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Use precise type for x in case x @ (_: A, _: B) #25734

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5aff77f
wrong
SolalPirelli Apr 8, 2026
6adfd28
dubious but works
SolalPirelli Apr 8, 2026
d812ec3
minimize diff
SolalPirelli Apr 8, 2026
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14 changes: 13 additions & 1 deletion compiler/src/dotty/tools/dotc/typer/Applications.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1717,7 +1717,19 @@ trait Applications extends Compatibility {
def typedUnApply(tree: untpd.Apply, selType0: Type)(using Context): Tree = {
record("typedUnApply")
val Apply(qual, unadaptedArgs) = tree
val selType = selType0.stripNamedTuple
// Use the types of the args if available, which can be more precise than the selector type,
// which is important if using `@unchecked`
val selType1 = selType0 match
case AppliedType(selCon, selArgs) if selArgs.size == unadaptedArgs.size =>
val newSelTypes = selArgs.zip(unadaptedArgs).map((sa, ua) => ua match
case Typed(_, tpt: AppliedTypeTree) =>
typed(tpt)
if tpt.hasType then tpt.tpe else sa
case _ => sa
)
AppliedType(selCon, newSelTypes)
case _ => selType0
val selType = selType1.stripNamedTuple

def notAnExtractor(tree: Tree): Tree =
// prefer inner errors
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11 changes: 11 additions & 0 deletions tests/pos/match-precise-type-unchecked.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
import scala.collection.*
import scala.util.*

val (ss: Seq[Success[Int] @unchecked], fs: Seq[Failure[Int] @unchecked]) =
Seq.empty[Try[Int]].partition(_.isSuccess)

val (ss2: Seq[Success[Int]], fs2: Seq[Failure[Int]]) = Seq.empty[Try[Int]].partition(_.isSuccess) match
case (s: Seq[Success[Int] @unchecked], f: Seq[Failure[Int] @unchecked]) => (s, f)

val (ss3: Seq[Success[Int]], fs3: Seq[Failure[Int]]) = Seq.empty[Try[Int]].partition(_.isSuccess) match
case x @ (s: Seq[Success[Int] @unchecked], f: Seq[Failure[Int] @unchecked]) => x
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