gofmt: add -diff

Some code duplication with gofix.

R=rsc, gri, bradfitzgo, r2, adg, peterGo, r, brainman
CC=golang-dev
https://golang.org/cl/4430054

diff --git a/src/cmd/gofmt/gofmt.go b/src/cmd/gofmt/gofmt.go
index ce274aa21b16c7a824efc0f7356ccb045abed328..953a6dcd6b4a92e493824f688a53c46e55b10a00 100644 (file)
--- a/src/cmd/gofmt/gofmt.go
+++ b/src/cmd/gofmt/gofmt.go
@@ -6,6 +6,7 @@ package main
 
 import (
        "bytes"
+       "exec"
        "flag"
        "fmt"
        "go/ast"
@@ -28,6 +29,7 @@ var (
        write       = flag.Bool("w", false, "write result to (source) file instead of stdout")
        rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'α[β:len(α)] -> α[β:]')")
        simplifyAST = flag.Bool("s", false, "simplify code")
+       doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
 
        // layout control
        comments  = flag.Bool("comments", true, "print comments")
@@ -134,9 +136,17 @@ func processFile(filename string, in io.Reader, out io.Writer) os.Error {
                                return err
                        }
                }
+               if *doDiff {
+                       data, err := diff(src, res)
+                       if err != nil {
+                               return fmt.Errorf("computing diff: %s", err)
+                       }
+                       fmt.Printf("diff %s fixed/%s\n", filename, filename)
+                       out.Write(data)
+               }
        }
 
-       if !*list && !*write {
+       if !*list && !*write && !*doDiff {
                _, err = out.Write(res)
        }
 
@@ -230,3 +240,37 @@ func gofmtMain() {
                }
        }
 }
+
+
+func diff(b1, b2 []byte) (data []byte, err os.Error) {
+       f1, err := ioutil.TempFile("", "gofmt")
+       if err != nil {
+               return nil, err
+       }
+       defer os.Remove(f1.Name())
+       defer f1.Close()
+
+       f2, err := ioutil.TempFile("", "gofmt")
+       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", "-u", 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)
+}