[RFC PATCH 0/9][Outreachy] rebase -i: add options to fixup command

@@ -1757,11 +1757,13 @@ static int update_squash_messages(struct repository *r,
 			return error(_("could not read HEAD's commit message"));
 
 		find_commit_subject(head_message, &body);
-		if (write_message(body, strlen(body),
-				  rebase_path_fixup_msg(), 0)) {
-			unuse_commit_buffer(head_commit, head_message);
-			return error(_("cannot write '%s'"),
-				     rebase_path_fixup_msg());
+		if (command == TODO_FIXUP) {
+			if (write_message(body, strlen(body),
+					  rebase_path_fixup_msg(), 0)) {
+				unuse_commit_buffer(head_commit, head_message);
+				return error(_("cannot write '%s'"),
+					     rebase_path_fixup_msg());
+			}
 		}
 
 		strbuf_addf(&buf, "%c ", comment_line_char);

@@ -1718,6 +1718,17 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
+static void append_squash_message(struct strbuf *buf, const char *body,
+				  struct replay_opts *opts)
+{
+	unlink(rebase_path_fixup_msg());
+	strbuf_addf(buf, "\n%c ", comment_line_char);
+	strbuf_addf(buf, _("This is the commit message #%d:"),
+		    ++opts->current_fixup_count + 1);
+	strbuf_addstr(buf, "\n\n");
+	strbuf_addstr(buf, body);
+}
+
 static int update_squash_messages(struct repository *r,
 				  enum todo_command command,
 				  struct commit *commit,

@@ -1782,12 +1793,7 @@ static int update_squash_messages(struct repository *r,
 	find_commit_subject(message, &body);
 
 	if (command == TODO_SQUASH) {
-		unlink(rebase_path_fixup_msg());
-		strbuf_addf(&buf, "\n%c ", comment_line_char);
-		strbuf_addf(&buf, _("This is the commit message #%d:"),
-			    ++opts->current_fixup_count + 1);
-		strbuf_addstr(&buf, "\n\n");
-		strbuf_addstr(&buf, body);
+		append_squash_message(&buf, body, opts);
 	} else if (command == TODO_FIXUP) {
 		strbuf_addf(&buf, "\n%c ", comment_line_char);
 		strbuf_addf(&buf, _("The commit message #%d will be skipped:"),

@@ -1718,15 +1718,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
+static size_t subject_length(const char *body)
+{
+	size_t i, len = 0;
+	char c;
+	int blank_line = 1;
+	for (i = 0, c = body[i]; c; c = body[++i]) {
+		if (c == '\n') {
+			if (blank_line)
+				return len;
+			len = i + 1;
+			blank_line = 1;
+		} else if (!isspace(c)) {
+			blank_line = 0;
+		}
+	}
+	return blank_line ? len : i;
+}
+
 static void append_squash_message(struct strbuf *buf, const char *body,
 				  struct replay_opts *opts)
 {
+	size_t commented_len = 0;
+
 	unlink(rebase_path_fixup_msg());
+	if (starts_with(body, "squash!") || starts_with(body, "fixup!"))
+		commented_len = subject_length(body);
 	strbuf_addf(buf, "\n%c ", comment_line_char);
 	strbuf_addf(buf, _("This is the commit message #%d:"),
 		    ++opts->current_fixup_count + 1);
 	strbuf_addstr(buf, "\n\n");
-	strbuf_addstr(buf, body);
+	strbuf_add_commented_lines(buf, body, commented_len);
+	strbuf_addstr(buf, body + commented_len);
 }
 
 static int update_squash_messages(struct repository *r,

@@ -81,8 +81,7 @@ test_auto_squash () {
 	echo 1 >file1 &&
 	git add -u &&
 	test_tick &&
-	git commit -m "squash! first" &&
-
+	git commit -m "squash! first" -m "extra para for first" &&
 	git tag $1 &&
 	test_tick &&
 	git rebase $2 -i HEAD^^^ &&

@@ -139,7 +138,7 @@ test_expect_success 'auto squash that matches 2 commits' '
 	echo 1 >file1 &&
 	git add -u &&
 	test_tick &&
-	git commit -m "squash! first" &&
+	git commit -m "squash! first" -m "extra para for first" &&
 	git tag final-multisquash &&
 	test_tick &&
 	git rebase --autosquash -i HEAD~4 &&

@@ -192,7 +191,7 @@ test_expect_success 'auto squash that matches a sha1' '
 	git add -u &&
 	test_tick &&
 	oid=$(git rev-parse --short HEAD^) &&
-	git commit -m "squash! $oid" &&
+	git commit -m "squash! $oid" -m "extra para" &&
 	git tag final-shasquash &&
 	test_tick &&
 	git rebase --autosquash -i HEAD^^^ &&

