[Bug] Having a `tools` app in umbrella fails when running tests with coverage

[mindreframer]

Environment

• Elixir & Erlang/OTP versions (elixir --version):
• Operating system:

$ elixir --version
Erlang/OTP 24 [erts-12.0.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1]

Elixir 1.12.2 (compiled with Erlang/OTP 24)

OS: Mac OS Big Sur (11.5.11) on Apple M1

Current behavior

$ mix new toolstest --umbrella
$ cd  toolstest
$ pushd apps ; mix new app1 ; popd 
$ mix test --cover
==> app1
Cover compiling modules ...
..

Finished in 0.02 seconds (0.00s async, 0.02s sync)
1 doctest, 1 test, 0 failures

Randomized with seed 632509

Generating cover results ...

Percentage | Module
-----------|--------------------------
   100.00% | App1
-----------|--------------------------
   100.00% | Total

Generated HTML coverage results in "cover" directory

$ pushd apps ; mix new tools ; popd 
$ mix test --cover
==> tools
Compiling 1 file (.ex)
Generated tools app
==> app1
Cover compiling modules ...
..

Finished in 0.02 seconds (0.00s async, 0.02s sync)
1 doctest, 1 test, 0 failures

Randomized with seed 570422

Generating cover results ...

Percentage | Module
-----------|--------------------------
   100.00% | App1
-----------|--------------------------
   100.00% | Total

** (exit) an exception was raised:
    ** (MatchError) no match of right hand side value: {:error, :enoent}
        cover.erl:2937: :cover.read_stylesheet/0
        cover.erl:2893: :cover.create_header/2
        cover.erl:2780: :cover.do_analyse_to_file1/4
        cover.erl:2759: :cover.do_parallel_analysis_to_file/5
    cover.erl:774: :cover.call/1
    (mix 1.12.2) lib/mix/tasks/test.coverage.ex:209: anonymous fn/3 in Mix.Tasks.Test.Coverage.html/2
    (elixir 1.12.2) lib/enum.ex:2385: Enum."-reduce/3-lists^foldl/2-0-"/3
    (mix 1.12.2) lib/mix/tasks/test.coverage.ex:208: Mix.Tasks.Test.Coverage.html/2
    (mix 1.12.2) lib/mix/tasks/test.ex:520: Mix.Tasks.Test.do_run/3
    (mix 1.12.2) lib/mix/task.ex:394: anonymous fn/3 in Mix.Task.run_task/3
    (mix 1.12.2) lib/mix/project.ex:353: Mix.Project.in_project/4
    (elixir 1.12.2) lib/file.ex:1560: File.cd!/2
    (mix 1.12.2) lib/mix/task.ex:520: anonymous fn/4 in Mix.Task.recur/1
    (elixir 1.12.2) lib/enum.ex:2385: Enum."-reduce/3-lists^foldl/2-0-"/3
    (mix 1.12.2) lib/mix/task.ex:519: Mix.Task.recur/1
    (mix 1.12.2) lib/mix/project_stack.ex:181: Mix.ProjectStack.recur/1
    (mix 1.12.2) lib/mix/cli.ex:84: Mix.CLI.run_task/2
    (elixir 1.12.2) lib/code.ex:1261: Code.require_file/2

Expected behavior

It should be possible to have an app named tools in an umbrella project without issues.

[josevalim]

@mindreframer tools is an application that ships as part of otp and that cover belongs to. I will change the app generator to raise if you try to name an application :tools.

[josevalim]

To be clear, you will have to change your app name.

[mindreframer]

@josevalim Thanks for the quick response! Alright, that makes sense. I'll change the app name. And yes, raising for reserved app names sounds like a good approach.

[lukaszsamson]

@josevalim IMO b2e33b4 is not fuly solving the issue. Not all builtin OTP apps are loaded/available. You can create a debugger app and it will silently work until someone loads the OTP debugger. In fact exactly this happened in elixir-ls.

[josevalim]

@lukaszsamson yup. The goal for now is to provide some basic sanity checking. I also looked into checking this during compilation but it had issues with recompilations (since the previous app is often still loaded). But this should provide an immediate feedback at the earliest point possible.