Add regression tests for DevDiv #1134746.

src/ExpressionEvaluator/CSharp/Test/ExpressionCompiler/HoistedStateMachineLocalTests.cs

@@ -1289,6 +1289,51 @@ .maxstack  1
             AssertEx.SetEqual(GetLocalNames(context), "ch", "<>TypeVariables");
         }
 
+        [WorkItem(1134746, "DevDiv")]
+        [Fact]
+        public void Caching()
+        {
+            var source = @"
+using System.Collections.Generic;
+
+class C
+{
+    static IEnumerable<int> M()
+    {
+#line 100
+        int x = 1;
+        yield return x;
+
+        {
+#line 200
+            int y = x + 1;
+            yield return y;
+        }
+    }
+}";
+            var comp = CreateCompilationWithMscorlib(source, options: TestOptions.DebugDll);
+            var runtime = CreateRuntimeInstance(comp);
+            var context = CreateMethodContext(
+                runtime,
+                methodName: "C.<M>d__0.MoveNext",
+                atLineNumber: 100);
+            string error;
+            context.CompileExpression("x", out error);
+            Assert.Null(error);
+            context.CompileExpression("y", out error);
+            Assert.Equal("error CS0103: The name 'y' does not exist in the current context", error);
+
+            context = CreateMethodContext(
+                runtime,
+                methodName: "C.<M>d__0.MoveNext",
+                atLineNumber: 200,
+                previous: new CSharpMetadataContext(context));
+            context.CompileExpression("x", out error);
+            Assert.Null(error);
+            context.CompileExpression("y", out error);
+            Assert.Null(error);
+        }
+
         private static string[] GetLocalNames(EvaluationContext context)
         {
             string unused;

src/ExpressionEvaluator/VisualBasic/Test/ExpressionCompiler/HoistedStateMachineLocalTests.vb

@@ -1364,6 +1364,51 @@ End Class
             AssertEx.SetEqual(GetLocalNames(context), "ch", "<>TypeVariables")
         End Sub
 
+        <WorkItem(1134746, "DevDiv")>
+        <Fact>
+        Public Sub Caching()
+            Const source = "
+Imports System.Collections.Generic
+
+Class C
+    Shared Iterator Function M() As IEnumerable(Of Integer)
+#ExternalSource(""Test"", 100)
+        Dim x As Integer = 1
+        Yield x
+#End ExternalSource
+
+        If True Then
+#ExternalSource(""Test"", 200)
+            Dim y As Integer = x + 1
+            Yield y
+#End ExternalSource
+        End If
+    End Function
+End Class
+"
+            Dim comp = CreateCompilationWithMscorlib({source}, compOptions:=TestOptions.DebugDll)
+            Dim runtime = CreateRuntimeInstance(comp)
+            Dim context = CreateMethodContext(
+                runtime,
+                methodName:="C.VB$StateMachine_1_M.MoveNext",
+                atLineNumber:=100)
+            Dim errorMessage As String = Nothing
+            context.CompileExpression("x", errorMessage)
+            Assert.Null(errorMessage)
+            context.CompileExpression("y", errorMessage)
+            Assert.Equal("(1,2): error BC30451: 'y' is not declared. It may be inaccessible due to its protection level.", errorMessage)
+
+            context = CreateMethodContext(
+                runtime,
+                methodName:="C.VB$StateMachine_1_M.MoveNext",
+                atLineNumber:=200,
+                previous:=New VisualBasicMetadataContext(context))
+            context.CompileExpression("x", errorMessage)
+            Assert.Null(errorMessage)
+            context.CompileExpression("y", errorMessage)
+            Assert.Null(errorMessage)
+        End Sub
+
         Private Shared Function GetLocalNames(context As EvaluationContext) As String()
             Dim unused As String = Nothing
             Dim locals = New ArrayBuilder(Of LocalAndMethod)()