`Array.ofDim[Unit](0)` throws `IllegalArgumentException` on Scala.js

[armanbilge]

Compiler version

3.6.4-RC1-bin-20241216-7dc5008-NIGHTLY

Minimized code

//> using scala 3.6.4-RC1-bin-20241216-7dc5008-NIGHTLY
//> using platform js

@main def main = Array.ofDim[Unit](0)

Output

/tmp/main12667871020961532039.js:1141
      throw e;
      ^

java.lang.IllegalArgumentException
    at $TypeData.newArray (/tmp/main12667871020961532039.js:851:11)
    at $p_jl_reflect_Array$__rec$1__jl_Class__I__AI__O (/tmp/main12667871020961532039.js:1085:39)
    at $c_jl_reflect_Array$.newInstance__jl_Class__AI__O (/tmp/main12667871020961532039.js:1121:10)
    at $c_Lbug$package$.main__Ajl_Void (/tmp/main12667871020961532039.js:982:52)
    at $s_Lmain__main__AT__V (/tmp/main12667871020961532039.js:1135:24)
    at Object.<anonymous> (/tmp/main12667871020961532039.js:2184:1)
    at Object.<anonymous> (/tmp/main12667871020961532039.js:2185:4)
    at Module._compile (node:internal/modules/cjs/loader:1546:14)
    at Object..js (node:internal/modules/cjs/loader:1689:10)
    at Module.load (node:internal/modules/cjs/loader:1318:32) {
  jl_Throwable__f_s: null
}

Expectation

On the JVM it returns an array of scala.runtime.BoxedUnit.

Follow-up to scala-js/scala-js#5084.

[SethTisue]

“Doeraene reward check” when? https://en.wikipedia.org/wiki/Knuth_reward_check

[sjrd]

Thanks for the report.

It turns out it's also broken for new Array[Unit](0), and also Array.ofDim[Unit](0, 0).

In general this is because the ArrayConstructors phase uses classOf[Unit] as element type when calling newArray, but it's supposed to use classOf[BoxedUnit].

The JVM is not affected because it doesn't care about this first argument. The JVM backend rewrites calls to newArray in a way that doesn't use it.