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>

1 files changed, 36 insertions, 31 deletions

diff --git a/Makefile b/Makefile
index e53750ca01..ba6607b7e7 100644
--- a/Makefile
+++ b/Makefile
@@ -295,9 +295,6 @@ all::
 #
 # Define PERL_PATH to the path of your Perl binary (usually /usr/bin/perl).
 #
-# Define NO_PERL_MAKEMAKER if you cannot use Makefiles generated by perl's
-# MakeMaker (e.g. using ActiveState under Cygwin).
-#
 # Define NO_PERL if you do not want Perl scripts or libraries at all.
 #
 # Define PYTHON_PATH to the path of your Python binary (often /usr/bin/python
@@ -473,6 +470,7 @@ gitexecdir = libexec/git-core
 mergetoolsdir = $(gitexecdir)/mergetools
 sharedir = $(prefix)/share
 gitwebdir = $(sharedir)/gitweb
+perllibdir = $(sharedir)/perl5
 localedir = $(sharedir)/locale
 template_dir = share/git-core/templates
 htmldir = $(prefix)/share/doc/git-doc
@@ -486,7 +484,7 @@ mandir_relative = $(patsubst $(prefix)/%,%,$(mandir))
 infodir_relative = $(patsubst $(prefix)/%,%,$(infodir))
 htmldir_relative = $(patsubst $(prefix)/%,%,$(htmldir))
 
-export prefix bindir sharedir sysconfdir gitwebdir localedir
+export prefix bindir sharedir sysconfdir gitwebdir perllibdir localedir
 
 CC = cc
 AR = ar
@@ -1525,9 +1523,6 @@ ifdef SHA1_MAX_BLOCK_SIZE
 	LIB_OBJS += compat/sha1-chunked.o
 	BASIC_CFLAGS += -DSHA1_MAX_BLOCK_SIZE="$(SHA1_MAX_BLOCK_SIZE)"
 endif
-ifdef NO_PERL_MAKEMAKER
-	export NO_PERL_MAKEMAKER
-endif
 ifdef NO_HSTRERROR
 	COMPAT_CFLAGS += -DNO_HSTRERROR
 	COMPAT_OBJS += compat/hstrerror.o
@@ -1714,8 +1709,10 @@ 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))
 localedir_SQ = $(subst ','\'',$(localedir))
 gitexecdir_SQ = $(subst ','\'',$(gitexecdir))
 template_dir_SQ = $(subst ','\'',$(template_dir))
@@ -1825,9 +1822,6 @@ ifndef NO_TCLTK
 	$(QUIET_SUBDIR0)git-gui $(QUIET_SUBDIR1) gitexecdir='$(gitexec_instdir_SQ)' all
 	$(QUIET_SUBDIR0)gitk-git $(QUIET_SUBDIR1) all
 endif
-ifndef NO_PERL
-	$(QUIET_SUBDIR0)perl $(QUIET_SUBDIR1) PERL_PATH='$(PERL_PATH_SQ)' prefix='$(prefix_SQ)' localedir='$(localedir_SQ)' all
-endif
 	$(QUIET_SUBDIR0)templates $(QUIET_SUBDIR1) SHELL_PATH='$(SHELL_PATH_SQ)' PERL_PATH='$(PERL_PATH_SQ)'
 
 please_set_SHELL_PATH_to_a_more_modern_shell:
@@ -1907,7 +1901,8 @@ common-cmds.h: $(wildcard Documentation/git-*.txt)
 
 SCRIPT_DEFINES = $(SHELL_PATH_SQ):$(DIFF_SQ):$(GIT_VERSION):\
 	$(localedir_SQ):$(NO_CURL):$(USE_GETTEXT_SCHEME):$(SANE_TOOL_PATH_SQ):\
-	$(gitwebdir_SQ):$(PERL_PATH_SQ):$(SANE_TEXT_GREP):$(PAGER_ENV)
+	$(gitwebdir_SQ):$(PERL_PATH_SQ):$(SANE_TEXT_GREP):$(PAGER_ENV):\
+	$(perllibdir_SQ)
 define cmd_munge_script
 $(RM) $@ $@+ && \
 sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
@@ -1951,29 +1946,17 @@ git.res: git.rc GIT-VERSION-FILE
 $(SCRIPT_PERL_GEN): GIT-BUILD-OPTIONS
 
