Merge pull request #12693 from vslsnap/merge-dev15-preview-4-into-master20160723-150102

Merge dev15-preview-4 into master

src/Compilers/CSharp/Portable/Lowering/MethodToClassRewriter.cs

@@ -721,6 +721,15 @@ internal override void AddSynthesizedAttributes(ModuleCompilationState compilati
 
                 AddSynthesizedAttribute(ref attributes, this.DeclaringCompilation.TrySynthesizeAttribute(WellKnownMember.System_Diagnostics_DebuggerHiddenAttribute__ctor));
             }
+
+            internal override TypeSymbol IteratorElementType
+            {
+                get
+                {
+                    // BaseMethodWrapperSymbol should not be rewritten by the IteratorRewriter
+                    return null;
+                }
+            }
         }
     }
 }

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

@@ -339,5 +339,73 @@ public void TopLevelYieldBreak()
             Assert.NotNull(yieldNode);
             Assert.Equal(SyntaxKind.YieldBreakStatement, yieldNode.Kind());
         }
+
+        [Fact]
+        [WorkItem(11649, "https://github.com/dotnet/roslyn/issues/11649")]
+        public void IteratorRewriterShouldNotRewriteBaseMethodWrapperSymbol()
+        {
+            var text =
+@"using System.Collections.Generic;
+
+class Base
+{
+    protected virtual IEnumerable<int> M()
+    {
+        yield break;
+    }
+
+    class D : Base
+    {
+        protected override IEnumerable<int> M()
+        {
+            base.M(); // the rewriting of D.M() synthesizes a BaseMethodWrapperSymbol for this base call, with return type IEnumerable,
+                      // but it should not in turn be lowered by the IteratorRewriter
+            yield break;
+        }
+    }
+}";
+            var comp = CreateCompilationWithMscorlib(text, options: TestOptions.DebugDll);
+            comp.VerifyEmitDiagnostics(); // without the fix for bug 11649, the compilation would fail emitting
+            CompileAndVerify(comp);
+        }
+
+        [Fact]
+        [WorkItem(11649, "https://github.com/dotnet/roslyn/issues/11649")]
+        public void IteratorRewriterShouldNotRewriteBaseMethodWrapperSymbol2()
+        {
+            var source =
+@"using System.Collections.Generic;
+
+class Base
+{
+    public static void Main()
+    {
+        System.Console.WriteLine(string.Join("","", new D().M()));
+    }
+
+    protected virtual IEnumerable<int> M()
+    {
+        yield return 1;
+        yield return 2;
+        yield break;
+    }
+
+    class D : Base
+    {
+        protected override IEnumerable<int> M()
+        {
+            yield return 0;
+            foreach (var n in base.M())
+            {
+                yield return n;
+            }
+            yield return 3;
+            yield break;
+        }
+    }
+}";
+            var comp = CompileAndVerify(source, expectedOutput: "0,1,2,3", options: TestOptions.DebugExe);
+            comp.Compilation.VerifyDiagnostics();
+        }
    }
 }