Fixes #3174: Enable $select=colProperty/$count query option parser

src/Microsoft.OData.Core/PublicAPI/net8.0/PublicAPI.Unshipped.txt

@@ -0,0 +1,11 @@
+Microsoft.OData.UriParser.PathCountSelectItem
+Microsoft.OData.UriParser.PathCountSelectItem.Filter.get -> Microsoft.OData.UriParser.FilterClause
+Microsoft.OData.UriParser.PathCountSelectItem.NavigationSource.get -> Microsoft.OData.Edm.IEdmNavigationSource
+Microsoft.OData.UriParser.PathCountSelectItem.PathCountSelectItem(Microsoft.OData.UriParser.ODataSelectPath selectedPath) -> void
+Microsoft.OData.UriParser.PathCountSelectItem.PathCountSelectItem(Microsoft.OData.UriParser.ODataSelectPath selectedPath, Microsoft.OData.Edm.IEdmNavigationSource navigationSource, Microsoft.OData.UriParser.FilterClause filter, Microsoft.OData.UriParser.SearchClause search) -> void
+Microsoft.OData.UriParser.PathCountSelectItem.Search.get -> Microsoft.OData.UriParser.SearchClause
+Microsoft.OData.UriParser.PathCountSelectItem.SelectedPath.get -> Microsoft.OData.UriParser.ODataSelectPath
+override Microsoft.OData.UriParser.PathCountSelectItem.HandleWith(Microsoft.OData.UriParser.SelectItemHandler handler) -> void
+override Microsoft.OData.UriParser.PathCountSelectItem.TranslateWith<T>(Microsoft.OData.UriParser.SelectItemTranslator<T> translator) -> T
+virtual Microsoft.OData.UriParser.SelectItemHandler.Handle(Microsoft.OData.UriParser.PathCountSelectItem item) -> void
+virtual Microsoft.OData.UriParser.SelectItemTranslator<T>.Translate(Microsoft.OData.UriParser.PathCountSelectItem item) -> T

src/Microsoft.OData.Core/PublicAPI/net9.0/PublicAPI.Unshipped.txt

@@ -2488,4 +2488,15 @@ static Microsoft.OData.UriParser.ODataPathExtensions.ToResourcePathString(this M
 static Microsoft.OData.UriParser.ODataPathExtensions.TrimEndingKeySegment(this Microsoft.OData.UriParser.ODataPath path) -> Microsoft.OData.UriParser.ODataPath
 static Microsoft.OData.UriParser.ODataPathExtensions.TrimEndingTypeSegment(this Microsoft.OData.UriParser.ODataPath path) -> Microsoft.OData.UriParser.ODataPath
 Microsoft.OData.ODataResourceBase.SkipPropertyVerification.get -> bool
-Microsoft.OData.ODataResourceBase.SkipPropertyVerification.set -> void
+Microsoft.OData.ODataResourceBase.SkipPropertyVerification.set -> void
+Microsoft.OData.UriParser.PathCountSelectItem
+Microsoft.OData.UriParser.PathCountSelectItem.Filter.get -> Microsoft.OData.UriParser.FilterClause
+Microsoft.OData.UriParser.PathCountSelectItem.NavigationSource.get -> Microsoft.OData.Edm.IEdmNavigationSource
+Microsoft.OData.UriParser.PathCountSelectItem.PathCountSelectItem(Microsoft.OData.UriParser.ODataSelectPath selectedPath) -> void
+Microsoft.OData.UriParser.PathCountSelectItem.PathCountSelectItem(Microsoft.OData.UriParser.ODataSelectPath selectedPath, Microsoft.OData.Edm.IEdmNavigationSource navigationSource, Microsoft.OData.UriParser.FilterClause filter, Microsoft.OData.UriParser.SearchClause search) -> void
+Microsoft.OData.UriParser.PathCountSelectItem.Search.get -> Microsoft.OData.UriParser.SearchClause
+Microsoft.OData.UriParser.PathCountSelectItem.SelectedPath.get -> Microsoft.OData.UriParser.ODataSelectPath
+override Microsoft.OData.UriParser.PathCountSelectItem.HandleWith(Microsoft.OData.UriParser.SelectItemHandler handler) -> void
+override Microsoft.OData.UriParser.PathCountSelectItem.TranslateWith<T>(Microsoft.OData.UriParser.SelectItemTranslator<T> translator) -> T
+virtual Microsoft.OData.UriParser.SelectItemHandler.Handle(Microsoft.OData.UriParser.PathCountSelectItem item) -> void
+virtual Microsoft.OData.UriParser.SelectItemTranslator<T>.Translate(Microsoft.OData.UriParser.PathCountSelectItem item) -> T

