Regression in 2.12.9 with large string interpolation

[anilkumarmyla]

Small reproducible sample which compiles fine but fails during runtime. This runs fine with 2.12.8 upto a reasonable limit but fails right at size=33 with 2.12.9

scala> val a: Int = 1
a: Int = 1

scala> val b: String = s"$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a" // 32 times
b: String = 11111111111111111111111111111111

scala> val b: String = s"$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a" // 33 times
java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.String (java.lang.Integer and java.lang.String are in module java.base of loader 'bootstrap')
  ... 36 elided

Also happens with any Long/Float/Double values

val a: Int = 1
val a: Long = 1L
val a: Float = 1.1f
val a: Double = 1.1d

Note that when val a: String = "y" 2.12.8 fails with StackOverFlow error for large interpolation (128 times), 2.12.9 works fine

[SethTisue]

@retronym problem with scala/scala#7996 ?

[retronym]

Darn. I've submitted a PR to fix.

[som-snytt]

The workaround is to slap .toString at multiples of 32.

test(33, s"${a.toString}$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a${a.toString}")
test(34, s"${a.toString}$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a$a${a.toString}$a")

Oh, someone should write a Scalafix!

We need Scalatempfix, the migration tool which rewrites your code for one release only, then rewrites it back again.

[ShaneDelmore]

Point release scalafixes aren't a terrible idea. 2.12.8->2.12.9 would add them, 2.12.9->2.12.10 would remove them.