Improve active parameter highlighting

[afonsocarlos]

This is a kickoff to implement the feature requested on #30.

Note: although this PR already delivers the intended feature, it would be very nice to make this plugin override vim.lsp.buf.signature_help() with a formatted signature help and proper parameter highlighting. Unfortunately though, that's beyond my knowledge.

[pwang2]

@hrsh7th , can you help take a look at this. This is how it looks now.

After updating according to PR.

still look funky with function overload and typescript madness.

[ColinKennedy]

For anyone looking at this PR or the other issue - this still didn't work for me with Python. I think the reason is because the --- from if signature.documentation and parameter.documentation.

Before

Python:

Lua:

After

Python:

Lua:

Looking at the markdown with :InspectTree is useful here.

(`a: LiteralString`, /, *paths: LiteralString) -> LiteralString
---
```markdown
thing
```

(document ; [0, 0] - [5, 0] markdown
  (section ; [0, 0] - [5, 0] markdown
    (setext_heading ; [0, 0] - [2, 0] markdown
      heading_content: (paragraph ; [0, 0] - [1, 0] markdown
        (inline ; [0, 0] - [0, 63] markdown
          (inline ; [0, 0] - [0, 63] markdown_inline
            (code_span ; [0, 1] - [0, 19] markdown_inline
              (code_span_delimiter) ; [0, 1] - [0, 2] markdown_inline
              (code_span_delimiter))))) ; [0, 18] - [0, 19] markdown_inline
      (setext_h2_underline)) ; [1, 0] - [1, 3] markdown
    (fenced_code_block ; [2, 0] - [5, 0] markdown
      (fenced_code_block_delimiter) ; [2, 0] - [2, 3] markdown
      (info_string ; [2, 3] - [2, 11] markdown
        (language)) ; [2, 3] - [2, 11] markdown
      (block_continuation) ; [3, 0] - [3, 0] markdown
      (code_fence_content ; [3, 0] - [4, 0] markdown
        (document ; [3, 0] - [4, 0] markdown
          (section ; [3, 0] - [4, 0] markdown
            (paragraph ; [3, 0] - [4, 0] markdown
              (inline ; [3, 0] - [3, 5] markdown
                (inline))))) ; [3, 0] - [3, 5] markdown_inline
        (block_continuation)) ; [4, 0] - [4, 0] markdown
      (fenced_code_block_delimiter)))) ; [4, 0] - [4, 3] markdown

vs

(`a: LiteralString`, /, *paths: LiteralString) -> LiteralString

```markdown
thing
```

(document ; [0, 0] - [5, 0] markdown
  (section ; [0, 0] - [5, 0] markdown
    (paragraph ; [0, 0] - [1, 0] markdown
      (inline ; [0, 0] - [0, 63] markdown
        (inline ; [0, 0] - [0, 63] markdown_inline
          (code_span ; [0, 1] - [0, 19] markdown_inline
            (code_span_delimiter) ; [0, 1] - [0, 2] markdown_inline
            (code_span_delimiter))))) ; [0, 18] - [0, 19] markdown_inline
    (fenced_code_block ; [2, 0] - [5, 0] markdown
      (fenced_code_block_delimiter) ; [2, 0] - [2, 3] markdown
      (info_string ; [2, 3] - [2, 11] markdown
        (language)) ; [2, 3] - [2, 11] markdown
      (block_continuation) ; [3, 0] - [3, 0] markdown
      (code_fence_content ; [3, 0] - [4, 0] markdown
        (document ; [3, 0] - [4, 0] markdown
          (section ; [3, 0] - [4, 0] markdown
            (paragraph ; [3, 0] - [4, 0] markdown
              (inline ; [3, 0] - [3, 5] markdown
                (inline))))) ; [3, 0] - [3, 5] markdown_inline
        (block_continuation)) ; [4, 0] - [4, 0] markdown
      (fenced_code_block_delimiter)))) ; [4, 0] - [4, 3] markdown

Including the --- wraps the signature paragraph to setext_heading.

Anyway, the solution is to either fork this repo and remove the ---s from the code or to add a prefix before the signature.

https://github.com/hrsh7th/cmp-nvim-lsp-signature-help/compare/main...ColinKennedy:cmp-nvim-lsp-signature-help:main

e.g.

  if signature.label then
    table.insert(documentation, "Signature:")
    table.insert(documentation, "\n")
    table.insert(documentation, self:_signature_label(signature, parameter_index))
  end

Or removing this ---s. Not ideal but either way works.