Makefile: replace perl/Makefile.PL with simple make rules

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].

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.

We've since since started maintaining a fallback perl/Makefile, as
MakeMaker wouldn't work on some platforms[4]. That's just the tip of
the iceberg. We have the PM.stamp hack in the top-level Makefile[5] to
detect whether we need to regenerate the perl/perl.mak, which I fixed
just recently to deal with issues like the perl version changing from
under us[6].

There is absolutely no reason for why this needs to be so complex
anymore. All we're getting out of this elaborate Rube Goldberg machine
was copying perl/* to perl/blib/* as we do a string-replacement on
the *.pm files to hardcode @@LOCALEDIR@@ in the source, as well as
pod2man-ing Git.pm & friends.

So replace the whole thing with something that's pretty much a copy of
how we generate po/build/**.mo from po/*.po, just with a small sed(1)
command instead of msgfmt. As that's being done rename the files
from *.pm to *.pmc just to indicate that they're generated (see
"perldoc -f require").

While I'm at it, change the fallback for Error.pm from being something
where we'll ship our own Error.pm if one doesn't exist at build time
to one where we just use a Git::Error wrapper that'll always prefer
the system-wide Error.pm, only falling back to our own copy if it
really doesn't exist at runtime. It's now shipped as
Git::FromCPAN::Error, making it easy to add other modules to
Git::FromCPAN::* in the future if that's needed.

Functional changes:

 * 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.

 * The scripts themselves will 'use lib' the target directory, but if
   INSTLIBDIR is set it overrides it. It doesn't have to be this way,
   it could be set in addition to INSTLIBDIR, but my reading of [7] is
   that this is the desired behavior.

 * We don't build man pages for all of the perl modules as we used to,
   only Git(3pm). As discussed on-list[8] that we were building
   installed manpages for purely internal APIs like Git::I18N or
   private-Error.pm was always a bug anyway, and all the Git::SVN::*
   ones say they're internal APIs.

   There are apparently external users of Git.pm, but I don't expect
   there to be any of the others.

   As a side-effect of these general changes the perl documentation
   now only installed by install-{doc,man}, not a mere "install" as
   before.

1. 5e9637c629 ("i18n: add infrastructure for translating Git with
   gettext", 2011-11-18)

2. b1edc53d06 ("Introduce Git.pm (v4)", 2006-06-24)

3. 18b0fc1ce1 ("Git.pm: Kill Git.xs for now", 2006-09-23)

4. f848718a69 ("Make perl/ build procedure ActiveState friendly.",
   2006-12-04)

5. ee9be06770 ("perl: detect new files in MakeMaker builds",
   2012-07-27)

6. c59c4939c2 ("perl: regenerate perl.mak if perl -V changes",
   2017-03-29)

7. 0386dd37b1 ("Makefile: add PERLLIB_EXTRA variable that adds to
   default perl path", 2013-11-15)

8. 87bmjjv1pu.fsf@evledraar.booking.com ("Re: [PATCH] Makefile:
   replace perl/Makefile.PL with simple make rules"

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

7 files changed, 49 insertions, 162 deletions

diff --git a/perl/.gitignore b/perl/.gitignore
index 0f1fc27..84c048a 100644
--- a/perl/.gitignore
+++ b/perl/.gitignore
@@ -1,8 +1 @@
-perl.mak
-perl.mak.old
-MYMETA.json
-MYMETA.yml
-blib
-blibdirs
-pm_to_blib
-PM.stamp
+/build/
diff --git a/perl/Git.pm b/perl/Git.pm
index ffa09ac..02a3871 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -101,7 +101,7 @@ increase notwithstanding).
 
