string, useStdin bool) os.Error {
 	fmt.Fprintf(os.Stderr, "%s: %s\n", filename, buf.String()[1:])
 
 	buf.Reset()
-	_, err = (&printer.Config{printerMode, tabWidth}).Fprint(&buf, fset, file)
+	_, err = (&printer.Config{Mode: printerMode, Tabwidth: tabWidth}).Fprint(&buf, fset, file)
 	if err != nil {
 		return err
 	}

src/cmd/gofix/main_test.go

@@ -37,7 +37,7 @@ func parseFixPrint(t *testing.T, fn func(*ast.File) bool, desc, in string) (out
 
 	var buf bytes.Buffer
 	buf.Reset()
-	_, err = (&printer.Config{printerMode, tabWidth}).Fprint(&buf, fset, file)
+	_, err = (&printer.Config{Mode: printerMode, Tabwidth: tabWidth}).Fprint(&buf, fset, file)
 	if err != nil {
 		t.Errorf("%s: printing: %v", desc, err)
 		return
@@ -60,7 +60,7 @@ func parseFixPrint(t *testing.T, fn func(*ast.File) bool, desc, in string) (out
 	}
 
 	buf.Reset()
-	_, err = (&printer.Config{printerMode, tabWidth}).Fprint(&buf, fset, file)
+	_, err = (&printer.Config{Mode: printerMode, Tabwidth: tabWidth}).Fprint(&buf, fset, file)
 	if err != nil {
 		t.Errorf("%s: printing: %v", desc, err)
 		return

src/cmd/gofmt/gofmt.go

@@ -103,7 +103,7 @@ func processFile(f *os.File) os.Error {
 	}
 
 	var buf bytes.Buffer
-	_, err = (&printer.Config{printerMode, *tabWidth}).Fprint(&buf, fset, file)
+	_, err = (&printer.Config{Mode: printerMode, Tabwidth: *tabWidth}).Fprint(&buf, fset, file)
 	if err != nil {
 		return err
 	}

src/pkg/go/printer/nodes.go

@@ -108,17 +108,6 @@ func (p *printer) identList(list []*ast.Ident, indent bool, multiLine *bool) {
 }
 
 
-// Compute the key size of a key:value expression.
-// Returns 0 if the expression doesn't fit onto a single line.
-func (p *printer) keySize(pair *ast.KeyValueExpr) int {
-	if p.nodeSize(pair, infinity) <= infinity {
-		// entire expression fits on one line - return key size
-		return p.nodeSize(pair.Key, infinity)
-	}
-	return 0
-}
-
-
 // Print a list of expressions. If the list spans multiple
 // source lines, the original line breaks are respected between
 // expressions. Sets multiLine to true if the list spans multiple
@@ -1324,11 +1313,21 @@ func (p *printer) genDecl(d *ast.GenDecl, multiLine *bool) {
 // any control chars. Otherwise, the result is > maxSize.
 //
 func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
+	// nodeSize invokes the printer, which may invoke nodeSize
+	// recursively. For deep composite literal nests, this can
+	// lead to an exponential algorithm. Remember previous
+	// results to prune the recursion (was issue 1628).
+	if size, found := p.nodeSizes[n]; found {
+		return size
+	}
+
 	size = maxSize + 1 // assume n doesn't fit
+	p.nodeSizes[n] = size
+
 	// nodeSize computation must be indendent of particular
 	// style so that we always get the same decision; print
 	// in RawFormat
-	cfg := Config{Mode: RawFormat}
+	cfg := Config{Mode: RawFormat, nodeSizes: p.nodeSizes}
 	var buf bytes.Buffer
 	if _, err := cfg.Fprint(&buf, p.fset, n); err != nil {
 		return
@@ -1340,6 +1339,7 @@ func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
 			}
 		}
 		size = buf.Len() // n fits
+		p.nodeSizes[n] = size
 	}
 	return
 }

src/pkg/go/printer/printer.go

@@ -94,9 +94,6 @@ type printer struct {
 	// written using writeItem.
 	last token.Position
 
