Update Makefile to track dependencies better

c_src/Makefile

@@ -1,15 +1,11 @@
 MIX_APP_PATH ?= ..
-
 PREFIX = $(MIX_APP_PATH)/priv
 VIX = $(PREFIX)/vix.so
-
 VIX_COMPILATION_MODE ?= PRECOMPILED_NIF_AND_LIBVIPS
 VIX_COMPILATION_MODE := $(shell echo "$(VIX_COMPILATION_MODE)" | tr '[:lower:]' '[:upper:]')
 
 # System type and C compiler/flags.
-
 UNAME_SYS := $(shell uname -s)
-
 ifeq ($(UNAME_SYS), Darwin)
 	CFLAGS += -O2 -Wall -Werror -Wextra -Wno-unused-parameter -Wmissing-prototypes -std=c11
 	LDFLAGS += -flat_namespace -undefined suppress
@@ -26,18 +22,15 @@ ifeq ($(VIX_COMPILATION_MODE), PLATFORM_PROVIDED_LIBVIPS)
 	LDLIBS += `pkg-config vips --libs`
 else
 	PRECOMPILED_LIBVIPS_PATH = $(PREFIX)/precompiled_libvips
-
 	ifeq ($(VIX_COMPILATION_MODE), PRECOMPILED_LIBVIPS)
 		# force fetching libvips if previously configured to use PRECOMPILED_NIF_AND_LIBVIPS
 		# since the precompiled vix does not bundle `include`
 		PRECOMPILED_LIBVIPS_PREREQUISITE = $(PRECOMPILED_LIBVIPS_PATH)/include
 	else
 		PRECOMPILED_LIBVIPS_PREREQUISITE = $(PRECOMPILED_LIBVIPS_PATH)
 	endif
-
 	CFLAGS  += -pthread -I $(PRECOMPILED_LIBVIPS_PATH)/include -I $(PRECOMPILED_LIBVIPS_PATH)/lib/glib-2.0/include -I $(PRECOMPILED_LIBVIPS_PATH)/include/glib-2.0
 	LDLIBS  += -L $(PRECOMPILED_LIBVIPS_PATH)/lib
-
 	ifeq ($(UNAME_SYS), Darwin)
 		LDFLAGS += -Wl,-rpath,@loader_path/precompiled_libvips/lib
 		LDLIBS  += -lvips.42
@@ -48,19 +41,18 @@ else
 endif
 
 # Verbosity
-
 c_verbose_0 = @echo " C     " $(?F);
 c_verbose = $(c_verbose_$(V))
-
 link_verbose_0 = @echo " LD    " $(@F);
 link_verbose = $(link_verbose_$(V))
 
+# Source files and dependency management
 SRC = $(shell find . -type f -name "*.c")
-
-# Object files are put in `c_src` directory.
-# Maybe we should put in `${MIX_APP_PATH}/priv`?
-# but then we need to compile NIF for each env
 OBJ = $(addsuffix .o,$(basename $(SRC)))
+DEP = $(OBJ:.o=.d)
+
+# Add dependency generation to CFLAGS
+CFLAGS += -MMD -MP
 
 calling_from_make:
 	cd .. && mix compile
@@ -70,10 +62,12 @@ all: install
 
 install: $(PREFIX) $(VIX)
 
-$(OBJ): Makefile $(PRECOMPILED_LIBVIPS_PREREQUISITE)
+# Include generated dependency files
+-include $(DEP)
 
-%.o: %.c
-	$(c_verbose) $(CC) -c $(CFLAGS) -o $@ $<
+# Pattern rule for object files with prerequisite
+%.o: %.c $(PRECOMPILED_LIBVIPS_PREREQUISITE)
+	$(c_verbose) $(CC) $(CFLAGS) -c -o $@ $<
 
 $(VIX): $(OBJ)
 	$(link_verbose) $(CC) $^ -o $@ $(LDFLAGS) $(LDLIBS)
@@ -85,7 +79,7 @@ $(PRECOMPILED_LIBVIPS_PREREQUISITE):
 	@MIX_EXS="../mix.exs" mix run --no-start --no-compile --no-deps-check ../build_scripts/precompiler.exs
 
 clean:
-	$(RM) $(VIX) $(OBJ)
+	$(RM) $(VIX) $(OBJ) $(DEP)
 
 clean_precompiled_libvips: clean
 	$(RM) $(PREFIX)/libvips-*.tar.gz