am: support --allow-empty to record specific empty patches

This option helps to record specific empty patches in the middle
of an am session, which does create empty commits only when:

    1. the index has not changed
    2. lacking a branch

When the index has changed, "--allow-empty" will create a non-empty
commit like passing "--continue" or "--resolved".

Signed-off-by: 徐沛文 (Aleen) <aleen42@vip.qq.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 24 insertions, 8 deletions

diff --git a/builtin/am.c b/builtin/am.c
index 7a66ad2373..f2e7e53388 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1152,6 +1152,12 @@ static void NORETURN die_user_resolve(const struct am_state *state)
 
 		printf_ln(_("When you have resolved this problem, run \"%s --continue\"."), cmdline);
 		printf_ln(_("If you prefer to skip this patch, run \"%s --skip\" instead."), cmdline);
+
+		if (advice_enabled(ADVICE_AM_WORK_DIR) &&
+		    is_empty_or_missing_file(am_path(state, "patch")) &&
+		    !repo_index_has_changes(the_repository, NULL, NULL))
+			printf_ln(_("To record the empty patch as an empty commit, run \"%s --allow-empty\"."), cmdline);
+
 		printf_ln(_("To restore the original branch and stop patching, run \"%s --abort\"."), cmdline);
 	}
 
@@ -1900,19 +1906,24 @@ next:
 /**
  * Resume the current am session after patch application failure. The user did
  * all the hard work, and we do not have to do any patch application. Just
- * trust and commit what the user has in the index and working tree.
+ * trust and commit what the user has in the index and working tree. If `allow_empty`
+ * is true, commit as an empty commit when index has not changed and lacking a patch.
  */
-static void am_resolve(struct am_state *state)
+static void am_resolve(struct am_state *state, int allow_empty)
 {
 	validate_resume_state(state);
 
 	say(state, stdout, _("Applying: %.*s"), linelen(state->msg), state->msg);
 
 	if (!repo_index_has_changes(the_repository, NULL, NULL)) {
-		printf_ln(_("No changes - did you forget to use 'git add'?\n"
-			"If there is nothing left to stage, chances are that something else\n"
-			"already introduced the same changes; you might want to skip this patch."));
-		die_user_resolve(state);
+		if (allow_empty && is_empty_or_missing_file(am_path(state, "patch"))) {
+			printf_ln(_("No changes - recorded it as an empty commit."));
+		} else {
+			printf_ln(_("No changes - did you forget to use 'git add'?\n"
+				    "If there is nothing left to stage, chances are that something else\n"
+				    "already introduced the same changes; you might want to skip this patch."));
+			die_user_resolve(state);
+		}
 	}
 
 	if (unmerged_cache()) {
@@ -2239,7 +2250,8 @@ enum resume_type {
 	RESUME_SKIP,
 	RESUME_ABORT,
 	RESUME_QUIT,
-	RESUME_SHOW_PATCH
+	RESUME_SHOW_PATCH,
+	RESUME_ALLOW_EMPTY,
 };
 
 struct resume_mode {
@@ -2392,6 +2404,9 @@ int cmd_am(int argc, const char **argv, const char *prefix)
 		  N_("show the patch being applied"),
 		  PARSE_OPT_CMDMODE | PARSE_OPT_OPTARG | PARSE_OPT_NONEG | PARSE_OPT_LITERAL_ARGHELP,
 		  parse_opt_show_current_patch, RESUME_SHOW_PATCH },
+		OPT_CMDMODE(0, "allow-empty", &resume.mode,
+			N_("record the empty patch as an empty commit"),
+			RESUME_ALLOW_EMPTY),
 		OPT_BOOL(0, "committer-date-is-author-date",
 			&state.committer_date_is_author_date,
 			N_("lie about committer date")),
@@ -2500,7 +2515,8 @@ int cmd_am(int argc, const char **argv, const char *prefix)
 		am_run(&state, 1);
 		break;
 	case RESUME_RESOLVED:
-		am_resolve(&state);
+	case RESUME_ALLOW_EMPTY:
+		am_resolve(&state, resume.mode == RESUME_ALLOW_EMPTY ? 1 : 0);
 		break;
 	case RESUME_SKIP:
 		am_skip(&state);