From 11cc9c18162e952195235e8a29cc0232460989d7 Mon Sep 17 00:00:00 2001
From: Martijn Hoekstra <martijnhoekstra@gmail.com>
Date: Tue, 1 Dec 2020 11:13:53 +0100
Subject: [PATCH] make literal true extractors irrefutable

---
 .../tools/nsc/transform/patmat/MatchAnalysis.scala     | 10 +++++-----
 test/files/pos/{t12232_.scala => t12254.scala}         |  3 +++
 2 files changed, 8 insertions(+), 5 deletions(-)
 rename test/files/pos/{t12232_.scala => t12254.scala} (75%)

diff --git a/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala b/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
index 7da5e5e82bd8..89d12b2ec6cb 100644
--- a/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
+++ b/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
@@ -390,13 +390,13 @@ trait MatchApproximation extends TreeAndTypeAnalysis with ScalaLogic with MatchT
         // note: this assumes the other side-conditions implied by the extractor are met
         // (argument of the right type, length check succeeds for unapplySeq,...)
       private def irrefutableExtractorType(tp: Type): Boolean = tp.resultType.dealias match {
-        //Some(x) is always irrefutable
+        //Some(x) is irrefutable
         case TypeRef(_, SomeClass, _) => true
         //name based pattern matching checks for constant false `isEmpty`.
-        case TypeRef(_, res, _) => res.tpe.members.exists(isIrrefutabilityProof)
-        // probably not useful since this type won't be inferred nor can it be written down (yet)
-        case ConstantTrue => true
-        case _            => false
+        case TypeRef(_, res, _)       => res.tpe.members.exists(isIrrefutabilityProof)
+        //`true.type` is irrefutable for boolean extractors
+        case c: ConstantType          => c.value == Constant(true)
+        case _                        => false
       }
 
       private val irrefutableExtractor: PartialFunction[TreeMaker, Prop] = {
diff --git a/test/files/pos/t12232_.scala b/test/files/pos/t12254.scala
similarity index 75%
rename from test/files/pos/t12232_.scala
rename to test/files/pos/t12254.scala
index 098b62b565f3..a44393063d60 100644
--- a/test/files/pos/t12232_.scala
+++ b/test/files/pos/t12254.scala
@@ -1,3 +1,6 @@
+// scalac: -Xfatal-warnings -Xlint:strict-unsealed-patmat
+//
+
 object Test {
   sealed trait Foo
   final class Bar extends Foo