Yesterday I've got an issue (bug #543780 — my mistake):
>>> Failed to emerge x11-libs/gtk+-3.14.9, Log file:
* Messages for package x11-libs/gtk+-3.14.9:
* ERROR: x11-libs/gtk+-3.14.9::gentoo failed (compile phase):
* emake failed
* If you need support, post the output of `emerge --info '=x11-libs/gtk+-3.14.9::gentoo'`,
* the complete build log and the output of `emerge -pqv '=x11-libs/gtk+-3.14.9::gentoo'`.
* The complete build log is located at '/var/tmp/portage/x11-libs/gtk+-3.14.9/temp/build.log'.
* The ebuild environment file is located at '/var/tmp/portage/x11-libs/gtk+-3.14.9/temp/environment'.
* Working directory: '/var/tmp/portage/x11-libs/gtk+-3.14.9/work/gtk+-3.14.9-abi_x86_64.amd64'
* S: '/var/tmp/portage/x11-libs/gtk+-3.14.9/work/gtk+-3.14.9'
Build failure was the result of incorrectly applyed (incompatible with current version of library) userpatch.
It would be fine, if in such cases portage will remind user to verify custom patch.
Adding to standard error message something like:
* WARNING: failed build used custom patches:
* Please, first try to build $CATEGORY/$PACKAGE without them.
epatch_user() is provided by eutils.eclass, not sys-apps/portage.
I suggest that epatch_user() define a function (printing a message) and append its name to EBUILD_DEATH_HOOKS if epatch_user() applied any patches. (See java-utils-2.eclass.)
i've added it, but i'm not sure how useful it'll be in practice: