Completion - Expression extraction

[MartTave]

For now, the completion system extract the current 'expression' by splitting the current line from last space to current cursor position, and then split on each '.' char to get each part of the current 'expression'
Example :

  let res = a.m2.m1.<cursor position>
  // This becomes -> "a.m2.m1." and then -> ["a", "m2", "m1"]

This is a temporary solution and it has many shortcomings. I think that we should be able to get the closest AST node directly, and then work from here to get to the same point. This would enable us to have a single parsing method, which is the right way to go

[tothambrus11]

I heard some language servers inserting a dummy token after the dot so that it makes up a valid parseable expression. You could look at other language servers to see how they tackle these issues. E.g. V-lang, Roc, Odin, Zig are fairly new languages, they should give some inspiration.

[tothambrus11]

Current limitation: doesn't work on things that are not variables, e.g. a temporary object construction: A()..

[tothambrus11]

Take a look at this paper, it might be helpful: Error-Tolerant Parsing and Compilation for Hylo
https://repository.tudelft.nl/file/File_c8b9533c-f030-4f38-95ff-8f53c5665fca?preview=1

A technique that I heard for solving this autocompletion problem is to insert some marker token, which allows parsing of the line as a valid expression AST, having a dummy node inside. Then you can look for the dummy node and see how to autocomplete from there.

Scala's MetaLS project can be a great example, they have a very nice community and documentation, and they seem to be very mindful about what they are doing, so it can be a good idea to investigate their approach: https://scalameta.org/metals/

[MartTave]

This has been fixed. The expression parsing now works by adding a dummy node (if needed), and then getting the closest expression to the cursor.
This means that it works now for temporary object construction like A().