format-patch: do not respect diff.noprefix

The output of format-patch respects diff.noprefix, but this usually ends
up being a hassle for people receiving the patch, as they have to
manually specify "-p0" in order to apply it.

I don't think there was any specific intention for it to behave this
way. The noprefix option is handled by git_diff_ui_config(), and
format-patch exists in a gray area between plumbing and porcelain.
People do look at the output, and we'd expect it to colorize things,
respect their choice of algorithm, and so on. But this particular option
creates problems for the receiver (in theory so does diff.mnemonicprefix,
but since we are always formatting commits, the mnemonic prefixes will
always be "a/" and "b/").

So let's disable it. The slight downsides are:

  - people who have set diff.noprefix presumably like to see their
    patches without prefixes. If they use format-patch to review their
    series, they'll see prefixes. On the other hand, it is probably a
    good idea for them to look at what will actually get sent out.

    We could try to play games here with "is stdout a tty", as we do for
    color. But that's not a completely reliable signal, and it's
    probably not worth the trouble. If you want to see the patch with
    the usual bells and whistles, then you are better off using "git
    log" or "git show".

  - if a project really does have a workflow that likes prefix-less
    patches, and the receiver is prepared to use "-p0", then the sender
    now has to manually say "--no-prefix" for each format-patch
    invocation. That doesn't seem _too_ terrible given that the receiver
    has to manually say "-p0" for each git-am invocation.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index f3313b8c58..f5a41fd47e 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -2386,4 +2386,9 @@ test_expect_success 'interdiff: solo-patch' '
 	test_cmp expect actual
 '
 
+test_expect_success 'format-patch does not respect diff.noprefix' '
+	git -c diff.noprefix format-patch -1 --stdout >actual &&
+	grep "^--- a/blorp" actual
+'
+
 test_done