commit: give correct advice for empty commit during a rebase

In dcb500dc16 (cherry-pick/revert: advise using --skip, 2019-07-02),
`git commit` learned to suggest to run `git cherry-pick --skip` when
trying to cherry-pick an empty patch.

However, it was overlooked that there are more conditions than just a
`git cherry-pick` when this advice is printed (which originally
suggested the neutral `git reset`): the same can happen during a rebase.

Let's suggest the correct command, even during a rebase.

While at it, we adjust more places in `builtin/commit.c` that
incorrectly assumed that the presence of a `CHERRY_PICK_HEAD` meant that
surely this must be a `cherry-pick` in progress.

Note: we take pains to handle the situation when a user runs a `git
cherry-pick` _during_ a rebase. This is quite valid (e.g. in an `exec`
line in an interactive rebase). On the other hand, it is not possible to
run a rebase during a cherry-pick, meaning: if both `rebase-merge/` and
`sequencer/` exist or CHERRY_PICK_HEAD and REBASE_HEAD point to the same
commit , we still want to advise to use `git cherry-pick --skip`.

Original-patch-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -59,6 +59,9 @@ N_("The previous cherry-pick is now empty, possibly due to conflict resolution.\
 "    git commit --allow-empty\n"
 "\n");
 
+static const char empty_rebase_pick_advice[] =
+N_("Otherwise, please use 'git rebase --skip'\n");
+
 static const char empty_cherry_pick_advice_single[] =
 N_("Otherwise, please use 'git cherry-pick --skip'\n");
 
@@ -449,6 +452,8 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			die(_("cannot do a partial commit during a merge."));
 		else if (is_from_cherry_pick(whence))
 			die(_("cannot do a partial commit during a cherry-pick."));
+		else if (is_from_rebase(whence))
+			die(_("cannot do a partial commit during a rebase."));
 	}
 
 	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))
@@ -765,7 +770,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	 */
 	else if (whence == FROM_MERGE)
 		hook_arg1 = "merge";
-	else if (is_from_cherry_pick(whence)) {
+	else if (is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) {
 		hook_arg1 = "commit";
 		hook_arg2 = "CHERRY_PICK_HEAD";
 	}
@@ -942,12 +947,15 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		run_status(stdout, index_file, prefix, 0, s);
 		if (amend)
 			fputs(_(empty_amend_advice), stderr);
-		else if (is_from_cherry_pick(whence)) {
+		else if (is_from_cherry_pick(whence) ||
+			 whence == FROM_REBASE_PICK) {
 			fputs(_(empty_cherry_pick_advice), stderr);
 			if (whence == FROM_CHERRY_PICK_SINGLE)
 				fputs(_(empty_cherry_pick_advice_single), stderr);
-			else
+			else if (whence == FROM_CHERRY_PICK_MULTI)
 				fputs(_(empty_cherry_pick_advice_multi), stderr);
+			else
+				fputs(_(empty_rebase_pick_advice), stderr);
 		}
 		return 0;
 	}
@@ -1152,6 +1160,8 @@ static int parse_and_validate_options(int argc, const char *argv[],
 			die(_("You are in the middle of a merge -- cannot amend."));
 		else if (is_from_cherry_pick(whence))
 			die(_("You are in the middle of a cherry-pick -- cannot amend."));
+		else if (whence == FROM_REBASE_PICK)
+			die(_("You are in the middle of a rebase -- cannot amend."));
 	}
 	if (fixup_message && squash_message)
 		die(_("Options --squash and --fixup cannot be used together"));
@@ -1173,7 +1183,8 @@ static int parse_and_validate_options(int argc, const char *argv[],
 		use_message = edit_message;
 	if (amend && !use_message && !fixup_message)
 		use_message = "HEAD";
-	if (!use_message && !is_from_cherry_pick(whence) && renew_authorship)
+	if (!use_message && !is_from_cherry_pick(whence) &&
+	    !is_from_rebase(whence) && renew_authorship)
 		die(_("--reset-author can be used only with -C, -c or --amend."));
 	if (use_message) {
 		use_message_buffer = read_commit_message(use_message);
@@ -1182,7 +1193,8 @@ static int parse_and_validate_options(int argc, const char *argv[],
 			author_message_buffer = use_message_buffer;
 		}
 	}
-	if (is_from_cherry_pick(whence) && !renew_authorship) {
+	if ((is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) &&
+	    !renew_authorship) {
 		author_message = "CHERRY_PICK_HEAD";
 		author_message_buffer = read_commit_message(author_message);
 	}
@@ -1602,6 +1614,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		if (!reflog_msg)
 			reflog_msg = is_from_cherry_pick(whence)
 					? "commit (cherry-pick)"
+					: is_from_rebase(whence)
+					? "commit (rebase)"
 					: "commit";
 		commit_list_insert(current_head, &parents);
 	}

