git-prompt: improve cherry-pick/revert detection

If the user commits or resets a conflict resolution in the middle of a
sequence of cherry-picks or reverts then CHERRY_PICK_HEAD/REVERT_HEAD
will be removed and so in the absence of those files we need to check
.git/sequencer/todo to see if there is a cherry-pick or revert in
progress.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/completion/git-prompt.sh b/contrib/completion/git-prompt.sh
index 983e419..1d510cd 100644
--- a/contrib/completion/git-prompt.sh
+++ b/contrib/completion/git-prompt.sh
@@ -286,6 +286,37 @@
 	test -r "$1" && IFS=$'\r\n' read "$2" <"$1"
 }
 
+# see if a cherry-pick or revert is in progress, if the user has committed a
+# conflict resolution with 'git commit' in the middle of a sequence of picks or
+# reverts then CHERRY_PICK_HEAD/REVERT_HEAD will not exist so we have to read
+# the todo file.
+__git_sequencer_status ()
+{
+	local todo
+	if test -f "$g/CHERRY_PICK_HEAD"
+	then
+		r="|CHERRY-PICKING"
+		return 0;
+	elif test -f "$g/REVERT_HEAD"
+	then
+		r="|REVERTING"
+		return 0;
+	elif __git_eread "$g/sequencer/todo" todo
+	then
+		case "$todo" in
+		p[\ \	]|pick[\ \	]*)
+			r="|CHERRY-PICKING"
+			return 0
+		;;
+		revert[\ \	]*)
+			r="|REVERTING"
+			return 0
+		;;
+		esac
+	fi
+	return 1
+}
+
 # __git_ps1 accepts 0 or 1 arguments (i.e., format string)
 # when called from PS1 using command substitution
 # in this mode it prints text to add to bash PS1 prompt (includes branch name)
@@ -417,10 +448,8 @@
 			fi
 		elif [ -f "$g/MERGE_HEAD" ]; then
 			r="|MERGING"
-		elif [ -f "$g/CHERRY_PICK_HEAD" ]; then
-			r="|CHERRY-PICKING"
-		elif [ -f "$g/REVERT_HEAD" ]; then
-			r="|REVERTING"
+		elif __git_sequencer_status; then
+			:
 		elif [ -f "$g/BISECT_LOG" ]; then
 			r="|BISECTING"
 		fi