Mix.target() is :"" for ElixirLS

[mnishiguchi]

Maybe ElixirLS specific issue??? elixir-lsp/vscode-elixir-ls#132

• ElixirLS crashes (?) and gives mix.exs full of red underlines with the error message:

** (File.Error) could not read file "/Users/mnishiguchi/src/nerves_livebook/config/.exs": no such file or directory

• Presumably the error happens at the last line of config/target.exs (in my case).
• Other than ElixirLS errors and red underlies in mix.exs, everything is working fine.

Environment

• Elixir version (elixir -v):

Erlang/OTP 24 [erts-12.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]

Elixir 1.13.2 (compiled with Erlang/OTP 24)

• Nerves environment: (mix nerves.env --info)

==> nerves
==> nerves_livebook
|nerves_bootstrap| Environment Package List

  Pkg:         nerves_toolchain_armv6_nerves_linux_gnueabihf
  Vsn:         1.5.0
  Type:        toolchain
  BuildRunner: {Nerves.Artifact.BuildRunners.Local, []}

  Pkg:         nerves_toolchain_ctng
  Vsn:         1.8.5
  Type:        toolchain_platform
  BuildRunner: {nil, []}

  Pkg:         nerves_system_br
  Vsn:         1.18.3
  Type:        system_platform
  BuildRunner: {nil, []}

  Pkg:         nerves_system_rpi0
  Vsn:         1.18.1
  Type:        system
  BuildRunner: {Nerves.Artifact.BuildRunners.Docker, [make_args: ["source", "all", "legal-info"]]}

|nerves_bootstrap| Loadpaths Start


Nerves environment
  MIX_TARGET:   rpi0
  MIX_ENV:      dev

|nerves_bootstrap| Environment Variable List
  target:     rpi0
  toolchain:  /Users/mnishiguchi/.nerves/artifacts/nerves_toolchain_armv6_nerves_linux_gnueabihf-darwin_x86_64-1.5.0
  system:     /Users/mnishiguchi/.nerves/artifacts/nerves_system_rpi0-portable-1.18.1
  app:        .

|nerves_bootstrap| Loadpaths End

• Additional information about your host, target hardware or environment that
  may help

  • nerves_livebook 0.4.2
  • VS code 1.63.2
  • MacOS 11.6.2
  • ElixirLS v0.9.0

Current behavior

In mix.exs file, all lines are red-underlined, with the error message:

** (File.Error) could not read file "/Users/mnishiguchi/src/nerves_livebook/config/.exs": no such file or directory

Expected behavior

There should not be such an error...

Investigation

Looking at the output from ElixirLS, the error is caused by wrongly named configuration file: config/.exs!!!

MIX_ENV: test
MIX_TARGET:

14:43:29.317 [error] Process #PID<0.24004.0> raised an exception
** (File.Error) could not read file "/Users/mnishiguchi/src/nerves_livebook/config/.exs": no such file or directory
    (elixir 1.13.2) lib/file.ex:355: File.read!/1
    (elixir 1.13.2) lib/config.ex:245: Config.__import__!/1
    (stdlib 3.17) erl_eval.erl:685: :erl_eval.do_apply/6
    (stdlib 3.17) erl_eval.erl:123: :erl_eval.exprs/5
    (elixir 1.13.2) src/elixir.erl:289: :elixir.recur_eval/3
    (elixir 1.13.2) src/elixir.erl:274: :elixir.eval_forms/3
    (elixir 1.13.2) lib/code.ex:404: Code.validated_eval_string/3
    (stdlib 3.17) erl_eval.erl:685: :erl_eval.do_apply/6

In the nerves_livebook project, only location that generate a configuration file name is config/target.exs.

https://github.com/mnishiguchi/nerves_livebook/blob/a7b51e4d840a7304019a637746ba93476f2b7028/config/target.exs#L94

I inspected the outputs of both System.get_env("MIX_TARGET") and Mix.target() in config/target.exs.

IO.puts([
  "---\n",
  [~S[System.get_env("MIX_ENV")    => ], inspect(System.get_env("MIX_ENV")), "\n"],
  [~S[System.get_env("MIX_TARGET") => ], inspect(System.get_env("MIX_TARGET")), "\n"],
  [~S[Mix.env()                    => ], inspect(Mix.env()), "\n"],
  [~S[Mix.target()                 => ], inspect(Mix.target()), "\n"],
  "---\n"
])

Here are results when running mix deps.get. This looks GOOD.

