Dialyzer doesn't report problems after Elixir 1.12 upgrade

Symptoms

Sometimes after upgrading first to Erlang 24 and then later to Elixir 1.12 (can’t remember, the two was very close to each other in time but I think it was the Elixir upgrade) I noticed dialyzer warnings were gone.

Is this the right repo?

I notice this using VSCode, this is the “entry point” of the problem.

Environment

Most of this can be filled out by running the VSCode command (by default bound to Ctrl+Shift+P) “ElixirLS: Copy Debug Info”

• VSCode: 1.56.2
• Electron: 12.0.4
• Chrome: 89.0.4389.114
• Node.js: 14.16.0
• V8: 8.9.255.24-electron.0
• Elixir & Erlang versions (elixir --version): 1.12.0
• Erlang: 1:24.0.1-1
• VSCode ElixirLS version: 0.7.0
• Operating System Version: Ubuntu 20.04.2 LTS (5.4.0-73-generic #82-Ubuntu SMP x86_64 GNU/Linux)

Troubleshooting

• Restart your editor (which will restart ElixirLS) sometimes fixes issues
• Stop your editor, remove the entire .elixir_ls directory, then restart your editor

Nothing worked.

[Defman21]

@javobalazs I’d also go for removing the no_ options since they silence many useful reports from Dialyzer.

[javobalazs]

Update: Dialyzer warning options are empty by default, so even if Dialyzer is run, vscode-elixir-ls won’t report anything. But when I set Dialyzer Warn Opts to the list copied from the option definitions (below, JSON), the reporting comes back. I think somehow, during the (or “an”) update the list was set to the default. Or the default was set to the empty list.

"elixirLS.dialyzerWarnOpts": [
      "error_handling",
      "no_behaviours",
      "no_contracts",
      "no_fail_call",
      "no_fun_app",
      "no_improper_lists",
      "no_match",
      "no_missing_calls",
      "no_opaque",
      "no_return",
      "no_undefined_callbacks",
      "no_unused",
      "underspecs",
      "unknown",
      "unmatched_returns",
      "overspecs",
      "specdiffs"
    ]

(Note to fellow developers: overspecs and specdiffs are kinda producing counterintuitive warnings that are artifacts of the “success typing” of Erlang, and are more or less useless for the purpose one is usually using Dialyzer for. You can switch them off without loosing anything.)