Makefile: make script-related rules usable from subdirectories

Git's Makefile provides a few nice features for script build and
installation (substitute the first line with the right path, hardcode the
path to Git library, ...).

The Makefile already knows how to process files outside the toplevel
directory with e.g.

  make SCRIPT_PERL=path/to/file.perl path/to/file

but we can make it simpler for callers by exposing build, install and
clean rules as .PHONY targets.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -480,9 +480,38 @@ SCRIPT_PERL += git-svn.perl
 SCRIPT_PYTHON += git-remote-testpy.py
 SCRIPT_PYTHON += git-p4.py
 
-SCRIPTS = $(patsubst %.sh,%,$(SCRIPT_SH)) \
-	  $(patsubst %.perl,%,$(SCRIPT_PERL)) \
-	  $(patsubst %.py,%,$(SCRIPT_PYTHON)) \
+# Generated files for scripts
+SCRIPT_SH_GEN = $(patsubst %.sh,%,$(SCRIPT_SH))
+SCRIPT_PERL_GEN = $(patsubst %.perl,%,$(SCRIPT_PERL))
+SCRIPT_PYTHON_GEN = $(patsubst %.py,%,$(SCRIPT_PYTHON))
+
+# Individual rules to allow e.g.
+# "make -C ../.. SCRIPT_PERL=contrib/foo/bar.perl build-perl-script"
+# from subdirectories like contrib/*/
+.PHONY: build-perl-script build-sh-script build-python-script
+build-perl-script: $(SCRIPT_PERL_GEN)
+build-sh-script: $(SCRIPT_SH_GEN)
+build-python-script: $(SCRIPT_PYTHON_GEN)
+
+.PHONY: install-perl-script install-sh-script install-python-script
+install-sh-script: $(SCRIPT_SH_GEN)
+	$(INSTALL) $(SCRIPT_SH_GEN) '$(DESTDIR_SQ)$(gitexec_instdir_SQ)'
+install-perl-script: $(SCRIPT_PERL_GEN)
+	$(INSTALL) $(SCRIPT_PERL_GEN) '$(DESTDIR_SQ)$(gitexec_instdir_SQ)'
+install-python-script: $(SCRIPT_PYTHON_GEN)
+	$(INSTALL) $(SCRIPT_PYTHON_GEN) '$(DESTDIR_SQ)$(gitexec_instdir_SQ)'
+
+.PHONY: clean-perl-script clean-sh-script clean-python-script
+clean-sh-script:
+	$(RM) $(SCRIPT_SH_GEN)
+clean-perl-script:
+	$(RM) $(SCRIPT_PERL_GEN)
+clean-python-script:
+	$(RM) $(SCRIPT_PYTHON_GEN)
+
+SCRIPTS = $(SCRIPT_SH_GEN) \
+	  $(SCRIPT_PERL_GEN) \
+	  $(SCRIPT_PYTHON_GEN) \
 	  git-instaweb
 
 ETAGS_TARGET = TAGS