Re: [PATCH v3 4/8] merge-recursive: new function for better colliding conflict resolutions

[Elijah Newren <newren@gmail.com>]

On Wed, Oct 31, 2018 at 6:57 AM Derrick Stolee <stolee@gmail.com> wrote:
>
> On 10/31/2018 9:53 AM, Derrick Stolee wrote:
> > On 10/19/2018 3:31 PM, Elijah Newren wrote:
> >> +#if 0 // #if-0-ing avoids unused function warning; will make live in
> >> next commit
> >> +static int handle_file_collision(struct merge_options *o,
> >> +                 const char *collide_path,
> >> +                 const char *prev_path1,
> >> +                 const char *prev_path2,
> >> +                 const char *branch1, const char *branch2,
> >> +                 const struct object_id *a_oid,
> >> +                 unsigned int a_mode,
> >> +                 const struct object_id *b_oid,
> >> +                 unsigned int b_mode)
> >> +{
> >> +    struct merge_file_info mfi;
> >> +    struct diff_filespec null, a, b;
> >> +    char *alt_path = NULL;
> >> +    const char *update_path = collide_path;
> >> +
> >> +    /*
> >> +     * In the recursive case, we just opt to undo renames
> >> +     */
> >> +    if (o->call_depth && (prev_path1 || prev_path2)) {
> >> +        /* Put first file (a_oid, a_mode) in its original spot */
> >> +        if (prev_path1) {
> >> +            if (update_file(o, 1, a_oid, a_mode, prev_path1))
> >> +                return -1;
> >> +        } else {
> >> +            if (update_file(o, 1, a_oid, a_mode, collide_path))
> >
> > The latest test coverage report [1] shows this if statement is never
> > run, so
> > it appears that every call to this method in the test suite has either
> > o->call_depth positive, prev_path1 non-NULL, or both prev_path1 and
> > prev_path2
> > NULL.
> >
> > Is there a way we can add a test case that calls this method with
> > o->call_depth
> > positive, prev_path1 NULL, and prev_path2 non-NULL?
> >
> >> +                return -1;
> >> +        }
> >> +
> >> +        /* Put second file (b_oid, b_mode) in its original spot */
> >> +        if (prev_path2) {
> >> +            if (update_file(o, 1, b_oid, b_mode, prev_path2))
> >
> > Since this line is covered, we _do_ call the method with prev_path2
> > non-NULL, but
> > prev_path1 must be non-NULL in all cases.
> >
> > I may have found a reason why this doesn't happen in one of the
> > callers you introduced.
> > I'm going to comment on PATCH 8/8 to see if that is the case.
>
> Nevermind on the PATCH 8/8 situation. I thought I saw you pass (a->path,
> NULL) and
> (b->path, NULL) into the (prev_path1, prev_path2) pairs, but in each
> case the non-NULL
> parameter is actually for 'collide_path'.
>
> It is still interesting if we can hit this case. Perhaps we need a
> different kind of
> conflict, like (rename, delete) [but I struggle to make sense of how to
> do that].

rename/delete conflicts are sent through handle_rename_delete() which
do not call into handle_file_collision().  What you'd instead need is
a rename/add conflict, in the virtual merge base, on the appropriate
side.  The fact that the prev_path2 non-NULL case is covered means
there's already a regression test that's probably nearly good enough,
you'd just need to edit the committer timestamps of the two merge
bases so that a different one was older.  I'm pretty sure we can come
up with one without too much effort.  I'll take a look tomorrow; too
late tonight.