Makefile: Fix compilation after header removal.

When switching from an older git version which still contains some
header file to a newer version where it got removed, a .d file remains
in build/deps which lists the no longer existing header file as a
prerequisite. This causes the build to fail because the prerequisite
cannot be created. The problem can be worked around by removing the
stale .d file, for example by running make clean, but this is no real
fix, and is inefficient.

The root of the matter is that .d files depend on their .c counterpart,
but this dependency is not stated anywhere in the Makefile. Thus, we
need a rule for the .d target with the same prerequisites and the same
recipe as the object file target. GNU make supports multiple targets,
but the feature does not seem to work as advertised, regardless of
whether rules with independent targets or rules with grouped targets
(using the &: separator) are employed. Thus we bite the bullet and
use two separate rules.

diff --git a/Makefile.real b/Makefile.real
index 6e8084d542b8888e2a838671b6a9be845ac2cae2..e5ecfe4290118d83aa23b6bca4f69647f0f1f283 100644 (file)
--- a/Makefile.real
+++ b/Makefile.real
@@ -255,10 +255,19 @@ $(object_dir)/mm.o \
 
 $(object_dir)/compress_filter.o: CFLAGS += -O3
 
-$(object_dir)/%.o: %.c | $(object_dir) $(dep_dir) $(lsg_h) $(yy_h)
+define CC_CMD
        $(call SAY, CC $<)
-       $(CC) -c -o $@ -MMD -MF $(dep_dir)/$(*F).d -MT $@ $(CPPFLAGS) \
-               $(STRICT_CFLAGS) $(CFLAGS) $<
+       $(CC) -c -o $(object_dir)/$(*F).o -MMD -MF \
+               $(dep_dir)/$(*F).d -MT $(object_dir)/$(*F).o \
+               $(CPPFLAGS) $(STRICT_CFLAGS) $(CFLAGS) $<
+endef
+CC_PREREQUISITES := %.c | $(object_dir) $(dep_dir) $(lsg_h) $(yy_h)
+# These two have the same prerequisites and the same recipe. There should be a
+# better way to write this.
+$(object_dir)/%.o: $(CC_PREREQUISITES)
+       $(CC_CMD)
+$(dep_dir)/%.d: $(CC_PREREQUISITES)
+       $(CC_CMD)
 
 para_recv para_afh para_play para_server: LDFLAGS += $(id3tag_ldflags)
 para_write para_play para_audiod \