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Fix irrefutability checking in for with untupling #23273

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Merged
merged 1 commit into from
Jun 29, 2025
Merged

Fix irrefutability checking in for with untupling #23273

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4 changes: 3 additions & 1 deletion compiler/src/dotty/tools/dotc/typer/Typer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1938,9 +1938,11 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
// to
// (a1, ..., aN) => e
val params1 = desugar.patternsToParams(elems)
val matchCheck = scrut.getAttachment(desugar.CheckIrrefutable)
.getOrElse(desugar.MatchCheck.IrrefutablePatDef)
desugared = if params1.hasSameLengthAs(elems)
then cpy.Function(tree)(params1, rhs)
else desugar.makeCaseLambda(cases, desugar.MatchCheck.IrrefutablePatDef, protoFormals.length)
else desugar.makeCaseLambda(cases, matchCheck, protoFormals.length)
case _ =>

if desugared.isEmpty then
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12 changes: 12 additions & 0 deletions tests/neg/irrefutable-genfrom.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
object Test:
def one: Unit =
for
// Was already an error as expected
(i, Some(_)) <- List.empty[Int] zip List.empty[Option[String]] // error
do ()

def two: Unit =
for
// Used to be a warning
(i, Some(_)) <- List.empty[Int] lazyZip List.empty[Option[String]] // error
do ()
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