fix: add fix for bufio, gzip, zlib NewWriterXxx changes.

Fixes #2979.

R=rsc, r
CC=golang-dev
https://golang.org/cl/5664046

doc/go1.html

@@ -578,7 +578,7 @@ If they are installed, they now reside in <code>$GOROOT/bin/tool</code>.
 <em>Updating</em>:
 Code that uses packages in <code>exp</code> will need to be updated by hand,
 or else compiled from an installation that has <code>exp</code> available.
-The go fix tool or the compiler will complain about such uses.
+The <code>go fix</code> tool or the compiler will complain about such uses.
 </p>
 
 <h3 id="old">The package tree old</h3>
@@ -603,7 +603,7 @@ The packages in their new locations are:
 <em>Updating</em>:
 Code that uses packages now in <code>old</code> will need to be updated by hand,
 or else compiled from an installation that has <code>old</code> available.
-The go fix tool will warn about such uses.
+The <code>go fix</code> tool will warn about such uses.
 </p>
 
 <h3 id="deleted">Deleted packages</h3>
@@ -863,8 +863,8 @@ longer has a <code>Write</code> method. Its presence was a mistake.
 </p>
 
 <p>
-<i>Updating:</i> What little code is affected will be caught by the compiler
-and must be updated by hand. Such code is almost certainly incorrect.
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="bufio">The bufio package</h3>
@@ -879,7 +879,8 @@ If the argument size is too small or invalid, it is adjusted.
 
 <p>
 <em>Updating</em>:
-What little code is affected will be caught by the compiler and must be updated by hand.
+Running <code>go fix</code> will update calls that assign the error to _.
+Calls that aren't fixed will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="bufio">The compress/flate, compress/gzip and compress/zlib packages</h3>
@@ -898,7 +899,8 @@ to <code>Writer</code> and <code>Reader</code>. Package <code>flate</code>'s
 
 <p>
 <em>Updating</em>
-What little code is affected will be caught by the compiler and must be updated by hand.
+Running <code>go fix</code> will update old names and calls that assign the error to _.
+Calls that aren't fixed will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="crypto_aes_des">The crypto/aes and crypto/des packages</h3>
@@ -1425,8 +1427,10 @@ now takes a <code>uintptr</code> fd, instead of an <code>int</code>.
 The <a href="/pkg/os/#File.Fd"><code>Fd</code></a> method on files now
 also returns a <code>uintptr</code>.</p>
 
-<p><em>Updating</em>: Code will fail to compile and must be updated
-by hand.  </p>
+<p>
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
+</p>
 
 <h4 id="os_fileinfo">The os.FileInfo type</h4>
 
@@ -1669,7 +1673,7 @@ Running <code>go fix</code> will update almost all code affected by the change.
 <br>
 § <code>Atoi</code> persists but <code>Atoui</code> and <code>Atof32</code> do not, so
 they may require
-a cast that must be added by hand; the go fix tool will warn about it.
+a cast that must be added by hand; the <code>go fix</code> tool will warn about it.
 </p>
 
 

doc/go1.tmpl

@@ -502,7 +502,7 @@ If they are installed, they now reside in <code>$GOROOT/bin/tool</code>.
 <em>Updating</em>:
 Code that uses packages in <code>exp</code> will need to be updated by hand,
 or else compiled from an installation that has <code>exp</code> available.
-The go fix tool or the compiler will complain about such uses.
+The <code>go fix</code> tool or the compiler will complain about such uses.
 </p>
 
 <h3 id="old">The package tree old</h3>
@@ -527,7 +527,7 @@ The packages in their new locations are:
 <em>Updating</em>:
 Code that uses packages now in <code>old</code> will need to be updated by hand,
 or else compiled from an installation that has <code>old</code> available.
-The go fix tool will warn about such uses.
+The <code>go fix</code> tool will warn about such uses.
 </p>
 
 <h3 id="deleted">Deleted packages</h3>
@@ -767,8 +767,8 @@ longer has a <code>Write</code> method. Its presence was a mistake.
 </p>
 
 <p>
-<i>Updating:</i> What little code is affected will be caught by the compiler
-and must be updated by hand. Such code is almost certainly incorrect.
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="bufio">The bufio package</h3>
@@ -783,7 +783,8 @@ If the argument size is too small or invalid, it is adjusted.
 
 <p>
 <em>Updating</em>:
-What little code is affected will be caught by the compiler and must be updated by hand.
+Running <code>go fix</code> will update calls that assign the error to _.
+Calls that aren't fixed will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="bufio">The compress/flate, compress/gzip and compress/zlib packages</h3>
@@ -802,7 +803,8 @@ to <code>Writer</code> and <code>Reader</code>. Package <code>flate</code>'s
 
 <p>
 <em>Updating</em>
-What little code is affected will be caught by the compiler and must be updated by hand.
+Running <code>go fix</code> will update old names and calls that assign the error to _.
+Calls that aren't fixed will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="crypto_aes_des">The crypto/aes and crypto/des packages</h3>
@@ -1328,8 +1330,10 @@ now takes a <code>uintptr</code> fd, instead of an <code>int</code>.
 The <a href="/pkg/os/#File.Fd"><code>Fd</code></a> method on files now
 also returns a <code>uintptr</code>.</p>
 
-<p><em>Updating</em>: Code will fail to compile and must be updated
-by hand.  </p>
+<p>
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
+</p>
 
