Re: [PATCH v2 4/5] Makefile: respect build info declared in "config.mak"

On Fri, Dec 20, 2024 at 07:02:10PM +0100, Patrick Steinhardt wrote:

On Fri, Dec 20, 2024 at 12:51:36PM -0500, Jeff King wrote:

quoted

On Fri, Dec 20, 2024 at 05:47:14PM +0100, Patrick Steinhardt wrote:

quoted

quoted

This looks good. It fixes the issue, and I am happy that:

quoted

 asciidoctor-extensions.rb: asciidoctor-extensions.rb.in FORCE
-	$(QUIET_GEN)GIT_USER_AGENT="$(GIT_USER_AGENT)" $(SHELL_PATH) ../GIT-VERSION-GEN "$(shell pwd)/.." $< $@
+	$(QUIET_GEN)$(SHELL_PATH) ../GIT-VERSION-GEN "$(shell pwd)/.." $< $@

...these spots get even simpler.

Meh. I just noticed that this doesn't work: we include GIT-VERSION-FILE
and export its value, and consequently any subsequent invocation of
GIT-VERSION-GEN will continue to use the value that we have in
GIT-VERSION-FILE. So it's effectively only computed the first time.

I'm not sure what you mean.

I wondered earlier if we might into a chicken-and-egg problem like that,
but I tested and it seemed to work fine. The rule for GIT-VERSION-FILE
means we'll build it before make reads it, so that first run of it will
get the updated value. And:

  make GIT_VERSION=foo && bin-wrappers/git version
  make GIT_VERSION=bar && bin-wrappers/git version

does what you'd expect. And the docs work the same way:

  cd Documentation
  make GIT_VERSION=foo git.1 && man -l git.1
  make GIT_VERSION=bar git.1 && man -l git.1

Is there a case you found that doesn't work?

Yes:

    $ make GIT-VERSION-FILE GIT_VERSION=foo
    GIT_VERSION=foo
    make: 'GIT-VERSION-FILE' is up to date.
    $ cat GIT-VERSION-FILE
    GIT_VERSION=foo

    # And now run without GIT_VERSION set.
    make: 'GIT-VERSION-FILE' is up to date.
    GIT_VERSION=foo

So the value remains "sticky" in this case. And that is true whenever
you don't set GIT_VERSION at all, we always stick with what is currently
in that file.

I've got a version now that works for all cases, but I had to use
Makefile templates and some shuffling to make it work.

The root of the problem is this [1]:

    To this end, after reading in all makefiles make will consider each
    as a goal target, in the order in which they were processed, and
    attempt to update it. If parallel builds (see Parallel Execution)
    are enabled then makefiles will be rebuilt in parallel as well.

So the Makefile will _first_ read in all includes before deciding
whether or not it needs to regenerate any of them. So we already export
the current GIT_VERSION in case "GIT-VERSION-FILE" exists at the time
where we run "GIT-VERSION-GEN".

That behaviour is quite surprising to me, but it seems to work as
designed.

Patrick

[1]: https://www.gnu.org/software/make/manual/html_node/Remaking-Makefiles.html