Makefile: allow building without perl

For systems with a missing or broken perl, it is nicer to
explicitly say "we don't want perl" because:

  1. The Makefile knows not to bother with Perl-ish things
     like Git.pm.

  2. We can print a more user-friendly error message
     than "foo is not a git command" or whatever the broken
     perl might barf

  3. Test scripts that require perl can mark themselves and
     such and be skipped

This patch implements parts (1) and (2). The perl/
subdirectory is skipped entirely, gitweb is not built, and
any git commands which rely on perl will print a
human-readable message and exit with an error code.

This patch is based on one from Robin H. Johnson.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -145,6 +145,8 @@ all::
 # 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 NO_TCLTK if you do not want Tcl/Tk GUI.
 #
 # The TCL_PATH variable governs the location of the Tcl interpreter
@@ -353,7 +355,10 @@ BUILT_INS += git-whatchanged$X
 ALL_PROGRAMS = $(PROGRAMS) $(SCRIPTS)
 
 # what 'all' will build but not install in gitexecdir
-OTHER_PROGRAMS = git$X gitweb/gitweb.cgi
+OTHER_PROGRAMS = git$X
+ifndef NO_PERL
+OTHER_PROGRAMS += gitweb/gitweb.cgi
+endif
 
 # Set paths to tools early so that they can be used for version tests.
 ifndef SHELL_PATH
@@ -1104,6 +1109,10 @@ ifeq ($(TCLTK_PATH),)
 NO_TCLTK=NoThanks
 endif
 
+ifeq ($(PERL_PATH),)
+NO_PERL=NoThanks
+endif
+
 QUIET_SUBDIR0  = +$(MAKE) -C # space to separate -C and subdir
 QUIET_SUBDIR1  =
 
@@ -1178,7 +1187,9 @@ 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)' all
+endif
 	$(QUIET_SUBDIR0)templates $(QUIET_SUBDIR1)
 
 please_set_SHELL_PATH_to_a_more_modern_shell:
@@ -1226,6 +1237,7 @@ $(patsubst %.sh,%,$(SCRIPT_SH)) : % : %.sh
 	chmod +x $@+ && \
 	mv $@+ $@
 
+ifndef NO_PERL
 $(patsubst %.perl,%,$(SCRIPT_PERL)): perl/perl.mak
 
 perl/perl.mak: GIT-CFLAGS perl/Makefile perl/Makefile.PL
@@ -1285,6 +1297,15 @@ git-instaweb: git-instaweb.sh gitweb/gitweb.cgi gitweb/gitweb.css
 	    $@.sh > $@+ && \
 	chmod +x $@+ && \
 	mv $@+ $@
+else # NO_PERL
+$(patsubst %.perl,%,$(SCRIPT_PERL)) git-instaweb: % : unimplemented.sh
+	$(QUIET_GEN)$(RM) $@ $@+ && \
+	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
+	    -e 's|@@REASON@@|NO_PERL=$(NO_PERL)|g' \
+	    unimplemented.sh >$@+ && \
+	chmod +x $@+ && \
+	mv $@+ $@
+endif # NO_PERL
 
 configure: configure.ac
 	$(QUIET_GEN)$(RM) $@ $<+ && \
@@ -1603,9 +1624,11 @@ clean:
 	$(RM) -r $(GIT_TARNAME) .doc-tmp-dir
 	$(RM) $(GIT_TARNAME).tar.gz git-core_$(GIT_VERSION)-*.tar.gz
 	$(RM) $(htmldocs).tar.gz $(manpages).tar.gz
-	$(RM) gitweb/gitweb.cgi
 	$(MAKE) -C Documentation/ clean
+ifndef NO_PERL
+	$(RM) gitweb/gitweb.cgi
 	$(MAKE) -C perl clean
+endif
 	$(MAKE) -C templates/ clean
 	$(MAKE) -C t/ clean
 ifndef NO_TCLTK

unimplemented.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+echo >&2 "fatal: git was built without support for `basename $0` (@@REASON@@)."
+exit 128