-	// HTML support
-	lastTaggedLine int // last line for which a line tag was written
-
 	// The list of all source comments, in order of appearance.
 	comments        []*ast.CommentGroup // may be nil
 	cindex          int                 // current comment index
@@ -989,8 +986,9 @@ const (
 
 // A Config node controls the output of Fprint.
 type Config struct {
-	Mode     uint // default: 0
-	Tabwidth int  // default: 8
+	Mode      uint             // default: 0
+	Tabwidth  int              // default: 8
+	nodeSizes map[ast.Node]int // memoized node sizes as computed by nodeSize
 }
 
 
@@ -1001,6 +999,12 @@ type Config struct {
 // ast.Decl, ast.Spec, or ast.Stmt.
 //
 func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) (int, os.Error) {
+	// only if Fprint is called recursively (via nodeSize)
+	// does cfg.nodeSizes exist - set it up otherwise
+	if cfg.nodeSizes == nil {
+		cfg.nodeSizes = make(map[ast.Node]int)
+	}
+
 	// redirect output through a trimmer to eliminate trailing whitespace
 	// (Input to a tabwriter must be untrimmed since trailing tabs provide
 	// formatting information. The tabwriter could provide trimming

src/pkg/go/printer/printer_test.go

@@ -13,6 +13,7 @@ import (
 	"go/token"
 	"path/filepath"
 	"testing"
+	"time"
 )
 
 
@@ -45,7 +46,7 @@ const (
 )
 
 
-func check(t *testing.T, source, golden string, mode checkMode) {
+func runcheck(t *testing.T, source, golden string, mode checkMode) {
 	// parse source
 	prog, err := parser.ParseFile(fset, source, nil, parser.ParseComments)
 	if err != nil {
@@ -109,6 +110,32 @@ func check(t *testing.T, source, golden string, mode checkMode) {
 }
 
 
+func check(t *testing.T, source, golden string, mode checkMode) {
+	// start a timer to produce a time-out signal
+	tc := make(chan int)
+	go func() {
+		time.Sleep(2e9) // plenty of a safety margin, even for very slow machines
+		tc <- 0
+	}()
+
+	// run the test
+	cc := make(chan int)
+	go func() {
+		runcheck(t, source, golden, mode)
+		cc <- 0
+	}()
+
+	// wait for the first finisher
+	select {
+	case <-tc:
+		// test running past time out
+		t.Errorf("%s: running too slowly", source)
+	case <-cc:
+		// test finished within alloted time margin
+	}
+}
+
+
 type entry struct {
 	source, golden string
 	mode           checkMode
@@ -124,6 +151,7 @@ var data = []entry{
 	{"expressions.input", "expressions.raw", rawFormat},
 	{"declarations.input", "declarations.golden", 0},
 	{"statements.input", "statements.golden", 0},
+	{"slow.input", "slow.golden", 0},
 }
 
 

