gofix: add a fix for hash.Sum.

This fix adds an output argument to hash.Sum.

Tree changes in https://golang.org/cl/5448065

R=rsc
CC=golang-dev
https://golang.org/cl/5450051

src/cmd/gofix/Makefile

@@ -10,6 +10,7 @@ GOFILES=\
 	filepath.go\
 	fix.go\
 	go1pkgrename.go\
+	hashsum.go\
 	htmlerr.go\
 	httpfinalurl.go\
 	httpfs.go\

src/cmd/gofix/hashsum.go

@@ -0,0 +1,94 @@
+// 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 main
+
+import (
+	"go/ast"
+)
+
+func init() {
+	register(hashSumFix)
+}
+
+var hashSumFix = fix{
+	"hashsum",
+	"2011-11-30",
+	hashSumFn,
+	`Pass a nil argument to calls to hash.Sum
+
+This fix rewrites code so that it passes a nil argument to hash.Sum.
+The additional argument will allow callers to avoid an
+allocation in the future.
+
+http://codereview.appspot.com/5448065
+`,
+}
+
+// Type-checking configuration: tell the type-checker this basic
+// information about types, functions, and variables in external packages.
+var hashSumTypeConfig = &TypeConfig{
+	Var: map[string]string{
+		"crypto.MD4":       "crypto.Hash",
+		"crypto.MD5":       "crypto.Hash",
+		"crypto.SHA1":      "crypto.Hash",
+		"crypto.SHA224":    "crypto.Hash",
+		"crypto.SHA256":    "crypto.Hash",
+		"crypto.SHA384":    "crypto.Hash",
+		"crypto.SHA512":    "crypto.Hash",
+		"crypto.MD5SHA1":   "crypto.Hash",
+		"crypto.RIPEMD160": "crypto.Hash",
+	},
+
+	Func: map[string]string{
+		"adler32.New":    "hash.Hash",
+		"crc32.New":      "hash.Hash",
+		"crc32.NewIEEE":  "hash.Hash",
+		"crc64.New":      "hash.Hash",
+		"fnv.New32a":     "hash.Hash",
+		"fnv.New32":      "hash.Hash",
+		"fnv.New64a":     "hash.Hash",
+		"fnv.New64":      "hash.Hash",
+		"hmac.New":       "hash.Hash",
+		"hmac.NewMD5":    "hash.Hash",
+		"hmac.NewSHA1":   "hash.Hash",
+		"hmac.NewSHA256": "hash.Hash",
+		"md4.New":        "hash.Hash",
+		"md5.New":        "hash.Hash",
+		"ripemd160.New":  "hash.Hash",
+		"sha1.New224":    "hash.Hash",
+		"sha1.New":       "hash.Hash",
+		"sha256.New224":  "hash.Hash",
+		"sha256.New":     "hash.Hash",
+		"sha512.New384":  "hash.Hash",
+		"sha512.New":     "hash.Hash",
+	},
+
+	Type: map[string]*Type{
+		"crypto.Hash": &Type{
+			Method: map[string]string{
+				"New": "func() hash.Hash",
+			},
+		},
+	},
+}
+
+func hashSumFn(f *ast.File) bool {
+	typeof, _ := typecheck(hashSumTypeConfig, f)
+
+	fixed := false
+
+	walk(f, func(n interface{}) {
+		call, ok := n.(*ast.CallExpr)
+		if ok && len(call.Args) == 0 {
+			sel, ok := call.Fun.(*ast.SelectorExpr)
+			if ok && sel.Sel.Name == "Sum" && typeof[sel.X] == "hash.Hash" {
+				call.Args = append(call.Args, ast.NewIdent("nil"))
+				fixed = true
+			}
+		}
+	})
+
+	return fixed
+}

src/cmd/gofix/hashsum_test.go

@@ -0,0 +1,99 @@
+// 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 main
+
+func init() {
+	addTestCases(hashSumTests, hashSumFn)
+}
+
+var hashSumTests = []testCase{
+	{
+		Name: "hashsum.0",
+		In: `package main
+
+import "crypto/sha256"
+
+func f() []byte {
+	h := sha256.New()
+	return h.Sum()
+}
+`,
+		Out: `package main
+
+import "crypto/sha256"
+
+func f() []byte {
+	h := sha256.New()
+	return h.Sum(nil)
+}
+`,
+	},
+
+	{
+		Name: "hashsum.1",
+		In: `package main
+
+func f(h hash.Hash) []byte {
+	return h.Sum()
+}
+`,
+		Out: `package main
+
+func f(h hash.Hash) []byte {
+	return h.Sum(nil)
+}
+`,
+	},
+
+	{
+		Name: "hashsum.0",
+		In: `package main
+
+import "crypto/sha256"
+
+func f() []byte {
+	h := sha256.New()
+	h.Write([]byte("foo"))
+	digest := h.Sum()
+}
+`,
+		Out: `package main
+
+import "crypto/sha256"
+
+func f() []byte {
+	h := sha256.New()
+	h.Write([]byte("foo"))
+	digest := h.Sum(nil)
+}
+`,
+	},
+
+	{
+		Name: "hashsum.0",
+		In: `package main
+
+import _ "crypto/sha256"
+import "crypto"
+
+func f() []byte {
+	hashType := crypto.SHA256
+	h := hashType.New()
+	digest := h.Sum()
+}
+`,
+		Out: `package main
+
+import _ "crypto/sha256"
+import "crypto"
+
+func f() []byte {
+	hashType := crypto.SHA256
+	h := hashType.New()
+	digest := h.Sum(nil)
+}
+`,
+	},
+}