typespecs do not work for implemented behaviour functions

[pauldemarco]

Environment

• Elixir & Erlang versions (elixir --version): 1.17.0 0.27
• Elixir Language Server version: v0.22.0
• Operating system: Ubuntu
• Editor or IDE name (e.g. Emacs/VSCode): VSCode
• Editor Plugin/LSP Client name and version:

Current behavior

There is no autocomplete for function arguments that are keywords. This applies to Modules that implement a behaviour function and have their own typespec.

Reproduction steps:

This is our goal -- notice how autocomplete works with GenServer's start_link options:

Let's try to recreate this awesomeness with our own Module:

1. Now, define a behaviour that has a @callback method with an options (keyword) argument.
2. Use the behaviour in a Module with @behaviour MyBehaviour.
3. Implement the function and add the typespec for the options.
4. Now in a calling function, try to use the method, and notice there is no autocomplete as it bypasses the Module's typespec and gives you the Behaviours definition.

[lukaszsamson]

The reason for what you observe is there are 2 separate mechanisms generating completions. One is used for remote functions and the other for local buffer completions. The remote one relies on compiled beams - it extracts info from EEP48 doc chunks and typespec chunks. The local one relies on AST analysis. Keyword argument completions are only implemented for remote typespec (as returned by Code.Typespec.fetch_specs internal elixir API). We would need something similar that extracts keyword lists from typespec AST in current buffer. Side note: typespecs are going to be deprecated in elixir and replaced with typesystem. There is a plan for typesystem to handle keyword lists but it most likely will not land soon

[pauldemarco]

Thanks for the clarification. Looking forward to the typesystem!

[lukaszsamson]

Keyword list completions from the current buffer are already tracked in https://github.com/elixir-lsp/elixir-ls/issues/1070