completion: use __gitcomp_builtin for format-patch

This helps format-patch gain completion for a couple new options,
notably --range-diff.

Since send-email completion relies on $__git_format_patch_options
which is now reduced, we need to do something not to regress
send-email completion.

The workaround here is implement --git-completion-helper in
send-email.perl just as a bridge to "format-patch --git-completion-helper".
This is enough to use __gitcomp_builtin on send-email (to take
advantage of caching).

In the end, send-email.perl can probably reuse the same info it passes
to GetOptions() to generate full --git-completion-helper output so
that we don't need to keep track of its options in git-completion.bash
anymore. But that's something for another boring day.

Helped-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/git-send-email.perl b/git-send-email.perl
index 2be5dac..ed0714e 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -119,6 +119,11 @@ EOT
 	exit(1);
 }
 
+sub completion_helper {
+    print Git::command('format-patch', '--git-completion-helper');
+    exit(0);
+}
+
 # most mail servers generate the Date: header, but not all...
 sub format_2822_time {
 	my ($time) = @_;
@@ -311,6 +316,7 @@ $SIG{INT}  = \&signal_handler;
 # needing, first, from the command line:
 
 my $help;
+my $git_completion_helper;
 my $rc = GetOptions("h" => \$help,
                     "dump-aliases" => \$dump_aliases);
 usage() unless $rc;
@@ -373,9 +379,11 @@ $rc = GetOptions(
 		    "no-xmailer" => sub {$use_xmailer = 0},
 		    "batch-size=i" => \$batch_size,
 		    "relogin-delay=i" => \$relogin_delay,
+		    "git-completion-helper" => \$git_completion_helper,
 	 );
 
 usage() if $help;
+completion_helper() if $git_completion_helper;
 unless ($rc) {
     usage();
 }