From d07de1274b96653007800eaa3069c579dbd5d1e5 Mon Sep 17 00:00:00 2001
From: vsadov <vsadov@microsoft.com>
Date: Fri, 19 Feb 2016 11:42:21 -0800
Subject: [PATCH] Disallow local byref void methods.

Fixes #8441
---
 .../Symbols/Source/LocalFunctionSymbol.cs     |  7 ++++++
 .../Test/Symbol/Symbols/Source/MethodTests.cs | 22 +++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.cs b/src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.cs
index c292462eed906..c592b6667a462 100644
--- a/src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.cs
+++ b/src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.cs
@@ -168,6 +168,13 @@ internal TypeSymbol ComputeReturnType()
                 // The return type of an async method must be void, Task or Task<T>
                 diagnostics.Add(ErrorCode.ERR_BadAsyncReturn, this.Locations[0]);
             }
+
+            var returnsVoid = returnType.SpecialType == SpecialType.System_Void;
+            if (this.RefKind != RefKind.None && returnsVoid)
+            {
+                diagnostics.Add(ErrorCode.ERR_VoidReturningMethodCannotReturnByRef, this.Locations[0]);
+            }
+
             // TODO: note there is a race condition here that will ultimately need to be fixed.
             // Specifically, the Interlocked.CompareExchange above succeeds, and will be seen by
             // other threads, before the diagnostics have been recorded in this symbol, below.
diff --git a/src/Compilers/CSharp/Test/Symbol/Symbols/Source/MethodTests.cs b/src/Compilers/CSharp/Test/Symbol/Symbols/Source/MethodTests.cs
index e3a42c4451fe4..bfd5c85528bca 100644
--- a/src/Compilers/CSharp/Test/Symbol/Symbols/Source/MethodTests.cs
+++ b/src/Compilers/CSharp/Test/Symbol/Symbols/Source/MethodTests.cs
@@ -2072,6 +2072,28 @@ static ref void M() { }
                 Diagnostic(ErrorCode.ERR_VoidReturningMethodCannotReturnByRef, "ref").WithLocation(4, 12));
         }
 
+        [Fact]
+        public void RefReturningVoidMethodNested()
+        {
+            var source = @"
+static class C
+{
+    static void Main()
+    {
+        ref void M() { }
+    }
+}
+";
+
+            CreateExperimentalCompilationWithMscorlib45(source).VerifyDiagnostics(
+    // (6,18): error CS8898: Void-returning methods cannot return by reference
+    //         ref void M() { }
+    Diagnostic(ErrorCode.ERR_VoidReturningMethodCannotReturnByRef, "M").WithLocation(6, 18),
+    // (6,18): warning CS0168: The variable 'M' is declared but never used
+    //         ref void M() { }
+    Diagnostic(ErrorCode.WRN_UnreferencedVar, "M").WithArguments("M").WithLocation(6, 18));
+        }
+
         [Fact]
         public void RefReturningAsyncMethod()
         {