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Fix untupling of functions in for comprehensions #19620

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Merged
dwijnand merged 1 commit into from
Feb 23, 2024
Merged

Fix untupling of functions in for comprehensions #19620

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7 changes: 4 additions & 3 deletions compiler/src/dotty/tools/dotc/typer/Typer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1621,15 +1621,16 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
case untpd.Annotated(scrut1, _) => isParamRef(scrut1)
case untpd.Ident(id) => id == params.head.name
fnBody match
case untpd.Match(scrut, untpd.CaseDef(untpd.Tuple(elems), untpd.EmptyTree, rhs) :: Nil)
case untpd.Match(scrut, cases @ untpd.CaseDef(untpd.Tuple(elems), untpd.EmptyTree, rhs) :: Nil)
if scrut.span.isSynthetic && isParamRef(scrut) && elems.hasSameLengthAs(protoFormals) =>
// If `pt` is N-ary function type, convert synthetic lambda
// x$1 => x$1 match case (a1, ..., aN) => e
// to
// (a1, ..., aN) => e
val params1 = desugar.patternsToParams(elems)
if params1.hasSameLengthAs(elems) then
desugared = cpy.Function(tree)(params1, rhs)
desugared = if params1.hasSameLengthAs(elems)
then cpy.Function(tree)(params1, rhs)
else desugar.makeCaseLambda(cases, desugar.MatchCheck.IrrefutablePatDef, protoFormals.length)
case _ =>

if desugared.isEmpty then
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6 changes: 6 additions & 0 deletions tests/pos/i19576.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@

object Test:
val z = Seq(0 -> 1, 2 -> 3).lazyZip(Seq("A", "B"))
for case ((beg, end), c) <- z yield c // Ok: a withFilter is inserted before map
for (range, c) <- z yield c // Ok: exact shape
for ((beg, end), c) <- z yield c // Error before changes: Wrong number of parameters, expected 2