Fix makefile not recompiling on header change

We currently do not keep track of header files in our Makefile so if one
is changed it can lead to multiple incompatible binary files being
linked. Instead we now create dependency lists for each source file and
recompile them if the need arises.

Fixes #594

.gitignore

@@ -1,4 +1,5 @@
 *.o
+*.d
 *.gcda
 *.gcno
 *.gcov

Makefile

@@ -42,13 +42,15 @@ $(error "$(PKG_CONFIG) failed!")
 endif
 endif
 
-CFLAGS  := ${DEFAULT_CPPFLAGS} ${CPPFLAGS} ${DEFAULT_CFLAGS} ${CFLAGS} ${INCS}
+CFLAGS  := ${DEFAULT_CPPFLAGS} ${CPPFLAGS} ${DEFAULT_CFLAGS} ${CFLAGS} ${INCS} -MMD -MP
 LDFLAGS := ${DEFAULT_LDFLAGS} ${LDFLAGS} ${LIBS}
 
 SRC := $(sort $(shell find src/ -name '*.c'))
 OBJ := ${SRC:.c=.o}
 TEST_SRC := $(sort $(shell find test/ -name '*.c'))
 TEST_OBJ := $(TEST_SRC:.c=.o)
+DEPS := ${SRC:.c=.d} ${TEST_SRC:.c=.d}
+
 
 .PHONY: all debug
 all: doc dunst service
@@ -58,11 +60,13 @@ debug: LDFLAGS  += ${LDFLAGS_DEBUG}
 debug: CPPFLAGS += ${CPPFLAGS_DEBUG}
 debug: all
 
+-include $(DEPS)
+
+${OBJ} ${TEST_OBJ}: Makefile config.mk
+
 %.o: %.c
 	${CC} -o $@ -c $< ${CFLAGS}
 
-${OBJ}: config.mk
-
 dunst: ${OBJ} main.o
 	${CC} -o ${@} ${OBJ} main.o ${CFLAGS} ${LDFLAGS}
 
@@ -122,7 +126,7 @@ endif
 clean: clean-dunst clean-dunstify clean-doc clean-tests clean-coverage clean-coverage-run
 
 clean-dunst:
-	rm -f dunst ${OBJ} main.o
+	rm -f dunst ${OBJ} main.o main.d ${DEPS}
 	rm -f org.knopwob.dunst.service
 	rm -f dunst.systemd.service
 
@@ -136,7 +140,7 @@ clean-doc:
 	rm -fr docs/internal/coverage
 
 clean-tests:
-	rm -f test/test test/*.o
+	rm -f test/test test/*.o test/*.d
 
 clean-coverage: clean-coverage-run
 	find . -type f -name '*.gcno' -delete