Re: [PATCH v2] fetch: document and test --refmap=""

[Derrick Stolee <stolee@gmail.com>]

On 1/21/2020 11:24 AM, Jeff King wrote:
> On Tue, Jan 21, 2020 at 01:38:12AM +0000, Derrick Stolee via GitGitGadget wrote:
> 
>> Update the documentation to clarify how '--refmap=""' works and
>> create tests to guarantee this behavior remains in the future.
> 
> Yeah, this looks like a good solution to me.
> 
>> This can be accomplished by overriding the configured refspec using
>> '--refmap=' along with a custom refspec:
>>
>>   git fetch <remote> --refmap= +refs/heads/*:refs/hidden/<remote>/*
> 
> This isn't strictly related to your patch, but since the rationale here
> describes the concept of a background job and people might end up using
> it as a reference, do you want to add in --no-tags to help them out?

That's a good idea. I keep forgetting about that. It's interesting that
tags are fetched even though my refpsec does not include refs/tags.

>>     Thanks for all the feedback leading to absolutely no code change. It's
>>     good we already have the flexibility for this. I'm a bit embarrassed
>>     that I did not discover this, so perhaps this doc change and new tests
>>     will help clarify the behavior.

> Anyway, I wasn't at all sure that a blank --refmap= would do what you
> want until I tried it. But it was always intended to work that way. From
> c5558f80c3 (fetch: allow explicit --refmap to override configuration,
> 2014-05-29):
> 
>   +static int parse_refmap_arg(const struct option *opt, const char *arg, int unset)
>   +{
>   +       ALLOC_GROW(refmap_array, refmap_nr + 1, refmap_alloc);
>   +
>   +       /*
>   +        * "git fetch --refmap='' origin foo"
>   +        * can be used to tell the command not to store anywhere
>   +        */
>   +       if (*arg)
>   +               refmap_array[refmap_nr++] = arg;
>   +       return 0;
>   +}
> 
> At first I thought the comment was wrong, since we don't actually
> increment refmap_nr. But the ALLOC_GROW makes refmap_array non-NULL,
> which is what triggers the "do not use configured refspecs" logic.

This works due to a subtle arrangement of things, like a non-NULL
but "empty" array. That justifies the test even more.
 
> This code switched to refspec_append() in e4cffacc80 (fetch: convert
> refmap to use struct refspec, 2018-05-16), and I think we actually do
> push an empty string onto the list. Which then triggers the "do not use
> configured refspecs" logic, but doesn't match anything itself. I'm not
> sure whether that behavior was entirely planned, or just what the code
> happens to do. So it's doubly useful to add a test here covering the
> expected behavior.

Excellent. Glad I'm not just adding test bloat for now reason.

-Stolee