[Fixes #472] Added temporary parse error for helper directive

src/Microsoft.AspNet.Razor/Parser/CSharpCodeParser.cs

@@ -224,6 +224,14 @@ namespace Microsoft.AspNet.Razor.Parser
                             }
                             else
                             {
+                                if (CurrentSymbol.Content.Equals(SyntaxConstants.CSharp.HelperKeyword))
+                                {
+                                    Context.OnError(
+                                        CurrentLocation,
+                                        RazorResources.FormatParseError_HelperDirectiveNotAvailable(SyntaxConstants.CSharp.HelperKeyword),
+                                        CurrentSymbol.Content.Length);
+                                }
+
                                 Context.CurrentBlock.Type = BlockType.Expression;
                                 Context.CurrentBlock.ChunkGenerator = new ExpressionChunkGenerator();
                                 ImplicitExpression();

src/Microsoft.AspNet.Razor/Parser/SyntaxConstants.cs

@@ -27,6 +27,9 @@ namespace Microsoft.AspNet.Razor.Parser
             public static readonly string ElseIfKeyword = "else if";
             public static readonly string NamespaceKeyword = "namespace";
             public static readonly string ClassKeyword = "class";
+
+            // Not supported. Only used for error cases.
+            public static readonly string HelperKeyword = "helper";
         }
     }
 }

src/Microsoft.AspNet.Razor/Properties/RazorResources.Designer.cs

@@ -1546,6 +1546,22 @@ namespace Microsoft.AspNet.Razor
             return string.Format(CultureInfo.CurrentCulture, GetString("TagHelperParseTreeRewriter_InvalidNestedTag"), p0, p1, p2);
         }
 
+        /// <summary>
+        /// The {0} directive is not supported.
+        /// </summary>
+        internal static string ParseError_HelperDirectiveNotAvailable
+        {
+            get { return GetString("ParseError_HelperDirectiveNotAvailable"); }
+        }
+
+        /// <summary>
+        /// The {0} directive is not supported.
+        /// </summary>
+        internal static string FormatParseError_HelperDirectiveNotAvailable(object p0)
+        {
+            return string.Format(CultureInfo.CurrentCulture, GetString("ParseError_HelperDirectiveNotAvailable"), p0);
+        }
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.AspNet.Razor/RazorResources.resx

@@ -425,4 +425,7 @@ Instead, wrap the contents of the block in "{{}}":
   <data name="TagHelperParseTreeRewriter_InvalidNestedTag" xml:space="preserve">
     <value>The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tag helper(s) targeting tag name(s) '{2}' are allowed.</value>
   </data>
+  <data name="ParseError_HelperDirectiveNotAvailable" xml:space="preserve">
+    <value>The {0} directive is not supported.</value>
+  </data>
 </root>

test/Microsoft.AspNet.Razor.Test/Parser/CSharp/CSharpErrorTest.cs

@@ -27,6 +27,21 @@ namespace Microsoft.AspNet.Razor.Test.Parser.CSharp
                                length: 1));
         }
 
+        [Fact]
+        public void ParseBlockWithHelperDirectiveProducesError()
+        {
+            ParseBlockTest("@helper fooHelper { }",
+                new ExpressionBlock(
+                    Factory.CodeTransition(),
+                    Factory.Code("helper")
+                        .AsImplicitExpression(KeywordSet)
+                        .Accepts(AcceptedCharacters.NonWhiteSpace)),
+                new RazorError(
+                    RazorResources.FormatParseError_HelperDirectiveNotAvailable(SyntaxConstants.CSharp.HelperKeyword),
+                    new SourceLocation(1, 0, 1),
+                    length: 6));
+        }
+
         [Fact]
         public void ParseBlockCapturesWhitespaceToEndOfLineInInvalidUsingStatementAndTreatsAsFileCode()
         {