 ifndef NO_PERL
-$(SCRIPT_PERL_GEN): perl/perl.mak
-
-perl/perl.mak: perl/PM.stamp
-
-perl/PM.stamp: FORCE
-	@$(FIND) perl -type f -name '*.pm' | sort >$@+ && \
-	$(PERL_PATH) -V >>$@+ && \
-	{ cmp $@+ $@ >/dev/null 2>/dev/null || mv $@+ $@; } && \
-	$(RM) $@+
-
-perl/perl.mak: GIT-CFLAGS GIT-PREFIX perl/Makefile perl/Makefile.PL
-	$(QUIET_SUBDIR0)perl $(QUIET_SUBDIR1) PERL_PATH='$(PERL_PATH_SQ)' prefix='$(prefix_SQ)' $(@F)
+$(SCRIPT_PERL_GEN):
 
-PERL_DEFINES = $(PERL_PATH_SQ):$(PERLLIB_EXTRA_SQ)
-$(SCRIPT_PERL_GEN): % : %.perl perl/perl.mak GIT-PERL-DEFINES GIT-VERSION-FILE
+PERL_DEFINES = $(PERL_PATH_SQ):$(PERLLIB_EXTRA_SQ):$(perllibdir_SQ)
+$(SCRIPT_PERL_GEN): % : %.perl GIT-PERL-DEFINES GIT-VERSION-FILE
 	$(QUIET_GEN)$(RM) $@ $@+ && \
-	INSTLIBDIR=`MAKEFLAGS= $(MAKE) -C perl -s --no-print-directory instlibdir` && \
 	INSTLIBDIR_EXTRA='$(PERLLIB_EXTRA_SQ)' && \
 	INSTLIBDIR="$$INSTLIBDIR$${INSTLIBDIR_EXTRA:+:$$INSTLIBDIR_EXTRA}" && \
 	sed -e '1{' \
 	    -e '	s|#!.*perl|#!$(PERL_PATH_SQ)|' \
 	    -e '	h' \
-	    -e '	s=.*=use lib (split(/$(pathsep)/, $$ENV{GITPERLLIB} || "'"$$INSTLIBDIR"'"));=' \
+	    -e '	s=.*=use lib (split(/$(pathsep)/, $$ENV{GITPERLLIB} || "'"$$INSTLIBDIR"'" || "'"$(perllibdir_SQ)"'"));=' \
 	    -e '	H' \
 	    -e '	x' \
 	    -e '}' \
@@ -2291,6 +2274,21 @@ 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)
+PMCFILES := $(patsubst perl/%.pm,perl/build/lib/%.pmc,$(PMFILES))
+
+ifndef NO_PERL
+all:: $(PMCFILES)
+endif
+
+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 $< $@
+
 FIND_SOURCE_FILES = ( \
 	git ls-files \
 		'*.[hcS]' \
@@ -2550,7 +2548,9 @@ ifndef NO_GETTEXT
 	(cd '$(DESTDIR_SQ)$(localedir_SQ)' && umask 022 && $(TAR) xof -)
 endif
 ifndef NO_PERL
-	$(MAKE) -C perl prefix='$(prefix_SQ)' DESTDIR='$(DESTDIR_SQ)' install
+	$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(perllibdir_SQ)'
+	(cd perl/build/lib && $(TAR) cf - .) | \
+	(cd '$(DESTDIR_SQ)$(perllibdir_SQ)' && umask 022 && $(TAR) xof -)
 	$(MAKE) -C gitweb install
 endif
 ifndef NO_TCLTK
@@ -2600,12 +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
 
@@ -2697,7 +2702,7 @@ clean: profile-clean coverage-clean
 	$(MAKE) -C Documentation/ clean
 ifndef NO_PERL
 	$(MAKE) -C gitweb clean
-	$(MAKE) -C perl clean
+	$(RM) -r perl/build/
 endif
 	$(MAKE) -C templates/ clean
 	$(MAKE) -C t/ clean