 
 use Carp qw(carp croak); # but croak is bad - throw instead
-use Error qw(:try);
+use Git::Error qw(:try);
 use Cwd qw(abs_path cwd);
 use IPC::Open2 qw(open2);
 use Fcntl qw(SEEK_SET SEEK_CUR);
diff --git a/perl/Git/Error.pm b/perl/Git/Error.pm
new file mode 100644
index 0000000..5874672
--- /dev/null
+++ b/perl/Git/Error.pm
@@ -0,0 +1,46 @@
+package Git::Error;
+use 5.008;
+use strict;
+use warnings;
+
+=head1 NAME
+
+Git::Error - Wrapper for the L<Error> module, in case it's not installed
+
+=head1 DESCRIPTION
+
+Wraps the import function for the L<Error> module.
+
+This module is only intended to be used for code shipping in the
+C<git.git> repository. Use it for anything else at your peril!
+
+=cut
+
+sub import {
+    shift;
+    my $caller = caller;
+
+    eval {
+	require Error;
+	1;
+    } or do {
+	my $error = $@ || "Zombie Error";
+
+	my $Git_Error_pm_path = $INC{"Git/Error.pm"} || die "BUG: Should have our own path from %INC!";
+
+	require File::Basename;
+	my $Git_Error_pm_root = File::Basename::dirname($Git_Error_pm_path) || die "BUG: Can't figure out lib/Git dirname from '$Git_Error_pm_path'!";
+
+	require File::Spec;
+	my $Git_pm_FromCPAN_root = File::Spec->catdir($Git_Error_pm_root, 'FromCPAN');
+	die "BUG: '$Git_pm_FromCPAN_root' should be a directory!" unless -d $Git_pm_FromCPAN_root;
+
+	local @INC = ($Git_pm_FromCPAN_root, @INC);
+	require Error;
+    };
+
+    local @_ = ($caller, @_);
+    goto &Error::import;
+}
+
+1;
diff --git a/perl/private-Error.pm b/perl/Git/FromCPAN/Error.pm
index 6098135..6098135 100644
--- a/perl/private-Error.pm
+++ b/perl/Git/FromCPAN/Error.pm
diff --git a/perl/Git/I18N.pm b/perl/Git/I18N.pm
index 836a5c2..dba96ff 100644
--- a/perl/Git/I18N.pm
+++ b/perl/Git/I18N.pm
@@ -18,7 +18,7 @@ our @EXPORT_OK = @EXPORT;
 
 sub __bootstrap_locale_messages {
 	our $TEXTDOMAIN = 'git';
-	our $TEXTDOMAINDIR = $ENV{GIT_TEXTDOMAINDIR} || '++LOCALEDIR++';
+	our $TEXTDOMAINDIR = $ENV{GIT_TEXTDOMAINDIR} || '@@LOCALEDIR@@';
 
