gofix: add -diff, various fixes and helpers

  * add -diff command line option
  * use scoping information in refersTo, isPkgDot, isPtrPkgDot.
  * add new scoping-based helpers countUses, rewriteUses, assignsTo, isTopName.
  * rename rewrite to walk, add walkBeforeAfter.
  * add toy typechecker, a placeholder for go/types

R=gri
CC=golang-dev
https://golang.org/cl/4285053

src/cmd/gofix/httpserver.go

@@ -41,7 +41,7 @@ func httpserver(f *ast.File) bool {
 		if !ok {
 			continue
 		}
-		rewrite(fn.Body, func(n interface{}) {
+		walk(fn.Body, func(n interface{}) {
 			// Want to replace expression sometimes,
 			// so record pointer to it for updating below.
 			ptr, ok := n.(*ast.Expr)

src/cmd/gofix/main.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"bytes"
+	"exec"
 	"flag"
 	"fmt"
 	"go/parser"
@@ -29,8 +30,10 @@ var allowedRewrites = flag.String("r", "",
 
 var allowed map[string]bool
 
+var doDiff = flag.Bool("diff", false, "display diffs instead of rewriting files")
+
 func usage() {
-	fmt.Fprintf(os.Stderr, "usage: gofix [-r fixname,...] [path ...]\n")
+	fmt.Fprintf(os.Stderr, "usage: gofix [-diff] [-r fixname,...] [path ...]\n")
 	flag.PrintDefaults()
 	fmt.Fprintf(os.Stderr, "\nAvailable rewrites are:\n")
 	for _, f := range fixes {
@@ -85,10 +88,16 @@ const (
 	printerMode = printer.TabIndent | printer.UseSpaces
 )
 
+var printConfig = &printer.Config{
+	printerMode,
+	tabWidth,
+}
 
 func processFile(filename string, useStdin bool) os.Error {
 	var f *os.File
 	var err os.Error
+	var fixlog bytes.Buffer
+	var buf bytes.Buffer
 
 	if useStdin {
 		f = os.Stdin
@@ -110,34 +119,77 @@ func processFile(filename string, useStdin bool) os.Error {
 		return err
 	}
 
+	// Apply all fixes to file.
+	newFile := file
 	fixed := false
-	var buf bytes.Buffer
 	for _, fix := range fixes {
 		if allowed != nil && !allowed[fix.desc] {
 			continue
 		}
-		if fix.f(file) {
+		if fix.f(newFile) {
 			fixed = true
-			fmt.Fprintf(&buf, " %s", fix.name)
+			fmt.Fprintf(&fixlog, " %s", fix.name)
+
+			// AST changed.
+			// Print and parse, to update any missing scoping
+			// or position information for subsequent fixers.
+			buf.Reset()
+			_, err = printConfig.Fprint(&buf, fset, newFile)
+			if err != nil {
+				return err
+			}
+			newSrc := buf.Bytes()
+			newFile, err = parser.ParseFile(fset, filename, newSrc, parserMode)
+			if err != nil {
+				return err
+			}
 		}
 	}
 	if !fixed {
 		return nil
 	}
-	fmt.Fprintf(os.Stderr, "%s: fixed %s\n", filename, buf.String()[1:])
+	fmt.Fprintf(os.Stderr, "%s: fixed %s\n", filename, fixlog.String()[1:])
 
+	// Print AST.  We did that after each fix, so this appears
+	// redundant, but it is necessary to generate gofmt-compatible
+	// source code in a few cases.  The official gofmt style is the
+	// output of the printer run on a standard AST generated by the parser,
+	// but the source we generated inside the loop above is the
+	// output of the printer run on a mangled AST generated by a fixer.
 	buf.Reset()
-	_, err = (&printer.Config{printerMode, tabWidth}).Fprint(&buf, fset, file)
+	_, err = printConfig.Fprint(&buf, fset, newFile)
 	if err != nil {
 		return err
 	}
+	newSrc := buf.Bytes()
+
+	if *doDiff {
+		data, err := diff(src, newSrc)
+		if err != nil {
+			return fmt.Errorf("computing diff: %s", err)
+		}
+		fmt.Printf("diff %s fixed/%s\n", filename, filename)
+		os.Stdout.Write(data)
+		return nil
+	}
 
 	if useStdin {
-		os.Stdout.Write(buf.Bytes())
+		os.Stdout.Write(newSrc)
 		return nil
 	}
 
-	return ioutil.WriteFile(f.Name(), buf.Bytes(), 0)
+	return ioutil.WriteFile(f.Name(), newSrc, 0)
+}
+
+var gofmtBuf bytes.Buffer
+
+func gofmt(n interface{}) string {
+	gofmtBuf.Reset()
+	_, err := printConfig.Fprint(&gofmtBuf, fset, n)
+	if err != nil {
+		return "<" + err.String() + ">"
+	}
+	return gofmtBuf.String()
 }
 
 func report(err os.Error) {
@@ -177,3 +229,36 @@ func isGoFile(f *os.FileInfo) bool {
 	// ignore non-Go files
 	return f.IsRegular() && !strings.HasPrefix(f.Name, ".") && strings.HasSuffix(f.Name, ".go")
 }
+
+func diff(b1, b2 []byte) (data []byte, err os.Error) {
+	f1, err := ioutil.TempFile("", "gofix")
+	if err != nil {
+		return nil, err
+	}
+	defer os.Remove(f1.Name())
+	defer f1.Close()
+
+	f2, err := ioutil.TempFile("", "gofix")
+	if err != nil {
+		return nil, err
+	}
+	defer os.Remove(f2.Name())
+	defer f2.Close()
+
+	f1.Write(b1)
+	f2.Write(b2)
+
+	diffcmd, err := exec.LookPath("diff")
+	if err != nil {
+		return nil, err
+	}
+
+	c, err := exec.Run(diffcmd, []string{"diff", f1.Name(), f2.Name()}, nil, "",
+		exec.DevNull, exec.Pipe, exec.MergeWithStdout)
+	if err != nil {
+		return nil, err
+	}
+	defer c.Close()
+
+	return ioutil.ReadAll(c.Stdout)
+}

src/cmd/gofix/main_test.go

@@ -6,12 +6,10 @@ package main
 
 import (
 	"bytes"
-	"exec"
 	"go/ast"
 	"go/parser"
 	"go/printer"
-	"io/ioutil"
-	"os"
+	"strings"
 	"testing"
 )
 
