From e4cb7b8a75a78b13347cee226f747a13f9fcfcc9 Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Mon, 3 Oct 2022 14:58:22 +0200
Subject: [PATCH] Type match with a match type when a match type is expected

---
 .../src/dotty/tools/dotc/typer/Typer.scala    |  2 ++
 tests/pos/match-type-inference.scala          | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 tests/pos/match-type-inference.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 6a1e6e0b671f..580c9f71ad29 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1609,6 +1609,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             }
 
         val result = pt match {
+          case mt: MatchType if isMatchTypeShaped(mt) =>
+            typedDependentMatchFinish(tree, sel1, selType, tree.cases, mt)
           case MatchType.InDisguise(mt) if isMatchTypeShaped(mt) =>
             typedDependentMatchFinish(tree, sel1, selType, tree.cases, mt)
           case _ =>
diff --git a/tests/pos/match-type-inference.scala b/tests/pos/match-type-inference.scala
new file mode 100644
index 000000000000..4105e788c207
--- /dev/null
+++ b/tests/pos/match-type-inference.scala
@@ -0,0 +1,22 @@
+type IsString[T <: Any] = T match {
+  case String => true
+  case _ => false
+}
+
+def isString(x: Any): IsString[x.type] = x match
+  case _: String => true
+  case _ => false
+
+def isString2(x: Any): x.type match {
+  case String => true
+  case _ => false
+} = x match
+  case _: String => true
+  case _ => false
+
+def isString3[T](x: T): T match {
+  case String => true
+  case _ => false
+} = x match
+  case _: String => true
+  case _ => false