How does this format the file?

[cvkmohan]

When we press Ctrl+Shift+F or editor.formatOnSave is true - does this call mix.format? If I add a plugin in the formatter.exs the sigil is not getting formatted on save.
How to make it work?

[axelson]

Hi! ElixirLS doesn't call mix format directly for two main reasons:

• It would be very slow because we'd have to wait for the BEAM to startup
• We want to support undo/redo via LSP

Here's the code that does the formatting: https://github.com/elixir-lsp/elixir-ls/blob/1f1922db65f0ee7b1d2e754dffdba487ae3f2f01/apps/language_server/lib/language_server/providers/formatting.ex

ElixirLS hasn't added support for this new Elixir 1.13 feature yet so I've create a feature request for this: elixir-lsp/elixir-ls#660

[msaraiva]

@zachdaniel those are valid questions but I believe addressing them is probably out of our scope here. I mean, those concerns are also valid when running mix format, right? If so, there's not much we can do about it and they should be handled at the Elixir core level. So I believe if we manage to keep the same behavior of mix format, we'll be just fine.

[zachdaniel]

Yeah, my point only is that

It would be very slow because we'd have to wait for the BEAM to startup

May not be a concern because now that plugins are supported, we basically must wait for those modules to be compiled ?

[zachdaniel]

Otherwise we risk making unfixable (except manually) changes to codebases that use plugins.

[msaraiva]

@zachdaniel I didn't mean we should call mix format. That would certainly be too slow. What I meant is that there must be already a VM up and running for ElixirLS and since the plugin modules all belong to dependencies, they should've already been compiled. If so, we could load those modules then use Code.format_string, passing the same options that mix format would use. As far as I know that's all mix format does. Unless, of course, I'm missing something here :)

[zachdaniel]

Understood 👍🏻 There is warning output if a plugin is passed but isn't loaded IIRC, so maybe we can see in elixirls output if that is what happening.