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fix(patmat): Add subtype-based fallback in inferPrefixMap and recalculate constraints after application #23771

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fix(patmat): Add subtype-based fallback in inferPrefixMap and recalculate constraints after application #23771

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ea6bca1
fix(patmat): Use childPrefix to resolve path-dependent sealed children
nox213 Aug 17, 2025
8b711e8
add new line
nox213 Aug 20, 2025
192c959
second approach
nox213 Sep 2, 2025
f583b70
revert previous approach
nox213 Sep 2, 2025
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17 changes: 16 additions & 1 deletion compiler/src/dotty/tools/dotc/core/TypeOps.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -748,7 +748,22 @@ object TypeOps:
//
if (child.name == tpnme.LOCAL_CHILD) return child.typeRef

val childTp = if (child.isTerm) child.termRef else child.typeRef
val childTp = {
val parentSym = parent.typeSymbol
val parentPre = parent.normalizedPrefix
val defaultRef = if (child.isTerm) child.termRef else child.typeRef

if (parentSym.isClass && parentPre.isInstanceOf[TermRef]) {
val newPrefix = childPrefix(parentPre, parentSym, child)
if (newPrefix.exists)
if (child.isTerm) TermRef(newPrefix, child.asTerm)
else TypeRef(newPrefix, child.asType)
else
defaultRef
}
else
defaultRef
}

inContext(ctx.fresh.setExploreTyperState().setFreshGADTBounds.addMode(Mode.GadtConstraintInference)) {
instantiateToSubType(childTp, parent, mixins).dealias
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16 changes: 16 additions & 0 deletions tests/warn/i23369.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
class Module {
type BarTy
sealed trait Adt[A]
case class Foo() extends Adt[String]
case class Bar[A <: BarTy](x: BarTy) extends Adt[A]
}

object Basic extends Module {
type BarTy = String
}

def test(a: Basic.Adt[String]) = {
a match { // warn: match may not be exhaustive
case Basic.Foo() =>
}
}
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