completion: support completing full refs after '--option=refs/<TAB>'

Completing full refs currently only works when the full ref stands on
in its own on the command line, but doesn't work when the current word
to be completed contains a prefix before the full ref, e.g.
'--option=refs/<TAB>' or 'master..refs/bis<TAB>'.

The reason is that __git_refs() looks at the current word to be
completed ($cur) as a whole to decide whether it has to list full (if
it starts with 'refs/') or short refs (otherwise).  However, $cur also
holds said '--option=' or 'master..' prefixes, which of course throw
off this decision.  Luckily, the default action is to list short refs,
that's why completing short refs happens to work even after a
'master..<TAB>' prefix and similar cases.

Pass only the ref part of the current word to be completed to
__git_refs() as a new positional parameter, so it can make the right
decision even if the whole current word contains some kind of a
prefix.

Make this new parameter the 4. positional parameter and leave the 3.
as an ignored placeholder for now (it will be used later in this patch
series).

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

contrib/completion/git-completion.bash

@@ -354,6 +354,8 @@ __git_tags ()
 #    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).
+# 3: Currently ignored.
+# 4: The current ref to be completed (optional).
 #
 # Use __git_complete_refs() instead.
 __git_refs ()
@@ -361,6 +363,7 @@ __git_refs ()
 	local i hash dir track="${2-}"
 	local list_refs_from=path remote="${1-}"
 	local format refs pfx
+	local cur_="${4-$cur}"
 
 	__git_find_repo_path
 	dir="$__git_repo_path"
@@ -384,14 +387,17 @@ __git_refs ()
 	fi
 
 	if [ "$list_refs_from" = path ]; then
-		case "$cur" in
+		case "$cur_" in
 		refs|refs/*)
 			format="refname"
-			refs="${cur%/*}"
+			refs="${cur_%/*}"
 			track=""
 			;;
 		*)
-			[[ "$cur" == ^* ]] && pfx="^"
+			if [[ "$cur_" == ^* ]]; then
+				pfx="^"
+				cur_=${cur_#^}
+			fi
 			for i in HEAD FETCH_HEAD ORIG_HEAD MERGE_HEAD; do
 				if [ -e "$dir/$i" ]; then echo $pfx$i; fi
 			done
@@ -411,16 +417,16 @@ __git_refs ()
 			while read -r entry; do
 				eval "$entry"
 				ref="${ref#*/}"
-				if [[ "$ref" == "$cur"* ]]; then
+				if [[ "$ref" == "$cur_"* ]]; then
 					echo "$ref"
 				fi
 			done | sort | uniq -u
 		fi
 		return
 	fi
-	case "$cur" in
+	case "$cur_" in
 	refs|refs/*)
-		__git ls-remote "$remote" "$cur*" | \
+		__git ls-remote "$remote" "$cur_*" | \
 		while read -r hash i; do
 			case "$i" in
 			*^{}) ;;
@@ -475,7 +481,8 @@ __git_complete_refs ()
 		shift
 	done
 
-	__gitcomp_nl "$(__git_refs "$remote" "$track")" "$pfx" "$cur_" "$sfx"
+	__gitcomp_nl "$(__git_refs "$remote" "$track" "" "$cur_")" \
+		"$pfx" "$cur_" "$sfx"
 }
 
 # __git_refs2 requires 1 argument (to pass to __git_refs)

t/t9902-completion.sh

@@ -775,6 +775,37 @@ test_expect_success '__git_refs - unique remote branches for git checkout DWIMer
 	test_cmp expected "$actual"
 '
 
+test_expect_success '__git_refs - after --opt=' '
+	cat >expected <<-EOF &&
+	HEAD
+	master
+	matching-branch
+	other/branch-in-other
+	other/master-in-other
+	matching-tag
+	EOF
+	(
+		cur="--opt=" &&
+		__git_refs "" "" "" "" >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
+test_expect_success '__git_refs - after --opt= - full refs' '
+	cat >expected <<-EOF &&
+	refs/heads/master
+	refs/heads/matching-branch
+	refs/remotes/other/branch-in-other
+	refs/remotes/other/master-in-other
+	refs/tags/matching-tag
+	EOF
+	(
+		cur="--opt=refs/" &&
+		__git_refs "" "" "" refs/ >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
 test_expect_success '__git_complete_refs - simple' '
 	sed -e "s/Z$//" >expected <<-EOF &&
 	HEAD Z