rebase-interactive: warn if commit is dropped with `rebase --edit-todo'

When set to "warn" or "error", `rebase.missingCommitsCheck' would make
`rebase -i' warn if the user removed commits from the todo list to
prevent mistakes.  Unfortunately, `rebase --edit-todo' and `rebase
--continue' don't take it into account.

This adds the ability for `rebase --edit-todo' and `rebase --continue'
to check if commits were dropped by the user.  As both edit_todo_list()
and complete_action() parse the todo list and check for dropped commits,
the code doing so in the latter is removed to reduce duplication.
`edit_todo_list_advice' is removed from sequencer.c as it is no longer
used there.

This changes when a backup of the todo list is made.  Until now, it was
saved only once, before the initial edit.  Now, it is also made if the
original todo list has no errors or no dropped commits.  Thus, the
backup should be error-free.  Without this, sequencer_continue()
(`rebase --continue') could only compare the current todo list against
the original, unedited list.  Before this change, this file was only
used by edit_todo_list() and `rebase -p' to create the backup before
the initial edit, and check_todo_list_from_file(), only used by
`rebase -p' to check for dropped commits after its own initial edit.

If the edited list has an error, a file, `dropped', is created to
report the issue.  Otherwise, it is deleted.  Usually, the edited list
is compared against the list before editing, but if this file exists,
it will be compared to the backup.  Also, if the file exists,
sequencer_continue() checks the list for dropped commits.  If the
check was performed every time, it would fail when resuming a rebase
after resolving a conflict, as the backup will contain commits that
were picked, but they will not be in the new list.  It's safe to
ignore this check if `dropped' does not exist, because that means that
no errors were found at the last edition, so any missing commits here
have already been picked.

Five tests are added to t3404.  The tests for
`rebase.missingCommitsCheck = warn' and `rebase.missingCommitsCheck =
error' have a similar structure.  First, we start a rebase with an
incorrect command on the first line.  Then, we edit the todo list,
removing the first and the last lines.  This demonstrates that
`--edit-todo' notices dropped commits, but not when the command is
incorrect.  Then, we restore the original todo list, and edit it to
remove the last line.  This demonstrates that if we add a commit after
the initial edit, then remove it, `--edit-todo' will notice that it
has been dropped.  Then, the actual rebase takes place.  In the third
test, it is also checked that `--continue' will refuse to resume the
rebase if commits were dropped.  The fourth test checks that no errors
are raised when resuming a rebase after resolving a conflict, the fifth
checks that no errors are raised when editing the todo list after
pausing the rebase.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 179 insertions, 21 deletions

diff --git a/rebase-interactive.c b/rebase-interactive.c
index 45f29c2..ac001de 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -5,6 +5,7 @@
 #include "strbuf.h"
 #include "commit-slab.h"
 #include "config.h"
+#include "dir.h"
 
 static const char edit_todo_list_advice[] =
 N_("You can fix this with 'git rebase --edit-todo' "
@@ -97,21 +98,24 @@ int edit_todo_list(struct repository *r, struct todo_list *todo_list,
 		   struct todo_list *new_todo, const char *shortrevisions,
 		   const char *shortonto, unsigned flags)
 {
-	const char *todo_file = rebase_path_todo();
+	const char *todo_file = rebase_path_todo(),
+		*todo_backup = rebase_path_todo_backup();
 	unsigned initial = shortrevisions && shortonto;
+	int incorrect = 0;
 
 	/* If the user is editing the todo list, we first try to parse
 	 * it.  If there is an error, we do not return, because the user
 	 * might want to fix it in the first place. */
 	if (!initial)
-		todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list);
+		incorrect = todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list) |
+			file_exists(rebase_path_dropped());
 
 	if (todo_list_write_to_file(r, todo_list, todo_file, shortrevisions, shortonto,
 				    -1, flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP))
 		return error_errno(_("could not write '%s'"), todo_file);
 