@@ -203,7 +202,7 @@ test_expect_success 'auto squash that matches a sha1' '
 	git cat-file blob HEAD^:file1 >actual &&
 	test_cmp expect actual &&
 	git cat-file commit HEAD^ >commit &&
-	grep squash commit >actual &&
+	grep "extra para" commit >actual &&
 	test_line_count = 1 actual
 '
 

@@ -213,7 +212,7 @@ test_expect_success 'auto squash that matches longer sha1' '
 	git add -u &&
 	test_tick &&
 	oid=$(git rev-parse --short=11 HEAD^) &&
-	git commit -m "squash! $oid" &&
+	git commit -m "squash! $oid" -m "extra para" &&
 	git tag final-longshasquash &&
 	test_tick &&
 	git rebase --autosquash -i HEAD^^^ &&

@@ -224,7 +223,7 @@ test_expect_success 'auto squash that matches longer sha1' '
 	git cat-file blob HEAD^:file1 >actual &&
 	test_cmp expect actual &&
 	git cat-file commit HEAD^ >commit &&
-	grep squash commit >actual &&
+	grep "extra para" commit >actual &&
 	test_line_count = 1 actual
 '
 

@@ -233,7 +232,7 @@ test_auto_commit_flags () {
 	echo 1 >file1 &&
 	git add -u &&
 	test_tick &&
-	git commit --$1 first-commit &&
+	git commit --$1 first-commit -m "extra para for first" &&
 	git tag final-commit-$1 &&
 	test_tick &&
 	git rebase --autosquash -i HEAD^^^ &&

@@ -261,11 +260,11 @@ test_auto_fixup_fixup () {
 	echo 1 >file1 &&
 	git add -u &&
 	test_tick &&
-	git commit -m "$1! first" &&
+	git commit -m "$1! first" -m "extra para for first" &&
 	echo 2 >file1 &&
 	git add -u &&
 	test_tick &&
-	git commit -m "$1! $2! first" &&
+	git commit -m "$1! $2! first" -m "second extra para for first" &&
 	git tag "final-$1-$2" &&
 	test_tick &&
 	(

@@ -326,12 +325,12 @@ test_expect_success C_LOCALE_OUTPUT 'autosquash with custom inst format' '
 	git add -u &&
 	test_tick &&
 	oid=$(git rev-parse --short HEAD^) &&
-	git commit -m "squash! $oid" &&
+	git commit -m "squash! $oid" -m "extra para for first" &&
 	echo 1 >file1 &&
 	git add -u &&
 	test_tick &&
 	subject=$(git log -n 1 --format=%s HEAD~2) &&
-	git commit -m "squash! $subject" &&
+	git commit -m "squash! $subject" -m "second extra para for first" &&
 	git tag final-squash-instFmt &&
 	test_tick &&
 	git rebase --autosquash -i HEAD~4 &&

@@ -342,8 +341,8 @@ test_expect_success C_LOCALE_OUTPUT 'autosquash with custom inst format' '
 	git cat-file blob HEAD^:file1 >actual &&
 	test_cmp expect actual &&
 	git cat-file commit HEAD^ >commit &&
-	grep squash commit >actual &&
-	test_line_count = 2 actual
+	grep first commit >actual &&
+	test_line_count = 3 actual
 '
 
 test_expect_success 'autosquash with empty custom instructionFormat' '

@@ -226,10 +226,6 @@ test_commit_autosquash_multi_encoding () {
 		git rev-list HEAD >actual &&
 		test_line_count = 3 actual &&
 		iconv -f $old -t UTF-8 "$TEST_DIRECTORY"/t3900/$msg >expect &&
-		if test $flag = squash; then
-			subject="$(head -1 expect)" &&
-			printf "\nsquash! %s\n" "$subject" >>expect
-		fi &&
 		git cat-file commit HEAD^ >raw &&
 		(sed "1,/^$/d" raw | iconv -f $new -t utf-8) >actual &&
 		test_cmp expect actual

@@ -1884,8 +1884,7 @@ static void record_in_rewritten(struct object_id *oid,
 }
 
 static int do_pick_commit(struct repository *r,
-			  enum todo_command command,
-			  struct commit *commit,
+			  struct todo_item *item,
 			  struct replay_opts *opts,
 			  int final_fixup, int *check_todo)
 {

