Inlined nowarn warns

[som-snytt]

Compiler version

3.7.4

Minimized code

//> using scala 3.7.4
//> using options -Wunused:all -Wnonunit-statement -Vprint:ty,inlining,ref -deprecation

import annotation.*

object X:
  @deprecated("use f instead for noise suppression")
  def b(s: String): Boolean = s.length > 3

  inline transparent def f(inline cond: Boolean = false) =
    inline if cond then b("hello"): @nowarn else b("goodbye"): Unit @nowarn
    //inline if cond then b("hello") else b("goodbye"): Unit

@main def test = println:
  //b("hello")
  X.f()
  X.f(cond = true)
  //"hello, world"

Output

-- Warning: /home/amarki/snips/union-usage.scala:11:24 -------------------------
11 |    inline if cond then b("hello"): @nowarn else b("goodbye"): Unit @nowarn
   |                        ^^^^^^^^^^^^^^^^^^^
   |@nowarn annotation does not suppress any warnings but matches a diagnostic
-- Warning: /home/amarki/snips/union-usage.scala:11:68 -------------------------
11 |    inline if cond then b("hello"): @nowarn else b("goodbye"): Unit @nowarn
   |                                                                    ^^^^^^^
   |                       @nowarn annotation does not suppress any warnings

without nowarn

-- [E176] Potential Issue Warning: /home/amarki/snips/union-usage.scala:16:5 ---
16 |  X.f()
   |  ^^^^^
   |  unused value of type Boolean
   |----------------------------------------------------------------------------
   |Inline stack trace
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   |This location contains code that was inlined from union-usage.scala:12
12 |    inline if cond then b("hello") else b("goodbye"): Unit
   |                                        ^^^^^^^^^^^^
    ----------------------------------------------------------------------------
-- Deprecation Warning: /home/amarki/snips/union-usage.scala:12:24 -------------
12 |    inline if cond then b("hello") else b("goodbye"): Unit
   |                        ^
   | method b in object X is deprecated: use f instead for noise suppression

This might be more intended:

11 |    inline if cond then (b("hello"): @nowarn) else ((b("goodbye"): @nowarn): Unit)
   |                                                     ^^^^^^^^^^^^^^^^^^^^^
   |@nowarn annotation does not suppress any warnings but matches a diagnostic

Expectation

The intention is to "suppress" -Wnonunit-statement by conditionally inlining : Unit. That doesn't work with the current lint at typer.

Additionally, deprecate the method that is delegated to; it's not desirable to hide it by inlining that body.

That deprecation is suppressed by annotating with nowarn; but the mechanism incurs further warnings.