frontend/lsp: Signature of Nodes

[flofriday]

When hovering over a definition or the usage of a definition it might be handy do show a signature like other languages.

IntelliJ Example

While the LSP could attempt to recreate that on it's own, I think it makes much more sense if that information comes straight from the AST.

@jaraonthe-dot-net what would you need in the LSP to implement such hover contents?
I don't think with the current structure and reasonable effort we can get comments or docstrings etc but besides that.

Suggestion:

@Nullable
public String signature()

For definitions that would always return something but most expressions won't like I cannot make out what a binary expression should return here but a LetExpression could return the variables it defines. Or should we just limit it to definitions?

[jaraonthe-dot-net]

• I can display in the LSP hover whatever you want. The simplest case is if it is plaintext - markdown is also possible, but then we need to think about a) is it always markdown or should the content type be communicated somehow? and b) how to fall back if client doesn't support markdown.
• The hover is assigned to a specific range in the document that you're hovering over (which e.g. VSCode highlights). That information can be taken from the AST node's location. ✅
• Ideally, there is one singular way for the language server to retrieve the hover text from a node. E.g. all Nodes have the signature() method you proposed, and they either return the hover text or null if they don't have one. Alternatively, we could check for a HasSignature interface.
• Should a node's hover text be displayed whenever any part of it is hovered, or only e.g. its name or first line? E.g if you have hover text for an isa definition, then that would be displayed throughout what is possibly a rather large section.

[flofriday]

I can display in the LSP hover whatever you want. The simplest case is if it is plaintext - markdown is also possible, but then we need to think about a) is it always markdown or should the content type be communicated somehow? and b) how to fall back if client doesn't support markdown.

The signature itself would be code so if the client supports it I would wrap it in markdown in a codeblock and otherwise just send it as plain text.

If we ever have more information we would want to dispay then I would suggest moving to structured datatype instead of a simple string so that you can piece it together for the different formats.

[...] all Nodes have the signature() method you proposed

Great I'm fine with that.

Should a node's hover text be displayed whenever any part of it is hovered, or only e.g. its name or first line? E.g if you have hover text for an isa definition, then that would be displayed throughout what is possibly a rather large section.

I don't think this falls under the scope of this issue. But even if it were, I don't know that answer but I'm sure you can figure out how other Language Servers deal with that, having large definitions like ISA isn't really that different to large class definitions in other languages.