@@ -1898,6 +1897,8 @@ static int do_pick_commit(struct repository *r,
 	struct commit_message msg = { NULL, NULL, NULL, NULL };
 	struct strbuf msgbuf = STRBUF_INIT;
 	int res, unborn = 0, reword = 0, allow, drop_commit;
+	enum todo_command command = item->command;
+	struct commit *commit = item->commit;
 
 	if (opts->no_commit) {
 		/*

@@ -4147,8 +4148,8 @@ static int pick_commits(struct repository *r,
 				setenv(GIT_REFLOG_ACTION, reflog_message(opts,
 					command_to_string(item->command), NULL),
 					1);
-			res = do_pick_commit(r, item->command, item->commit,
-					     opts, is_final_fixup(todo_list),
+			res = do_pick_commit(r, item, opts,
+					     is_final_fixup(todo_list),
 					     &check_todo);
 			if (is_rebase_i(opts))
 				setenv(GIT_REFLOG_ACTION, prev_reflog_action, 1);

@@ -4610,11 +4611,14 @@ static int single_pick(struct repository *r,
 		       struct replay_opts *opts)
 {
 	int check_todo;
+	struct todo_item item;
+
+	item.command = opts->action == REPLAY_PICK ?
+			TODO_PICK : TODO_REVERT;
+	item.commit = cmit;
 
 	setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
-	return do_pick_commit(r, opts->action == REPLAY_PICK ?
-			      TODO_PICK : TODO_REVERT, cmit, opts, 0,
-			      &check_todo);
+	return do_pick_commit(r, &item, opts, 0, &check_todo);
 }
 
 int sequencer_pick_revisions(struct repository *r,

@@ -1736,6 +1736,15 @@ static size_t subject_length(const char *body)
 	return blank_line ? len : i;
 }
 
+static const char first_commit_msg_str[] =
+N_("This is the 1st commit message:");
+static const char nth_commit_msg_fmt[] =
+N_("This is the commit message #%d:");
+static const char skip_nth_commit_msg_fmt[] =
+N_("The commit message #%d will be skipped:");
+static const char combined_commit_msg_str[] =
+N_("This is a combination of %d commits.");
+
 static void append_squash_message(struct strbuf *buf, const char *body,
 				  struct replay_opts *opts)
 {

@@ -1745,7 +1754,7 @@ static void append_squash_message(struct strbuf *buf, const char *body,
 	if (starts_with(body, "squash!") || starts_with(body, "fixup!"))
 		commented_len = subject_length(body);
 	strbuf_addf(buf, "\n%c ", comment_line_char);
-	strbuf_addf(buf, _("This is the commit message #%d:"),
+	strbuf_addf(buf, _(nth_commit_msg_fmt),
 		    ++opts->current_fixup_count + 1);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len);

@@ -1774,7 +1783,7 @@ static int update_squash_messages(struct repository *r,
 			buf.buf : strchrnul(buf.buf, '\n');
 
 		strbuf_addf(&header, "%c ", comment_line_char);
-		strbuf_addf(&header, _("This is a combination of %d commits."),
+		strbuf_addf(&header, _(combined_commit_msg_str),
 			    opts->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);

@@ -1801,9 +1810,9 @@ static int update_squash_messages(struct repository *r,
 		}
 
 		strbuf_addf(&buf, "%c ", comment_line_char);
-		strbuf_addf(&buf, _("This is a combination of %d commits."), 2);
+		strbuf_addf(&buf, _(combined_commit_msg_str), 2);
 		strbuf_addf(&buf, "\n%c ", comment_line_char);
-		strbuf_addstr(&buf, _("This is the 1st commit message:"));
+		strbuf_addstr(&buf, _(first_commit_msg_str));
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_addstr(&buf, body);
 

@@ -1819,7 +1828,7 @@ static int update_squash_messages(struct repository *r,
 		append_squash_message(&buf, body, opts);
 	} else if (command == TODO_FIXUP) {
 		strbuf_addf(&buf, "\n%c ", comment_line_char);
-		strbuf_addf(&buf, _("The commit message #%d will be skipped:"),
+		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
 			    ++opts->current_fixup_count + 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body));

@@ -44,7 +44,9 @@ void append_todo_help(int command_count,
 "r, reword <commit> = use commit, but edit the commit message\n"
 "e, edit <commit> = use commit, but stop for amending\n"
 "s, squash <commit> = use commit, but meld into previous commit\n"
-"f, fixup <commit> = like \"squash\", but discard this commit's log message\n"
+"f, fixup [-C | -c] <commit> = like \"squash\", but discard this\n"
+"                   commit's log message. Use -C to replace with this\n"
+"                   commit message or -c to edit the commit message\n"
 "x, exec <command> = run command (the rest of the line) using shell\n"
 "b, break = stop here (continue rebase later with 'git rebase --continue')\n"
 "d, drop <commit> = remove commit\n"