sequencer.c

@@ -1429,9 +1429,19 @@ out:
 	return res;
 }
 
+static int write_rebase_head(struct object_id *oid)
+{
+	if (update_ref("rebase", "REBASE_HEAD", oid,
+		       NULL, REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR))
+		return error(_("could not update %s"), "REBASE_HEAD");
+
+	return 0;
+}
+
 static int do_commit(struct repository *r,
 		     const char *msg_file, const char *author,
-		     struct replay_opts *opts, unsigned int flags)
+		     struct replay_opts *opts, unsigned int flags,
+		     struct object_id *oid)
 {
 	int res = 1;
 
@@ -1456,8 +1466,12 @@ static int do_commit(struct repository *r,
 			return res;
 		}
 	}
-	if (res == 1)
+	if (res == 1) {
+		if (is_rebase_i(opts) && oid)
+			if (write_rebase_head(oid))
+			    return -1;
 		return run_git_commit(r, msg_file, opts, flags);
+	}
 
 	return res;
 }
@@ -1945,7 +1959,8 @@ static int do_pick_commit(struct repository *r,
 		flags |= ALLOW_EMPTY;
 	if (!opts->no_commit) {
 		if (author || command == TODO_REVERT || (flags & AMEND_MSG))
-			res = do_commit(r, msg_file, author, opts, flags);
+			res = do_commit(r, msg_file, author, opts, flags,
+					commit? &commit->object.oid : NULL);
 		else
 			res = error(_("unable to parse commit author"));
 		*check_todo = !!(flags & EDIT_MSG);
@@ -2964,9 +2979,7 @@ static int make_patch(struct repository *r,
 	p = short_commit_name(commit);
 	if (write_message(p, strlen(p), rebase_path_stopped_sha(), 1) < 0)
 		return -1;
-	if (update_ref("rebase", "REBASE_HEAD", &commit->object.oid,
+	res |= write_rebase_head(&commit->object.oid);
-		       NULL, REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR))
-		res |= error(_("could not update %s"), "REBASE_HEAD");
 
 	strbuf_addf(&buf, "%s/patch", get_dir(opts));
 	memset(&log_tree_opt, 0, sizeof(log_tree_opt));
@@ -5316,8 +5329,18 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
 {
 	if (file_exists(git_path_cherry_pick_head(r))) {
-		*whence = file_exists(git_path_seq_dir()) ?
+		struct object_id cherry_pick_head, rebase_head;
-			FROM_CHERRY_PICK_MULTI : FROM_CHERRY_PICK_SINGLE;
+
+		if (file_exists(git_path_seq_dir()))
+			*whence = FROM_CHERRY_PICK_MULTI;
+		if (file_exists(rebase_path()) &&
+		    !get_oid("REBASE_HEAD", &rebase_head) &&
+		    !get_oid("CHERRY_PICK_HEAD", &cherry_pick_head) &&
+		    oideq(&rebase_head, &cherry_pick_head))
+			*whence = FROM_REBASE_PICK;
+		else
+			*whence = FROM_CHERRY_PICK_SINGLE;
+
 		return 1;
 	}
 

t/t3403-rebase-skip.sh

@@ -97,9 +97,9 @@ test_expect_success 'correct advice upon picking empty commit' '
 	test_must_fail git rebase -i --onto goodbye \
 		amended-goodbye^ amended-goodbye 2>err &&
 	test_i18ngrep "previous cherry-pick is now empty" err &&
-	test_i18ngrep "git cherry-pick --skip" err &&
+	test_i18ngrep "git rebase --skip" err &&
 	test_must_fail git commit &&
-	test_i18ngrep "git cherry-pick --skip" err
+	test_i18ngrep "git rebase --skip" err
 '
 
