Re: [PATCH 2/3] rebase -i: re-fix short SHA-1 collision

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Junio,

On Fri, 17 Jan 2020, Junio C Hamano wrote:

> "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
> writes:
>
> > +	/* Expand the commit IDs */
> > +	todo_list_to_strbuf(r, &new_todo, &buf2, -1, 0);
> > +	strbuf_swap(&new_todo.buf, &buf2);
> > +	strbuf_release(&buf2);
> > +	new_todo.total_nr -= new_todo.nr;
> > +	if (todo_list_parse_insn_buffer(r, new_todo.buf.buf, &new_todo) < 0) {
> > +		fprintf(stderr, _(edit_todo_list_advice));
> > +		checkout_onto(r, opts, onto_name, &onto->object.oid, orig_head);
> > +		todo_list_release(&new_todo);
> > +		return error(_("invalid todo list after expanding IDs"));
> > +	}
>
> The above happens after edit_todo_list() returns and then the
> resulting data (i.e. new_todo) that came from the on-disk file has
> been parsed with an existing call to todo_lsit_parse_insn_buffer()?
>
> I am wondering when this if() statement would trigger, iow, under
> what condition the result of "Expand the commit IDs" operation fails
> to be parsed correctly, and what the user can do to remedy it.

You're right, this is defensive code to guard against bugs, but the error
message suggests that it might be a user error: it isn't.

> Especially given that incoming new_todo has passed the existing
> parse and check without hitting "return -1" we see above in the
> context, I am not sure if there is anything, other than any
> potential glitch in the added code above, that can cause this second
> parse_insn_buffer() to fail.  Shouldn't the body of if() be simply a
> BUG()?

It should.

Will fix,
Dscho

> Or am I somehow missing a hunk that removes an existing call to
> parse&check?
>
> > diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> > index ae6e55ce79..1cc9f36bc7 100755
> > --- a/t/t3404-rebase-interactive.sh
> > +++ b/t/t3404-rebase-interactive.sh
> > @@ -1264,13 +1264,24 @@ test_expect_success SHA1 'short SHA-1 setup' '
> >  test_expect_success SHA1 'short SHA-1 collide' '
> >  	test_when_finished "reset_rebase && git checkout master" &&
> >  	git checkout collide &&
> > +	colliding_sha1=6bcda37 &&
> > +	test $colliding_sha1 = "$(git rev-parse HEAD | cut -c 1-7)" &&
> >  	(
> >  		unset test_tick &&
> >  		test_tick &&
> >  		set_fake_editor &&
> >  		FAKE_COMMIT_MESSAGE="collide2 ac4f2ee" \
> > -		FAKE_LINES="reword 1 2" git rebase -i HEAD~2
> > -	)
> > +		FAKE_LINES="reword 1 break 2" git rebase -i HEAD~2 &&
> > +		test $colliding_sha1 = "$(git rev-parse HEAD | cut -c 1-7)" &&
> > +		grep "^pick $colliding_sha1 " \
> > +			.git/rebase-merge/git-rebase-todo.tmp &&
> > +		grep "^pick [0-9a-f]\{40\}" \
> > +			.git/rebase-merge/git-rebase-todo &&
> > +		git rebase --continue
> > +	) &&
> > +	collide2="$(git rev-parse HEAD~1 | cut -c 1-4)" &&
> > +	collide3="$(git rev-parse collide3 | cut -c 1-4)" &&
> > +	test "$collide2" = "$collide3"
> >  '
> >
> >  test_expect_success 'respect core.abbrev' '
>
>