@@ -1718,6 +1718,12 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 static size_t subject_length(const char *body)
 {
 	size_t i, len = 0;

@@ -1740,34 +1746,177 @@ static const char first_commit_msg_str[] =
 N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] =
 N_("This is the commit message #%d:");
+static const char skip_first_commit_msg_str[] =
+N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] =
 N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_str[] =
 N_("This is a combination of %d commits.");
 
-static void append_squash_message(struct strbuf *buf, const char *body,
-				  struct replay_opts *opts)
+static int check_fixup_flag(enum todo_command command,
+			    enum todo_item_flags flag)
+{
+	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
+					 (flag & TODO_EDIT_FIXUP_MSG));
+}
+
+/*
+ * Wrapper around strbuf_add_commented_lines() which avoids double
+ * commenting commit subjects.
+ */
+static void add_commented_lines(struct strbuf *buf, const void *str, size_t len)
+{
+	const char *s = str;
+	while (len > 0 && s[0] == comment_line_char) {
+		size_t count;
+		const char *n = memchr(s, '\n', len);
+		if (!n)
+			count = len;
+		else
+			count = n - s + 1;
+		strbuf_add(buf, s, count);
+		s += count;
+		len -= count;
+	}
+	strbuf_add_commented_lines(buf, s, len);
+}
+
+/* Does the current fixup chain contain a squash command? */
+static int seen_squash(struct replay_opts *opts)
 {
-	size_t commented_len = 0;
+	return starts_with(opts->current_fixups.buf, "squash") ||
+		strstr(opts->current_fixups.buf, "\nsquash");
+}
 
-	unlink(rebase_path_fixup_msg());
-	if (starts_with(body, "squash!") || starts_with(body, "fixup!"))
+static void update_comment_bufs(struct strbuf *buf1, struct strbuf *buf2, int n)
+{
+	strbuf_setlen(buf1, 2);
+	strbuf_addf(buf1, nth_commit_msg_fmt, n);
+	strbuf_addch(buf1, '\n');
+	strbuf_setlen(buf2, 2);
+	strbuf_addf(buf2, skip_nth_commit_msg_fmt, n);
+	strbuf_addch(buf2, '\n');
+}
+
+/*
+ * Comment out any un-commented commit messages, updating the message comments
+ * to say they will be skipped but do not comment out the empty lines that
+ * surround commit messages and their comments.
+ */
+static void update_squash_message_for_fixup(struct strbuf *msg)
+{
+	void (*copy_lines)(struct strbuf *, const void *, size_t) = strbuf_add;
+	struct strbuf buf1 = STRBUF_INIT, buf2 = STRBUF_INIT;
+	const char *s, *start;
+	char *orig_msg;
+	size_t orig_msg_len;
+	int i = 1;
+
+	strbuf_addf(&buf1, "# %s\n", first_commit_msg_str);
+	strbuf_addf(&buf2, "# %s\n", skip_first_commit_msg_str);
+	s = start = orig_msg = strbuf_detach(msg, &orig_msg_len);
+	while (s) {
+		const char *next;
+		size_t off;
+		if (skip_prefix(s, buf1.buf, &next)) {
+			/*
+			 * Copy the last message, preserving the blank line
+			 * preceding the current line
+			 */
+			off = (s > start + 1 && s[-2] == '\n') ? 1 : 0;
+			copy_lines(msg, start, s - start - off);
+			if (off)
+				strbuf_addch(msg, '\n');
+			/*
+			 * The next message needs to be commented out but the
+			 * message header is already commented out so just copy
+			 * it and the blank line that follows it.
+			 */
+			strbuf_addbuf(msg, &buf2);
+			if (*next == '\n')
+				strbuf_addch(msg, *next++);
+			start = s = next;
+			copy_lines = add_commented_lines;
+			update_comment_bufs(&buf1, &buf2, ++i);
+		} else if (skip_prefix(s, buf2.buf, &next)) {
+			off = (s > start + 1 && s[-2] == '\n') ? 1 : 0;
+			copy_lines(msg, start, s - start - off);
+			start = s - off;
+			s = next;
+			copy_lines = strbuf_add;
+			update_comment_bufs(&buf1, &buf2, ++i);
+		} else {
+			s = strchr(s, '\n');
+			if (s)
+				s++;
+		}
+	}
+	copy_lines(msg, start, orig_msg_len - (start - orig_msg));
+	free(orig_msg);
+	strbuf_release(&buf1);
+	strbuf_release(&buf2);
+}
+
+static int append_squash_message(struct strbuf *buf, const char *body,
+			 enum todo_command command, struct replay_opts *opts,
+			 enum todo_item_flags flag)
+{
+	const char *fixup_msg;
+	size_t commented_len = 0, fixup_off;
+	/*
+	 * amend is non-interactive and not normally used with fixup!
+	 * or squash! commits, so only comment out those subjects when
+	 * squashing commit messages.
+	 */
+	if (starts_with(body, "amend!") ||
+	    ((command == TODO_SQUASH || seen_squash(opts)) &&
+	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
 		commented_len = subject_length(body);
+
 	strbuf_addf(buf, "\n%c ", comment_line_char);
 	strbuf_addf(buf, _(nth_commit_msg_fmt),
 		    ++opts->current_fixup_count + 1);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len);
+	/* buf->buf may be reallocated so store an offset into the buffer */
+	fixup_off = buf->len;
 	strbuf_addstr(buf, body + commented_len);
+
+	/* fixup -C after squash behaves like squash */
+	if (check_fixup_flag(command, flag) && !seen_squash(opts)) {
+		/*
+		 * We're replacing the commit message so we need to
+		 * append the Signed-off-by: trailer if the user
+		 * requested '--signoff'.
+		 */
+		if (opts->signoff)
+			append_signoff(buf, 0, 0);
+
+		if ((command == TODO_FIXUP) &&
+		    (flag & TODO_REPLACE_FIXUP_MSG)) {
+			fixup_msg = skip_blank_lines(buf->buf + fixup_off);
+			if (write_message(fixup_msg, strlen(fixup_msg),
+					rebase_path_fixup_msg(), 0))
+				return error(_("cannot write '%s'"),
+					rebase_path_fixup_msg());
+		} else {
+			unlink(rebase_path_fixup_msg());
+		}
+	} else  {
+		unlink(rebase_path_fixup_msg());
+	}
+
+	return 0;
 }
 
