Runtime semantics difference under better-fors #25077
Description
Compiler version
3.8
Workaround: Run with -source:3.7
Minimized code
def f(x: Int): (Int, Int) = (1, 0)
val result: Iterable[(Int, Int)] =
for
(k, v) <- Map(1 -> 1, 2 -> 1, 3 -> 1)
x = k + v
(a, b) = f(x)
yield (a, b)
@main def Test() =
assert(result.size == 3, "Expected 3 elements, got ${result.size}")Output
> scala-cli run -S 3.7 bug.scala
Compiling project (Scala 3.7.4, JVM (21))
Compiled project (Scala 3.7.4, JVM (21))
> scala-cli run -S 3.nightly bug.scala
Compiling project (Scala 3.8.3-RC1-bin-20260123-506b8a0-NIGHTLY, JVM (21))
Compiled project (Scala 3.8.3-RC1-bin-20260123-506b8a0-NIGHTLY, JVM (21))
Exception in thread "main" java.lang.AssertionError: assertion failed: Expected 3 elements, got 1
at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:10)
at bug$package$.Test(bug.scala:11)
at Test.main(bug.scala:10)Expectation
Should produce the same results as version without better-fors (using Scala 3.7, or 3.8 with -source:3.7)