"gofmt -d" is broken. (and "gofix -diff" too)

[gopherbot]

by fvbommel:

What steps will reproduce the problem?
1. Create a Go file that's not formatted right. For example:
===
package main

func main() {
return
}
===
(Note the lack of indentation before 'return')
2. Run 'gofmt -d' on it.
3. Wonder where your diff output is.

Bonus bug:
4) Create a Go file that contains something gofix would change, such as:
=====
package main

import "http"

func foo() (a, b interface{}) {
    resp, _, err := http.Get(url)
    return resp, err
}
=====
5) Run 'gofix -diff' on it.
6) Experience a deja-vu.

What is the expected output?
A diff between the on-disk version and the reformatted/fixed version, something like
this (for the gofmt example above):
=====
diff gofmt-test.go gofmt/gofmt-test.go
--- /tmp/gofmt793939221 2011-06-04 17:13:50.000000000 +0200
+++ /tmp/gofmt532065648 2011-06-04 17:13:50.000000000 +0200
@@ -1,5 +1,5 @@
 package main
 
 func main() {
-return
+   return
 }
=====

What do you see instead?
computing diff: exit status 1

Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
Ubuntu 10.10

Which revision are you using?  (hg identify)
3418f22c39eb weekly/weekly.2011-06-02
The current tip (0f1980acc591 tip) has the same issue.

Please provide any additional information below.
The diff program returns a non-zero exit status when it finds differences, and the
redesigned exec package returns this as a non-nil 'err', which makes gofmt and gofix
stop with an error before showing the diff output.

The diff() function in gofmt/gofmt.go should return a nil err instead of an *os.Waitmsg
indicating that the program exited with non-zero exit status.
gofix/main.go includes almost identical code (for gofix -diff), which is equally broken
and should be fixed the same way.

P.S. I also noticed that 'gofix -diff' doesn't pass '-u' to diff, but 'gofmt -d' does.

[rsc]

Comment 1:

Owner changed to @bradfitz.

Status changed to Accepted.

[bradfitz]

Comment 2:

This issue was closed by revision 687102e.

Status changed to Fixed.

[gopherbot]

Comment 3 by fvbommel:

That revision only fixes gofmt, not gofix.

[bradfitz]

Comment 4:

Oh, whoops.

[bradfitz]

Comment 5:

gofix is in
http://code.google.com/p/go/source/detail?r=4b41b2daf7a025efde197ab99fe8f6a920384c34