LSP signature helper should not appear when inside a lambda

[dead10ck]

The new LSP signature helper pops up when you're inside the body of a lambda that's being passed to a function, which is a little annoying.

We could probably fix it by only making the pop-up visible when the node under the cursor is a direct descendent of the function arguments.

[the-mikedavis]

I was thinking the same about it being noisy when writing funs in Erlang erlang-ls/erlang_ls#1344. It might be good to propose this upstream in rust-analyzer as well.

The direct descendant idea I think is interesting though. I would definitely be interested in trying that out if it existed. I suspect it may have some bugs though:

• it could be too selective
  • for example, typing tuples of variables in a function call in rust I would like to continue seeing the signature help
  • in these cases it might be better to have a manual keybind to summon signature-help like auto-complete's C-x
• I'm not sure how well it would work for temporarily errored syntax trees
  • if you're typing a comma to separate params and the grammar is very unforgiving, would it complicate the direct descendant check?

[dead10ck]

Hmm, yeah, you're right. It seems like where it is desirable and where it is not is very language specific, so a solution might not be simple. A manual trigger would be helpful, because right now it's either all or nothing.