@@ -28,6 +26,8 @@ func addTestCases(t []testCase) {
 	testCases = append(testCases, t...)
 }
 
+func fnop(*ast.File) bool { return false }
+
 func parseFixPrint(t *testing.T, fn func(*ast.File) bool, desc, in string) (out string, fixed, ok bool) {
 	file, err := parser.ParseFile(fset, desc, in, parserMode)
 	if err != nil {
@@ -42,7 +42,7 @@ func parseFixPrint(t *testing.T, fn func(*ast.File) bool, desc, in string) (out
 		t.Errorf("%s: printing: %v", desc, err)
 		return
 	}
-	if s := buf.String(); in != s {
+	if s := buf.String(); in != s && fn != fnop {
 		t.Errorf("%s: not gofmt-formatted.\n--- %s\n%s\n--- %s | gofmt\n%s",
 			desc, desc, in, desc, s)
 		tdiff(t, in, s)
@@ -77,8 +77,17 @@ func TestRewrite(t *testing.T) {
 			continue
 		}
 
+		// reformat to get printing right
+		out, _, ok = parseFixPrint(t, fnop, tt.Name, out)
+		if !ok {
+			continue
+		}
+
 		if out != tt.Out {
-			t.Errorf("%s: incorrect output.\n--- have\n%s\n--- want\n%s", tt.Name, out, tt.Out)
+			t.Errorf("%s: incorrect output.\n", tt.Name)
+			if !strings.HasPrefix(tt.Name, "testdata/") {
+				t.Errorf("--- have\n%s\n--- want\n%s", out, tt.Out)
+			}
 			tdiff(t, out, tt.Out)
 			continue
 		}
@@ -108,44 +117,10 @@ func TestRewrite(t *testing.T) {
 }
 
 func tdiff(t *testing.T, a, b string) {
-	f1, err := ioutil.TempFile("", "gofix")
-	if err != nil {
-		t.Error(err)
-		return
-	}
-	defer os.Remove(f1.Name())
-	defer f1.Close()
-
-	f2, err := ioutil.TempFile("", "gofix")
-	if err != nil {
-		t.Error(err)
-		return
-	}
-	defer os.Remove(f2.Name())
-	defer f2.Close()
-
-	f1.Write([]byte(a))
-	f2.Write([]byte(b))
-
-	diffcmd, err := exec.LookPath("diff")
-	if err != nil {
-		t.Error(err)
-		return
-	}
-
-	c, err := exec.Run(diffcmd, []string{"diff", f1.Name(), f2.Name()}, nil, "",
-		exec.DevNull, exec.Pipe, exec.MergeWithStdout)
+	data, err := diff([]byte(a), []byte(b))
 	if err != nil {
 		t.Error(err)
 		return
 	}
-	defer c.Close()
-
-	data, err := ioutil.ReadAll(c.Stdout)
-	if err != nil {
-		t.Error(err)
-		return
-	}
-
 	t.Error(string(data))
 }

src/cmd/gofix/netdial.go

@@ -47,7 +47,7 @@ func netdial(f *ast.File) bool {
 	}
 
 	fixed := false
-	rewrite(f, func(n interface{}) {
+	walk(f, func(n interface{}) {
 		call, ok := n.(*ast.CallExpr)
 		if !ok || !isPkgDot(call.Fun, "net", "Dial") || len(call.Args) != 3 {
 			return
@@ -70,7 +70,7 @@ func tlsdial(f *ast.File) bool {
 	}
 
 	fixed := false
-	rewrite(f, func(n interface{}) {
+	walk(f, func(n interface{}) {
 		call, ok := n.(*ast.CallExpr)
 		if !ok || !isPkgDot(call.Fun, "tls", "Dial") || len(call.Args) != 4 {
 			return
@@ -94,7 +94,7 @@ func netlookup(f *ast.File) bool {
 	}
 
 	fixed := false
-	rewrite(f, func(n interface{}) {
+	walk(f, func(n interface{}) {
 		as, ok := n.(*ast.AssignStmt)
 		if !ok || len(as.Lhs) != 3 || len(as.Rhs) != 1 {
 			return

src/cmd/gofix/osopen.go

@@ -27,7 +27,7 @@ func osopen(f *ast.File) bool {
 	}
 
 	fixed := false
-	rewrite(f, func(n interface{}) {
+	walk(f, func(n interface{}) {
 		// Rename O_CREAT to O_CREATE.
 		if expr, ok := n.(ast.Expr); ok && isPkgDot(expr, "os", "O_CREAT") {
 			expr.(*ast.SelectorExpr).Sel.Name = "O_CREATE"

src/cmd/gofix/procattr.go

@@ -28,7 +28,7 @@ func procattr(f *ast.File) bool {
 	}
 
 	fixed := false
-	rewrite(f, func(n interface{}) {
+	walk(f, func(n interface{}) {
 		call, ok := n.(*ast.CallExpr)
 		if !ok || len(call.Args) != 5 {
 			return