Subject: Re: [PATCH] Makefile: replace perl/Makefile.PL with simple make rules

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 30 Nov 2017 23:30:37 +0100

On Thu, Nov 30 2017, Jeff King jotted:

> On Wed, Nov 29, 2017 at 07:54:30PM +0000, Ævar Arnfjörð Bjarmason wrote:
>
>> Replace the perl/Makefile.PL and the fallback perl/Makefile used under
>> NO_PERL_MAKEMAKER=NoThanks with a much simpler implementation heavily
>> inspired by how the i18n infrastructure's build process works[1].
>
> I'm very happy to see the recursive make invocation go away. The perl
> makefile generation was one of the few places where parallel make could
> racily get confused (though I haven't seen that for a while, so maybe it
> was fixed alongside some of the other .stamp work you did).
>
>> The reason for having the Makefile.PL in the first place is that it
>> was initially[2] building a perl C binding to interface with libgit,
>> this functionality, that was removed[3] before Git.pm ever made it to
>> the master branch.
>
> Thanks for doing all this history digging. I agree that it doesn't seem
> like there's really any reason to carry the complexity. Of your
> functional changes, the only one that gives me pause is:
>
>>  * This will not always install into perl's idea of its global
>>    "installsitelib". This only potentially matters for packagers that
>>    need to expose Git.pm for non-git use, and as explained in the
>>    INSTALL file there's a trivial workaround.
>
> This could be a minor hiccup for people using Git.pm from other scripts.
> But maybe only in funny setups? It seems like $prefix/share/perl5 would
> be in most people's @INC unless they are doing something exotic.

I think so, but I'm not 100% sure. I'm hoping downstream maintainers
will catch this one if it's an issue, but in many cases it'll just work,
e.g. I have /usr/share/perl5 in /usr/bin/perl's @INC on Debian even
though that's not the target install dir EU::MM would have picked.

Whether there's perl configurations that don't have $prefix/share/perl5
in @INC at all I don't know.

>>  * We don't build the Git(3) Git::I18N(3) etc. man pages from the
>>    embedded perldoc. I suspect nobody really cares, these are mostly
>>    internal APIs, and if someone's developing against them they likely
>>    know enough to issue a "perldoc" against the installed file to get
>>    the same result.
>
> I don't have a real opinion on this, but it sounds from the rest of the
> thread like we should maybe build these to be on the safe side.

Indeed, we'll need to ship at least the Git.3pm manpage.

I tried coming up with something that worked like the current
Makefile.PL but couldn't figure out how I'd generate
a::file::like::this.3pm from a/file/like/this.pm

So I hacked up the following minimal patch to just build Git.3pm:

	diff --git a/Makefile b/Makefile
	index 48f1b868d1..ba6607b7e7 100644
	--- a/Makefile
	+++ b/Makefile
	@@ -1709,6 +1709,7 @@ ETC_GITATTRIBUTES_SQ = $(subst ','\'',$(ETC_GITATTRIBUTES))
	 DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
	 bindir_SQ = $(subst ','\'',$(bindir))
	 bindir_relative_SQ = $(subst ','\'',$(bindir_relative))
	+mandir_SQ = $(subst ','\'',$(mandir))
	 mandir_relative_SQ = $(subst ','\'',$(mandir_relative))
	 infodir_relative_SQ = $(subst ','\'',$(infodir_relative))
	 perllibdir_SQ = $(subst ','\'',$(perllibdir))
	@@ -2284,6 +2285,10 @@ perl/build/lib/%.pmc: perl/%.pm
	 	$(QUIET_GEN)mkdir -p $(dir $@) && \
	 	sed -e 's|@@LOCALEDIR@@|$(localedir_SQ)|g' < $< > $@

	+perl/build/man/man3/Git.3pm: perl/Git.pm
	+	$(QUIET_GEN)mkdir -p $(dir $@) && \
	+	pod2man $< $@
	+
	 FIND_SOURCE_FILES = ( \
	 	git ls-files \
	 		'*.[hcS]' \
	@@ -2595,12 +2600,17 @@ endif
	 install-gitweb:
	 	$(MAKE) -C gitweb install

	-install-doc:
	+install-doc: install-man-perl
	 	$(MAKE) -C Documentation install

	-install-man:
	+install-man: install-man-perl
	 	$(MAKE) -C Documentation install-man

	+install-man-perl: perl/build/man/man3/Git.3pm
	+	$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(mandir_SQ)/man3'
	+	(cd perl/build/man/man3 && $(TAR) cf - .) | \
	+	(cd '$(DESTDIR_SQ)$(mandir_SQ)/man3' && umask 022 && $(TAR) xof -)
	+
	 install-html:
	 	$(MAKE) -C Documentation install-html

Maybe this approach is bad, I don't know. This might be a better fit for
Documentation/Makefile since it has some "man" logic already, but do we
want it to be depending on stuff in ../perl?

On my Debian install I have these from existing Git:

    /usr/share/man/man3/Git.3pm.gz
    /usr/share/man/man3/Git::I18N.3pm.gz
    /usr/share/man/man3/private-Error.3pm.gz

We definitely don't want the 2nd two ones to have manpages, that was
always an accident. git-svn has a few more:

    /usr/share/man/man3/Git::SVN::Editor.3pm.gz
    /usr/share/man/man3/Git::SVN::Fetcher.3pm.gz
    /usr/share/man/man3/Git::SVN::Memoize::YAML.3pm.gz
    /usr/share/man/man3/Git::SVN::Prompt.3pm.gz
    /usr/share/man/man3/Git::SVN::Ra.3pm.gz
    /usr/share/man/man3/Git::SVN::Utils.3pm.gz

But those all say that they're internal API only. So maybe this hack of
mine is fine. What do others think?

In any case, a solution that tries to build all the manpages with a glob
is going to suck currently since some of them have POD, and others
don't, which gets us into the headache of trying to distinguish whether
something has POD v.s. whether we just had pod2man fail.

So it seems better just to whitelist the man3 pages that get build,
which to me seems like just one currently.

>> @@ -2291,6 +2273,17 @@ endif
>>  po/build/locale/%/LC_MESSAGES/git.mo: po/%.po
>>  	$(QUIET_MSGFMT)mkdir -p $(dir $@) && $(MSGFMT) -o $@ $<
>>
>> +PMFILES := $(wildcard perl/*.pm perl/*/*.pm perl/*/*/*.pm perl/*/*/*/*.pm)
>
> Yuck. :) I don't think there's a better wildcard solution within make,
> though. And I'd rather see this than doing a $(shell) to "find" or
> similar.
>
> The other option is to actually list the files, as we do for .o files.
> That's a minor pain to update, but it would allow things like
> differentiating which ones get their documentation built.
>
>> +PMCFILES := $(patsubst perl/%.pm,perl/build/%.pmc,$(PMFILES))
>
> TIL about pmc files. It sounds like they've had a storied history, but
> should be supported everywhere.
>
>> [...]
>
> The rest of the patch all looked good to me. Thanks for working on this.
>
> -Peff