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src/Compilers/CSharp/Portable/CSharpResources.Designer.cs

@@ -10606,9 +10606,9 @@ internal static string ERR_RefReturnParameter
         /// <summary>
         ///   Looks up a localized string similar to readonly references.
         /// </summary>
-        internal static string IDS_FeatureReadonlyReferences {
+        internal static string IDS_FeatureReadOnlyReferences {
             get {
-                return ResourceManager.GetString("IDS_FeatureReadonlyReferences", resourceCulture);
+                return ResourceManager.GetString("IDS_FeatureReadOnlyReferences", resourceCulture);
             }
         }
         

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -4245,7 +4245,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="IDS_FeatureRefLocalsReturns" xml:space="preserve">
     <value>byref locals and returns</value>
   </data>
-  <data name="IDS_FeatureReadonlyReferences" xml:space="preserve">
+  <data name="IDS_FeatureReadOnlyReferences" xml:space="preserve">
     <value>readonly references</value>
   </data>
   <data name="IDS_FeatureRefStructs" xml:space="preserve">

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -1501,7 +1501,7 @@ internal enum ErrorCode
         ERR_NamedArgumentSpecificationBeforeFixedArgumentInDynamicInvocation = 8324,
         #endregion diagnostics introduced for C# 7.2
 
-        #region diagnostics introduced for `ref readonly`, `ref ternary` and`ref-like` features in C# 7.2
+        #region diagnostics introduced for `ref readonly`, `ref ternary` and `ref-like` features in C# 7.2
         ERR_RefConditionalAndAwait = 8325,
         ERR_RefConditionalNeedsTwoRefs = 8326,
         ERR_RefConditionalDifferentTypes = 8327,
@@ -1536,6 +1536,6 @@ internal enum ErrorCode
         ERR_EscapeLocal = 8352,
         ERR_EscapeStackAlloc = 8353,
         ERR_RefReturnThis = 8354,
-        #endregion diagnostics introduced for `ref readonly`, `ref ternary` and`ref-like` features in C# 7.2
+        #endregion diagnostics introduced for `ref readonly`, `ref ternary` and `ref-like` features in C# 7.2
     }
 }

src/Compilers/CSharp/Portable/Errors/MessageID.cs

@@ -139,7 +139,7 @@ internal enum MessageID
         IDS_FeatureLeadingDigitSeparator = MessageBase + 12723,
         IDS_FeatureNonTrailingNamedArguments = MessageBase + 12724,
 
-        IDS_FeatureReadonlyReferences = MessageBase + 12725,
+        IDS_FeatureReadOnlyReferences = MessageBase + 12725,
         IDS_FeatureRefStructs = MessageBase + 12726,
         IDS_FeatureReadOnlyStructs = MessageBase + 12727,
         IDS_FeatureRefExtensionMethods = MessageBase + 12728,
@@ -203,7 +203,7 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
                 // C# 7.2 features.
                 case MessageID.IDS_FeatureNonTrailingNamedArguments: // semantic check
                 case MessageID.IDS_FeatureLeadingDigitSeparator:
-                case MessageID.IDS_FeatureReadonlyReferences:
+                case MessageID.IDS_FeatureReadOnlyReferences:
                 case MessageID.IDS_FeatureRefStructs:
                 case MessageID.IDS_FeatureReadOnlyStructs:
                 case MessageID.IDS_FeatureRefExtensionMethods:

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

@@ -3900,7 +3900,7 @@ private void ParseParameterModifiers(SyntaxListBuilder modifiers)
                             // "ref readonly"
                             if (nextKind == SyntaxKind.ReadOnlyKeyword)
                             {
-                                modifier = CheckFeatureAvailability(modifier, MessageID.IDS_FeatureReadonlyReferences);
+                                modifier = CheckFeatureAvailability(modifier, MessageID.IDS_FeatureReadOnlyReferences);
                                 nextKind = PeekToken(1).Kind;
                             }
 
@@ -6156,7 +6156,7 @@ private enum ParseTypeMode
                 if (this.CurrentToken.Kind == SyntaxKind.ReadOnlyKeyword)
                 {
                     readonlyKeyword = this.EatToken();
-                    readonlyKeyword = this.CheckFeatureAvailability(readonlyKeyword, MessageID.IDS_FeatureReadonlyReferences);
+                    readonlyKeyword = this.CheckFeatureAvailability(readonlyKeyword, MessageID.IDS_FeatureReadOnlyReferences);
                 }
 
                 var type = ParseTypeCore(mode, expectSizes);

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenRefConditionalOperatorTests.cs

