wish: add key to kill-ring-save the inferred type

[nahuel]

Many times I want to type an inferred type, it will be nice to have a shorcut to copy the type below the cursor. Typescript example:

type SomeType = 'q' | 'w'
const b = () => 'q' as SomeType

function a(arg /* here I want to type " : " and then paste "SomeType" */ ) {
  const x = b() 
     // ^ Cursor here
}

Here cursor is over x, so the inferred type is shown in the minibuffer as const x: SomeType. Now it will be nice to press a (new) shorcut that copies the x type name to the clipboard, so then you can move the cursor after arg, type : and then C-Y to paste SomeType, to declare the type of arg as the same of x.

[yyoncho]

so the inferred type is shown in the minibuffer as const x: SomeType

The issue is that this information is not structured and might not be the type itself. I think that the only reliable server-side method for that matter is documentSymbols call(corresponds to imenu). We could use it to copy the name of the wrapping function, copy the name of the wrapping class, etc.

[nahuel]

Can the mechanism behind lsp-rust-analyzer-inlay-hints-mode be reused for getting the expression type in a way generic for all LSP backends? (note, I didn't read the LSP spec)

[nahuel]

Note, I filled a similar wish for vscode: microsoft/vscode#98267

[yyoncho]

Can the mechanism behind lsp-rust-analyzer-inlay-hints-mode be reused for getting the expression type in a way generic for all LSP backends?

This is RA specific. We could provide a mechanism to copy the inlay-hint on the line, this will be easy, but it will work only for rust analyzer.

[nahuel]

Another option maybe is to parse what the minibuffer shows, at least for const / let declarations, and extract the type from here. FYI just found a proposal from the Rust people to add inlay hints to the LSP spec: microsoft/language-server-protocol#956 . But maybe the LSP spec needs a more general "get the type at position" functionality than that?

[yyoncho]

But maybe the LSP spec needs a more general "get the type at position" functionality than that?

Yep, in order to work consistently.

Another option maybe is to parse what the minibuffer shows, at least for const / let declarations,

I tend to avoid such ad-hoc solutions because they cause trouble. After all, lsp protocol is to avoid client side parsing.

[nahuel]

ok, I understand. Note, others are finding this same LSP limitation and for a more general usage, as getting the type of a selected expression instead of only of the symbol at cursor:
rust-lang/rust-analyzer#389
https://github.com/digital-asset/ghcide/issues/70

[yyoncho]

yep, unfortunately, the spec is designed for point-and-click usage.

[yyoncho]

closing based on the previous comment. Once the spec adds support for it we can implement the client-side code.