 static int update_squash_messages(struct repository *r,
 				  enum todo_command command,
 				  struct commit *commit,
-				  struct replay_opts *opts)
+				  struct replay_opts *opts,
+				  enum todo_item_flags flag)
 {
 	struct strbuf buf = STRBUF_INIT;
-	int res;
+	int res = 0;
 	const char *message, *body;
 	const char *encoding = get_commit_output_encoding();
 

@@ -1787,6 +1936,8 @@ static int update_squash_messages(struct repository *r,
 			    opts->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
+		if (check_fixup_flag(command, flag) && !seen_squash(opts))
+			update_squash_message_for_fixup(&buf);
 	} else {
 		struct object_id head;
 		struct commit *head_commit;

@@ -1800,7 +1951,7 @@ static int update_squash_messages(struct repository *r,
 			return error(_("could not read HEAD's commit message"));
 
 		find_commit_subject(head_message, &body);
-		if (command == TODO_FIXUP) {
+		if (command == TODO_FIXUP && !flag) {
 			if (write_message(body, strlen(body),
 					  rebase_path_fixup_msg(), 0)) {
 				unuse_commit_buffer(head_commit, head_message);

@@ -1808,13 +1959,17 @@ static int update_squash_messages(struct repository *r,
 					     rebase_path_fixup_msg());
 			}
 		}
-
 		strbuf_addf(&buf, "%c ", comment_line_char);
 		strbuf_addf(&buf, _(combined_commit_msg_str), 2);
 		strbuf_addf(&buf, "\n%c ", comment_line_char);
-		strbuf_addstr(&buf, _(first_commit_msg_str));
+		strbuf_addstr(&buf, check_fixup_flag(command, flag) ?
+			      _(skip_first_commit_msg_str) :
+			      _(first_commit_msg_str));
 		strbuf_addstr(&buf, "\n\n");
-		strbuf_addstr(&buf, body);
+		if (check_fixup_flag(command, flag))
+			strbuf_add_commented_lines(&buf, body, strlen(body));
+		else
+			strbuf_addstr(&buf, body);
 
 		unuse_commit_buffer(head_commit, head_message);
 	}

@@ -1824,8 +1979,8 @@ static int update_squash_messages(struct repository *r,
 			     oid_to_hex(&commit->object.oid));
 	find_commit_subject(message, &body);
 
-	if (command == TODO_SQUASH) {
-		append_squash_message(&buf, body, opts);
+	if (command == TODO_SQUASH || check_fixup_flag(command, flag)) {
+		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
 		strbuf_addf(&buf, "\n%c ", comment_line_char);
 		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),

@@ -1836,7 +1991,9 @@ static int update_squash_messages(struct repository *r,
 		return error(_("unknown command: %d"), command);
 	unuse_commit_buffer(commit, message);
 
