LSP: Signature Help

[iluuu1994]

I've been investigating on how to implement the SignatureHelp API. Can you give me a few pointers? It's pretty similar to Hover. The main challenge is that Codebase::getReferenceAtPosition can't be used because it only records the position of the identifier (excluding the parentheses). Furthermore we need to not only know which method is being called but also at what parameter the cursor is at.

[muglug]

What do you want exactly? Something like Codebase::getFunctionArgumentAtPosition that returns the method id and arg offset? Or do you also need the arg name?

[iluuu1994]

Yeah something like that. So I should probably extend Analyzer to store the parameters in a $parameter_map, right?

Or do you also need the arg name?

Just the arg index is fine.

[muglug]

Yeah, the general idea being that all these maps are cached, and only updated/invalidated when individual methods are changed. Which is to say I think this would only work for methods, not functions (at the moment at least)

[iluuu1994]

Cool, I'll give that a shot.

[iluuu1994]

This is not quite as easy to implement as I thought. The main issue is that the whitespace and , argument separator tokens are just thrown away by the parser. Currently I'm looking for the next , after the arguments getEndFilePos. This can be quite easily fooled with a comment:

We could use token_get_all here but I wanted to avoid tokenizing again.

There are other issues too. The parser is not as fault tolerant as I'd like. For example, more than one trailing comma results in the entire method call missing from the AST:

$this->foo($foo,,); // Poof!

Thus the argument positions won't be recorded and you'll get no signature help.

Kind of a bummer, those are likely not easily fixable.

[muglug]

This can be quite easily fooled with a comment

Yeah, it's not the best, but it wouldn't be too hard to add some functionality that detects comments - I have this code block that could probably be extracted and reused.

For example, more than one trailing comma results in the entire method call missing from the AST

I've ticketed that here: nikic/PHP-Parser#616, but I'm not sure it's a blocker - I think the usability benefit of this massively outweighs the edge-case annoyance.

[iluuu1994]

In that case I think I'll just use token_get_all after all. The only thing that needs to be tokenized is the source code from the getEndFilePos of the previous argument to the getStartFilePos of the next argument.

I've ticketed that here

Thanks!