-	if (initial &&
-	    todo_list_write_to_file(r, todo_list, rebase_path_todo_backup(),
+	if (!incorrect &&
+	    todo_list_write_to_file(r, todo_list, todo_backup,
 				    shortrevisions, shortonto, -1,
 				    (flags | TODO_LIST_APPEND_TODO_HELP) & ~TODO_LIST_SHORTEN_IDS) < 0)
 		return error(_("could not write '%s'."), rebase_path_todo_backup());
@@ -123,10 +127,23 @@ int edit_todo_list(struct repository *r, struct todo_list *todo_list,
 	if (initial && new_todo->buf.len == 0)
 		return -3;
 
-	/* For the initial edit, the todo list gets parsed in
-	 * complete_action(). */
-	if (!initial)
-		return todo_list_parse_insn_buffer(r, new_todo->buf.buf, new_todo);
+	if (todo_list_parse_insn_buffer(r, new_todo->buf.buf, new_todo)) {
+		fprintf(stderr, _(edit_todo_list_advice));
+		return -4;
+	}
+
+	if (incorrect) {
+		if (todo_list_check_against_backup(r, new_todo)) {
+			write_file(rebase_path_dropped(), "");
+			return -4;
+		}
+
+		if (incorrect > 0)
+			unlink(rebase_path_dropped());
+	} else if (todo_list_check(todo_list, new_todo)) {
+		write_file(rebase_path_dropped(), "");
+		return -4;
+	}
 
 	return 0;
 }
@@ -191,11 +208,27 @@ int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo)
 		"the level of warnings.\n"
 		"The possible behaviours are: ignore, warn, error.\n\n"));
 
+	fprintf(stderr, _(edit_todo_list_advice));
+
 leave_check:
 	clear_commit_seen(&commit_seen);
 	return res;
 }
 
+int todo_list_check_against_backup(struct repository *r, struct todo_list *todo_list)
+{
+	struct todo_list backup = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file(&backup.buf, rebase_path_todo_backup(), 0) > 0) {
+		todo_list_parse_insn_buffer(r, backup.buf.buf, &backup);
+		res = todo_list_check(&backup, todo_list);
+	}
+
+	todo_list_release(&backup);
+	return res;
+}
+
 int check_todo_list_from_file(struct repository *r)
 {
 	struct todo_list old_todo = TODO_LIST_INIT, new_todo = TODO_LIST_INIT;
@@ -214,10 +247,10 @@ int check_todo_list_from_file(struct repository *r)
 	res = todo_list_parse_insn_buffer(r, old_todo.buf.buf, &old_todo);
 	if (!res)
 		res = todo_list_parse_insn_buffer(r, new_todo.buf.buf, &new_todo);
-	if (!res)
-		res = todo_list_check(&old_todo, &new_todo);
 	if (res)
 		fprintf(stderr, _(edit_todo_list_advice));
+	if (!res)
+		res = todo_list_check(&old_todo, &new_todo);
 out:
 	todo_list_release(&old_todo);
 	todo_list_release(&new_todo);
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 5f41bf5..4af0c1f 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -11,7 +11,10 @@ void append_todo_help(unsigned keep_empty, int command_count,
 int edit_todo_list(struct repository *r, struct todo_list *todo_list,
 		   struct todo_list *new_todo, const char *shortrevisions,
 		   const char *shortonto, unsigned flags);
+
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
+int todo_list_check_against_backup(struct repository *r,
+				   struct todo_list *todo_list);
 
 int check_todo_list_from_file(struct repository *r);
 
diff --git a/sequencer.c b/sequencer.c
index 9365fc3..638098b 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -57,6 +57,8 @@ static GIT_PATH_FUNC(rebase_path, "rebase-merge")
 GIT_PATH_FUNC(rebase_path_todo, "rebase-merge/git-rebase-todo")
 GIT_PATH_FUNC(rebase_path_todo_backup, "rebase-merge/git-rebase-todo.backup")
 