-	res = write_message(buf.buf, buf.len, rebase_path_squash_msg(), 0);
+	if (!res)
+		res = write_message(buf.buf, buf.len, rebase_path_squash_msg(),
+				    0);
 	strbuf_release(&buf);
 
 	if (!res) {

@@ -2037,7 +2194,8 @@ static int do_pick_commit(struct repository *r,
 	if (command == TODO_REWORD)
 		reword = 1;
 	else if (is_fixup(command)) {
-		if (update_squash_messages(r, command, commit, opts))
+		if (update_squash_messages(r, command, commit,
+					   opts, item->flags))
 			return -1;
 		flags |= AMEND_MSG;
 		if (!final_fixup)

@@ -2202,10 +2360,6 @@ static int read_and_refresh_cache(struct repository *r,
 	return 0;
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG = 1
-};
-
 void todo_list_release(struct todo_list *todo_list)
 {
 	strbuf_release(&todo_list->buf);

@@ -2292,6 +2446,18 @@ static int parse_insn_line(struct repository *r, struct todo_item *item,
 		return 0;
 	}
 
+	if (item->command == TODO_FIXUP) {
+		if (skip_prefix(bol, "-C", &bol) &&
+		   (*bol == ' ' || *bol == '\t')) {
+			bol += strspn(bol, " \t");
+			item->flags |= TODO_REPLACE_FIXUP_MSG;
+		} else if (skip_prefix(bol, "-c", &bol) &&
+				  (*bol == ' ' || *bol == '\t')) {
+			bol += strspn(bol, " \t");
+			item->flags |= TODO_EDIT_FIXUP_MSG;
+		}
+	}
+
 	if (item->command == TODO_MERGE) {
 		if (skip_prefix(bol, "-C", &bol))
 			bol += strspn(bol, " \t");

@@ -5298,6 +5464,14 @@ static void todo_list_to_strbuf(struct repository *r, struct todo_list *todo_lis
 					  short_commit_name(item->commit) :
 					  oid_to_hex(&item->commit->object.oid);
 
+			if (item->command == TODO_FIXUP) {
+				if (item->flags & TODO_EDIT_FIXUP_MSG)
+					strbuf_addstr(buf, " -c");
+				else if (item->flags & TODO_REPLACE_FIXUP_MSG) {
+					strbuf_addstr(buf, " -C");
+				}
+			}
+
 			if (item->command == TODO_MERGE) {
 				if (item->flags & TODO_EDIT_MERGE_MSG)
 					strbuf_addstr(buf, " -c");

@@ -5672,6 +5672,12 @@ static int subject2item_cmp(const void *fndata,
 
 define_commit_slab(commit_todo_item, struct todo_item *);
 
+static inline int skip_fixup_amend_squash(const char *subject, const char **p) {
+	return skip_prefix(subject, "fixup! ", p) ||
+	       skip_prefix(subject, "amend! ", p) ||
+	       skip_prefix(subject, "squash! ", p);
+}
+
 /*
  * Rearrange the todo list that has both "pick commit-id msg" and "pick
  * commit-id fixup!/squash! msg" in it so that the latter is put immediately

@@ -5730,15 +5736,13 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 		format_subject(&buf, subject, " ");
 		subject = subjects[i] = strbuf_detach(&buf, &subject_len);
 		unuse_commit_buffer(item->commit, commit_buffer);
-		if ((skip_prefix(subject, "fixup! ", &p) ||
-		     skip_prefix(subject, "squash! ", &p))) {
+		if (skip_fixup_amend_squash(subject, &p)) {
 			struct commit *commit2;
 
 			for (;;) {
 				while (isspace(*p))
 					p++;
-				if (!skip_prefix(p, "fixup! ", &p) &&
-				    !skip_prefix(p, "squash! ", &p))
+				if (!skip_fixup_amend_squash(p, &p))
 					break;
 			}
 

@@ -5768,9 +5772,14 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 		}
 		if (i2 >= 0) {
 			rearranged = 1;
-			todo_list->items[i].command =
-				starts_with(subject, "fixup!") ?
-				TODO_FIXUP : TODO_SQUASH;
+			if (starts_with(subject, "fixup!")) {
+				todo_list->items[i].command = TODO_FIXUP;
+			} else if (starts_with(subject, "amend!")) {
+				todo_list->items[i].command = TODO_FIXUP;
+				todo_list->items[i].flags = TODO_REPLACE_FIXUP_MSG;
+			} else {
+				todo_list->items[i].command = TODO_SQUASH;
+			}
 			if (tail[i2] < 0) {
 				next[i] = next[i2];
 				next[i2] = i;

