Run tests purely in Nix

[srid]

While #240 builds on Darwin, it doesn't on Linux. We could probably define all flakes as inputs, transitively, and build the various tests.

❯ nix --option sandbox false build -L --override-input haskell-flake . ./test#checks.aarch64-linux.tests
[..]
tests> ||| Testing ./nix/haskell-parsers
tests> ~/haskell-flake/nix/haskell-parsers ~/haskell-flake
tests> nix (Nix) 2.18.1
tests> warning: you don't have Internet access; disabling some network-dependent features
tests> warning: you don't have Internet access; disabling some network-dependent features
tests> m
tests> warning: you don't have Internet access; disabling some network-dependent features
tests> error:
tests>        … while evaluating the attribute 'cabal.project'
tests>          at /build/tmp.FYTZcVTgye/haskell-flake/nix/haskell-parsers/parser_tests.nix:65:3:
tests>            64| {
tests>            65|   "cabal.project" = runTestsFailing cabalProjectTests;
tests>              |   ^
tests>            66|   "foo-bar.cabal" = runTestsFailing cabalExecutableTests;
tests>        … while evaluating a branch condition
tests>          at /build/tmp.FYTZcVTgye/haskell-flake/nix/haskell-parsers/parser_tests.nix:60:5:
tests>            59|     in
tests>            60|     if res == builtins.trace "All tests passed" [ ]
tests>              |     ^
tests>            61|     then res
tests>        (stack trace truncated; use '--show-trace' to show the full trace)
tests>        error: unable to download 'https://channels.nixos.org/flake-registry.json': Couldn't resolve host name (6)

Tasks

• Run tests as a flake check; macOS CI for tests #240
• test: Make haskell-parser tests a flake check #242
• example test: Run example tests in nix #257
• test/{simple, project-module}: convert to flake checks #243
• test/with-subdir test: Port with-subdir as flake check #258
• docs doc: Run linkcheck as part of nixci #244

[srid]

All done. No more runtest.sh! Just run nix run github:srid/nixci to run the full CI (including tests) locally.

(Will nix'ify rundoc.sh next)