❯ mix deps.get
---
System.get_env("MIX_ENV"))    => nil
System.get_env("MIX_TARGET")) => "rpi0"
Mix.env()                     => :dev
Mix.target()                  => :rpi0
---

Here is the output from ElixirLS. This looks BAD.

• why Mix.target() is :""???!!!

MIX_ENV: test
MIX_TARGET:
---
System.get_env("MIX_ENV"))    => nil
System.get_env("MIX_TARGET")) => "rpi0"
Mix.env()                     => :test
Mix.target()                  => :""
---


15:00:31.873 [error] Process #PID<0.24074.0> raised an exception
** (File.Error) could not read file "/Users/mnishiguchi/src/nerves_livebook/config/.exs": no such file or directory
    (elixir 1.13.2) lib/file.ex:355: File.read!/1
    (elixir 1.13.2) lib/config.ex:245: Config.__import__!/1
    (stdlib 3.17) erl_eval.erl:685: :erl_eval.do_apply/6
    (stdlib 3.17) erl_eval.erl:123: :erl_eval.exprs/5
    (elixir 1.13.2) src/elixir.erl:289: :elixir.recur_eval/3
    (elixir 1.13.2) src/elixir.erl:274: :elixir.eval_forms/3
    (elixir 1.13.2) lib/code.ex:404: Code.validated_eval_string/3
    (stdlib 3.17) erl_eval.erl:685: :erl_eval.do_apply/6

Potential causes

• ElixirLS-specific issue?
• Elixir Mix.target/0's bug?

At least, Mix.target/0 and related code looks GOOD to me.

• https://github.com/mnishiguchi/elixir/blob/9a1babd709495e5baf1d76cd69dbf829bcdbd7ac/lib/mix/lib/mix/state.ex#L12-L28
• Default the mix target to :host when empty elixir-lang/elixir#10537

I do not know what is capable of setting Mix target to :""...

Quick fix

At least, I confirmed the following hack can avoid that error, but this does not address the root cause.

- import_config "#{Mix.target()}.exs"
+ try do
+   import_config "#{Mix.target()}.exs"
+ rescue
+   e in File.Error -> e
+ end

[fhunleth]

Ugh. I removed the workaround since I thought that the fix had been included for a sufficiently long time. I agree that the code looks good.

Could it be that there's white space in the MIX_TARGET environment variable?

[mnishiguchi]

Could it be that there's white space in the MIX_TARGET environment variable?

In case MIX_TARGET environment variable is white space for whatever reason, that value should looks the same after converted to Elixir atom. So we can say :"", atom was created from "" string somehow 🤯

iex> ["", " ", "\n", " \t\t "] |> Enum.map(&String.to_atom/1)
[:"", :" ", :"\n", :" \t\t "]

Looking at the elixir-lsp/elixir-ls codebase, Mix target shows in only a few locations.

• https://github.com/elixir-lsp/elixir-ls/search?q=Mix.target
• Support setting MIX_TARGET elixir-lsp/elixir-ls#299

Ah I think probably this is the root cause:

• https://github.com/elixir-lsp/elixir-ls/blob/2e7ac6d5ff555a62e9acba4067382dd07e398f17/apps/language_server/lib/language_server/server.ex#L1165
• https://github.com/elixir-lsp/elixir-ls/blob/2e7ac6d5ff555a62e9acba4067382dd07e398f17/apps/language_server/lib/language_server/server.ex#L1170

What can be done

• In elixir-lsp/elixir-ls, handle blank MIX_TARGET environment variable properly
• In Mix (Elixir), add def target(value) when is_binary(value) that handles string MIX_TARGET properly

I can make a PR for both.

[fhunleth]

Yes, I agree that you found an issue (hopefully the issue). I also agree with your proposal. Thank you for figuring this out!

[mnishiguchi]

OK, Elixir does not take responsibility of checking valid Mix target value. It is the user responsibility. That is fair.
Now only thing we can do is fix Elixir LS!

[fhunleth]

I misunderstood your proposal. Sorry about that. I really thought that it was to only change Elixir LS. I see that I read to quickly now.

[mnishiguchi]

NP! I was not sure what would be best. I am glad we are gradually getting there.

[mnishiguchi]

Close because now we know it is not directly related to Nerves.