src/pkg/go/printer/testdata/slow.golden

@@ -0,0 +1,85 @@
+// Copyright 2011 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 deepequal_test
+
+import (
+	"testing"
+	"google3/spam/archer/frontend/deepequal"
+)
+
+func TestTwoNilValues(t *testing.T) {
+	if err := deepequal.Check(nil, nil); err != nil {
+		t.Errorf("expected nil, saw %v", err)
+	}
+}
+
+type Foo struct {
+	bar	*Bar
+	bang	*Bar
+}
+
+type Bar struct {
+	baz	*Baz
+	foo	[]*Foo
+}
+
+type Baz struct {
+	entries		map[int]interface{}
+	whatever	string
+}
+
+func newFoo() *Foo {
+	return &Foo{bar: &Bar{baz: &Baz{
+		entries: map[int]interface{}{
+			42:	&Foo{},
+			21:	&Bar{},
+			11:	&Baz{whatever: "it's just a test"}}}},
+		bang: &Bar{foo: []*Foo{
+			&Foo{bar: &Bar{baz: &Baz{
+				entries: map[int]interface{}{
+					43:	&Foo{},
+					22:	&Bar{},
+					13:	&Baz{whatever: "this is nuts"}}}},
+				bang: &Bar{foo: []*Foo{
+					&Foo{bar: &Bar{baz: &Baz{
+						entries: map[int]interface{}{
+							61:	&Foo{},
+							71:	&Bar{},
+							11:	&Baz{whatever: "no, it's Go"}}}},
+						bang: &Bar{foo: []*Foo{
+							&Foo{bar: &Bar{baz: &Baz{
+								entries: map[int]interface{}{
+									0:	&Foo{},
+									-2:	&Bar{},
+									-11:	&Baz{whatever: "we need to go deeper"}}}},
+								bang: &Bar{foo: []*Foo{
+									&Foo{bar: &Bar{baz: &Baz{
+										entries: map[int]interface{}{
+											-2:	&Foo{},
+											-5:	&Bar{},
+											-7:	&Baz{whatever: "are you serious?"}}}},
+										bang:	&Bar{foo: []*Foo{}}},
+									&Foo{bar: &Bar{baz: &Baz{
+										entries: map[int]interface{}{
+											-100:	&Foo{},
+											50:	&Bar{},
+											20:	&Baz{whatever: "na, not really ..."}}}},
+										bang:	&Bar{foo: []*Foo{}}}}}}}}},
+					&Foo{bar: &Bar{baz: &Baz{
+						entries: map[int]interface{}{
+							2:	&Foo{},
+							1:	&Bar{},
+							-1:	&Baz{whatever: "... it's just a test."}}}},
+						bang:	&Bar{foo: []*Foo{}}}}}}}}}
+}
+
+func TestElaborate(t *testing.T) {
+	a := newFoo()
+	b := newFoo()
+
+	if err := deepequal.Check(a, b); err != nil {
+		t.Errorf("expected nil, saw %v", err)
+	}
+}

src/pkg/go/printer/testdata/slow.input

@@ -0,0 +1,85 @@
+// Copyright 2011 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 deepequal_test
+
+import (
+        "testing"
+        "google3/spam/archer/frontend/deepequal"
+)
+
+func TestTwoNilValues(t *testing.T) {
+        if err := deepequal.Check(nil, nil); err != nil {
+                t.Errorf("expected nil, saw %v", err)
+        }
+}
+
+type Foo struct {
+        bar *Bar
+        bang *Bar
+}
+
+type Bar struct {
+        baz *Baz
+        foo []*Foo
+}
+
+type Baz struct {
+        entries  map[int]interface{}
+        whatever string
+}
+
+func newFoo() (*Foo) {
+return &Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+42: &Foo{},
+21: &Bar{},
+11: &Baz{ whatever: "it's just a test" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+43: &Foo{},
+22: &Bar{},
+13: &Baz{ whatever: "this is nuts" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+61: &Foo{},
+71: &Bar{},
+11: &Baz{ whatever: "no, it's Go" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+0: &Foo{},
+-2: &Bar{},
+-11: &Baz{ whatever: "we need to go deeper" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+-2: &Foo{},
+-5: &Bar{},
+-7: &Baz{ whatever: "are you serious?" }}}},
+        bang: &Bar{foo: []*Foo{}}},
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+-100: &Foo{},
+50: &Bar{},
+20: &Baz{ whatever: "na, not really ..." }}}},
+        bang: &Bar{foo: []*Foo{}}}}}}}}},
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+2: &Foo{},
+1: &Bar{},
+-1: &Baz{ whatever: "... it's just a test." }}}},
+        bang: &Bar{foo: []*Foo{}}}}}}}}}
+}
+
+func TestElaborate(t *testing.T) {
+        a := newFoo()
+        b := newFoo()
+
+        if err := deepequal.Check(a, b); err != nil {
+                t.Errorf("expected nil, saw %v", err)
+        }
+}