Bug 718396

Summary:	sys-apps/portage: document non-incremental behavior for USE_EXPAND variable setting in make.conf
Product:	Portage Development	Reporter:	Zac Medico <zmedico>
Component:	Core - Configuration	Assignee:	Portage team <dev-portage>
Status:	CONFIRMED ---
Severity:	normal	CC:	bog, gentoo, josef64
Priority:	Normal
Version:	unspecified
Hardware:	All
OS:	All
See Also:	https://bugs.gentoo.org/show_bug.cgi?id=922307
Whiteboard:
Package list:		Runtime testing required:	---

Description Zac Medico gentoo-dev

2020-04-19 19:26:30 UTC

The make.conf behavior for USE_EXPAND variables is slightly different from make.defaults behavior in profiles. There has always been an expectation that you could set VIDEO_CARDS="foo" and have that disable all of the video_cards_* settings from the profile, as shown in examples here:

https://wiki.gentoo.org/wiki/Xorg/Guide#make.conf

In the implementation, the difference in behavior arises from special treatment of USE_EXPAND variables in the config.regenerate method, where it translates USE_EXPAND variable setting from make.defaults into USE settings (and there's no equivalent code for USE_EXPAND variable settings from make.conf):

https://gitweb.gentoo.org/proj/portage.git/commit/?id=637a13355cf4cc2906e34b61606d31d62acc9fcc