From aa14d560bffb9796d4520ca19678c60e027f07fa Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Mon, 24 Nov 2025 18:49:32 +0000
Subject: [PATCH] Dealias type of type constructor in `typedAppliedTypeTree`

---
 compiler/src/dotty/tools/dotc/typer/Typer.scala |  2 +-
 tests/pos/i23752.scala                          | 14 ++++++++++++++
 tests/pos/i23752min.scala                       |  7 +++++++
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i23752.scala
 create mode 100644 tests/pos/i23752min.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index f2e7e4a2c07c..4b54419bd7a2 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -2680,7 +2680,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     val tpt1 = withoutMode(Mode.Pattern):
       typed(tree.tpt, AnyTypeConstructorProto)
 
-    val tparams = tpt1.tpe.typeParams
+    val tparams = tpt1.tpe.dealiasKeepAnnotsAndOpaques.typeParams
      if tpt1.tpe.isError then
        val args1 = tree.args.mapconserve(typedType(_))
        assignType(cpy.AppliedTypeTree(tree)(tpt1, args1), tpt1, args1)
diff --git a/tests/pos/i23752.scala b/tests/pos/i23752.scala
new file mode 100644
index 000000000000..6e44f54c86f8
--- /dev/null
+++ b/tests/pos/i23752.scala
@@ -0,0 +1,14 @@
+trait MyOutput[T]
+final type MyOutputAlias1[T] = MyOutput[T]
+final type MyOutputAlias2 = MyOutput
+
+trait MyType
+object MyType {
+  val value1: MyOutput[MyType] = ???
+  val value2: MyOutputAlias1[MyType] = ???
+  val value3: MyOutputAlias2[MyType] = ??? // was COMPILATION ERROR
+}
+
+val value1: MyOutput[MyType] = ???
+val value2: MyOutputAlias1[MyType] = ???
+val value3: MyOutputAlias2[MyType] = ???
diff --git a/tests/pos/i23752min.scala b/tests/pos/i23752min.scala
new file mode 100644
index 000000000000..62cc74a95c99
--- /dev/null
+++ b/tests/pos/i23752min.scala
@@ -0,0 +1,7 @@
+trait MyOutput[T]
+type MyOutputAlias2 = MyOutput
+
+object MyType:
+  val v: MyOutputAlias2[String] = ??? // was COMPILATION ERROR
+
+@main def Test = ()