Re: [PATCH] cmake: ignore generated files

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 18, 2020, 16:21 UTC
Message-ID: <xmqq7dsrnjhi.fsf@gitster.c.googlers.com>
In-Reply-To: <20200918155015.GA1837@danh.dev>

Đoàn Trần Công Danh  <congdanhqx@gmail.com> writes:

Show 5 quoted lines

> Actually, in CMake land, people usually do this instead:
>
> 	mkdir build
> 	cmake [-Ggenerator] ..
> 	<make/ninja/msbuild>

I presume you "cd build" between steps 1 & 2? I take the "people usually do" is the best current practice?

Show 14 quoted lines

> Then, when they want to run something equivalent with make distclean,
> they run:
>
> 	cd ..
> 	rm -rf build
>
> instead.
>
> The change that Dscho suggested was meant for those people that run
> CMake in same directory of source dir, which is mostly discouraged
> in CMake land.
>
> In additional, CMake's default Generator in *nix is Unix Makefiles,
> which will clash with our Makefile, and totally unsupported.

I recall that our CMakeLists file asks the top-level Makefile about basic things so that we do not have to duplicate "list of files" etc. in places, so I can understand that it would lead to a disaster to do "cmake -Ggenerator" at the top-level.

> I think the original CMake proposal didn't touch .gitignore because
> they run in a separated build-dir.

If so, not only my "do we need a matching change to CMakeLists to teach how to clean crufts?" becomes unnecessary, but the original patch that started this thread to touch .gitignore at the top level, does, too.

I wonder what led Dscho not to follow the "create a 'build' dir and do things there" practice. Judging from the fact that the "because they run in a separate build directory" assumption did not hold to somebody as experienced as Dscho, it is likely others would do the same.

What can we do to make it easier for people to discover and follow the best current practice? Are there things in our build instruction document (e.g. the comment at the top of CMakeLists.txt) that needs updating?

Thanks.