From fb8389390a7db2f06f41fe2f3d7a9c2fcdec6bdd Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Tue, 12 Nov 2024 11:24:29 +0000
Subject: [PATCH 1/3] Fix Any#className decorator on null

---
 compiler/src/dotty/tools/dotc/core/Decorators.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/Decorators.scala b/compiler/src/dotty/tools/dotc/core/Decorators.scala
index 29d4b3fa4052..96a2d45db80d 100644
--- a/compiler/src/dotty/tools/dotc/core/Decorators.scala
+++ b/compiler/src/dotty/tools/dotc/core/Decorators.scala
@@ -292,7 +292,7 @@ object Decorators {
       case _ => String.valueOf(x).nn
 
     /** Returns the simple class name of `x`. */
-    def className: String = x.getClass.getSimpleName.nn
+    def className: String = if x == null then "<null>" else x.getClass.getSimpleName.nn
 
   extension [T](x: T)
     def assertingErrorsReported(using Context): T = {

From 3d79d407aff7cbcf70d8736459c231e9b73d55dd Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Tue, 12 Nov 2024 11:58:38 +0000
Subject: [PATCH 2/3] (Re-)Drop inaccessible subclasses from refineUsingParent

This reverts commit cecd05356beecd232053d4c593af54bcc12cad0e.
---
 compiler/src/dotty/tools/dotc/core/TypeOps.scala |  6 +++++-
 tests/pos/i21790.scala                           | 14 ++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i21790.scala

diff --git a/compiler/src/dotty/tools/dotc/core/TypeOps.scala b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
index 2403a6e22bc6..79eac7bde38d 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
@@ -930,7 +930,11 @@ object TypeOps:
       for tp <- mixins.reverseIterator do
         protoTp1 <:< tp
       maximizeType(protoTp1, NoSpan)
-      wildApprox(protoTp1)
+      val inst = wildApprox(protoTp1)
+      if !inst.classSymbol.exists then
+        // E.g. i21790, can't instantiate S#CA as a subtype of O.A, because O.CA isn't accessible
+        NoType
+      else inst
     }
 
     if (protoTp1 <:< tp2) instantiate()
diff --git a/tests/pos/i21790.scala b/tests/pos/i21790.scala
new file mode 100644
index 000000000000..0cc7db935ac7
--- /dev/null
+++ b/tests/pos/i21790.scala
@@ -0,0 +1,14 @@
+package p
+
+trait S:
+  sealed trait A
+  private class CA() extends A
+
+object O extends S
+
+trait T
+
+class Test:
+  def f(e: T) = e match
+    case _: O.A =>
+    case _      =>

From 21e5f3c40a156043622f2d400e2cb51cc138bab9 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Tue, 12 Nov 2024 12:01:35 +0000
Subject: [PATCH 3/3] Tweak refineUsingParent drop conditions

In tests/pos/i21790.scala, O.A has no class symbol, because it's an
inaccessible private class of S.  But in tests/warn/i21860.scala,
Shape.Triangle doesn't have a "classSymbol" because it has multiple -
Shape and Corners.  So use .classSymbols.isEmpty instead of
!.classSymbol.exists
---
 compiler/src/dotty/tools/dotc/core/TypeOps.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeOps.scala b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
index 79eac7bde38d..697e50c6a2a8 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
@@ -931,7 +931,7 @@ object TypeOps:
         protoTp1 <:< tp
       maximizeType(protoTp1, NoSpan)
       val inst = wildApprox(protoTp1)
-      if !inst.classSymbol.exists then
+      if inst.classSymbols.isEmpty then
         // E.g. i21790, can't instantiate S#CA as a subtype of O.A, because O.CA isn't accessible
         NoType
       else inst