[gentoo-dev] multiple inclusion protection with eclasses

[Mike Frysinger]

ferringb did some tests and found that doing multiple inclusion protection in 
eclasses gets us some nice speed ups.  it isn't nearly as nice as if we had a 
way of skipping the `source` altogether, but that that would require PMS/tree 
changes.  the change i'm proposing can be implemented $now and should work 
with all versions.  PMS extensions can thus be discussed in parallel.

simply put, it's the same thing as doing standard #ifdef logic in headers to 
protect against multiple inclusion errors.  on to the example:

--- autotools.eclass
+++ autotools.eclass
@@ -10,6 +10,9 @@
 # This eclass is for safely handling autotooled software packages that need
 # regenerate their build scripts.  All functions will abort in case of
 
+if [[ ${___ECLASS_ONCE_AUTOTOOLS} != "recur -_+^+_- spank" ]] ; then
+___ECLASS_ONCE_AUTOTOOLS="recur -_+^+_- spank"
+
 inherit eutils libtool
 
 # @ECLASS-VARIABLE: WANT_AUTOCONF
@@ -399,3 +402,5 @@
 
 	echo $include_opts
 }
+
+fi

this assumes that the eclass in question isn't doing something weird.  for 
example, if you had an ebuild today that did:
	inherit eutils
	epatch() { die erp; }
	inherit eutils

that local epatch() would get reset by the eutils inherit.  but i can't see 
any ebuild having a valid reason for doing things like this, so screw 'em.

i plan on implementing this in the eclasses i generally look over.  i don't 
plan on doing it for all eclasses since i'm not familiar with them.
-mike