+GIT_PATH_FUNC(rebase_path_dropped, "rebase-merge/dropped")
+
 /*
  * The rebase command lines that have already been processed. A line
  * is moved here when it is first handled, before any associated user
@@ -4239,6 +4241,14 @@ int sequencer_continue(struct repository *r, struct replay_opts *opts)
 	if (is_rebase_i(opts)) {
 		if ((res = read_populate_todo(r, &todo_list, opts)))
 			goto release_todo_list;
+
+		if (file_exists(rebase_path_dropped())) {
+			if ((res = todo_list_check_against_backup(r, &todo_list)))
+				goto release_todo_list;
+
+			unlink(rebase_path_dropped());
+		}
+
 		if (commit_staged_changes(r, opts, &todo_list)) {
 			res = -1;
 			goto release_todo_list;
@@ -4985,12 +4995,6 @@ int todo_list_write_to_file(struct repository *r, struct todo_list *todo_list,
 	return res;
 }
 
-static const char edit_todo_list_advice[] =
-N_("You can fix this with 'git rebase --edit-todo' "
-"and then run 'git rebase --continue'.\n"
-"Or you can abort the rebase with 'git rebase"
-" --abort'.\n");
-
 /* skip picking commits whose parents are unchanged */
 static int skip_unnecessary_picks(struct repository *r,
 				  struct todo_list *todo_list,
@@ -5088,11 +5092,7 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 		todo_list_release(&new_todo);
 
 		return error(_("nothing to do"));
-	}
-
-	if (todo_list_parse_insn_buffer(r, new_todo.buf.buf, &new_todo) ||
-	    todo_list_check(todo_list, &new_todo)) {
-		fprintf(stderr, _(edit_todo_list_advice));
+	} else if (res == -4) {
 		checkout_onto(r, opts, onto_name, &onto->object.oid, orig_head);
 		todo_list_release(&new_todo);
 
diff --git a/sequencer.h b/sequencer.h
index 5d4df08..84dc416 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -11,6 +11,7 @@ const char *git_path_commit_editmsg(void);
 const char *git_path_seq_dir(void);
 const char *rebase_path_todo(void);
 const char *rebase_path_todo_backup(void);
+const char *rebase_path_dropped(void);
 
 #define APPEND_SIGNOFF_DEDUP (1u << 0)
 
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b90ea0f..d79a3ef 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1463,6 +1463,127 @@ test_expect_success 'rebase -i respects rebase.missingCommitsCheck = error' '
 	test B = $(git cat-file commit HEAD^ | sed -ne \$p)
 '
 