@@ -929,8 +929,11 @@ static void Main(string[] args)
             var o1 = new C1();
 
             (args != null ? ref o.field : ref o1.field).ToString();
+            System.Console.Write(o.field.value);
 
-            System.Console.WriteLine(o.field.value);
+            // no copying expected
+            (args != null ? ref o.field : ref o1.field).RoExtension();
+            System.Console.Write(o.field.value);
         }
     }
 
@@ -939,7 +942,7 @@ class C1
         public readonly S1 field;
     }
 
-    struct S1
+    public struct S1
     {
         public int value;
 
@@ -949,14 +952,22 @@ public override string ToString()
             return base.ToString();
         }
     }
+
+    public static class S1Ext
+    {
+        public static void RoExtension(ref readonly this S1 self)
+        {
+            // do nothing
+        }
+    }
 ";
 
-            var comp = CompileAndVerify(source, additionalRefs: new[] { SystemRuntimeFacadeRef, ValueTupleRef }, expectedOutput: "0", verify: false);
+            var comp = CompileAndVerify(source, additionalRefs: new[] { SystemRuntimeFacadeRef, ValueTupleRef, SystemCoreRef }, expectedOutput: "00", verify: false);
             comp.VerifyDiagnostics();
 
             comp.VerifyIL("Program.Main", @"
 {
-  // Code size       61 (0x3d)
+  // Code size       99 (0x63)
   .maxstack  1
   .locals init (C1 V_0, //o
                 C1 V_1, //o1
@@ -980,8 +991,20 @@ .maxstack  1
   IL_002c:  ldloc.0
   IL_002d:  ldflda     ""S1 C1.field""
   IL_0032:  ldfld      ""int S1.value""
-  IL_0037:  call       ""void System.Console.WriteLine(int)""
-  IL_003c:  ret
+  IL_0037:  call       ""void System.Console.Write(int)""
+  IL_003c:  ldarg.0
+  IL_003d:  brtrue.s   IL_0047
+  IL_003f:  ldloc.1
+  IL_0040:  ldflda     ""S1 C1.field""
+  IL_0045:  br.s       IL_004d
+  IL_0047:  ldloc.0
+  IL_0048:  ldflda     ""S1 C1.field""
+  IL_004d:  call       ""void S1Ext.RoExtension(in S1)""
+  IL_0052:  ldloc.0
+  IL_0053:  ldflda     ""S1 C1.field""
+  IL_0058:  ldfld      ""int S1.value""
+  IL_005d:  call       ""void System.Console.Write(int)""
+  IL_0062:  ret
 }
 ");
         }

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

@@ -2831,7 +2831,28 @@ static void Main()
                 // warning CS1685: The predefined type 'ExtensionAttribute' is defined in multiple assemblies in the global alias; using definition from 'System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'
                 Diagnostic(ErrorCode.WRN_MultiplePredefTypes).WithArguments("System.Runtime.CompilerServices.ExtensionAttribute", "System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089").WithLocation(1, 1));
 
-            CompileAndVerify(comp, expectedOutput: "dynamic42", verify: false);
+            var compiled = CompileAndVerify(comp, expectedOutput: "dynamic42", verify: false);
+
+            compiled.VerifyIL("MyAwaiter.OnCompleted(System.Action)", @"
+{
+  // Code size       43 (0x2b)
+  .maxstack  3
+  .locals init (MyAwaiter.<>c__DisplayClass5_0 V_0) //CS$<>8__locals0
+  IL_0000:  newobj     ""MyAwaiter.<>c__DisplayClass5_0..ctor()""
+  IL_0005:  stloc.0
+  IL_0006:  ldloc.0
+  IL_0007:  ldarg.1
+  IL_0008:  stfld      ""System.Action MyAwaiter.<>c__DisplayClass5_0.continuation""
+  IL_000d:  ldarg.0
+  IL_000e:  ldflda     ""MyTask MyAwaiter.task""
+  IL_0013:  ldfld      ""System.Threading.Tasks.Task MyTask.task""
+  IL_0018:  ldloc.0
+  IL_0019:  ldftn      ""void MyAwaiter.<>c__DisplayClass5_0.<OnCompleted>b__0(System.Threading.Tasks.Task)""
+  IL_001f:  newobj     ""System.Action<System.Threading.Tasks.Task>..ctor(object, System.IntPtr)""
+  IL_0024:  callvirt   ""System.Threading.Tasks.Task System.Threading.Tasks.Task.ContinueWith(System.Action<System.Threading.Tasks.Task>)""
+  IL_0029:  pop
+  IL_002a:  ret
+}");
         }
     }
 }