[PATCH 03/14] parse-options: disable option abbreviation with PARSE_OPT_KEEP_UNKNOWN

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

parse-options can unambiguously find an abbreviation only if it sees
all available options. This is usually the case when you use
parse_options(). But there are other callers like blame or shortlog
which uses parse_options_start() in combination with a custom option
parser, like rev-list. parse-options cannot see all options in this
case and will get abbrev detection wrong. Disable it.

t7800 needs update because --symlink no longer expands to --symlinks
and will be passed down to git-diff, which will not recognize it. I
still think this is the correct thing to do. But if --symlink has been
actually used in the wild, we would just add an option alias for it.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 parse-options.c     | 3 ++-
 t/t7800-difftool.sh | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/parse-options.c b/parse-options.c
index 740ae5438f..779034e1fd 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -266,7 +266,8 @@ static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
 		}
 		if (!rest) {
 			/* abbreviated? */
-			if (!strncmp(long_name, arg, arg_end - arg)) {
+			if (!(p->flags & PARSE_OPT_KEEP_UNKNOWN) &&
+			    !strncmp(long_name, arg, arg_end - arg)) {
 is_abbreviated:
 				if (abbrev_option) {
 					/*
diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 22b9199d59..bb9a7f4ff9 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -546,7 +546,7 @@ do
 done >actual
 EOF
 
-test_expect_success SYMLINKS 'difftool --dir-diff --symlink without unstaged changes' '
+test_expect_success SYMLINKS 'difftool --dir-diff --symlinks without unstaged changes' '
 	cat >expect <<-EOF &&
 	file
 	$PWD/file
@@ -555,7 +555,7 @@ test_expect_success SYMLINKS 'difftool --dir-diff --symlink without unstaged cha
 	sub/sub
 	$PWD/sub/sub
 	EOF
-	git difftool --dir-diff --symlink \
+	git difftool --dir-diff --symlinks \
 		--extcmd "./.git/CHECK_SYMLINKS" branch HEAD &&
 	test_cmp expect actual
 '
-- 
2.20.1.560.g70ca8b83ee