Re: [PATCH] branch & tag: Add a --no-contains option

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Thu, Mar 9, 2017 at 11:09 AM, Jeff King <peff@peff.net> wrote:
> On Wed, Mar 08, 2017 at 08:20:25PM +0000, Ævar Arnfjörð Bjarmason wrote:
>
>> Change the branch & tag commands to have a --no-contains option in
>> addition to their longstanding --contains options.
>>
>> The use-case I have for this is mainly to find the last-good rollout
>> tag given a known-bad <commit>. Right given a hypothetically bad
>> commit v2.10.1-3-gcf5c7253e0 now you can find that with this hacky
>> one-liner:
>>
>>     (./git tag -l 'v[0-9]*'; ./git tag -l 'v[0-9]*' --contains v2.10.1-3-gcf5c7253e0)|sort|uniq -c|grep -E '^ *1 '|awk '{print $2}'
>>
>> But with the --no-contains option you can now get the exact same
>> output with:
>>
>>     ./git tag -l 'v[0-9]*' --no-contains v2.10.1-3-gcf5c7253e0 | sort
>
> I think that's a good goal.
>
> I'm not sure about the name. I would have expected "--no-contains" to
> reset the list of "--contains" commits to the empty set. That's an
> option convention we've been slowly moving towards (e.g., with
> OPT_STRING_LIST).
>
> What you've added here _does_ match "--no-merged", though. I'm not sure
> of the best way forward. At the very least, "--no-contains" is currently
> an error, so you would not be changing existing behavior.

I initially started hacking this up as --not-contains, but after
briefly chatting with Christian about it off-list he suggested --no-*.
Since as you point out it's consistent with --no-merge. I have no
strong view on it, I just want the feature whatever the flag is
called.

>> Once I'd implemented this for "tag" it was easy enough to add it for
>> "branch". I haven't added it to "for-each-ref" but that would be
>> trivial if anyone cares, but that use-case would be even more obscure
>> than adding it to "branch", so I haven't bothered.
>
> I'd prefer to have it consistently in all three. We should be able to
> tell people to use for-each-ref in their scripts, and that's harder if
> it is missing features.

Agreed. I'd already hacked that up this morning for a v2. It works &
has tests at https://github.com/avar/git/tree/avar/no-contains-2

>> The "describe" command also has a --contains option, but its semantics
>> are unrelated to what tag/branch/for-each-ref use --contains for, and
>> I don't see how a --no-contains option for it would make any sense.
>
> Yeah, I think that feature is orthogonal.

*Nod* just adding a note about it in case anyone's puzzled about why
describe doesn't have --no-contains, elaborated & clarified this a bit
in my WIP v2.

>> -static int commit_contains(struct ref_filter *filter, struct commit *commit)
>> +static int commit_contains(struct ref_filter *filter, struct commit *commit, const int with_commit)
>>  {
>> +     struct commit_list *tmp = with_commit ? filter->with_commit : filter->no_commit;
>>       if (filter->with_commit_tag_algo)
>> -             return contains_tag_algo(commit, filter->with_commit);
>> -     return is_descendant_of(commit, filter->with_commit);
>> +             return contains_tag_algo(commit, tmp);
>> +     return is_descendant_of(commit, tmp);
>>  }
>
> Perhaps it would be simpler if the caller just passed the right
> commit_list rather than a flag. We unfortunately do still need to pass
> the "filter" (for the algorithm field), but the caller is then:
>
>   if (filter->with_commit &&
>       !commit_contains(filter, filter->with_commit, commit))
>           return 0;
>   if (filter->no_commit &&
>       commit_contains(filter, filter->no_commit, commit))
>           return 0;
>
> which avoids the 0/1 flag whose meaning is not immediately apparent at
> the callsite. One day we can hopefully unify the two algorithms and
> ditch the extra filter parameter.

My C rustyness is showing. Yeah that's much better, thanks, changed it
to that in my WIP v2.

> I almost suggested that there simply be an option to invert the match
> (like --invert-contains or something).  But what you have here is more
> flexible, if somebody ever wanted to do:
>
>   git tag --contains X --no-contains Y

Yeah that's really useful. E.g. this shows the branches I branched off
(or have locally) from 2.6..2.8:

    $ ./git branch --contains v2.6.0 --no-contains v2.8.0
      avar/monkeypatch-untracked-cache-disabled
      avar/uc-notifs21
      dturner/pclouds-watchman-noshm

But I'd expect this to show all the tags between the two:

    $ ./git tag --contains v2.6.0 --no-contains v2.8.0
    $

But it just returns an empty list. Manually disabling the
contains_tag_algo() path (i.e. effectively locally reverting your
ffc4b8012d) makes it "work", but of course it's much slower now. I
haven't dug into why it's not working yet.

Also I wonder if this should be an error:

    $ ./git [tag|branch|for-each-ref] --contains A --no-contains A

I.e. when you give the same argument to both, this can never return
anything for obvious reasons.

>> @@ -1708,8 +1782,91 @@ run_with_limited_stack () {
>>
>>  test_lazy_prereq ULIMIT_STACK_SIZE 'run_with_limited_stack true'
>>
>> +# These are all the tags we've created above
>> +cat >expect.no-contains <<EOF
>> [...80 tags...]
>> +EOF
>
> That's a lot of tags, and I'd worry it makes the test a little brittle.
> Can we limit the set of tags with a name-match? It shouldn't affect the
> purpose of the test (the deep stack comes from traversing the commits,
> not the number of tags).

I'll make this less sucky in v2 somehow. I did it this way because no
existing test was checking all the tags we'd created at the end, so
this does that by proxy now, but I agree it's too verbose. Will fix
it.