NOTE: I'm well-aware that we have to be careful with this to avoid new
regressions on hydra.nixos.org, so this should only be merged after
extensive testing from more people.
Motivation: I updated Nix in my deployment to 2.9.1 and decided to also
update Hydra in one go (and compile it against the newer Nix). Given
that this also updates the C++ code in `hydra-{queue-runner,eval-jobs}`
this patch might become useful in the future though.
At the moment, aggregate jobs can easily break and cause the entire
evaluation to fail, which is not ideal. For Nixpkgs, we do have some
important aggregate jobs (like `tested`), but for debugging and building
purposes it's still useful to get a partial result even if the channel
won't actually advance.
This commit changes the behaviour of hydra-eval-jobs such that it
aggregates any errors found during the construction of an aggregate, and
will instead annotate the job with the evaluation failure such that it
shows up in a "cleaner" way.
There are really two types of failure that we care about: one is where
the attribute just ends up missing altogether in the final output, and
also where the attribute is in the output but fails to evaluate. Both
are handled here.
Note that this does mean that the same error message may be output
multiple times, but this aids debuggability because it'll be much
clearer what's blocking the job from being created.
It might happen that a job from the aggregate returned an error!
This is what the vague "[json.exception.type_error.302] type must be string, but is null"
was all about in this instance; there was no `drvPath` to stringify!
So we now actively watch for errors and copy them to the aggregate job.
The vague "[json.exception.type_error.302] type must be string, but is null"
is **absolutely** unhelpful in the way Hydra currently handles it on
evaluation.
This is handling *unexpected* errors only; the following commit will
handle the specific instance of the previously mentioned error.
Recently a few internal APIs have changed[1]. The `outputPaths` function
has been removed and a lot of data structures are modeled with
`std::optional` which broke compilation.
This patch updates the code in `hydra-queue-runner` accordingly to make
sure that Hydra compiles again.
[1] https://github.com/NixOS/nix/pull/3883
