Makefile: autobuild dependency rules

This uses gcc to generate dependency rules for each `.o` file, based on the
corresponding `.c` file, into a new set of `.d` files (which are also defined
to depend on the same set of source files as their `.o` files).

Result:
* all objectfile dependencies are correctly calculated
* only the necessary dependencies are recalculated when a sourcefile is updated

Inspiration for the build rules:
* http://www.gnu.org/software/make/manual/make.html#Automatic-Prerequisites
* http://make.paulandlesley.org/autodep.html

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

2 files changed, 11 insertions, 1 deletions

diff --git a/.gitignore b/.gitignore
index aa36ff7..1e016e5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 # Files I don't care to see in git-status/commit
 cgit
 cgit.conf
 VERSION
 *.o
+*.d
diff --git a/Makefile b/Makefile
index d1950cb..faf7b98 100644
--- a/Makefile
+++ b/Makefile
@@ -1,98 +1,107 @@
 CGIT_VERSION = v0.7.2
 CGIT_SCRIPT_NAME = cgit.cgi
 CGIT_SCRIPT_PATH = /var/www/htdocs/cgit
 CGIT_CONFIG = /etc/cgitrc
 CACHE_ROOT = /var/cache/cgit
 SHA1_HEADER = <openssl/sha.h>
 GIT_VER = 1.5.4.1
 GIT_URL = http://www.kernel.org/pub/software/scm/git/git-$(GIT_VER).tar.bz2
 
 #
 # Let the user override the above settings.
 #
 -include cgit.conf
 
 
+#
+# Define a pattern rule for automatic dependency building
+#
+%.d: %.c
+        $(CC) $(CFLAGS) -MM $< | sed -e 's/\($*\)\.o:/\1.o $@:/g' >$@
+
+
 EXTLIBS = git/libgit.a git/xdiff/lib.a -lz -lcrypto
 OBJECTS =
 OBJECTS += cache.o
 OBJECTS += cgit.o
 OBJECTS += cmd.o
 OBJECTS += html.o
 OBJECTS += parsing.o
 OBJECTS += shared.o
 OBJECTS += ui-blob.o
 OBJECTS += ui-commit.o
 OBJECTS += ui-diff.o
 OBJECTS += ui-log.o
 OBJECTS += ui-patch.o
 OBJECTS += ui-refs.o
 OBJECTS += ui-repolist.o
 OBJECTS += ui-shared.o
 OBJECTS += ui-snapshot.o
 OBJECTS += ui-summary.o
 OBJECTS += ui-tag.o
 OBJECTS += ui-tree.o
 
 ifdef NEEDS_LIBICONV
         EXTLIBS += -liconv
 endif
 
 
 .PHONY: all git test install clean distclean emptycache force-version get-git
 
 all: cgit git
 
 VERSION: force-version
         @./gen-version.sh "$(CGIT_VERSION)"
 -include VERSION
 
 
 CFLAGS += -g -Wall -Igit
 CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER)'
 CFLAGS += -DCGIT_VERSION='"$(CGIT_VERSION)"'
 CFLAGS += -DCGIT_CONFIG='"$(CGIT_CONFIG)"'
 CFLAGS += -DCGIT_SCRIPT_NAME='"$(CGIT_SCRIPT_NAME)"'
 CFLAGS += -DCGIT_CACHE_ROOT='"$(CACHE_ROOT)"'
 
 
 cgit: $(OBJECTS)
         $(CC) $(CFLAGS) -o cgit $(OBJECTS) $(EXTLIBS)
 
 $(OBJECTS): git/xdiff/lib.a git/libgit.a VERSION
 
+-include $(OBJECTS:.o=.d)
+
 git/xdiff/lib.a: | git
 
 git/libgit.a: | git
 
 git:
         cd git && $(MAKE) xdiff/lib.a
         cd git && $(MAKE) libgit.a
 
 test: all
         $(MAKE) -C tests
 
 install: all
         mkdir -p $(DESTDIR)$(CGIT_SCRIPT_PATH)
         install cgit $(DESTDIR)$(CGIT_SCRIPT_PATH)/$(CGIT_SCRIPT_NAME)
         install cgit.css $(DESTDIR)$(CGIT_SCRIPT_PATH)/cgit.css
         install cgit.png $(DESTDIR)$(CGIT_SCRIPT_PATH)/cgit.png
 
 uninstall:
         rm -f $(CGIT_SCRIPT_PATH)/$(CGIT_SCRIPT_NAME)
         rm -f $(CGIT_SCRIPT_PATH)/cgit.css
         rm -f $(CGIT_SCRIPT_PATH)/cgit.png
 
 clean:
-        rm -f cgit VERSION *.o
+        rm -f cgit VERSION *.o *.d
         cd git && $(MAKE) clean
 
 distclean: clean
         git clean -d -x
         cd git && git clean -d -x
 
 emptycache:
         rm -rf $(DESTDIR)$(CACHE_ROOT)/*
 
 get-git:
         curl $(GIT_URL) | tar -xj && rm -rf git && mv git-$(GIT_VER) git