fix build against nix 2.7

[ajs124]

Includes #1161 (@Ma27)

not particularly well tested, but builds and tests pass (I think)

[Ericson2314]

localStore might be null, please do not do this way.

Suggested change

	auto localStore = state.store.dynamic_pointer_cast<LocalFSStore>();
	auto drvPath = localStore->printStorePath(drv->requireDrvPath());
	auto drvPath = state.store->printStorePath(drv->requireDrvPath());

[Ericson2314]

Please put back

[Ericson2314]

Suggested change

	out[j.first] = localStore->printStorePath(j.second);
	out[j.first] = state.store->printStorePath(j.second);

[Ma27]

Deployed to my own Hydra, seems to work fine 👍

[Ericson2314]

@edolstra Feel comfortable merging this one?

[cole-h]

I feel like we should hold off on this, due to the recent issues with Hydra that maybe are connected to the bump to 2.6 (e.g. see the Infra and Infra alerts channels on Matrix, where this has been a ~hot topic).

[Ericson2314]

Oh, I didn't know about that. Bummer. Perhaps we need a way to disable non-blocking GC until the kinks are worked out? (Note, they could be Hydra side, e.g. a lack of temp roots, too.)

Per #1166 I would say we need a staging branch for every version of Nix newer than the on on master, in addition to Nix HEAD.

So we could revert 2,6 on master, but then revert the revert on staging-nix-2.6, and merge that and this into staging-nix-2.7, and then make staging-nix-head or so on top of that.

[edolstra]

@cole-h Do you have more info on those issues?

[grahamc]

@edolstra could you, @rbvermaa, and I do a call some time to go over them? They're a bit hard to track down and I think we might have an easier time sorting through them together and then writing them down.

[rbvermaa]

I would prefer it if we can allow Hydra to build against 2.4 and up. We had to revert back to 2.4, because we were getting builds that kept hanging, which significantly disrupted our builds.

[Ericson2314]

@rbvermaa The Nix internals change too much for that to be possible at this time. But we could keep the branches tied to older Nix around afterwords.

[rbvermaa]

It seems surprising to me to not support the versions of nix that are provided in NixOS stable channel.

[Ericson2314]

@rbvermaa Hydra has always been built against a single version of Nix. The daemon protocol is meant to be interoperable, so other Nix versions for the builders will work. (And I have unmerged PRs to test that interoperability.)

Hydra previously was pinned to random Nix versions. In recent months, The Nix it is pinned to is always stable version of Nix. This is definitely an improvement.

[grahamc]

Applied in #1188.