This method does *not* create a new type of goal. We instead just make
`DerivationGoal` more sophisticated, which is much easier to do now that
`DerivationBuildingGoal` has been split from it (and so many fields are
gone, or or local variables instead).
This avoids the need for a secondarily trampoline goal that interacted
poorly with `addWantedOutputs`. That, I hope, will mean the bugs from
before do not reappear.
There may in fact be a reason to introduce such a trampoline in the
future, but it would only happen in conjunction with getting rid of
`addWantedOutputs`.
Restores the functionality (and tests) that was reverted in
f4f28cdd0e.
The bug reappeared after all, and the fix introduced a different bug. I
just reverted on 2.27 first, in #12576, but upon further introspection
and discussion with @roberth, with preparing for and travelling to
Planet Nix I will not be able to fix it on `master` soon enough for a
revert to not be warranted here in the meantime also.
This reverts commit c98525235f.
This fixes dynamic derivations, reverting #9081.
I believe that this time around, #9052 is fixed. When I first rebased
this, tests were failing (which wasn't the case before). The cause of
those test failures were due to the crude job in which the outer goal
tried to exit with the inner goal's status.
Now, that error handling has been reworked to be more faithful. The exit
exit status and exception of the inner goal is returned by the outer
goal. The exception was what was causing the test failures, but I
believe it was not having the right error code (there is more than one
for failure) that caused #9081.
The only cost of doing things the "right way" was that I had to
introduce a hacky `preserveException` boolean. I don't like this, but,
then again, none of us like anything about how the scheduler works.
Issue #11927 is still there to clean everything up, subsuming the need
for any `preserveException` because I doubt we will be fishing
information out of state machines like this at all.
This reverts commit 8440afbed7.
Co-Authored-By: Eelco Dolstra <edolstra@gmail.com>
