git-prompt: show 'CONFLICT' indicator at command prompt

When there are unresolved conflicts, show the word 'CONFLICT' on the
command prompt. Similar to other state indicators, this provides
information to the user about the current state of the repository.

Example prompt: (main|CONFLICT)

Signed-off-by: Justin Donnelly <justinrdonnelly@gmail.com>

contrib/completion/git-prompt.sh

@@ -84,6 +84,9 @@
 # single '?' character by setting GIT_PS1_COMPRESSSPARSESTATE, or omitted
 # by setting GIT_PS1_OMITSPARSESTATE.
 #
+# When there is a conflict, the prompt will include "|CONFLICT". This can
+# be omitted by setting GIT_PS1_OMITCONFLICTSTATE.
+#
 # 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 +511,12 @@ __git_ps1 ()
 		r="$r $step/$total"
 	fi
 
+	local conflict="" # state indicator for unresolved conflicts
+	if [[ -z "${GIT_PS1_OMITCONFLICTSTATE-}" ]] &&
+	   [[ $(git ls-files --unmerged 2>/dev/null) ]]; then
+		conflict="|CONFLICT"
+	fi
+
 	local w=""
 	local i=""
 	local s=""
@@ -572,7 +581,7 @@ __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

@@ -183,7 +183,7 @@ test_expect_success 'prompt - interactive rebase' '
 '
 
 test_expect_success 'prompt - rebase merge' '
-	printf " (b2|REBASE 1/3)" >expected &&
+	printf " (b2|REBASE 1/3|CONFLICT)" >expected &&
 	git checkout b2 &&
 	test_when_finished "git checkout main" &&
 	test_must_fail git rebase --merge b1 b2 &&
@@ -193,7 +193,7 @@ test_expect_success 'prompt - rebase merge' '
 '
 
 test_expect_success 'prompt - rebase am' '
-	printf " (b2|REBASE 1/3)" >expected &&
+	printf " (b2|REBASE 1/3|CONFLICT)" >expected &&
 	git checkout b2 &&
 	test_when_finished "git checkout main" &&
 	test_must_fail git rebase --apply b1 b2 &&
@@ -203,7 +203,7 @@ test_expect_success 'prompt - rebase am' '
 '
 
 test_expect_success 'prompt - merge' '
-	printf " (b1|MERGING)" >expected &&
+	printf " (b1|MERGING|CONFLICT)" >expected &&
 	git checkout b1 &&
 	test_when_finished "git checkout main" &&
 	test_must_fail git merge b2 &&
@@ -213,11 +213,12 @@ test_expect_success 'prompt - merge' '
 '
 
 test_expect_success 'prompt - cherry-pick' '
-	printf " (main|CHERRY-PICKING)" >expected &&
+	printf " (main|CHERRY-PICKING|CONFLICT)" >expected &&
 	test_must_fail git cherry-pick b1 b1^ &&
 	test_when_finished "git cherry-pick --abort" &&
 	__git_ps1 >"$actual" &&
 	test_cmp expected "$actual" &&
+	printf " (main|CHERRY-PICKING)" >expected &&
 	git reset --merge &&
 	test_must_fail git rev-parse CHERRY_PICK_HEAD &&
 	__git_ps1 >"$actual" &&