From d45fbe898b249643563576ba8a436dd8ece29b98 Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Wed, 13 Oct 2021 12:07:59 -0700
Subject: [PATCH] Can mark var impl as override

---
 compiler/src/dotty/tools/dotc/typer/RefChecks.scala |  3 +--
 tests/pos/i13019.scala                              | 13 +++++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/i13019.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
index 615e2915f6f8..4c20f5821ca4 100644
--- a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -466,8 +466,7 @@ object RefChecks {
           overrideError("needs `override` modifier")
       else if (other.is(AbsOverride) && other.isIncompleteIn(clazz) && !member.is(AbsOverride))
         overrideError("needs `abstract override` modifiers")
-      else if (member.is(Override) && other.is(Accessor) &&
-        other.accessedFieldOrGetter.is(Mutable, butNot = Lazy))
+      else if member.is(Override) && other.is(Accessor, butNot = Deferred) && other.accessedFieldOrGetter.is(Mutable, butNot = Lazy) then
         overrideError("cannot override a mutable variable")
       else if (member.isAnyOverride &&
         !(member.owner.thisType.baseClasses exists (_ isSubClass other.owner)) &&
diff --git a/tests/pos/i13019.scala b/tests/pos/i13019.scala
new file mode 100644
index 000000000000..491b6df03d0b
--- /dev/null
+++ b/tests/pos/i13019.scala
@@ -0,0 +1,13 @@
+
+trait Ok1 { var i: Int }
+class Ok1C extends Ok1 { var i: Int = 1 }
+
+trait Ok2 {
+  def i: Int
+  def i_=(v: Int): Unit
+}
+class Ok2C extends Ok2 { override var i: Int = 1 }
+
+// was: variable i of type Int cannot override a mutable variable
+trait NotOk {var i: Int}
+class NotOkC extends NotOk { override var i: Int = 1 }