Merge branch 'sh/completion-with-reftable' into seen

Command line completion script (in contrib/) learned to work better
with the reftable backend.

* sh/completion-with-reftable:
  completion: stop checking for reference existence via `test -f`
  completion: refactor existence checks for special refs

Author: gitster

contrib/completion/git-completion.bash

@@ -122,6 +122,38 @@ __git ()
 		${__git_dir:+--git-dir="$__git_dir"} "$@" 2>/dev/null
 }
 
+# Helper function to read the first line of a file into a variable.
+# __git_eread requires 2 arguments, the file path and the name of the
+# variable, in that order.
+#
+# This is taken from git-prompt.sh.
+__git_eread ()
+{
+	test -r "$1" && IFS=$'\r\n' read -r "$2" <"$1"
+}
+
+# Runs git in $__git_repo_path to determine whether a ref exists.
+# 1: The ref to search
+__git_ref_exists ()
+{
+	local ref=$1
+
+	# If the reftable is in use, we have to shell out to 'git rev-parse'
+	# to determine whether the ref exists instead of looking directly in
+	# the filesystem to determine whether the ref exists. Otherwise, use
+	# Bash builtins since executing Git commands are expensive on some
+	# platforms.
+	if __git_eread "$__git_repo_path/HEAD" head; then
+		b="${head#ref: }"
+		if [ "$b" == "refs/heads/.invalid" ]; then
+			__git -C "$__git_repo_path" rev-parse --verify --quiet "$ref" 2>/dev/null
+			return $?
+		fi
+	fi
+
+	[ -f "$__git_repo_path/$ref" ]
+}
+
 # Removes backslash escaping, single quotes and double quotes from a word,
 # stores the result in the variable $dequoted_word.
 # 1: The word to dequote.
@@ -1625,7 +1657,7 @@ __git_cherry_pick_inprogress_options=$__git_sequencer_inprogress_options
 _git_cherry_pick ()
 {
 	__git_find_repo_path
-	if [ -f "$__git_repo_path"/CHERRY_PICK_HEAD ]; then
+	if __git_ref_exists CHERRY_PICK_HEAD; then
 		__gitcomp "$__git_cherry_pick_inprogress_options"
 		return
 	fi
@@ -2067,7 +2099,7 @@ _git_log ()
 	__git_find_repo_path
 
 	local merge=""
-	if [ -f "$__git_repo_path/MERGE_HEAD" ]; then
+	if __git_ref_exists MERGE_HEAD; then
 		merge="--merge"
 	fi
 	case "$prev,$cur" in
@@ -2934,6 +2966,7 @@ _git_reset ()
 
 _git_restore ()
 {
+	__git_find_repo_path
 	case "$prev" in
 	-s)
 		__git_complete_refs
@@ -2952,7 +2985,7 @@ _git_restore ()
 		__gitcomp_builtin restore
 		;;
 	*)
-		if __git rev-parse --verify --quiet HEAD >/dev/null; then
+		if __git_ref_exists HEAD; then
 			__git_complete_index_file "--modified"
 		fi
 	esac
@@ -2963,7 +2996,7 @@ __git_revert_inprogress_options=$__git_sequencer_inprogress_options
 _git_revert ()
 {
 	__git_find_repo_path
-	if [ -f "$__git_repo_path"/REVERT_HEAD ]; then
+	if __git_ref_exists REVERT_HEAD; then
 		__gitcomp "$__git_revert_inprogress_options"
 		return
 	fi
@@ -3709,7 +3742,7 @@ __gitk_main ()
 	__git_find_repo_path
 
 	local merge=""
-	if [ -f "$__git_repo_path/MERGE_HEAD" ]; then
+	if __git_ref_exists MERGE_HEAD; then
 		merge="--merge"
 	fi
 	case "$cur" in