Allow configuring stdlib directories

[lukaszsamson]

This PR added necessary support to elixir_sense elixir-lsp/elixir_sense#277 (elixir only). We need to expose it to elixir-ls settings and make sure OTP works as well.

[cbecker]

I ran into this issue. @lukaszsamson thanks for the PRs for elixir_sense. Is there a current workaround or feature branch with the changes to allow elixir_ls to read the source directory from an env var?

[lukaszsamson]

No, it's not implemented on ElixirLS side. It shouldn't be difficult. Are you willing to submit a PR?

[cbecker]

thanks. Let me know if this works #1164

I haven't been able to test it, but i'll try later today

[lukaszsamson]

Nice. Now we need a PR adding the new setting to the vscode extension in https://github.com/elixir-lsp/vscode-elixir-ls/blob/5b1c42df7c4e105bf646ddc17f95e93672c51248/package.json#L66 and it should be easy to test

[cbecker]

thanks, here it goes! elixir-lsp/vscode-elixir-ls#452

[cbecker]

I also tested this PR with neovim and it works as expected :)

[lukaszsamson]

Nice @cbecker. Merged