config.environ: delay export of A and AA (bug 720180)

[zmedico]

Since variables like A and AA can contain extremely large values which
may trigger E2BIG errors during attempts to execute subprocesses, delay
export until the last moment, and unexport when appropriate.

Bug: https://bugs.gentoo.org/720180
Signed-off-by: Zac Medico [email protected]

[Flowdalic]

Thanks for your work on this (and https://bugs.gentoo.org/833567 " [Future EAPI] src_fetch_extra phase the runs after src_unpack"). I really appreciate that.

However, I wonder if it would not be better to have future EAPIs export a variable pointing to a file that contains a list the archives instead. Such a file could be trivially be converted to a non-exported variable via bash's mapfile and then consumed by unpacker in the traditional fashion. See my example at https://bugs.gentoo.org/721088#c16.

I am also not sure how the changes of this PR are supposed to help. Sorry for my ignorance. But the issue that the environment is potentially too large to spawn a process could already happen once portage fork+execs ebuild.sh. Therefore, unexporting A in ebuild.sh is too late. But maybe I am missing something? For newbies like me, portage's code isn't easy to understand.

[zmedico]

I am also not sure how the changes of this PR are supposed to help. Sorry for my ignorance. But the issue that the environment is potentially too large to spawn a process could already happen once portage fork+execs ebuild.sh. Therefore, unexporting A in ebuild.sh is too late. But maybe I am missing something? For newbies like me, portage's code isn't easy to understand.

The vars are written to a file so they can be sourced after exec. I'll close this PR though since it was more of a POC and I like your idea to use explicit files for this.

[Flowdalic]

I like your idea to use explicit files for this.

Glad that you like it. Posted a first PoC at #1357