completion: respect 'git --git-dir=<path>' when listing remote refs

In __git_refs() the git commands listing refs, both short and full,
from a given remote repository are run without giving them the path to
the git repository which might have been specified on the command line
via 'git --git-dir=<path>'.  This is bad, those git commands should
access the 'refs/remotes/<remote>/' hierarchy or the remote and
credentials configuration in that specified repository.

Use the __gitdir() helper only to find the path to the .git directory
and pass the resulting path to the 'git ls-remote' and 'for-each-ref'
executions that list remote refs.  While modifying that 'for-each-ref'
line, remove the superfluous disambiguating doubledash.

Don't use __gitdir() to check that the given remote is on the file
system: basically it performs only a single if statement for us at the
considerable cost of fork()ing a subshell for a command substitution.
We are better off to perform all the necessary checks of the remote in
__git_refs().

Though __git_refs() was the last remaining callsite that passed a
remote to __gitdir(), don't delete __gitdir()'s remote-handling part
yet, just in case some users' custom completion scriptlets depend on
it.

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

contrib/completion/git-completion.bash

@@ -342,9 +342,21 @@ __git_tags ()
 #    'git checkout's tracking DWIMery (optional; ignored, if set but empty).
 __git_refs ()
 {
-	local i hash dir="$(__gitdir "${1-}")" track="${2-}"
+	local i hash dir="$(__gitdir)" track="${2-}"
+	local list_refs_from=path remote="${1-}"
 	local format refs pfx
-	if [ -d "$dir" ]; then
+
+	if [ -n "$remote" ]; then
+		if [ -d "$remote/.git" ]; then
+			dir="$remote/.git"
+		elif [ -d "$remote" ]; then
+			dir="$remote"
+		else
+			list_refs_from=remote
+		fi
+	fi
+
+	if [ "$list_refs_from" = path ] && [ -d "$dir" ]; then
 		case "$cur" in
 		refs|refs/*)
 			format="refname"
@@ -381,7 +393,7 @@ __git_refs ()
 	fi
 	case "$cur" in
 	refs|refs/*)
-		git ls-remote "$dir" "$cur*" 2>/dev/null | \
+		git --git-dir="$dir" ls-remote "$remote" "$cur*" 2>/dev/null | \
 		while read -r hash i; do
 			case "$i" in
 			*^{}) ;;
@@ -391,8 +403,8 @@ __git_refs ()
 		;;
 	*)
 		echo "HEAD"
-		git for-each-ref --format="%(refname:short)" -- \
+		git --git-dir="$dir" for-each-ref --format="%(refname:short)" \
-			"refs/remotes/$dir/" 2>/dev/null | sed -e "s#^$dir/##"
+			"refs/remotes/$remote/" 2>/dev/null | sed -e "s#^$remote/##"
 		;;
 	esac
 }

t/t9902-completion.sh

@@ -486,7 +486,7 @@ test_expect_success '__git_refs - configured remote - full refs' '
 	test_cmp expected "$actual"
 '
 
-test_expect_failure '__git_refs - configured remote - repo given on the command line' '
+test_expect_success '__git_refs - configured remote - repo given on the command line' '
 	cat >expected <<-EOF &&
 	HEAD
 	branch-in-other
@@ -501,7 +501,7 @@ test_expect_failure '__git_refs - configured remote - repo given on the command
 	test_cmp expected "$actual"
 '
 
-test_expect_failure '__git_refs - configured remote - full refs - repo given on the command line' '
+test_expect_success '__git_refs - configured remote - full refs - repo given on the command line' '
 	cat >expected <<-EOF &&
 	refs/heads/branch-in-other
 	refs/heads/master-in-other