Parallel compiler error when running tests on Github Actions

Hello!

I have an umbrella project and more often than not it fails when trying to run the tests, with the following error. This does not happen when running the tests locally.

Run mix ecto.setup && mix test
==> ornithologue

== Compilation error in file test/ornitho/schema/taxon_test.exs ==
** (MatchError) no match of right hand side value: {:error, :enoent}
    (elixir 1.16.2) lib/kernel/parallel_compiler.ex:540: Kernel.ParallelCompiler.require_file/2
    (elixir 1.16.2) lib/kernel/parallel_compiler.ex:430: anonymous fn/5 in Kernel.ParallelCompiler.spawn_workers/8
Error: .01:19:51.566 [error] GenServer Mix.ProjectStack terminating
** (FunctionClauseError) no function clause matching in anonymous fn/1 in Mix.ProjectStack.recur/1
    (mix 1.16.2) lib/mix/project_stack.ex:239: anonymous fn([]) in Mix.ProjectStack.recur/1
** (exit) exited in: GenServer.call(Mix.ProjectStack, {:update_stack, #Function<24.103597203/1 in Mix.ProjectStack.recur/1>}, :infinity)
    ** (EXIT) an exception was raised:
        ** (FunctionClauseError) no function clause matching in anonymous fn/1 in Mix.ProjectStack.recur/1
            (mix 1.16.2) lib/mix/project_stack.ex:239: anonymous fn([]) in Mix.ProjectStack.recur/1
            (mix 1.16.2) lib/mix/project_stack.ex:326: Mix.ProjectStack.handle_call/3
            (stdlib 5.2) gen_server.erl:1131: :gen_server.try_handle_call/4
            (stdlib 5.2) gen_server.erl:1160: :gen_server.handle_msg/6
            (stdlib 5.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3
    (elixir 1.16.2) lib/gen_server.ex:1114: GenServer.call/3
    (mix 1.16.2) lib/mix/project_stack.ex:239: Mix.ProjectStack.recur/1
    (mix 1.16.2) lib/mix/cli.ex:96: Mix.CLI.run_task/2
    /home/runner/work/_temp/.setup-beam/elixir/bin/mix:2: (file)
    (elixir 1.16.2) lib/code.ex:1489: Code.require_file/2
    (mix 1.16.2) lib/mix/project_stack.ex:326: Mix.ProjectStack.handle_call/3
    (stdlib 5.2) gen_server.erl:1131: :gen_server.try_handle_call/4
    (stdlib 5.2) gen_server.erl:1160: :gen_server.handle_msg/6
    (stdlib 5.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3
Last message (from #PID<0.99.0>): {:update_stack, #Function<24.103597203/1 in Mix.ProjectStack.recur/1>}

As I said, it passes sometimes, but much more often it fails.

I found one topic here with the same/similar situation from 2018: Parallel compiler cannot find files sometimes, where the topic starter had error like this:

== Compilation error in file lib/sentry/logger.ex ==
** (MatchError) no match of right hand side value: {:error, :enoent}
    (elixir) lib/kernel/parallel_compiler.ex:198: anonymous fn/4 in Kernel.ParallelCompiler.spawn_workers/6
could not compile dependency :sentry, "mix compile" failed. You can recompile this dependency with "mix deps.compile sentry", update it with "mix deps.update sentry" or clean it with "mix deps.clean sentry"

I immediately see two differences:

1. They had it failing during project building, while I have it failing when compiling a test script.
2. Their error mentions the dependency compiler cannot find, in my case there is nothing.

This makes me think that maybe the not found dependency in my case is one of my umbrella dependencies?

First I suspected this may be caused by build caching in Github actions, but even disabling cache does not fix this.

Now I think maybe I declared the umberlla dependencies incorrectly, or running tests is not setup properly.

Any advice on how to investigate / debug this is greatly appreciated!

• My project

Thanks!