@@ -187,4 +187,16 @@ test_expect_success 'first fixup -C commented out in sequence fixup fixup -C fix
 	test_commit_message HEAD expected-message
 '
 
+test_expect_success 'fixup -C works upon --autosquash with amend!' '
+	git checkout --detach branch &&
+	FAKE_COMMIT_AMEND=squashed \
+		FAKE_MESSAGE_COPY=actual-squash-message \
+		git -c commit.status=false rebase -ik --autosquash \
+						--signoff A &&
+	git diff-tree --exit-code --patch HEAD branch -- &&
+	test_cmp_rev HEAD^ A &&
+	test_i18ncmp "$TEST_DIRECTORY/t3437/expected-squash-message" \
+		actual-squash-message
+'
+
 test_done

@@ -4,6 +4,7 @@
 #
 # - override the commit message with $FAKE_COMMIT_MESSAGE
 # - amend the commit message with $FAKE_COMMIT_AMEND
+# - copy the original commit message to a file with $FAKE_MESSAGE_COPY
 # - check that non-commit messages have a certain line count with $EXPECT_COUNT
 # - check the commit count in the commit message header with $EXPECT_HEADER_COUNT
 # - rewrite a rebase -i script as directed by $FAKE_LINES.

@@ -33,6 +34,7 @@ set_fake_editor () {
 			exit
 		test -z "$FAKE_COMMIT_MESSAGE" || echo "$FAKE_COMMIT_MESSAGE" > "$1"
 		test -z "$FAKE_COMMIT_AMEND" || echo "$FAKE_COMMIT_AMEND" >> "$1"
+		test -z "$FAKE_MESSAGE_COPY" || cat "$1" >"$FAKE_MESSAGE_COPY"
 		exit
 		;;
 	esac

@@ -51,6 +53,8 @@ set_fake_editor () {
 			action="$line";;
 		exec_*|x_*|break|b)
 			echo "$line" | sed 's/_/ /g' >> "$1";;
+		merge_*|fixup_*)
+			action=$(echo "$line" | sed 's/_/ /g');;
 		"#")
 			echo '# comment' >> "$1";;
 		">")

