status: show 'revert' state and status hint

This is the logical equivalent for "git status" of 3ee4452 (bash: teach
__git_ps1 about REVERT_HEAD).

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7512-status-help.sh

@@ -678,4 +678,61 @@ test_expect_success 'status showing detached from a tag' '
 	test_i18ncmp expected actual
 '
 
+test_expect_success 'status while reverting commit (conflicts)' '
+	git checkout master &&
+	echo before >to-revert.txt &&
+	test_commit before to-revert.txt &&
+	echo old >to-revert.txt &&
+	test_commit old to-revert.txt &&
+	echo new >to-revert.txt &&
+	test_commit new to-revert.txt &&
+	test_must_fail git revert HEAD^ &&
+	cat >expected <<-EOF
+	# On branch master
+	# You are currently reverting a commit.
+	#   (fix conflicts and run "git revert --continue")
+	#   (use "git revert --abort" to cancel the revert operation)
+	#
+	# Unmerged paths:
+	#   (use "git reset HEAD <file>..." to unstage)
+	#   (use "git add <file>..." to mark resolution)
+	#
+	#	both modified:      to-revert.txt
+	#
+	no changes added to commit (use "git add" and/or "git commit -a")
+	EOF
+	git status --untracked-files=no >actual &&
+	test_i18ncmp expected actual
+'
+
+test_expect_success 'status while reverting commit (conflicts resolved)' '
+	echo reverted >to-revert.txt &&
+	git add to-revert.txt &&
+	cat >expected <<-EOF
+	# On branch master
+	# You are currently reverting a commit.
+	#   (all conflicts fixed: run "git revert --continue")
+	#   (use "git revert --abort" to cancel the revert operation)
+	#
+	# Changes to be committed:
+	#   (use "git reset HEAD <file>..." to unstage)
+	#
+	#	modified:   to-revert.txt
+	#
+	# Untracked files not listed (use -u option to show untracked files)
+	EOF
+	git status --untracked-files=no >actual &&
+	test_i18ncmp expected actual
+'
+
+test_expect_success 'status after reverting commit' '
+	git revert --continue &&
+	cat >expected <<-\EOF
+	# On branch master
+	nothing to commit (use -u to show untracked files)
+	EOF
+	git status --untracked-files=no >actual &&
+	test_i18ncmp expected actual
+'
+
 test_done

wt-status.c

@@ -965,6 +965,24 @@ static void show_cherry_pick_in_progress(struct wt_status *s,
 	wt_status_print_trailer(s);
 }
 
+static void show_revert_in_progress(struct wt_status *s,
+					struct wt_status_state *state,
+					const char *color)
+{
+	status_printf_ln(s, color, _("You are currently reverting a commit."));
+	if (advice_status_hints) {
+		if (has_unmerged(s))
+			status_printf_ln(s, color,
+				_("  (fix conflicts and run \"git revert --continue\")"));
+		else
+			status_printf_ln(s, color,
+				_("  (all conflicts fixed: run \"git revert --continue\")"));
+		status_printf_ln(s, color,
+			_("  (use \"git revert --abort\" to cancel the revert operation)"));
+	}
+	wt_status_print_trailer(s);
+}
+
 static void show_bisect_in_progress(struct wt_status *s,
 				struct wt_status_state *state,
 				const char *color)
@@ -1113,6 +1131,9 @@ void wt_status_get_state(struct wt_status_state *state,
 		state->bisect_in_progress = 1;
 		state->branch = read_and_strip_branch("BISECT_START");
 	}
+	if (!stat(git_path("REVERT_HEAD"), &st)) {
+		state->revert_in_progress = 1;
+	}
 
 	if (get_detached_from)
 		wt_status_get_detached_from(state);
@@ -1130,6 +1151,8 @@ static void wt_status_print_state(struct wt_status *s,
 		show_rebase_in_progress(s, state, state_color);
 	else if (state->cherry_pick_in_progress)
 		show_cherry_pick_in_progress(s, state, state_color);
+	else if (state->revert_in_progress)
+		show_revert_in_progress(s, state, state_color);
 	if (state->bisect_in_progress)
 		show_bisect_in_progress(s, state, state_color);
 }

wt-status.h

@@ -80,6 +80,7 @@ struct wt_status_state {
 	int rebase_interactive_in_progress;
 	int cherry_pick_in_progress;
 	int bisect_in_progress;
+	int revert_in_progress;
 	char *branch;
 	char *onto;
 	char *detached_from;