So I've been running with --disable-md for a bit trying to track down potential dependency problems and I ran across this one. We're not tracking configure-level define changes in non-md builds. In a -md build, we generate config-defs.h and use gcc's -include flag to include that file whenever we compile a file. That include is tracked by gcc's -MD dependency generator and is listed in the various .deps/*.pp files. Anytime that config-defs.h gets changed, we basically have a tree rebuild. In a non-md build, we just put the defines in autoconf.mk. We don't have any extra dependencies upon autoconf.mk as we didn't want to trigger a tree rebuild everytime someone just added a configure option (which may or may not add defines). I see two acceptible ways to fix this: 1) Always create config-defs.h (possibly rename it) and have that file be included by every source file in the main Mozilla tree. It only requires touching ~5800 or so files. :-P 2) Generate a separate config/defs.mk and have every compile rule depend upon it. I much prefer (1) as it allows us to use the same dependency "path" for both -md & non-md builds. It should also workaround the longstanding Forte problem in bug 80812. It does have the unfortunate side-effect of requiring developers to add a #ifdef HAVE_CONFIG_DEFS_H/#include/#endif to every new file that they add. Hmm, thinking about this a bit longer; it may be just enough to have config-defs.h always be generated and add the compile rule dependencies but still use the defines from autoconf.mk. It still leaves us in our hacky md/non-md split state but should fix this particular dependency problem.

This patch: * always generates config-defs.h with an updated message about config-defs.h being used for dependency purposes. * adds explicit dependencies to $(DEPTH)/config-defs.h for $(OBJS)

> In a non-md build, we just put the defines in autoconf.mk. A slight correction is needed here. If we're using gcc, we *still* use the -include flag which is partially (maybe wholly) why mkdepend misses the flags set in define. If we don't use the -include flag, the defines should be all on the commandline and mkdepend should catch them accordingly. So an alternative fix may be just to stop using -include if --disable-md is specified.

Comment on attachment 83313 [details] [diff] [review] do not use -include if --disable-md is set r=bryner

.

verified