fix: use alternative with stripped synthetic filename$package.

[kasiaMarek]

fixes: #6852

Root cause of the problem

A toplevel object that is a companion for a top-level type has a synthetic parent - filename$package. This is not reflected by Metals symbol indexer (ScalaMtags). It would be problematic, since the the type definition might be after the object definition

Example

For this code:

// demo.scala
object Foo
type Foo = String

Symbols in compiler and what is in semanticDB is

_empty_/demo$package.Foo#
_empty_/demo$package.Foo.

Where Metals symbol indexer produces:

_empty_/demo$package.Foo#
_empty_/Foo.

Solution

1. Add symbols with filename$package to alternatives in definition search
2. When searching for docstring fallback to docs from found definition symbol

[tgodzik]

Do we need to validate this? Could there be an option where we have both object with the $package prefix and without?

And if we really need to we should have something like:

case class Alternative(private val symbol: Symbol, validation: (loc: SymbolLocation) => Boolean = true) {
  def symbol(loc: SymbolLocation) = {
   if (validation(loc)) Some(symbol)
   else None
  }
}

this way we make sure that Validation is not ignored at any point

[kasiaMarek]

I think we can skip it... One would have to specifically create an object / package object called something$package (where I think that $ is generally reserved for the compiler) and still this is only a fallback...

[tgodzik]

Let's maybe skip it then.

[tgodzik]

Nice idea! LGTM aside from the small nitpick

[tgodzik]

This is not needed now I think