completion: list short refs from a remote given as a URL

e832f5c096 (completion: avoid ls-remote in certain scenarios,
2013-05-28) turned a 'git ls-remote <remote>' query into a 'git
for-each-ref refs/remotes/<remote>/' to improve responsiveness of
remote refs completion by avoiding potential network communication.
However, it inadvertently made impossible to complete short refs from
a remote given as a URL, e.g. 'git fetch git://server.com/repo.git
<TAB>', because there is, of course, no such thing as
'refs/remotes/git://server.com/repo.git'.

Since the previous commit we tell apart configured remotes, i.e. those
that can have a hierarchy under 'refs/remotes/', from others that
don't, including remotes given as URL, so we know when we can't use
the faster 'git for-each-ref'-based approach.

Resurrect the old, pre-e832f5c09680 'git ls-remote'-based code for the
latter case to support listing short refs from remotes given as a URL.
The code is slightly updated from the original to

  - take into account the path to the repository given on the command
    line (if any), and
  - omit 'ORIG_HEAD' from the query, as 'git ls-remote' will never
    list it anyway.

When the remote given to __git_refs() doesn't exist, then it will be
handled by this resurrected 'git ls-remote' query.  This code path
doesn't list 'HEAD' unconditionally, which has the nice side effect of
fixing two more expected test failures.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -338,6 +338,7 @@ __git_tags ()
 # Lists refs from the local (by default) or from a remote repository.
 # It accepts 0, 1 or 2 arguments:
 # 1: The remote to list refs from (optional; ignored, if set but empty).
+#    Can be the name of a configured remote, a path, or a URL.
 # 2: In addition to local refs, list unique branches from refs/remotes/ for
 #    'git checkout's tracking DWIMery (optional; ignored, if set but empty).
 __git_refs ()
@@ -410,9 +411,21 @@ __git_refs ()
 		done
 		;;
 	*)
-		echo "HEAD"
-		git --git-dir="$dir" for-each-ref --format="%(refname:short)" \
-			"refs/remotes/$remote/" 2>/dev/null | sed -e "s#^$remote/##"
+		if [ "$list_refs_from" = remote ]; then
+			echo "HEAD"
+			git --git-dir="$dir" for-each-ref --format="%(refname:short)" \
+				"refs/remotes/$remote/" 2>/dev/null | sed -e "s#^$remote/##"
+		else
+			git --git-dir="$dir" ls-remote "$remote" HEAD \
+				"refs/tags/*" "refs/heads/*" "refs/remotes/*" 2>/dev/null |
+			while read -r hash i; do
+				case "$i" in
+				*^{})	;;
+				refs/*)	echo "${i#refs/*/}" ;;
+				*)	echo "$i" ;;  # symbolic refs
+				esac
+			done
+		fi
 		;;
 	esac
 }

t/t9902-completion.sh

@@ -540,7 +540,7 @@ test_expect_success '__git_refs - configured remote - remote name matches a dire
 	test_cmp expected "$actual"
 '
 
-test_expect_failure '__git_refs - URL remote' '
+test_expect_success '__git_refs - URL remote' '
 	cat >expected <<-EOF &&
 	HEAD
 	branch-in-other
@@ -567,7 +567,7 @@ test_expect_success '__git_refs - URL remote - full refs' '
 	test_cmp expected "$actual"
 '
 
-test_expect_failure '__git_refs - non-existing remote' '
+test_expect_success '__git_refs - non-existing remote' '
 	(
 		cur= &&
 		__git_refs non-existing >"$actual"
@@ -583,7 +583,7 @@ test_expect_success '__git_refs - non-existing remote - full refs' '
 	test_must_be_empty "$actual"
 '
 
-test_expect_failure '__git_refs - non-existing URL remote' '
+test_expect_success '__git_refs - non-existing URL remote' '
 	(
 		cur= &&
 		__git_refs "file://$ROOT/non-existing" >"$actual"