@@ -0,0 +1,190 @@
+#!/bin/sh
+#
+# Copyright (c) 2018 Phillip Wood
+#
+
+test_description='git rebase interactive fixup options
+
+This test checks the "fixup [-C|-c]" command of rebase interactive.
+In addition to amending the contents of the commit, "fixup -C"
+replaces the original commit message with the message of the fixup
+commit. "fixup -c" also replaces the original message, but opens the
+editor to allow the user to edit the message before committing.
+'
+
+. ./test-lib.sh
+
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+EMPTY=""
+
+test_commit_message () {
+	rev="$1" && # commit or tag we want to test
+	file="$2" && # test against the content of a file
+	git show --no-patch --pretty=format:%B "$rev" >actual-message &&
+	if test "$2" = -m
+	then
+		str="$3" && # test against a string
+		printf "%s\n" "$str" >tmp-expected-message &&
+		file="tmp-expected-message"
+	fi
+	test_cmp "$file" actual-message
+}
+
+get_author () {
+	rev="$1" &&
+	git log -1 --pretty=format:"%an %ae" "$rev"
+}
+
+test_expect_success 'setup' '
+	cat >message <<-EOF &&
+		amend! B
+		${EMPTY}
+		new subject
+		${EMPTY}
+		new
+		body
+		EOF
+
+	sed "1,2d" message >expected-message &&
+
+	test_commit A A &&
+	test_commit B B &&
+	get_author HEAD >expected-author &&
+	ORIG_AUTHOR_NAME="$GIT_AUTHOR_NAME" &&
+	ORIG_AUTHOR_EMAIL="$GIT_AUTHOR_EMAIL" &&
+	GIT_AUTHOR_NAME="Amend Author" &&
+	GIT_AUTHOR_EMAIL="amend@example.com" &&
+	test_commit "$(cat message)" A A1 A1 &&
+	test_commit A2 A &&
+	test_commit A3 A &&
+	GIT_AUTHOR_NAME="$ORIG_AUTHOR_NAME" &&
+	GIT_AUTHOR_EMAIL="$ORIG_AUTHOR_EMAIL" &&
+	git checkout -b conflicts-branch A &&
+	test_commit conflicts A &&
+
+	set_fake_editor &&
+	git checkout -b branch B &&
+	echo B1 >B &&
+	test_tick &&
+	git commit --fixup=HEAD -a &&
+	test_tick &&
+	git commit --allow-empty -F - <<-EOF &&
+		amend! B
+		${EMPTY}
+		B
+		${EMPTY}
+		edited 1
+		EOF
+	test_tick &&
+	git commit --allow-empty -F - <<-EOF &&
+		amend! amend! B
+		${EMPTY}
+		B
+		${EMPTY}
+		edited 1
+		${EMPTY}
+		edited 2
+		EOF
+	echo B2 >B &&
+	test_tick &&
+	FAKE_COMMIT_AMEND="edited squash" git commit --squash=HEAD -a &&
+	echo B3 >B &&
+	test_tick &&
+	git commit -a -F - <<-EOF &&
+		amend! amend! amend! B
+		${EMPTY}
+		B
+		${EMPTY}
+		edited 1
+		${EMPTY}
+		edited 2
+		${EMPTY}
+		edited 3
+		EOF
+
+	GIT_AUTHOR_NAME="Rebase Author" &&
+	GIT_AUTHOR_EMAIL="rebase.author@example.com" &&
+	GIT_COMMITTER_NAME="Rebase Committer" &&
+	GIT_COMMITTER_EMAIL="rebase.committer@example.com"
+'
+
+test_expect_success 'simple fixup -C works' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout --detach A2 &&
+	FAKE_LINES="1 fixup_-C 2" git rebase -i B &&
+	test_cmp_rev HEAD^ B &&
+	test_cmp_rev HEAD^{tree} A2^{tree} &&
+	test_commit_message HEAD -m "A2"
+'
+
+test_expect_success 'simple fixup -c works' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout --detach A2 &&
+	git log -1 --pretty=format:%B >expected-fixup-message &&
+	test_write_lines "" "Modified A2" >>expected-fixup-message &&
+	FAKE_LINES="1 fixup_-c 2" \
+		FAKE_COMMIT_AMEND="Modified A2" \
+		git rebase -i B &&
+	test_cmp_rev HEAD^ B &&
+	test_cmp_rev HEAD^{tree} A2^{tree} &&
+	test_commit_message HEAD expected-fixup-message
+'
+
+test_expect_success 'fixup -C removes amend! from message' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout --detach A1 &&
+	FAKE_LINES="1 fixup_-C 2" git rebase -i A &&
+	test_cmp_rev HEAD^ A &&
+	test_cmp_rev HEAD^{tree} A1^{tree} &&
+	test_commit_message HEAD expected-message &&
+	get_author HEAD >actual-author &&
+	test_cmp expected-author actual-author
+'
+
+test_expect_success 'fixup -C with conflicts gives correct message' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout --detach A1 &&
+	test_must_fail env FAKE_LINES="1 fixup_-C 2" git rebase -i conflicts &&
+	git checkout --theirs -- A &&
+	git add A &&
+	FAKE_COMMIT_AMEND=edited git rebase --continue &&
+	test_cmp_rev HEAD^ conflicts &&
+	test_cmp_rev HEAD^{tree} A1^{tree} &&
+	test_write_lines "" edited >>expected-message &&
+	test_commit_message HEAD expected-message &&
+	get_author HEAD >actual-author &&
+	test_cmp expected-author actual-author
+'
+
+test_expect_success 'skipping fixup -C after fixup gives correct message' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout --detach A3 &&
+	test_must_fail env FAKE_LINES="1 fixup 2 fixup_-C 4" git rebase -i A &&
+	git reset --hard &&
+	FAKE_COMMIT_AMEND=edited git rebase --continue &&
+	test_commit_message HEAD -m "B"
+'
+
+test_expect_success 'sequence of fixup, fixup -C & squash --signoff works' '
+	git checkout --detach branch &&
+	FAKE_LINES="1 fixup 2 fixup_-C 3 fixup_-C 4 squash 5 fixup_-C 6" \
+		FAKE_COMMIT_AMEND=squashed \
+		FAKE_MESSAGE_COPY=actual-squash-message \
+		git -c commit.status=false rebase -ik --signoff A &&
+	git diff-tree --exit-code --patch HEAD branch -- &&
+	test_cmp_rev HEAD^ A &&
+	test_i18ncmp "$TEST_DIRECTORY/t3437/expected-squash-message" \
+		actual-squash-message
+'
+
+test_expect_success 'first fixup -C commented out in sequence fixup fixup -C fixup -C' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout branch && git checkout --detach branch~2 &&
+	git log -1 --pretty=format:%b >expected-message &&
+	FAKE_LINES="1 fixup 2 fixup_-C 3 fixup_-C 4" git rebase -i A &&
+	test_cmp_rev HEAD^ A &&
+	test_commit_message HEAD expected-message
+'
+
+test_done