 test_expect_success 'correct authorship when committing empty pick' '
@@ -120,9 +120,9 @@ test_expect_success 'correct advice upon rewording empty commit' '
 			--onto goodbye amended-goodbye^ amended-goodbye 2>err
 	) &&
 	test_i18ngrep "previous cherry-pick is now empty" err &&
-	test_i18ngrep "git cherry-pick --skip" err &&
+	test_i18ngrep "git rebase --skip" err &&
 	test_must_fail git commit &&
-	test_i18ngrep "git cherry-pick --skip" err
+	test_i18ngrep "git rebase --skip" err
 '
 
 test_expect_success 'correct advice upon editing empty commit' '
@@ -133,8 +133,34 @@ test_expect_success 'correct advice upon editing empty commit' '
 			--onto goodbye amended-goodbye^ amended-goodbye 2>err
 	) &&
 	test_i18ngrep "previous cherry-pick is now empty" err &&
-	test_i18ngrep "git cherry-pick --skip" err &&
+	test_i18ngrep "git rebase --skip" err &&
 	test_must_fail git commit &&
+	test_i18ngrep "git rebase --skip" err
+'
+
+test_expect_success 'correct advice upon cherry-picking an empty commit during a rebase' '
+	test_when_finished "git rebase --abort" &&
+	(
+		set_fake_editor &&
+		test_must_fail env FAKE_LINES="1 exec_git_cherry-pick_amended-goodbye" \
+			git rebase -i goodbye^ goodbye 2>err
+	) &&
+	test_i18ngrep "previous cherry-pick is now empty" err &&
+	test_i18ngrep "git cherry-pick --skip" err &&
+	test_must_fail git commit 2>err &&
+	test_i18ngrep "git cherry-pick --skip" err
+'
+
+test_expect_success 'correct advice upon multi cherry-pick picking an empty commit during a rebase' '
+	test_when_finished "git rebase --abort" &&
+	(
+		set_fake_editor &&
+		test_must_fail env FAKE_LINES="1 exec_git_cherry-pick_goodbye_amended-goodbye" \
+			git rebase -i goodbye^^ goodbye 2>err
+	) &&
+	test_i18ngrep "previous cherry-pick is now empty" err &&
+	test_i18ngrep "git cherry-pick --skip" err &&
+	test_must_fail git commit 2>err &&
 	test_i18ngrep "git cherry-pick --skip" err
 '
 

t/t3404-rebase-interactive.sh

@@ -1599,6 +1599,32 @@ test_expect_success 'post-commit hook is called' '
 	test_cmp expect actual
 '
 
+test_expect_success 'correct error message for partial commit after empty pick' '
+	test_when_finished "git rebase --abort" &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="2 1 1" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A D
+	) &&
+	echo x >file1 &&
+	test_must_fail git commit file1 2>err &&
+	test_i18ngrep "cannot do a partial commit during a rebase." err
+'
+
+test_expect_success 'correct error message for commit --amend after empty pick' '
+	test_when_finished "git rebase --abort" &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 1" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A D
+	) &&
+	echo x>file1 &&
+	test_must_fail git commit -a --amend 2>err &&
+	test_i18ngrep "middle of a rebase -- cannot amend." err
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
 	test_editor_unchanged

wt-status.h

@@ -39,7 +39,8 @@ enum commit_whence {
 	FROM_COMMIT,     /* normal */
 	FROM_MERGE,      /* commit came from merge */
 	FROM_CHERRY_PICK_SINGLE, /* commit came from cherry-pick */
-	FROM_CHERRY_PICK_MULTI /* commit came from a sequence of cherry-picks */
+	FROM_CHERRY_PICK_MULTI, /* commit came from a sequence of cherry-picks */
+	FROM_REBASE_PICK /* commit came from a pick/reword/edit */
 };
 
 static inline int is_from_cherry_pick(enum commit_whence whence)
@@ -48,6 +49,11 @@ static inline int is_from_cherry_pick(enum commit_whence whence)
 		whence == FROM_CHERRY_PICK_MULTI;
 }
 
+static inline int is_from_rebase(enum commit_whence whence)
+{
+	return whence == FROM_REBASE_PICK;
+}
+
 struct wt_status_change_data {
 	int worktree_status;
 	int index_status;