git-prompt: show presence of unresolved conflicts at command prompt

If GIT_PS1_SHOWCONFLICTSTATE is set to "yes", show the word "CONFLICT"
on the command prompt when there are unresolved conflicts.

Example prompt: (main|CONFLICT)

Signed-off-by: Justin Donnelly <justinrdonnelly@gmail.com>
Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-prompt.sh

@@ -84,6 +84,10 @@
 # single '?' character by setting GIT_PS1_COMPRESSSPARSESTATE, or omitted
 # by setting GIT_PS1_OMITSPARSESTATE.
 #
+# If you would like to see a notification on the prompt when there are
+# unresolved conflicts, set GIT_PS1_SHOWCONFLICTSTATE to "yes". The
+# prompt will include "|CONFLICT".
+#
 # If you would like to see more information about the identity of
 # commits checked out as a detached HEAD, set GIT_PS1_DESCRIBE_STYLE
 # to one of these values:
@@ -508,6 +512,12 @@ __git_ps1 ()
 		r="$r $step/$total"
 	fi
 
+	local conflict="" # state indicator for unresolved conflicts
+	if [[ "${GIT_PS1_SHOWCONFLICTSTATE}" == "yes" ]] &&
+	   [[ $(git ls-files --unmerged 2>/dev/null) ]]; then
+		conflict="|CONFLICT"
+	fi
+
 	local w=""
 	local i=""
 	local s=""
@@ -572,7 +582,7 @@ __git_ps1 ()
 	fi
 
 	local f="$h$w$i$s$u$p"
-	local gitstring="$c$b${f:+$z$f}${sparse}$r${upstream}"
+	local gitstring="$c$b${f:+$z$f}${sparse}$r${upstream}${conflict}"
 
 	if [ $pcmode = yes ]; then
 		if [ "${__git_printf_supports_v-}" != yes ]; then

t/t9903-bash-prompt.sh

@@ -759,4 +759,20 @@ test_expect_success 'prompt - hide if pwd ignored - inside gitdir' '
 	test_cmp expected "$actual"
 '
 
+test_expect_success 'prompt - conflict indicator' '
+	printf " (main|CONFLICT)" >expected &&
+	echo "stash" >file &&
+	git stash &&
+	test_when_finished "git stash drop" &&
+	echo "commit" >file &&
+	git commit -m "commit" file &&
+	test_when_finished "git reset --hard HEAD~" &&
+	test_must_fail git stash apply &&
+	(
+		GIT_PS1_SHOWCONFLICTSTATE="yes" &&
+		__git_ps1 >"$actual"
+	) &&
+	test_cmp expected "$actual"
+'
+
 test_done