[PATCH] Makefile: Fix occasional GIT-CFLAGS breakage

[PATCH] Makefile: Fix occasional GIT-CFLAGS breakage

[Jonathan Nieder]

GNU make’s target-specific variables facility has one weird facet: any
variables set for a given target apply to all of its dependencies,
too.  For example, when running “make exec_cmd.o”, since exec_cmd.o
depends on GIT-CFLAGS, the variable assignment in

	exec_cmd.s exec_cmd.o: ALL_CFLAGS += \
		'-DGIT_EXEC_PATH="$(gitexecdir_SQ)"' \
		'-DBINDIR="$(bindir_relative_SQ)"' \
		'-DPREFIX="$(prefix_SQ)"'

applies when refreshing GIT-CFLAGS, and the extra options get included
in the tracked compiler flags.  If an object file like this is the
first target built, GIT-CFLAGS will appear to be out of date,
resulting in useless rebuilds and the dreaded “new build flags or
prefix” message.

This does not happen with every build because GIT-CFLAGS is only
refreshed once in a given “make” run, and usually the first target
does not set any variables.  When this problem does rear its head, it
is very annoying.

So put target-specific flags in a separate EXTRA_CPPFLAGS variable
that is not included in $(TRACK_CFLAGS).

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
Ran into this today.  Reproducible by running "make tag.o" and then
"make exec_cmd.o".  Presumably caused by my commit 373a5ed (Makefile:
use target-specific variable to pass flags to cc, 2010-01-06); sorry.

 Makefile |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index 7c616f8..fc03436 100644
--- a/Makefile
+++ b/Makefile
@@ -316,6 +316,7 @@ BUILTIN_OBJS =
 BUILT_INS =
 COMPAT_CFLAGS =
 COMPAT_OBJS =
+EXTRA_CPPFLAGS =
 LIB_H =
 LIB_OBJS =
 PROGRAM_OBJS =
@@ -1480,7 +1481,7 @@ strip: $(PROGRAMS) git$X
 	$(STRIP) $(STRIP_OPTS) $(PROGRAMS) git$X
 
 git.o: common-cmds.h
-git.s git.o: ALL_CFLAGS += -DGIT_VERSION='"$(GIT_VERSION)"' \
+git.s git.o: EXTRA_CPPFLAGS = -DGIT_VERSION='"$(GIT_VERSION)"' \
 	'-DGIT_HTML_PATH="$(htmldir_SQ)"'
 
 git$X: git.o $(BUILTIN_OBJS) $(GITLIBS)
@@ -1488,7 +1489,7 @@ git$X: git.o $(BUILTIN_OBJS) $(GITLIBS)
 		$(BUILTIN_OBJS) $(ALL_LDFLAGS) $(LIBS)
 
 builtin/help.o: common-cmds.h
-builtin/help.s builtin/help.o: ALL_CFLAGS += \
+builtin/help.s builtin/help.o: EXTRA_CPPFLAGS = \
 	'-DGIT_HTML_PATH="$(htmldir_SQ)"' \
 	'-DGIT_MAN_PATH="$(mandir_SQ)"' \
 	'-DGIT_INFO_PATH="$(infodir_SQ)"'
@@ -1714,13 +1715,13 @@ endif
 
 ifndef CHECK_HEADER_DEPENDENCIES
 $(C_OBJ): %.o: %.c GIT-CFLAGS $(missing_dep_dirs)
-	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $<
+	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
 $(ASM_OBJ): %.o: %.S GIT-CFLAGS $(missing_dep_dirs)
-	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $<
+	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
 endif
 
 %.s: %.c GIT-CFLAGS FORCE
-	$(QUIET_CC)$(CC) -S $(ALL_CFLAGS) $<
+	$(QUIET_CC)$(CC) -S $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
 
 ifdef USE_COMPUTED_HEADER_DEPENDENCIES
 # Take advantage of gcc's on-the-fly dependency generation
@@ -1760,20 +1761,20 @@ xdiff-interface.o $(XDIFF_OBJS): \
 	xdiff/xutils.h xdiff/xprepare.h xdiff/xdiffi.h xdiff/xemit.h
 endif
 
-exec_cmd.s exec_cmd.o: ALL_CFLAGS += \
+exec_cmd.s exec_cmd.o: EXTRA_CPPFLAGS = \
 	'-DGIT_EXEC_PATH="$(gitexecdir_SQ)"' \
 	'-DBINDIR="$(bindir_relative_SQ)"' \
 	'-DPREFIX="$(prefix_SQ)"'
 
-builtin/init-db.s builtin/init-db.o: ALL_CFLAGS += \
+builtin/init-db.s builtin/init-db.o: EXTRA_CPPFLAGS = \
 	-DDEFAULT_GIT_TEMPLATE_DIR='"$(template_dir_SQ)"'
 
-config.s config.o: ALL_CFLAGS += -DETC_GITCONFIG='"$(ETC_GITCONFIG_SQ)"'
+config.s config.o: EXTRA_CPPFLAGS = -DETC_GITCONFIG='"$(ETC_GITCONFIG_SQ)"'
 
-http.s http.o: ALL_CFLAGS += -DGIT_USER_AGENT='"git/$(GIT_VERSION)"'
+http.s http.o: EXTRA_CPPFLAGS = -DGIT_USER_AGENT='"git/$(GIT_VERSION)"'
 
 ifdef NO_EXPAT
-http-walker.s http-walker.o: ALL_CFLAGS += -DNO_EXPAT
+http-walker.s http-walker.o: EXTRA_CPPFLAGS = -DNO_EXPAT
 endif
 
 git-%$X: %.o $(GITLIBS)
-- 
1.7.0