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Fix exhaustivity warning #16168

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Merged
merged 1 commit into from
Nov 7, 2022
Merged

Fix exhaustivity warning #16168

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4 changes: 4 additions & 0 deletions compiler/src/dotty/tools/dotc/core/TypeOps.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -861,6 +861,10 @@ object TypeOps:
}

def instantiate(): Type = {
// if there's a change in variance in type parameters (between subtype tp1 and supertype tp2)
// then we don't want to maximise the type variables in the wrong direction.
// For instance 15967, A[-Z] and B[Y] extends A[Y], we don't want to maximise Y to Any
maximizeType(protoTp1.baseType(tp2.classSymbol), NoSpan)
maximizeType(protoTp1, NoSpan)
wildApprox(protoTp1)
}
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10 changes: 10 additions & 0 deletions tests/pos/i15967.scala
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@@ -0,0 +1,10 @@
// scalac: -Werror
sealed trait A[-Z]
final case class B[Y]() extends A[Y]

class Test:
def t1[X](a: A[X]) = a match // was inexhaustive
case _: B[X] @unchecked =>

//def t2[X](a: A[X]) = a match // was inexhaustive
// case _: B[X] => // expected unchecked warning