PATCH: Break annoying make dependency cycle

PATCH: Break annoying make dependency cycle

[Bart Schaefer]

After weeks of being annoyed when init.o was unexpectedly recompiled, I at
last noticed that zsh always recompiles at least twice whenever there is
a change to any of the .mk or .in files.  Try it:  With an existing build
tree, run

    touch Src/Makefile.in
    make
    make

You'll see that zsh recreates modules-bltin and consequently recompiles on
the second make, even if it already relinked the zsh binary the first time.
(Maybe this is GNU-make-specific?)

This happens because the first make executes config.status to recreate the
Makefile, but it has already considered modules-bltin to be up to date at
that point -- so it doesn't rebuild *that* until the *second* make, even
though (and because) there's a dependency of modules-bltin on Makefile.

The reason for the dependency of modules-bltin on Makefile appears to be
the reference to the @D@ substitution in the modules-bltin action.  To
break this loop and assure that the *first* make really rebuilds anything
that may need rebuilding, the dependency should be on config.status, which
is guaranteed to change any time the @D@ substitution would change.

Almost two hundred times as many words to explain it as to fix it.  Whew.

Index: Src/Makefile.in
===================================================================
@@ -137,7 +137,7 @@
 	    cat mymods.conf > $@; \
 	fi
 
-modules-bltin:: Makefile $(sdir)/xmods.conf
+modules-bltin:: $(dir_top)/config.status $(sdir)/xmods.conf
 	if test -f mymods.conf; then \
 	    cat mymods.conf > $@; \
 	elif test @D@ = N; then \

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com