x/tools/gopls: add autocomplete for generic function type aliases

[nohns]

type Foo[T any] func() T

func Bar[T any](f Foo[T]) {}
// Or 
func FooBar[T any](val T, f Foo[T]) {}

func main() {
    // When writing out this function call, with all the needed type parameters already specified, 
    // gopls should suggest the "func(...) {}" autocomplete, so the function signature is automatically generated.
    Bar[int](/* "func(...) {}" autocomplete should be suggested here. Foo[int] signature would be generated */)

    // The same should happen if the required type parameters can be inferred from already given parameters e.g
    var input string
    FooBar(input, /* "func(...) {}" autocomplete should be suggested here. Foo[string] signature would be generated */)
}

If any help is needed with this proposal I will be happy to look into it.

[gopherbot]

Change https://go.dev/cl/400614 mentions this issue: lsp/completion: further improve generic func arg ranking

[muirdm]

The above cl helps with your first case. I don't think we can fix the second case without changes to go/types.