Hydra used to support aggregate jobs that only succeeded when their
constituents succeed. This is still used by e.g. nixpkgs[1].
Prior art:
* https://git.lix.systems/lix-project/nix-eval-jobs/pulls/17: got ported
into the CppNix implementation[2]
* https://github.com/nix-community/nix-eval-jobs/pull/349: implements
glob expressions for constituents - something we needed at work. This
also restructures the code a bit which is what I re-used here. The
globbing is not part of this patch.
Essentially, the following things happen here (assuming `--constituents`
is set):
* Derivations with `_hydraAggregate = true;` are considered aggregates.
These are not written to stdout when received by a worker, but stored
until the end.
* Constituents can be drv paths or strings (that must be the `attr` of
another job). In that case, the derivation of the aggregate job is
rewritten so that it depends on the drv of the constituent job.
* At the very end the aggregate jobs are also written to stdout.
Additionally, this fixes one bug, the old `hydra-eval-jobs`
implementation had (and we actually hit at work):
Given the leaf jobs `packages.foo` & `packages.bar`, an aggregate job
`aggregate0` with
_hydraAggregate = true;
constituents = [ "packages.bar" "packages.foo" ];
and an aggregate job `aggregate1` with
constituents = [ "aggregate0" ];
then it may happen depending on the order of evaluation that `aggregate1`
depends on the old derivation of `aggregate0` (i.e. the one without
rewritten constituents) and doesn't depend on `packages.foo` and
`packages.bar` because it was rewritten before `aggregate0` was
rewritten.
This is done in here correctly, but topologically sorting the aggregate
jobs before rewriting those.
[1] https://github.com/NixOS/nixpkgs/blob/bba6b37c9d0898867a7d9c38a1b5b77efcfb07b9/nixos/release-combined.nix#L69
[2] https://github.com/nix-community/nix-eval-jobs/pull/340
Change-Id: I5baad5e57336b4985ef8595e903814de83eb01c1
Maximilian Bosch
8cb2306138