 	require POSIX;
 	POSIX->import(qw(setlocale));
diff --git a/perl/Makefile b/perl/Makefile
deleted file mode 100644
index f657de2..0000000
--- a/perl/Makefile
+++ /dev/null
@@ -1,90 +0,0 @@
-#
-# Makefile for perl support modules and routine
-#
-makfile:=perl.mak
-modules =
-
-PERL_PATH_SQ = $(subst ','\'',$(PERL_PATH))
-prefix_SQ = $(subst ','\'',$(prefix))
-localedir_SQ = $(subst ','\'',$(localedir))
-
-ifndef V
-	QUIET = @
-endif
-
-all install instlibdir: $(makfile)
-	$(QUIET)$(MAKE) -f $(makfile) $@
-
-clean:
-	$(QUIET)test -f $(makfile) && $(MAKE) -f $(makfile) $@ || exit 0
-	$(RM) ppport.h
-	$(RM) $(makfile)
-	$(RM) $(makfile).old
-	$(RM) PM.stamp
-
-$(makfile): PM.stamp
-
-ifdef NO_PERL_MAKEMAKER
-instdir_SQ = $(subst ','\'',$(prefix)/lib)
-
-modules += Git
-modules += Git/I18N
-modules += Git/IndexInfo
-modules += Git/Packet
-modules += Git/SVN
-modules += Git/SVN/Memoize/YAML
-modules += Git/SVN/Fetcher
-modules += Git/SVN/Editor
-modules += Git/SVN/GlobSpec
-modules += Git/SVN/Log
-modules += Git/SVN/Migration
-modules += Git/SVN/Prompt
-modules += Git/SVN/Ra
-modules += Git/SVN/Utils
-
-$(makfile): ../GIT-CFLAGS Makefile
-	echo all: private-Error.pm Git.pm Git/I18N.pm > $@
-	set -e; \
-	for i in $(modules); \
-	do \
-		if test $$i = $${i%/*}; \
-		then \
-			subdir=; \
-		else \
-			subdir=/$${i%/*}; \
-		fi; \
-		echo '	$(RM) blib/lib/'$$i'.pm' >> $@; \
-		echo '	mkdir -p blib/lib'$$subdir >> $@; \
-		echo '	cp '$$i'.pm blib/lib/'$$i'.pm' >> $@; \
-	done
-	echo '	$(RM) blib/lib/Error.pm' >> $@
-	'$(PERL_PATH_SQ)' -MError -e 'exit($$Error::VERSION < 0.15009)' || \
-	echo '	cp private-Error.pm blib/lib/Error.pm' >> $@
-	echo install: >> $@
-	set -e; \
-	for i in $(modules); \
-	do \
-		if test $$i = $${i%/*}; \
-		then \
-			subdir=; \
-		else \
-			subdir=/$${i%/*}; \
-		fi; \
-		echo '	$(RM) "$$(DESTDIR)$(instdir_SQ)/'$$i'.pm"' >> $@; \
-		echo '	mkdir -p "$$(DESTDIR)$(instdir_SQ)'$$subdir'"' >> $@; \
-		echo '	cp '$$i'.pm "$$(DESTDIR)$(instdir_SQ)/'$$i'.pm"' >> $@; \
-	done
-	echo '	$(RM) "$$(DESTDIR)$(instdir_SQ)/Error.pm"' >> $@
-	'$(PERL_PATH_SQ)' -MError -e 'exit($$Error::VERSION < 0.15009)' || \
-	echo '	cp private-Error.pm "$$(DESTDIR)$(instdir_SQ)/Error.pm"' >> $@
-	echo instlibdir: >> $@
-	echo '	echo $(instdir_SQ)' >> $@
-else
-$(makfile): Makefile.PL ../GIT-CFLAGS
-	$(PERL_PATH) $< PREFIX='$(prefix_SQ)' INSTALL_BASE='' --localedir='$(localedir_SQ)'
-endif
-
-# this is just added comfort for calling make directly in perl dir
-# (even though GIT-CFLAGS aren't used yet. If ever)
-../GIT-CFLAGS:
-	$(MAKE) -C .. GIT-CFLAGS
diff --git a/perl/Makefile.PL b/perl/Makefile.PL
deleted file mode 100644
index 3f29ba9..0000000
--- a/perl/Makefile.PL
+++ /dev/null
@@ -1,62 +0,0 @@
-use strict;
-use warnings;
-use ExtUtils::MakeMaker;
-use Getopt::Long;
-use File::Find;
-
-# Don't forget to update the perl/Makefile, too.
-# Don't forget to test with NO_PERL_MAKEMAKER=YesPlease
-
-# Sanity: die at first unknown option
-Getopt::Long::Configure qw/ pass_through /;
-
-my $localedir = '';
-GetOptions("localedir=s" => \$localedir);
-
-sub MY::postamble {
-	return <<'MAKE_FRAG';
-instlibdir:
-	@echo '$(INSTALLSITELIB)'
-
-ifneq (,$(DESTDIR))
-ifeq (0,$(shell expr '$(MM_VERSION)' '>' 6.10))
-$(error ExtUtils::MakeMaker version "$(MM_VERSION)" is older than 6.11 and so \
-	is likely incompatible with the DESTDIR mechanism.  Try setting \
-	NO_PERL_MAKEMAKER=1 instead)
-endif
-endif
-
-MAKE_FRAG
-}
-
-# Find all the .pm files in "Git/" and Git.pm
-my %pm;
-find sub {
-	return unless /\.pm$/;
-
-	# sometimes File::Find prepends a ./  Strip it.
-	my $pm_path = $File::Find::name;
-	$pm_path =~ s{^\./}{};
-
-	$pm{$pm_path} = '$(INST_LIBDIR)/'.$pm_path;
-}, "Git", "Git.pm";
-
-
-# We come with our own bundled Error.pm. It's not in the set of default
-# Perl modules so install it if it's not available on the system yet.
-if ( !eval { require Error } || $Error::VERSION < 0.15009) {
-	$pm{'private-Error.pm'} = '$(INST_LIBDIR)/Error.pm';
-}
-
-# redirect stdout, otherwise the message "Writing perl.mak for Git"
-# disrupts the output for the target 'instlibdir'
-open STDOUT, ">&STDERR";
-
-WriteMakefile(
-	NAME            => 'Git',
-	VERSION_FROM    => 'Git.pm',
-	PM		=> \%pm,
-	PM_FILTER	=> qq[\$(PERL) -pe "s<\\Q++LOCALEDIR++\\E><$localedir>"],
-	MAKEFILE	=> 'perl.mak',
-	INSTALLSITEMAN3DIR => '$(SITEPREFIX)/share/man/man3'
-);