Subject: Re: [PATCH] ls-files: add pathspec matching for submodules

From: Junio C Hamano <[email-masked]>
Date: Mon, 19 Sep 2016 11:04:04 -0700

Brandon Williams <[email-masked]> writes:

>> Again, what do we have in "name" and "item" at this point?  If we
>> have a submodule at "sub/" and we are checking a pathspec element
>> "sub/dir1/*", what is the non-wildcard part of the pathspec and what
>> is the "string"?  Aren't they "sub/dir1/" and "sub/" respectively,
>> which would not pass ps_strncmp() and produce a (false) negative?
>
> item will be the pathspec_item struct that we are trying to match against.

... which would mean "sub/dir1/" in the above example (which is
followed by '*' that is wildcard).

> name will be the file we are trying to match, which should already have the
> 'prefix' cut off (this is the prefix that is used as an optimization
> in the common
> case, which isn't used in the submodule case).  

... which would be "sub/" in the above example, because we disable
the common-prefix optimization.

So in short, the answer to the last questions in the first quoted
paragraph are yes, yes, and "no they do not pass ps_strncmp()"?

>> I am starting to have a feeling that the best we can do in this
>> function safely is to see if prefix (i.e. the constant part of the
>> pathspec before the first wildcard) is long enough to cover the
>> "name" and if "name" part [matches or does not match] ...
>> If these two checks cannot decide, we may have to be pessimistic and
>> say "it may match; we don't know until we descend into it".
>> ...
>> So I would think we'd be in the business of counting slashes in the
>> name (called "string" in this function) and the pathspec, while
>> noticing '*' and '**' in the latter, and we may be able to be more
>> precise, but I am not sure how complex the end result would become.
>
> I agree, I'm not too sure how much more complex the logic would need
> to be to handle
> all matters of wildcard characters.  We could initially be more
> lenient on what qualifies as
> a match and then later (or in the near future) revisit the wildmatch
> function (which is complex)
> and see if we can add better matching capabilities more suited for
> submodules while at the
> same time fixing that bug discussed above.

I think it is reasonable to start a function that is meant to never
have false negatives pessimistic and return "might match" from it
when in doubt.

Thanks.