Enable checktvarinvariant on CI

[edsko]

In IntersectMBO/ouroboros-network#1040 I added an invariant to enable assertions on StrictTVars. We should enable this on CI.

[mrBliss]

Maybe somebody with Nix experience can help us out? We need the test-storage and test-consensus testsuites from ouroboros-consensus to run with the checktvarinvariant flag (for the io-sim-classes package) enabled.

Running the tests with that flag enabled takes quite long, so it should not be part of the CI checks for PRs. That would slow down the merge process even more. We want a nightly CI job for this.

@nc6 You wrote https://github.com/input-output-hk/ouroboros-network/blob/master/nix/validate-mainnet.nix, maybe you know what to do?

[mrBliss]

I have received some pointers:

• @angerman: Add

  package.ouroboros-consensus.component.test.test-storage.flags = { checktvarinvariant = true; };
  

  to https://github.com/input-output-hk/ouroboros-network/blob/da1bd0117399d12e485c112f8413e865fed5bb0f/nix/pkgs.nix#L44
  But we want to build that component with the flag enabled for io-sim-classes? We actually want to define an additional variant of an existing component with different flags.
• @cleverca22: To define a nightly job, create .buildkite/nightly.yml (look at the other .yml file for inspiration). Create a new pipeline in Buildkite: https://buildkite.com/input-output-hk/cardano-sl-nightly/settings/schedules. You can use the new build button to force a build instead of waiting a day.

Update:

• @angerman: I don’t think you can have two different instances of the same component in one build plan. I agree that there are cases where I wanted to specify a special flavour it some package as a build dependency at some point but that would require cabal to understand and support something like build-depends: <pkg>[:<comp>][[+|-]<flag>]* or something.