Auto complete (missing) extension methods

[tanishiking]

Is your feature request related to a problem? Please describe.

Somehow related to #141

In the code example below, Metals doesn't complete incr, and only if we import a.IntEnrichment.incr in B.scala Metals can complete incr there.

// A.scala
package a
object IntEnrichment:
  extension (num: Int)
    def incr: Int = num + 1

// B.scala
package b

def main =
  1.in@@

As a result of the lack of code completion for the missing extension method, developers have to seek the extension method and import it manually. It is quite time-consuming and sometimes leads developers to write the duplicated method because they couldn't find the one.

Describe the solution you'd like

// A.scala
package a
object IntEnrichment:
  extension (num: Int)
    def incr: Int = num + 1

// B.scala
package b

def main =
  1.in@@

complete for incr and auto-import a.IntEnrichment.incr.

// B.scala
package b

import a.IntEnrichment.incr

def main =
  1.incr

Describe alternatives you've considered

auto-importing missing extension method may help scalameta/metals#4141 but it doesn't make us easier to find an extension method we want without knowing.

Additional contex

No response

Search terms

extension method / auto-completion

[tanishiking]

I think this will be possible as we index the extension method in scalameta/metals#4141

[tanishiking]

closing for scalameta/metals#4183