[PATCH] rebase -i: reread the todo list if `exec` touched it

[PATCH] rebase -i: reread the todo list if `exec` touched it

[Johannes Schindelin]

From: Stephen Hicks <sdh@google.com>

In the scripted version of the interactive rebase, there was no internal
representation of the todo list; it was re-read before every command.
That allowed the hack that an `exec` command could append (or even
completely rewrite) the todo list.

This hack was broken by the partial conversion of the interactive rebase
to C, and this patch reinstates it.

We also add a small test to verify that this fix does not regress in the
future.

Signed-off-by: Stephen Hicks <sdh@google.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
Published-As: https://github.com/dscho/git/releases/tag/rebase-reread-todo-v1
Fetch-It-Via: git fetch https://github.com/dscho/git rebase-reread-todo-v1

	Based on https://github.com/git/git/pull/343

 sequencer.c                 | 22 ++++++++++++++++++++++
 t/t3428-rebase-edit-todo.sh | 14 ++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100755 t/t3428-rebase-edit-todo.sh

diff --git a/sequencer.c b/sequencer.c
index 77afecaebf0..3fe9fcdab72 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1200,6 +1200,7 @@ struct todo_list {
 	struct todo_item *items;
 	int nr, alloc, current;
 	int done_nr, total_nr;
+	struct stat_data stat;
 };
 
 #define TODO_LIST_INIT { STRBUF_INIT }
@@ -1330,6 +1331,7 @@ static int count_commands(struct todo_list *todo_list)
 static int read_populate_todo(struct todo_list *todo_list,
 			struct replay_opts *opts)
 {
+	struct stat st;
 	const char *todo_file = get_todo_path(opts);
 	int fd, res;
 
@@ -1343,6 +1345,11 @@ static int read_populate_todo(struct todo_list *todo_list,
 	}
 	close(fd);
 
+	res = stat(todo_file, &st);
+	if (res)
+		return error(_("could not stat '%s'"), todo_file);
+	fill_stat_data(&todo_list->stat, &st);
+
 	res = parse_insn_buffer(todo_list->buf.buf, todo_list);
 	if (res) {
 		if (is_rebase_i(opts))
@@ -2028,10 +2035,25 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 		} else if (item->command == TODO_EXEC) {
 			char *end_of_arg = (char *)(item->arg + item->arg_len);
 			int saved = *end_of_arg;
+			struct stat st;
 
 			*end_of_arg = '\0';
 			res = do_exec(item->arg);
 			*end_of_arg = saved;
+
+			/* Reread the todo file if it has changed. */
+			if (res)
+				; /* fall through */
+			else if (stat(get_todo_path(opts), &st))
+				res = error_errno(_("could not stat '%s'"),
+						  get_todo_path(opts));
+			else if (match_stat_data(&todo_list->stat, &st)) {
+				todo_list_release(todo_list);
+				if (read_populate_todo(todo_list, opts))
+					res = -1; /* message was printed */
+				/* `current` will be incremented below */
+				todo_list->current = -1;
+			}
 		} else if (!is_noop(item->command))
 			return error(_("unknown command %d"), item->command);
 
diff --git a/t/t3428-rebase-edit-todo.sh b/t/t3428-rebase-edit-todo.sh
new file mode 100755
index 00000000000..b9292dfc2a3
--- /dev/null
+++ b/t/t3428-rebase-edit-todo.sh
@@ -0,0 +1,14 @@
+#!/bin/sh
+
+test_description='rebase should reread the todo file if an exec modifies it'
+
+. ./test-lib.sh
+
+test_expect_success 'rebase exec modifies rebase-todo' '
+	test_commit initial &&
+	todo=.git/rebase-merge/git-rebase-todo &&
+	git rebase HEAD -x "echo exec touch F >>$todo" &&
+	test -e F
+'
+
+test_done

base-commit: e2cb6ab84c94f147f1259260961513b40c36108a
-- 
2.12.2.windows.2.406.gd14a8f8640f

Re: [PATCH] rebase -i: reread the todo list if `exec` touched it

[Steve Hicks]

On Wed, Apr 26, 2017 at 12:17 PM, Johannes Schindelin
<johannes.schindelin@gmx.de> wrote:
> From: Stephen Hicks <sdh@google.com>
>
> In the scripted version of the interactive rebase, there was no internal
> representation of the todo list; it was re-read before every command.
> That allowed the hack that an `exec` command could append (or even
> completely rewrite) the todo list.
>
> This hack was broken by the partial conversion of the interactive rebase
> to C, and this patch reinstates it.
>
> We also add a small test to verify that this fix does not regress in the
> future.
>
> Signed-off-by: Stephen Hicks <sdh@google.com>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Thanks for shepherding this through, Johannes!

For context on this "hack", I have a script [1] that allows passing
multiple branches at once (or all branches beneath a given root).  It
rewrites the todo file with some extra operations, like "branch",
"push", and "pop", allows editing the modified todo, and then rewrites
back to exec's.  The "branch" operation, in particular, appends an
"exec git checkout $branch; git reset --hard $commit" to the end of
the todo, so that no branches are moved until after all rebases are
successful.  I've found this multi-branch rebase workflow to be very
productive, and have been missing it the last few months, so I'm
looking forward to it working again soon.

[1] https://github.com/shicks/git-ir

Re: [PATCH] rebase -i: reread the todo list if `exec` touched it

[Johannes Schindelin]

Hi Steve,

On Wed, 26 Apr 2017, Steve Hicks wrote:

> On Wed, Apr 26, 2017 at 12:17 PM, Johannes Schindelin
> <johannes.schindelin@gmx.de> wrote:
> > From: Stephen Hicks <sdh@google.com>
> >
> > In the scripted version of the interactive rebase, there was no
> > internal representation of the todo list; it was re-read before every
> > command.  That allowed the hack that an `exec` command could append
> > (or even completely rewrite) the todo list.
> >
> > This hack was broken by the partial conversion of the interactive
> > rebase to C, and this patch reinstates it.
> >
> > We also add a small test to verify that this fix does not regress in
> > the future.
> 
> For context on this "hack", I have a script [1] that allows passing
> multiple branches at once (or all branches beneath a given root).  It
> rewrites the todo file with some extra operations, like "branch",
> "push", and "pop", allows editing the modified todo, and then rewrites
> back to exec's.

For what it's worth, I used a slightly different approach in the Git
garden shears [*1*] (essentially, `git rebase -i -p` Done Right): I
override the GIT_SEQUENCE_EDITOR to call the script in a specific mode
that rewrites the todo and then launches the editor as per `git var
GIT_EDITOR`.

Ciao,
Johannes

Footnote *1*:
https://github.com/git-for-windows/build-extra/blob/master/shears.sh