From e8136b724e74c8c3661a92f2489b52a83b4aed22 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Tue, 22 Oct 2024 10:01:21 +0100
Subject: [PATCH] Avoid orphan param from default arg

---
 compiler/src/dotty/tools/dotc/typer/Namer.scala |  5 +++++
 tests/pos/i21558.orig.scala                     | 10 ++++++++++
 tests/pos/i21558.scala                          |  8 ++++++++
 3 files changed, 23 insertions(+)
 create mode 100644 tests/pos/i21558.orig.scala
 create mode 100644 tests/pos/i21558.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index 6167db62fbe0..b1b94288bcbf 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -2130,6 +2130,11 @@ class Namer { typer: Typer =>
       val pt = inherited.orElse(expectedDefaultArgType).orElse(fallbackProto).widenExpr
       val tp = typedAheadRhs(pt).tpe
       if (defaultTp eq pt) && (tp frozen_<:< defaultTp) then
+        // See i21558, the default argument new A(1.0) is of type A[?T]
+        // With an uninterpolated, invariant ?T type variable.
+        // So before we return the default getter parameter type (A[? <: Double])
+        // we want to force ?T to instantiate, so it's poly is removed from the constraint
+        isFullyDefined(tp, ForceDegree.all)
         // When possible, widen to the default getter parameter type to permit a
         // larger choice of overrides (see `default-getter.scala`).
         // For justification on the use of `@uncheckedVariance`, see
diff --git a/tests/pos/i21558.orig.scala b/tests/pos/i21558.orig.scala
new file mode 100644
index 000000000000..3a955920a1c7
--- /dev/null
+++ b/tests/pos/i21558.orig.scala
@@ -0,0 +1,10 @@
+class Base
+class A[T <: Float](val f: T) extends Base
+
+def test() = {
+  m1(new A(m2()));
+
+}
+
+def m1(x: Base) = {}
+def m2(p: A[? <: Float] = new A(1.0f)): Int = 1
diff --git a/tests/pos/i21558.scala b/tests/pos/i21558.scala
new file mode 100644
index 000000000000..80168992cea9
--- /dev/null
+++ b/tests/pos/i21558.scala
@@ -0,0 +1,8 @@
+class Base
+class A[T <: Double](val f: T) extends Base
+
+class Test:
+  def test() = m1(new A(m2()))
+
+  def m1(x: Base): Unit = {}
+  def m2(p: A[? <: Double] = new A(1.0)): Int = 2