WarnUnsued false positive when using aliased imports from local value

[WojciechMazur]

Compiler version

3.3.0-RC4

Minimized code

//> using scala "3.3.0-RC4"
//> using option "-Wunused:all"

import java.io.DataOutputStream

val buffer: DataOutputStream = ???

import buffer.{write => put}

def usage() = {
  put(0: Byte)
}

Output

Compiling project (Scala 3.3.0-RC4, JVM)
[warn] ./test.scala:8:16
[warn] unused import
[warn] import buffer.{write => put, writeInt}
[warn]                

Expectation

Should not give warning

[KacperFKorban]

I think that this is a very similar issue to transparent inline def. That is, in typer rename imports from vals are expanded to their fully qualified paths. e.g.

//> using scala "3.3.0-RC4"
//> using option "-Wunused:all"
//> using options "-Xprint:typer", "-Yplain-printer"

class baz {
  def write(x: Int) = ???
}

object foo extends baz

val bar: baz = ???

import bar.{write => put1}
import foo.{write => put2}

def usage() = {
  put1(0)
  put2(0)
}

The body of usage is (after typer):

Block(
  List(
    Apply(Select(Ident(bar), write), List(Literal(0)))
  ),
  Apply(Ident(put2), List(Literal(0)))
)

So this is again a choice between a possible false positive and a possible false negative. (Unless we think that adding attachments to trees just for unused is worth it)

[som-snytt]

Duplicated by #18366