Re: [PATCH v2 3/3] Makefile: replace most hardcoded object lists with $(wildcard)

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 9, 2021, 21:38 UTC
Message-ID: <xmqqtugl102l.fsf@gitster.g>
In-Reply-To: <40dbf962-2ccd-b4d6-7110-31317eb35e34@gmail.com>

Phillip Wood <phillip.wood123@gmail.com> writes:

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>> We can also have some DEVOPTS knob so we'll prune out files found if
>> a
>> $(shell)-out to "git status" tells us they're untracked. I wouldn't mind
>> that (and could implement it) if it was optional.
>> Also note that you've got some of this already, e.g. we'll pick up
>> *.h
>> files via a glob for "make TAGS", the dependency graph etc.
>
> I'd be happier using 'git ls-files' with a glob if we need to move
> away from listing the files explicitly rather than having to pass some 
> exclude list when running make. Having seen your comments below about
> ls-files/find I had a look at the Makefile and they always seem to be 
> used together as "git ls-files ... || find ...". Doing that would mean
> we wouldn't try to build any untracked files but still find everything 
> in a tarball.

I've been quiet on this topic because honestly I do not find the pros-and-cons favourable for more use of wildcards [*]. Tools like git (especially .gitignore) and Makefile are to help users to be safely sloppy by ensuring that random crufts the users may create in the working tree for their convenience are not picked up by default unless the project to consciously expresses the desire to use them.

Allowing to be sloppy while maintaining Makefile feels like a false economy, and having to paper it over by adding exceptions and forcing developers to learn such ad-hoc rules even more so.

    Side note: TAGS generation and some other minor things may use
    $(wildcard) and can throw tokens in cruft files in the output,
    which is not ideal, but the damage is local.  We cannot treat
    that the same as building binaries and tarballs.

If we could use "git ls-files" consistently, that may make it somewhat safer; you'd at least need to "git add" a new file before it gets into the picture. But it would be impossible, because we need to be able to bootstrap Git from a tarball extract.

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>>>> We could make this simpler still for the Makefile by moving
>>>> "unix-socket.c" etc. to e.g. a "conditional-src/" directory, likewise
>>>> for $(PROGRAM_OBJS) to e.g. "programs/". If we did that we would not
>>>> need the "$(filter-out)" for LIB_OBJS. I don't think that's worth it,
>>>> e.g. due to "git log -- <path>" on the files now needing a "--follow".

And it is not quite clear to me why we want to even more pile workaround like this on top. This also is to paper over the mistake of being sloppy and using $(wildcard), which makes it unable to distinguish, among the ones that match a pattern, between FOO_OBJS and BAR_OBJS, no? Moving files around in the working tree to group related things together is a good thing, and it has been a good move to separate built-ins and library-ish parts into different directories. But the above does not sound like it.

Other than "these source files may or may not be compiled depending", what trait do files in conditional-src/ share, other than "dividing them into a separate category makes it simpler to write Makefile using $(wildcard)"? I do not think of a good one.

The only time I found that the large list of files in Makefile was problematic was *NOT* when multiple topics added, renamed or removed the files (it is pretty much bog standard merge conflicts that do not happen very often to begin with). It is when this kind of "large scale refactoring" for the sake of refactoring happens.

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> I'm not so worried about those other targets, but being able to
> reliably build and test git with some cruft lying around is useful
> though. I'm still not entirely sure what the motivation for this
> change is (adding new files is not that common) but I think using the
> established "git ls-files || find" pattern would be a good way of
> globbing without picking up rubbish if there is a compelling reason to
> drop the lists.

Yes.