From 8b7eedfe394b9ae0d2395f5717ca6634e509b718 Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Fri, 23 Sep 2022 08:38:28 -0700
Subject: [PATCH] Avoid warning on setter in trait

The setter can be detected as isVar. Ignore its synthetic parameter.
---
 .../scala/tools/nsc/typechecker/TypeDiagnostics.scala |  2 +-
 test/files/pos/t12646.scala                           | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 test/files/pos/t12646.scala

diff --git a/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala b/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala
index ba79b1de5322..cc8655546ce7 100644
--- a/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala
@@ -547,7 +547,7 @@ trait TypeDiagnostics extends splain.SplainDiagnostics {
               if (sym.isPrimaryConstructor)
                 for (cpa <- sym.owner.constrParamAccessors if cpa.isPrivateLocal) params += cpa
               else if (sym.isSynthetic && sym.isImplicit) return
-              else if (!sym.isConstructor && !isTrivial(rhs))
+              else if (!sym.isConstructor && !sym.isVar && !isTrivial(rhs))
                 for (vs <- vparamss) params ++= vs.map(_.symbol)
               defnTrees += m
             case _ =>
diff --git a/test/files/pos/t12646.scala b/test/files/pos/t12646.scala
new file mode 100644
index 000000000000..72118974d5fb
--- /dev/null
+++ b/test/files/pos/t12646.scala
@@ -0,0 +1,11 @@
+
+// scalac: -Werror -Wunused:params
+
+trait T {
+  private var x: String = _
+
+  def y: String = {
+    if (x eq null) x = "hello, world"
+    x
+  }
+}