Removing compiler warnings, adding negative test case, removing redun…

…dant code and adding comments referencing issue OData#758.

src/Microsoft.OData.Core/UriParser/Aggregation/ApplyBinder.cs

@@ -118,6 +118,7 @@ private IEdmTypeReference CreateAggregateExpressionTypeReference(SingleValueNode
 
                 case AggregationMethod.VirtualPropertyCount:
                 case AggregationMethod.CountDistinct:
+                    // Issue #758: CountDistinct and $Count should return type Edm.Decimal with Scale="0" and sufficient Precision.
                     return EdmCoreModel.Instance.GetPrimitive(EdmPrimitiveTypeKind.Int64, false);
                 case AggregationMethod.Max:
                 case AggregationMethod.Min:

src/Microsoft.OData.Core/UriParser/Parsers/UriQueryExpressionParser.cs

@@ -287,11 +287,12 @@ internal AggregateExpressionToken ParseAggregateExpression()
             var endPathExpression = expression as EndPathToken;
             AggregationMethod verb;
 
+            // e.g. aggregate($count as Count)
             if (endPathExpression != null && endPathExpression.Identifier == ExpressionConstants.QueryOptionCount)
             {
-                expression = new EndPathToken("$count", endPathExpression.NextToken);
                 verb = AggregationMethod.VirtualPropertyCount; 
             }
+            // e.g. aggregate(UnitPrice with sum as Total)
             else
             {
                 // "with" verb

src/Microsoft.OData.Core/UriParser/SemanticAst/CountVirtualPropertyNode.cs

@@ -1,25 +1,38 @@
-using Microsoft.OData.Edm;
+//---------------------------------------------------------------------
+// <copyright file="CountVirtualPropertyNode.cs" company="Microsoft">
+//      Copyright (C) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
+// </copyright>
+//---------------------------------------------------------------------
+using Microsoft.OData.Edm;
 
 namespace Microsoft.OData.UriParser
 {
     /// <summary>
-    /// Dummy class that allows virtual property $count 
+    /// Dummy class that allows virtual property $count
     /// to work like any other aggregation method.
     /// </summary>
     public sealed class CountVirtualPropertyNode : SingleValueNode
     {
-        public CountVirtualPropertyNode() { }
+        /// <summary>Constructor.</summary>
+        public CountVirtualPropertyNode()
+        {
+        }
 
+        /// <summary>Kind of the single value node.</summary>
         public override QueryNodeKind Kind
         {
             get
             {
-                return QueryNodeKind.None;
+                return QueryNodeKind.Count;
             }
         }
 
-        public override IEdmTypeReference TypeReference {
-            get {
+        /// <summary>Type returned by the $count virtual property.</summary>
+        public override IEdmTypeReference TypeReference
+        {
+            get
+            {
+                // Issue #758: CountDistinct and $Count should return type Edm.Decimal with Scale="0" and sufficient Precision.
                 return EdmCoreModel.Instance.GetPrimitive(EdmPrimitiveTypeKind.Int64, false);
             }
         }

test/FunctionalTests/Microsoft.OData.Core.Tests/UriParser/Parsers/UriQueryExpressionParserTests.cs

@@ -180,6 +180,15 @@ public void ParseApplyWithSingleCountExpressionShouldReturnAggregateToken()
             VerifyAggregateExpressionToken("$count", AggregationMethod.VirtualPropertyCount, "Count", aggregate.Expressions.First());
         }
 
+        [Fact]
+        public void ParseApplyWithSingleCountExpressionCannotHaveWithKeyWord()
+        {
+            var apply = "aggregate($count with sum as Count)";
+
+            Action parse = () => this.testSubject.ParseApply(apply);
+            parse.ShouldThrow<ODataException>().Where(e => e.Message == ErrorStrings.UriQueryExpressionParser_AsExpected(17, apply));
+        }
+
         [Fact]
         public void ParseApplyWithCountAndOtherAggregationExpressionShouldReturnAggregateToken()
         {