140171 - non-md dependencies are broken when ACDEFINES change

Status: VERIFIED FIXED

(SeaMonkey :: Build Config, defect, P2)

Description

[hacker formerly known as [e-mail]]

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.

Comment 1

[hacker formerly known as [e-mail]]

Attachment: config-defs.h deps v1

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)

Comment 2

[hacker formerly known as [e-mail]]

> 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 3

[hacker formerly known as [e-mail]]

Attachment: do not use -include if --disable-md is set

Comment 4

[Brian Ryner (not reading)]

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

r=bryner

Comment 5

[hacker formerly known as [e-mail]]

.

Comment 6

[Tracy Walker [:tracy]]

verified