From 54ec3c8a18684cb4a09a2e8c6e2c3677eb348ede Mon Sep 17 00:00:00 2001
From: ovska <ovaskasi@gmail.com>
Date: Thu, 4 Dec 2025 10:25:24 +0200
Subject: [PATCH] Fix RCS1085 with ref backing field

Fixes #1717
---
 .../Analysis/UseAutoPropertyAnalyzer.cs       |  5 ++++
 .../RCS1085UseAutoPropertyTests.cs            | 26 +++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/src/Analyzers/CSharp/Analysis/UseAutoPropertyAnalyzer.cs b/src/Analyzers/CSharp/Analysis/UseAutoPropertyAnalyzer.cs
index c7691ce7a0..61b8e8aa9f 100644
--- a/src/Analyzers/CSharp/Analysis/UseAutoPropertyAnalyzer.cs
+++ b/src/Analyzers/CSharp/Analysis/UseAutoPropertyAnalyzer.cs
@@ -108,6 +108,11 @@ private static void AnalyzePropertyDeclaration(SyntaxNodeAnalysisContext context
             return;
         }
 
+#if ROSLYN_4_4
+        if (fieldSymbol.RefKind is RefKind.Ref or RefKind.RefReadOnly)
+            return;
+#endif
+
         if (!CheckPreprocessorDirectives(property))
             return;
 
diff --git a/src/Tests/Analyzers.Tests/RCS1085UseAutoPropertyTests.cs b/src/Tests/Analyzers.Tests/RCS1085UseAutoPropertyTests.cs
index 3b72a81dbc..7cfb284267 100644
--- a/src/Tests/Analyzers.Tests/RCS1085UseAutoPropertyTests.cs
+++ b/src/Tests/Analyzers.Tests/RCS1085UseAutoPropertyTests.cs
@@ -981,4 +981,30 @@ private static void Write2(ref readonly ReadOnlySequence<byte> data, IBufferWrit
     }
 }");
     }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseAutoProperty)]
+    public async Task TestNoDiagnostic_BackingFieldRef()
+    {
+        await VerifyNoDiagnosticAsync(
+            @"
+public ref struct Example(ref int value1, ref int value2)
+{
+    private ref int _value1 = ref value1;
+    private readonly ref int _value2 = ref value2;
+
+    public int Value1
+    {
+        get => _value1;
+        set => _value1 = value;
+    }
+
+    public int Value2
+    {
+        get => _value2;
+        set => _value2 = value;
+    }
+}
+"
+        );
+    }
 }