Clarify error message when attempting to ref a property

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -985,7 +985,7 @@
     <value>Cannot call an abstract base member: '{0}'</value>
   </data>
   <data name="ERR_RefProperty" xml:space="preserve">
-    <value>A property or indexer may not be passed as an out or ref parameter</value>
+    <value>An indexer or auto-implemented property may not be used as an out or ref value</value>
   </data>
   <data name="ERR_ManagedAddr" xml:space="preserve">
     <value>Cannot take the address of, get the size of, or declare a pointer to a managed type ('{0}')</value>

src/Compilers/CSharp/Test/Semantic/Semantics/ArglistTests.cs

@@ -229,7 +229,7 @@ static void Main()
     // (9,40): error CS1510: A ref or out value must be an assignable variable
     //         TypedReference tr3 = __makeref(123); // CS1510
     Diagnostic(ErrorCode.ERR_RefLvalueExpected, "123").WithLocation(9, 40),
-    // (10,40): error CS0206: A property or indexer may not be passed as an out or ref parameter
+    // (10,40): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
     //         TypedReference tr4 = __makeref(P); // CS0206
     Diagnostic(ErrorCode.ERR_RefProperty, "P").WithLocation(10, 40),
     // (11,40): error CS0199: A static readonly field cannot be used as a ref or out value (except in a static constructor)

src/Compilers/CSharp/Test/Semantic/Semantics/InitOnlyMemberTests.cs

@@ -1278,7 +1278,7 @@ void M()
 ";
             var comp = CreateCompilation(new[] { source, IsExternalInitTypeDefinition }, parseOptions: TestOptions.Regular9);
             comp.VerifyEmitDiagnostics(
-                // (8,16): error CS0206: A property or indexer may not be passed as an out or ref parameter
+                // (8,16): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
                 //         M2(out Property); // 1
                 Diagnostic(ErrorCode.ERR_RefProperty, "Property").WithLocation(8, 16)
                 );

src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

@@ -33580,7 +33580,7 @@ public void M()
                 // (12,9): warning CS8602: Dereference of a possibly null reference.
                 //         field.ToString(); // 4
                 Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "field").WithLocation(12, 9),
-                // (14,15): error CS0206: A property or indexer may not be passed as an out or ref parameter
+                // (14,15): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
                 //         M(ref Property); // 5
                 Diagnostic(ErrorCode.ERR_RefProperty, "Property").WithLocation(14, 15),
                 // (15,20): warning CS8625: Cannot convert null literal to non-nullable reference type.

src/Compilers/CSharp/Test/Semantic/Semantics/RefFieldTests.cs

@@ -8828,6 +8828,67 @@ static void Main()
                 Diagnostic(ErrorCode.ERR_RefLocalOrParamExpected, "s.P2").WithLocation(22, 9));
         }
 
+        [Fact]
+        [WorkItem(60807, "https://github.com/dotnet/roslyn/issues/60807")]
+        public void RefAndOut_PropertiesAndIndexers_As_ValuesAndParameters()
+        {
+            var source =
+@"
+var c = new C();
+var r = new R();
+//expressions
+ref int n = ref c.N;  //CS0206
+ref var l = ref c[0]; //CS0206
+ref var l2 = ref r[0];//OK
+_ = M(ref c.N);       //CS0206
+_ = M(ref r.N);       //OK
+_ = M(ref c[0]);      //CS0206
+_ = M(ref r[0]);      //OK
+_ = M2(out c.N);      //CS0206
+_ = M2(out r.N);      //OK
+_ = M2(out c[0]);     //CS0206
+_ = M2(out r[0]);     //OK
+//defenitions
+static string M(ref int number) { return """"; }
+static string M2(out int number) { number = 42; return """"; }
+class C
+{
+    public int N { get; set; }    
+    private int[] arr = new int[100];
+    public int this[int i] => arr[i];
+}
+ref struct R
+{
+    public R(){}
+    private ref int n;
+    public ref int N => ref n;
+    private ref int[] arr = new int[1];
+    public ref int this[int i] => ref arr[i];
+}
+";
+            var comp = CreateCompilation(source, targetFramework: TargetFramework.Net70);
+            comp.VerifyEmitDiagnostics(
+                // (5,17): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
+                // ref int n = ref c.N;  //CS0206
+                Diagnostic(ErrorCode.ERR_RefProperty, "c.N").WithLocation(5, 17),
+                // (6,17): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
+                // ref var l = ref c[0]; //CS0206
+                Diagnostic(ErrorCode.ERR_RefProperty, "c[0]").WithLocation(6, 17),
+                // (8,11): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
+                // _ = M(ref c.N);       //CS0206
+                Diagnostic(ErrorCode.ERR_RefProperty, "c.N").WithLocation(8, 11),
+                // (10,11): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
+                // _ = M(ref c[0]);      //CS0206
+                Diagnostic(ErrorCode.ERR_RefProperty, "c[0]").WithLocation(10, 11),
+                // (12,12): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
+                // _ = M2(out c.N);      //CS0206
+                Diagnostic(ErrorCode.ERR_RefProperty, "c.N").WithLocation(12, 12),
+                // (14,12): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
+                // _ = M2(out c[0]);     //CS0206
+                Diagnostic(ErrorCode.ERR_RefProperty, "c[0]").WithLocation(14, 12)
+            );
+        }
+
         [Fact]
         public void RefAccessor_Value()
         {

src/Compilers/CSharp/Test/Semantic/Semantics/RefLocalsAndReturnsTests.cs

@@ -3178,7 +3178,7 @@ static void M()
 ";
 
             CreateCompilationWithMscorlib46(text).VerifyDiagnostics(
-                // (8,26): error CS0206: A property or indexer may not be passed as an out or ref parameter
+                // (8,26): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
                 //         ref int rl = ref P;
                 Diagnostic(ErrorCode.ERR_RefProperty, "P").WithLocation(8, 26));
         }
@@ -3199,7 +3199,7 @@ void M()
 ";
 
             CreateCompilationWithMscorlib46(text).VerifyDiagnostics(
-                // (8,26): error CS0206: A property or indexer may not be passed as an out or ref parameter
+                // (8,26): error CS0206: An indexer or auto-implemented property may not be used as an out or ref value
                 //         ref int rl = ref this[0];
                 Diagnostic(ErrorCode.ERR_RefProperty, "this[0]").WithLocation(8, 26));
         }