 <h4 id="os_fileinfo">The os.FileInfo type</h4>
 
@@ -1572,7 +1576,7 @@ Running <code>go fix</code> will update almost all code affected by the change.
 <br>
 § <code>Atoi</code> persists but <code>Atoui</code> and <code>Atof32</code> do not, so
 they may require
-a cast that must be added by hand; the go fix tool will warn about it.
+a cast that must be added by hand; the <code>go fix</code> tool will warn about it.
 </p>
 
 

src/cmd/fix/newwriter.go

@@ -0,0 +1,90 @@
+// Copyright 2012 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 main
+
+import (
+	"go/ast"
+)
+
+func init() {
+	register(newWriterFix)
+}
+
+var newWriterFix = fix{
+	"newWriter",
+	"2012-02-14",
+	newWriter,
+	`Adapt bufio, gzip and zlib NewWriterXxx calls for whether they return errors.
+
+Also rename gzip.Compressor and gzip.Decompressor to gzip.Writer and gzip.Reader.
+
+http://codereview.appspot.com/5639057 and
+http://codereview.appspot.com/5642054
+`,
+}
+
+func newWriter(f *ast.File) bool {
+	if !imports(f, "bufio") && !imports(f, "compress/gzip") && !imports(f, "compress/zlib") {
+		return false
+	}
+
+	fixed := false
+	walk(f, func(n interface{}) {
+		switch n := n.(type) {
+		case *ast.SelectorExpr:
+			if isTopName(n.X, "gzip") {
+				switch n.Sel.String() {
+				case "Compressor":
+					n.Sel = &ast.Ident{Name: "Writer"}
+					fixed = true
+				case "Decompressor":
+					n.Sel = &ast.Ident{Name: "Reader"}
+					fixed = true
+				}
+			} else if isTopName(n.X, "zlib") {
+				if n.Sel.String() == "NewWriterDict" {
+					n.Sel = &ast.Ident{Name: "NewWriterLevelDict"}
+					fixed = true
+				}
+			}
+
+		case *ast.AssignStmt:
+			// Drop the ", _" in assignments of the form:
+			//	w0, _ = gzip.NewWriter(w1)
+			if len(n.Lhs) != 2 || len(n.Rhs) != 1 {
+				return
+			}
+			i, ok := n.Lhs[1].(*ast.Ident)
+			if !ok {
+				return
+			}
+			if i.String() != "_" {
+				return
+			}
+			c, ok := n.Rhs[0].(*ast.CallExpr)
+			if !ok {
+				return
+			}
+			s, ok := c.Fun.(*ast.SelectorExpr)
+			if !ok {
+				return
+			}
+			sel := s.Sel.String()
+			switch {
+			case isTopName(s.X, "bufio") && (sel == "NewReaderSize" || sel == "NewWriterSize"):
+				// No-op.
+			case isTopName(s.X, "gzip") && sel == "NewWriter":
+				// No-op.
+			case isTopName(s.X, "zlib") && sel == "NewWriter":
+				// No-op.
+			default:
+				return
+			}
+			n.Lhs = n.Lhs[:1]
+			fixed = true
+		}
+	})
+	return fixed
+}

src/cmd/fix/newwriter_test.go

@@ -0,0 +1,83 @@
+// Copyright 2012 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 main
+
+func init() {
+	addTestCases(newWriterTests, newWriter)
+}
+
+var newWriterTests = []testCase{
+	{
+		Name: "newWriter.0",
+		In: `package main
+
+import (
+	"bufio"
+	"compress/gzip"
+	"compress/zlib"
+	"io"
+
+	"foo"
+)
+
+func f() *gzip.Compressor {
+	var (
+		_ gzip.Compressor
+		_ *gzip.Decompressor
+		_ struct {
+			W *gzip.Compressor
+			R gzip.Decompressor
+		}
+	)
+
+	var w io.Writer
+	br := bufio.NewReader(nil)
+	br, _ = bufio.NewReaderSize(nil, 256)
+	bw, err := bufio.NewWriterSize(w, 256) // Unfixable, as it declares an err variable.
+	bw, _ = bufio.NewWriterSize(w, 256)
+	fw, _ := foo.NewWriter(w)
+	gw, _ := gzip.NewWriter(w)
+	gw, _ = gzip.NewWriter(w)
+	zw, _ := zlib.NewWriter(w)
+	_ = zlib.NewWriterDict(zw, 0, nil)
+	return gw
+}
+`,
+		Out: `package main
+
+import (
+	"bufio"
+	"compress/gzip"
+	"compress/zlib"
+	"io"
+
+	"foo"
+)
+
+func f() *gzip.Writer {
+	var (
+		_ gzip.Writer
+		_ *gzip.Reader
+		_ struct {
+			W *gzip.Writer
+			R gzip.Reader
+		}
+	)
+
+	var w io.Writer
+	br := bufio.NewReader(nil)
+	br = bufio.NewReaderSize(nil, 256)
+	bw, err := bufio.NewWriterSize(w, 256) // Unfixable, as it declares an err variable.
+	bw = bufio.NewWriterSize(w, 256)
+	fw, _ := foo.NewWriter(w)
+	gw := gzip.NewWriter(w)
+	gw = gzip.NewWriter(w)
+	zw := zlib.NewWriter(w)
+	_ = zlib.NewWriterLevelDict(zw, 0, nil)
+	return gw
+}
+`,
+	},
+}