[Fixes #804] Fixed unsafe cast in CSharpCodeVisitor

src/Microsoft.AspNetCore.Razor/CodeGenerators/Visitors/CSharpCodeVisitor.cs

@@ -399,36 +399,47 @@ protected override void Visit(SectionChunk chunk)
 
         public void RenderDesignTimeExpressionBlockChunk(ExpressionBlockChunk chunk)
         {
-            var firstChild = (ExpressionChunk)chunk.Children.FirstOrDefault();
-
-            if (firstChild != null)
+            var firstChild = chunk.Children.FirstOrDefault();
+            if (firstChild == null)
             {
-                var currentIndent = Writer.CurrentIndent;
-                var designTimeAssignment = "__o = ";
-                Writer.ResetIndent();
+                return;
+            }
 
-                var documentLocation = firstChild.Association.Start;
-                // This is only here to enable accurate formatting by the C# editor.
-                Writer.WriteLineNumberDirective(documentLocation, Context.SourceFile);
+            var currentIndent = Writer.CurrentIndent;
+            Writer.ResetIndent();
 
+            var documentLocation = firstChild.Association.Start;
+
+            // This is only here to enable accurate formatting by the C# editor.
+            Writer.WriteLineNumberDirective(documentLocation, Context.SourceFile);
+
+            var designTimeAssignment = "__o = ";
+            var firstChildExpressionChunk = firstChild as ExpressionChunk;
+            if (firstChildExpressionChunk != null)
+            {
                 // We build the padding with an offset of the design time assignment statement.
-                Writer.Write(_paddingBuilder.BuildExpressionPadding((Span)firstChild.Association, designTimeAssignment.Length))
-                      .Write(designTimeAssignment);
+                Writer.Write(_paddingBuilder.BuildExpressionPadding((Span)firstChildExpressionChunk.Association, designTimeAssignment.Length))
+                        .Write(designTimeAssignment);
 
                 // We map the first line of code but do not write the line pragmas associated with it.
-                CreateRawCodeMapping(firstChild.Code, documentLocation);
+                CreateRawCodeMapping(firstChildExpressionChunk.Code, documentLocation);
 
                 // Render all but the first child.
                 // The reason why we render the other children differently is because when formatting the C# code
                 // the formatter expects the start line to have the assignment statement on it.
                 Accept(chunk.Children.Skip(1).ToList());
-
-                Writer.WriteLine(";")
-                      .WriteLine()
-                      .WriteLineDefaultDirective()
-                      .WriteLineHiddenDirective()
-                      .SetIndent(currentIndent);
             }
+            else
+            {
+                // First child is not an expression chunk
+                Accept(chunk.Children);
+            }
+
+            Writer.WriteLine(";")
+                    .WriteLine()
+                    .WriteLineDefaultDirective()
+                    .WriteLineHiddenDirective()
+                    .SetIndent(currentIndent);
         }
 
         public void RenderRuntimeExpressionBlockChunk(ExpressionBlockChunk chunk)

test/Microsoft.AspNetCore.Razor.Test/CodeGenerators/CSharpRazorCodeGeneratorTest.cs

@@ -72,6 +72,7 @@ public void ConstructorAllowsEmptyRootNamespaceName()
         [InlineData("ConditionalAttributes")]
         [InlineData("Await")]
         [InlineData("CodeBlockWithTextElement")]
+        [InlineData("ExplicitExpressionWithMarkup")]
         public void CSharpChunkGeneratorCorrectlyGeneratesRunTimeCode(string testType)
         {
             RunTest(testType);
@@ -404,6 +405,15 @@ public void CSharpChunkGeneratorCorrectlyGeneratesDesignTimePragmasMarkupAndExpr
             });
         }
 
+        [Fact]
+        public void CSharpChunkGeneratorCorrectlyGeneratesDesignTimePragmasForExplicitExpressionContainingMarkup()
+        {
+            RunTest(
+                "ExplicitExpressionWithMarkup",
+                "ExplicitExpressionWithMarkup.DesignTime",
+                designTimeMode: true,
+                expectedDesignTimePragmas: new List<LineMapping>());
+        }
 
         [Fact]
         public void CSharpChunkGeneratorCorrectlyGeneratesDesignTimePragmasForImplicitExpressionStartedAtEOF()

test/Microsoft.AspNetCore.Razor.Test/TestFiles/CodeGenerator/Output/ExplicitExpressionWithMarkup.DesignTime.cs

@@ -0,0 +1,33 @@
+namespace TestOutput
+{
+    using System;
+    using System.Threading.Tasks;
+
+    public class ExplicitExpressionWithMarkup
+    {
+        private static object @__o;
+        private void @__RazorDesignTimeHelpers__()
+        {
+            #pragma warning disable 219
+            #pragma warning restore 219
+        }
+        #line hidden
+        public ExplicitExpressionWithMarkup()
+        {
+        }
+
+        #pragma warning disable 1998
+        public override async Task ExecuteAsync()
+        {
+#line 1 "ExplicitExpressionWithMarkup.cshtml"
+item => new Template(async(__razor_template_writer) => {
+}
+)
+;
+
+#line default
+#line hidden
+        }
+        #pragma warning restore 1998
+    }
+}

test/Microsoft.AspNetCore.Razor.Test/TestFiles/CodeGenerator/Output/ExplicitExpressionWithMarkup.cs

@@ -0,0 +1,36 @@
+#pragma checksum "ExplicitExpressionWithMarkup.cshtml" "{ff1816ec-aa5e-4d10-87f7-6f4963833460}" "1252c799cdeb86a71e4304f01ebaae540fa26894"
+namespace TestOutput
+{
+    using System;
+    using System.Threading.Tasks;
+
+    public class ExplicitExpressionWithMarkup
+    {
+        #line hidden
+        public ExplicitExpressionWithMarkup()
+        {
+        }
+
+        #pragma warning disable 1998
+        public override async Task ExecuteAsync()
+        {
+            Instrumentation.BeginContext(0, 5, true);
+            WriteLiteral("<div>");
+            Instrumentation.EndContext();
+            Instrumentation.BeginContext(14, 0, false);
+#line 1 "ExplicitExpressionWithMarkup.cshtml"
+        Write(item => new Template(async(__razor_template_writer) => {
+    Instrumentation.BeginContext(8, 6, true);
+    WriteLiteralTo(__razor_template_writer, "</div>");
+    Instrumentation.EndContext();
+}
+)
+);
+
+#line default
+#line hidden
+            Instrumentation.EndContext();
+        }
+        #pragma warning restore 1998
+    }
+}

test/Microsoft.AspNetCore.Razor.Test/TestFiles/CodeGenerator/Source/ExplicitExpressionWithMarkup.cshtml

@@ -0,0 +1 @@
+<div>@(@</div>