Spawing external diff fails with 'Bad file descriptor'

[John A Meinel]

For an unknown reason, when running

'bzr diff --diff-options -b'

We get this error:
=== modified file 'bzrlib/transport/sftp.py'
diff: standard output: Bad file descriptor
bzr: ERROR: external diff failed with 2; command: ['diff', '--label', u'bzrlib/transport/sftp.py\t2006-07-28 16:52:19 +0000', '/tmp/bzr-diff-old-hA9Pci', '--label', u'bzrlib/transport/sftp.py\t2006-07-30 13:38:00 +0000', '/tmp/bzr-diff-new-SCWKi9', '--binary', '-u', '-b']

Looking closer, I can tell we are passing stdout as the file descriptor (fileno() == 1).
It seems we have to be doing something weird to stdout to cause it to complain that it is a bad file descriptor.

This probably should block 0.9, since it means external diff support is broken.

[John A Meinel (jameinel)]

There is a bug in subprocess where it closes the original stdin/stdout/etc if you pass in an alternative one.
So if you pass in the real stdin, it gets closed.
Found by Adeodato Simó.

[John A Meinel (jameinel)]

Adding a patch to subprocess.py that seems to fix the python module. (Written by Adeodato Simó)

[John A Meinel (jameinel)]

A possible patch against bzr, which works around the bug by passing in None, if it detects that it would otherwise pass in stdout. Also written by Adeodato Simó.

[John A Meinel (jameinel)]

The associated branch contains a test and a fix