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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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9 changes: 7 additions & 2 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 @@ -805,9 +805,13 @@ object TypeOps:
prefixTVar.uncheckedNN
case ThisType(tref) if !tref.symbol.isStaticOwner =>
val symbol = tref.symbol
val compatibleSingleton = singletons.valuesIterator.find(_.underlying.derivesFrom(symbol))
if singletons.contains(symbol) then
prefixTVar = singletons(symbol) // e.g. tests/pos/i16785.scala, keep Outer.this
prefixTVar.uncheckedNN
else if compatibleSingleton.isDefined then
prefixTVar = compatibleSingleton.get
prefixTVar.uncheckedNN
else if symbol.is(Module) then
TermRef(this(tref.prefix), symbol.sourceModule)
else if (prefixTVar != null)
Expand Down Expand Up @@ -905,10 +909,11 @@ object TypeOps:
}

val inferThisMap = new InferPrefixMap
val tvars = tp1.etaExpand match
val prefixInferredTp = inferThisMap(tp1)
val tvars = prefixInferredTp.etaExpand match
case eta: TypeLambda => constrained(eta)
case _ => Nil
val protoTp1 = inferThisMap.apply(tp1).appliedTo(tvars)
val protoTp1 = prefixInferredTp.appliedTo(tvars)

if gadtSyms.nonEmpty then
ctx.gadtState.addToConstraint(gadtSyms)
Expand Down
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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