[PATCHv3] Makefile: implement help target

@@ -1,4 +1,10 @@
 # The default target of this Makefile is...
+help-Build::
+	$(H) 'Build Git and the documentation'
+
+help-Build::
+	$(HH) all 'Build the Git suite'
+
 all::
 
 # Define V=1 to have a more verbose compile.

@@ -1952,29 +1958,56 @@ $(XDIFF_LIB): $(XDIFF_OBJS)
 $(VCSSVN_LIB): $(VCSSVN_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) rcs $@ $(VCSSVN_OBJS)
 
+help-Build::
+	$(HH) doc 'Build man pages and HTML docs'
+
 doc:
 	$(MAKE) -C Documentation all
 
+help-Build::
+	$(HH) man 'Build man pages'
+
 man:
 	$(MAKE) -C Documentation man
 
+help-Build::
+	$(HH) html 'Build HTML doc'
+
 html:
 	$(MAKE) -C Documentation html
 
+help-Build::
+	$(HH) info 'Build info docs'
+
 info:
 	$(MAKE) -C Documentation info
 
+help-Build::
+	$(HH) pdf 'Build PDF docs'
+
 pdf:
 	$(MAKE) -C Documentation pdf
 
+help-Develop::
+	$(H) 'Making development easier'
+
+help-Develop::
+	$(HH) TAGS 'Generate tags using etags'
+
 TAGS:
 	$(RM) TAGS
 	$(FIND) . -name '*.[hcS]' -print | xargs etags -a
 
+help-Develop::
+	$(HH) tags 'Generate tags using ctags'
+
 tags:
 	$(RM) tags
 	$(FIND) . -name '*.[hcS]' -print | xargs ctags -a
 
+help-Develop::
+	$(HH) cscope 'Generate cscope index'
+
 cscope:
 	$(RM) cscope*
 	$(FIND) . -name '*.[hcS]' -print | xargs cscope -b

@@ -2040,6 +2073,12 @@ export NO_SVN_TESTS
 
 ### Testing rules
 
+help-Test::
+	$(H) 'Testing source and build'
+
+help-Test::
+	$(HH) test 'Check the build by running the test suite'
+
 test: all
 	$(MAKE) -C t/ all
 

@@ -2099,6 +2138,12 @@ export gitexec_instdir
 
 install_bindir_programs := $(patsubst %,%$X,$(BINDIR_PROGRAMS_NEED_X)) $(BINDIR_PROGRAMS_NO_X)
 
+help-Install::
+	$(H) 'Installing the Git suite and documentation'
+
+help-Install::
+	$(HH) install 'Install the Git suite'
+
 install: all
 	$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(bindir_SQ)'
 	$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(gitexec_instdir_SQ)'

@@ -2155,27 +2200,51 @@ endif
 install-gitweb:
 	$(MAKE) -C gitweb install
 
+help-Install::
+	$(HH) install-doc 'Install man pages'
+
 install-doc:
 	$(MAKE) -C Documentation install
 
+help-Install::
+	$(HH) install-man 'Install man pages'
+
 install-man:
 	$(MAKE) -C Documentation install-man
 
+help-Install::
+	$(HH) install-html 'Install HTML docs'
+
 install-html:
 	$(MAKE) -C Documentation install-html
 
+help-Install::
+	$(HH) install-info 'Install info docs'
+
 install-info:
 	$(MAKE) -C Documentation install-info
 
+help-Install::
+	$(HH) install-pdf 'Install PDF docs'
+
 install-pdf:
 	$(MAKE) -C Documentation install-pdf
 
+help-Install::
+	$(HH) quick-install-doc 'Install pregenerated man pages from origin/man'
+
 quick-install-doc:
 	$(MAKE) -C Documentation quick-install
 
+help-Install::
+	$(HH) quick-install-man 'Install pregenerated man pages from origin/man'
+
 quick-install-man:
 	$(MAKE) -C Documentation quick-install-man
 
+help-Install::
+	$(HH) quick-install-html 'Install pregenerated HTML pages from origin/html'
+
 quick-install-html:
 	$(MAKE) -C Documentation quick-install-html
 

@@ -2188,6 +2257,9 @@ git.spec: git.spec.in
 	mv $@+ $@
 
 GIT_TARNAME=git-$(GIT_VERSION)
+help-Build::
+	$(HH) dist 'Build git-$(GIT_VERSION).tar.gz source archive'
+
 dist: git.spec git-archive$(X) configure
 	./git-archive --format=tar \
 		--prefix=$(GIT_TARNAME)/ HEAD^{tree} > $(GIT_TARNAME).tar

@@ -2203,6 +2275,9 @@ dist: git.spec git-archive$(X) configure
 	@$(RM) -r $(GIT_TARNAME)
 	gzip -f -9 $(GIT_TARNAME).tar
 
+help-Build::
+	$(HH) rpm 'Build source and binary RPM packages'
+
 rpm: dist
 	$(RPMBUILD) \
 		--define "_source_filedigest_algorithm md5" \

@@ -2211,6 +2286,10 @@ rpm: dist
 
 htmldocs = git-htmldocs-$(GIT_VERSION)
 manpages = git-manpages-$(GIT_VERSION)
+
+help-Build::
+	$(HH) dist-doc 'Build $(manpages).tar.gz and $(htmldocs).tar.gz'
+
 dist-doc:
 	$(RM) -r .doc-tmp-dir
 	mkdir .doc-tmp-dir

@@ -2230,10 +2309,18 @@ dist-doc:
 	$(RM) -r .doc-tmp-dir
 
 ### Cleaning rules
+help-Clean::
+	$(H) 'Cleaning up after a build'
+
+help-Clean::
+	$(HH) distclean 'Remove generated files and the configure script'
 
 distclean: clean
 	$(RM) configure
 
+help-Clean::
+	$(HH) clean 'Remove generated files but keep the configure script'
+
 clean:
 	$(RM) *.o block-sha1/*.o ppc/*.o compat/*.o compat/*/*.o xdiff/*.o vcs-svn/*.o \
 		builtin/*.o $(LIB_FILE) $(XDIFF_LIB) $(VCSSVN_LIB)

@@ -2268,7 +2355,9 @@ endif
 .PHONY: FORCE TAGS tags cscope
 
 ### Check documentation
-#
+help-Test::
+	$(HH) check-docs 'Check documentation coverage'
+
 check-docs::
 	@(for v in $(ALL_PROGRAMS) $(SCRIPT_LIB) $(BUILT_INS) git gitk; \
 	do \

@@ -2335,6 +2424,9 @@ check-builtins::
 #
 .PHONY: coverage coverage-clean coverage-build coverage-report
 
+help-Test::
+	$(HH) coverage 'Check test coverage'
+
 coverage:
 	$(MAKE) coverage-build
 	$(MAKE) coverage-report

@@ -2370,5 +2462,20 @@ coverage-untested-functions: coverage-report
 cover_db: coverage-report
 	gcov2perl -db cover_db *.gcov
 
+help-Test::
+	$(HH) cover_db_html 'Check test coverage and create HTML report'
+
 cover_db_html: cover_db
 	cover -report html -outputdir cover_db_html cover_db
+
+H=@printf "%s:\n"
+HH=@printf "    %-18s - %s\n"
+
+help-Help::
+	$(H) Help
+
+help-Help::
+	$(HH) help 'Show help for main make targets'
+	$(HH) help-X 'Show help for category X (Build, Test, Install, Clean, Develop)'
+
+help: help-Help help-Build help-Test help-Install help-Clean help-Develop