Re: [PATCH] Makefile: add and use the ".DELETE_ON_ERROR" flag

On Wed, Jun 23 2021, Felipe Contreras wrote:

Ævar Arnfjörð Bjarmason wrote:

quoted

As in db10fc6c09f this allows us to remove patterns of removing
leftover $@ files at the start of rules, since previous failing runs
of the Makefile won't have left those littered around anymore.

I'm not as confident that we should be replacing the "mv $@+ $@"
pattern entirely, since that means that external programs or one of
our other Makefiles might race and get partial content.

The reason I did it in db10fc6c09 is because both asciidoctor and
asciidoc should deal with temporary files by themselves (like gcc). If
you interrupt the build nothing gets generated.

If you interrupt the build default make behavior without
.DELETE_ON_ERROR kicks in.

My gcc 8.3.0 just does an unlink()/openat(..., O_RDWR|O_CREAT|O_TRUNC)
dance followed by chmod() when I do e.g.:

    gcc -o main main.c

So no in-place atomic renaming, does yours do something different?

But yes, some tools do this themselves, I think in general it's less
annoying to deal with it yourself in a case like git's, because if they
do it their idea of an in-tree tempfile may not jive with your
.gitignore, so you'll racily see ghost files during build, or those
files getting left behind if the tool hard dies.

However, other scripts like build-docdep.perl would indeed generate
partial output.

In my opinion it's the scripts themselves that should be fixed, and not
the Makefile, *if* we care about this at all.

I don't think default tool/make/*nix semantics are broken, I just think
it's neat to do that rename dance yourself, it's a cheap way to
guarantee that we always have working tools for use by other concurrent
scripts.

Many build systems or modes of running them don't care about that
use-case.