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>

contrib/completion/git-completion.bash

@@ -1532,13 +1532,9 @@ _git_fetch ()
 	__git_complete_remote_or_refspec
 }
-__git_format_patch_options="
-	--stdout --attach --no-attach --thread --thread= --no-thread
-	--numbered --start-number --numbered-files --keep-subject --signoff
-	--signature --no-signature --in-reply-to= --cc= --full-index --binary
-	--not --all --cover-letter --no-prefix --src-prefix= --dst-prefix=
-	--inline --suffix= --ignore-if-in-upstream --subject-prefix=
-	--output-directory --reroll-count --to= --quiet --notes
+__git_format_patch_extra_options="
+	--full-index --not --all --no-prefix --src-prefix=
+	--dst-prefix= --notes
 "
 _git_format_patch ()
@@ -1551,7 +1547,7 @@ _git_format_patch ()
 		return
 		;;
 	--*)
-		__gitcomp "$__git_format_patch_options"
+		__gitcomp_builtin format-patch "$__git_format_patch_extra_options"
 		return
 		;;
 	esac
@@ -2081,7 +2077,7 @@ _git_send_email ()
 		return
 		;;
 	--*)
-		__gitcomp "--annotate --bcc --cc --cc-cmd --chain-reply-to
+		__gitcomp_builtin send-email "--annotate --bcc --cc --cc-cmd --chain-reply-to
 			--compose --confirm= --dry-run --envelope-sender
 			--from --identity
 			--in-reply-to --no-chain-reply-to --no-signed-off-by-cc
@@ -2090,7 +2086,7 @@ _git_send_email ()
 			--smtp-server-port --smtp-encryption= --smtp-user
 			--subject --suppress-cc= --suppress-from --thread --to
 			--validate --no-validate
-			$__git_format_patch_options"
+			$__git_format_patch_extra_options"
 		return
 		;;
 	esac

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();
 }