Add diff-option --ext-diff

To prevent funky games with external diff engines, git-log and
friends prevent external diff engines from being called. That makes
sense in the context of git-format-patch or git-rebase.

However, for "git log -p" it is not so nice to get the message
that binary files cannot be compared, while "git diff" has no
problems with them, if you provided an external diff driver.

With this patch, "git log --ext-diff -p" will do what you expect,
and the option "--no-ext-diff" can be used to override that
setting.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/diff.c b/diff.c
index 93eca79c1..b6eb72be0 100644
--- a/diff.c
+++ b/diff.c
@@ -2241,6 +2241,10 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		options->exit_with_status = 1;
 	else if (!strcmp(arg, "--quiet"))
 		options->quiet = 1;
+	else if (!strcmp(arg, "--ext-diff"))
+		options->allow_external = 1;
+	else if (!strcmp(arg, "--no-ext-diff"))
+		options->allow_external = 0;
 	else
 		return 0;
 	return 1;