Subject: Re: [PATCH v3 03/15] merge-tree: add option parsing and initial shell for real merge function

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 03 Feb 2022 11:26:27 +0100

On Thu, Feb 03 2022, Elijah Newren wrote:

> On Wed, Feb 2, 2022 at 6:09 PM Ævar Arnfjörð Bjarmason <[email-masked]> wrote:
>>
>> On Wed, Feb 02 2022, Elijah Newren via GitGitGadget wrote:
>>
>> > From: Elijah Newren <[email-masked]>
>> >
>> > Let merge-tree accept a `--write-tree` parameter for choosing real
>> > merges instead of trivial merges, and accept an optional
>> > `--trivial-merge` option to get the traditional behavior.  Note that
>> > these accept different numbers of arguments, though, so these names
>> > need not actually be used.
>>
>> Maybe that ship has sailed, but just my 0.02: I thought this whole thing
>> was much less confusing with your initial merge-tree-ort proposal at
>> https://lore.kernel.org/git/CABPp-BEeBpJoU4yXdfA6vRAYVAUbd2gRhEV6j4VEqoqcu=[email-masked]/;
>> I.e. the end-state of merge-tree.c is that you end up reading largely
>> unrelated code (various static functions only used by one side or
>> another).
>
> Christian's merge-tree-ort proposal?

Yes. I'm clearly getting the chronology wrong here. Sorry.

>> But maybe that's all water under the bridge etc, however...
>>
>> >  int cmd_merge_tree(int argc, const char **argv, const char *prefix)
>> >  {
>> > -     if (argc != 4)
>> > -             usage(merge_tree_usage);
>> > -     return trivial_merge(argc, argv);
>> > +     struct merge_tree_options o = { 0 };
>> > +     int expected_remaining_argc;
>> > +
>> > +     const char * const merge_tree_usage[] = {
>> > +             N_("git merge-tree [--write-tree] <branch1> <branch2>"),
>> > +             N_("git merge-tree [--trivial-merge] <base-tree> <branch1> <branch2>"),
>> > +             NULL
>> > +     };
>> > +     struct option mt_options[] = {
>> > +             OPT_CMDMODE(0, "write-tree", &o.mode,
>> > +                         N_("do a real merge instead of a trivial merge"),
>> > +                         'w'),
>> > +             OPT_CMDMODE(0, "trivial-merge", &o.mode,
>> > +                         N_("do a trivial merge only"), 't'),
>> > +             OPT_END()
>> > +     };
>> > +
>> > +     /* Parse arguments */
>> > +     argc = parse_options(argc, argv, prefix, mt_options,
>> > +                          merge_tree_usage, PARSE_OPT_STOP_AT_NON_OPTION);
>> > +     if (o.mode) {
>> > +             expected_remaining_argc = (o.mode == 'w' ? 2 : 3);
>> > +             if (argc != expected_remaining_argc)
>> > +                     usage_with_options(merge_tree_usage, mt_options);
>> > +     } else {
>> > +             if (argc < 2 || argc > 3)
>> > +                     usage_with_options(merge_tree_usage, mt_options);
>> > +             o.mode = (argc == 2 ? 'w' : 't');
>> > +     }
>>
>> Do we really need to make this interface more special-casey by
>> auto-guessing based on argc what argument you want? I.e. instead of
>> usage like:
>>
>>         N_("git merge-tree [--write-tree] <branch1> <branch2>"),
>>         N_("git merge-tree [--trivial-merge] <base-tree> <branch1> <branch2>"),
>>
>> Wouldn't it be simpler to just have the equivalent of:
>>
>>         # old
>>         git merge-tree ...
>>         # new
>>         git merge-tree --new-thing ...
>>
>> And not have to look at ... to figure out if we're dispatching to the
>> new or old thing.
>
> You seem to be focusing on code simplicity?  Sure, that'd be simpler
> code, it'd just be a less useful feature.
>
> I think passing --write-tree all the time would be an annoyance.  I
> don't see why anyone would ever use the other mode.  However, for as
> long as both exist in the manual, it makes the manual easier to
> explain to users, and example testcases more self-documenting by
> having the flag there.  That's the sole purpose of the flag.
>
> I'm never going to actually use it when I invoke it from the command
> line.  And I suspect most would leave it off.

I think I mostly covered this in
https://lore.kernel.org/git/[email-masked]/
in the side-thread.

I'm not opposed to them being in the same command, it just seems like
more work for those reasons in every way.

E.g. the current manual page doesn't really describe the format the
--trivial-merge emits, so we could do with a section on that, but then
it would say "only for this option, not the other" etc.