String iterpolation warnings should have a error id

[eejbyfeldt]

Compiler version

3.7.2

Minimized example

object test {
  val _ = s"${Some(1)}"
}

Output Error/Warning message

Using the flag -Wtostring-interpolated

-- Warning: to_string.scala:2:18 -------------------------
2 |  val _ = s"${Some(1)}"
  |              ^^^^^^^
  |              interpolation uses toString
1 warning found

Why this Error/Warning was not helpful

The message does not contain a error id like most other warnings.

Suggested improvement

It could be made more useful by containing a error id.

[som-snytt]

I think that is because the DX for adding an ErrorID is so poor.

f uses the new warning, or rather misuses it:

scala-cli repl --server=false -S 3.7.2 -Wall
Welcome to Scala 3.7.2 (23.0.2, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> case class K(i: Int)
// defined case class K

scala> val k = K(42)
val k: K = K(42)

scala> s"hi $k"
1 warning found
-- Warning: --------------------------------------------------------------------
1 |s"hi $k"
  |      ^
  |      interpolation uses toString
val res0: String = hi K(42)

scala> f"hi $k"
1 warning found
-- [E209] Interpolation Warning: -----------------------------------------------
1 |f"hi $k"
  |      ^
  |      interpolation uses toString
val res1: String = "hi "

[som-snytt]

I made it a bug for a) the bug in f and b) probably (?) it was intended to also use E209 for s or raw.

Edit: the bug is when format is inferred:

scala> f"hi $k%s"
1 warning found
-- [E209] Interpolation Warning: -----------------------------------------------
1 |f"hi $k%s"
  |        ^
  |        interpolation uses toString
val res4: String = hi K(42)