+test_expect_success 'rebase --edit-todo respects rebase.missingCommitsCheck = ignore' '
+	test_config rebase.missingCommitsCheck ignore &&
+	rebase_setup_and_clean missing-commit &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="break 1 2 3 4 5" git rebase -i --root &&
+		FAKE_LINES="1 2 3 4" git rebase --edit-todo &&
+		git rebase --continue 2>actual
+	) &&
+	test D = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test_i18ngrep \
+		"Successfully rebased and updated refs/heads/missing-commit" \
+		actual
+'
+
+test_expect_success 'rebase --edit-todo respects rebase.missingCommitsCheck = warn' '
+	cat >expect <<-EOF &&
+	error: invalid line 1: badcmd $(git rev-list --pretty=oneline --abbrev-commit -1 master~4)
+	Warning: some commits may have been dropped accidentally.
+	Dropped commits (newer to older):
+	 - $(git rev-list --pretty=oneline --abbrev-commit -1 master)
+	 - $(git rev-list --pretty=oneline --abbrev-commit -1 master~4)
+	To avoid this message, use "drop" to explicitly remove a commit.
+	EOF
+	head -n4 expect >expect.2 &&
+	tail -n1 expect >>expect.2 &&
+	tail -n4 expect.2 >expect.3 &&
+	test_config rebase.missingCommitsCheck warn &&
+	rebase_setup_and_clean missing-commit &&
+	(
+		set_fake_editor &&
+		test_must_fail env FAKE_LINES="bad 1 2 3 4 5" \
+			git rebase -i --root &&
+		cp .git/rebase-merge/git-rebase-todo.backup orig &&
+		FAKE_LINES="2 3 4" git rebase --edit-todo 2>actual.2 &&
+		head -n6 actual.2 >actual &&
+		test_i18ncmp expect actual &&
+		cp orig .git/rebase-merge/git-rebase-todo &&
+		FAKE_LINES="1 2 3 4" git rebase --edit-todo 2>actual.2 &&
+		head -n4 actual.2 >actual &&
+		test_i18ncmp expect.3 actual &&
+		git rebase --continue 2>actual
+	) &&
+	test D = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test_i18ngrep \
+		"Successfully rebased and updated refs/heads/missing-commit" \
+		actual
+'
+
+test_expect_success 'rebase --edit-todo respects rebase.missingCommitsCheck = error' '
+	cat >expect <<-EOF &&
+	error: invalid line 1: badcmd $(git rev-list --pretty=oneline --abbrev-commit -1 master~4)
+	Warning: some commits may have been dropped accidentally.
+	Dropped commits (newer to older):
+	 - $(git rev-list --pretty=oneline --abbrev-commit -1 master)
+	 - $(git rev-list --pretty=oneline --abbrev-commit -1 master~4)
+	To avoid this message, use "drop" to explicitly remove a commit.
+
+	Use '\''git config rebase.missingCommitsCheck'\'' to change the level of warnings.
+	The possible behaviours are: ignore, warn, error.
+
+	You can fix this with '\''git rebase --edit-todo'\'' and then run '\''git rebase --continue'\''.
+	Or you can abort the rebase with '\''git rebase --abort'\''.
+	EOF
+	tail -n11 expect >expect.2 &&
+	head -n3 expect.2 >expect.3 &&
+	tail -n7 expect.2 >>expect.3 &&
+	test_config rebase.missingCommitsCheck error &&
+	rebase_setup_and_clean missing-commit &&
+	(
+		set_fake_editor &&
+		test_must_fail env FAKE_LINES="bad 1 2 3 4 5" \
+			git rebase -i --root &&
+		cp .git/rebase-merge/git-rebase-todo.backup orig &&
+		test_must_fail env FAKE_LINES="2 3 4" \
+			git rebase --edit-todo 2>actual &&
+		test_i18ncmp expect actual &&
+		test_must_fail git rebase --continue 2>actual &&
+		test_i18ncmp expect.2 actual &&
+		test_must_fail git rebase --edit-todo &&
+		cp orig .git/rebase-merge/git-rebase-todo &&
+		test_must_fail env FAKE_LINES="1 2 3 4" \
+			git rebase --edit-todo 2>actual &&
+		test_i18ncmp expect.3 actual &&
+		test_must_fail git rebase --continue 2>actual &&
+		test_i18ncmp expect.3 actual &&
+		cp orig .git/rebase-merge/git-rebase-todo &&
+		FAKE_LINES="1 2 3 4 drop 5" git rebase --edit-todo &&
+		git rebase --continue 2>actual
+	) &&
+	test D = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test_i18ngrep \
+		"Successfully rebased and updated refs/heads/missing-commit" \
+		actual
+'
+
+test_expect_success 'rebase.missingCommitsCheck = error after resolving conflicts' '
+	test_config rebase.missingCommitsCheck error &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="drop 1 break 2 3 4" git rebase -i A E
+	) &&
+	git rebase --edit-todo &&
+	test_must_fail git rebase --continue &&
+	echo x >file1 &&
+	git add file1 &&
+	git rebase --continue
+'
+
+test_expect_success 'rebase.missingCommitsCheck = error when editing for a second time' '
+	test_config rebase.missingCommitsCheck error &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 break 2 3" git rebase -i A D &&
+		cp .git/rebase-merge/git-rebase-todo todo &&
+		test_must_fail env FAKE_LINES=2 git rebase --edit-todo &&
+		GIT_SEQUENCE_EDITOR="cp todo" git rebase --edit-todo &&
+		git rebase --continue
+	)
+'
+
 test_expect_success 'respects rebase.abbreviateCommands with fixup, squash and exec' '
 	rebase_setup_and_clean abbrevcmd &&
 	test_commit "first" file1.txt "first line" first &&