Re: [PATCH RFC] diff --no-index: teach option to exclude files by pattern

From: Junio C Hamano <gitster@pobox.com>
Date: May 14, 2025, 21:10 UTC
Message-ID: <xmqqzffe7vbh.fsf@gitster.g>
In-Reply-To: <20250514204014.3106177-1-jacob.e.keller@intel.com>

Jacob Keller <jacob.e.keller@intel.com> writes:

Show 7 quoted lines

> From: Jacob Keller <jacob.keller@gmail.com>
>
> Teach git diff --no-index the ability to exclude files by wildmatch
> pattern when recursing through directories. The '--exclude' option
> builds up a string list containing the patterns. These are checked with
> wildmatch() in the read_directory_contents function. If any pattern
> matches, then the file is not included in the directory contents.

A quite natural question that comes to mind is:

    How would we do this for the normal "git diff" that is not the
    bolted on '--no-index' mode?

but ...

> The --exclude option is only supported by the --no-index mode. Standard
> diff modes support negative pathspecs which is more powerful. I tried to
> see if there was a way to add support for negative pathspecs themselves,
> but haven't yet figured out if this is possible.

... of course you have thought about it already. I do agree with you that we should figure out how and teach this mode to also use pathspec, not necessarily only the negative ones but positive ones.

After all,

    $ git diff --no-index [<option>...] dirA dirB

is like running

    $ diff -r [<option>...] dirA dirB

after preparing these two directories like so:

    $ git archive revA | ( mkdir dirA && tar Cxf dirA - )
    $ git archive revB | ( mkdir dirB && tar Cxf dirB - )

Hence it is natural for users to expect that anything you can do with

    $ git diff revA revB

should be doable, in

    $ git diff --no-index dirA dirB

and vice versa. And as you said, when comparing two revisions, you'd use pathspec for this kind of thing.

    $ git diff revA revB -- Documentation/ t/ ':!po/'

So, I pretty much agree with the need to be able to exclude some parts of the tree(s) from comparison in "diff --no-index" mode, but I doubt it is a good idea to tell what to exclude the "--no-index" mode in a completely different way.

The last time I looked at it, I got an impression that the command line argument parsing of "git diff --no-index" was messy (which is sort of inevitable, since unlike the normal "git diff", it can compare more than just two "collections"---it can take two paths to regular files, for example, and in such a case pathspec arguments can play no role), so teaching it pathspec parsing might be a bit of work, though.

Thanks for starting an interesting topic.