src/Microsoft.OData.Core/SRResources.resx

@@ -2087,6 +2087,18 @@
   <data name="SelectExpandBinder_SystemTokenInSelect" xml:space="preserve">
     <value>Found a system token, '{0}', while parsing a select clause.</value>
   </data>
+  <data name="SelectExpandBinder_NoSegmentAllowedAfterDollarCount" xml:space="preserve">
+    <value>No more segment '{0}' is allowed after '/$count' segment.</value>
+  </data>
+  <data name="SelectExpandBinder_NotAllowedDollarCountAsFirstSegment" xml:space="preserve">
+    <value>'/$count' segment is not allowed as first segment.</value>
+  </data>
+  <data name="SelectExpandBinder_NotAllowedDollarCountOnNonCollection" xml:space="preserve">
+    <value>'/$count' segment is only allowed on the collection type segment.</value>
+  </data>
+  <data name="SelectExpandBinder_NotAllowedDollarCountOnNavigationPropertyInDollarSelect" xml:space="preserve">
+    <value>In $select query option, '/$count' segment is not allowed on the navigation property segment '{0}'.</value>
+  </data>
   <data name="SelectionItemBinder_NoExpandForSelectedProperty" xml:space="preserve">
     <value>Only properties specified in $expand can be traversed in $select query options. Selected item was '{0}'.</value>
   </data>
@@ -2444,9 +2456,6 @@
   <data name="ExpressionToken_OnlyRefAllowWithStarInExpand" xml:space="preserve">
     <value>Only $ref is allowed with star in $expand option.</value>
   </data>
-  <data name="ExpressionToken_DollarCountNotAllowedInSelect" xml:space="preserve">
-    <value>$count is not allowed in $select option.</value>
-  </data>
   <data name="ExpressionToken_NoPropAllowedAfterDollarCount" xml:space="preserve">
     <value>No property is allowed after $count segment.</value>
   </data>

src/Microsoft.OData.Core/UriParser/Binders/SelectExpandBinder.cs

@@ -265,7 +265,7 @@ private SelectItem GenerateSelectItem(SelectTermToken tokenIn)
             ExceptionUtils.CheckArgumentNotNull(tokenIn, "tokenIn");
             ExceptionUtils.CheckArgumentNotNull(tokenIn.PathToProperty, "pathToProperty");
 
-            VerifySelectedPath(tokenIn);
+            VerifySelectedPath(tokenIn, configuration.EnableCaseInsensitiveUriFunctionIdentifier, out bool isCount);
 
             SelectItem newSelectItem;
             if (ProcessWildcardTokenPath(tokenIn, out newSelectItem))
@@ -277,7 +277,7 @@ private SelectItem GenerateSelectItem(SelectTermToken tokenIn)
             Debug.Assert(selectedPath.Count > 0);
 
             // Navigation property should be the last segment in select path.
-            if (VerifySelectedNavigationProperty(selectedPath, tokenIn))
+            if (VerifySelectedNavigationProperty(selectedPath, tokenIn, isCount))
             {
                 return new PathSelectItem(new ODataSelectPath(selectedPath));
             }
@@ -290,6 +290,10 @@ private SelectItem GenerateSelectItem(SelectTermToken tokenIn)
             {
                 targetElementType = collection.ElementType.Definition;
             }
+            else if (isCount && lastSegment is not PathTemplateSegment)
+            {
+                throw new ODataException(SRResources.SelectExpandBinder_NotAllowedDollarCountOnNonCollection);
+            }
 
             IEdmTypeReference elementTypeReference = targetElementType.ToTypeReference();
 
@@ -319,6 +323,15 @@ private SelectItem GenerateSelectItem(SelectTermToken tokenIn)
             parsedPath.AddRange(selectedPath);
             SelectExpandClause selectExpand = BindSelectExpand(null, tokenIn.SelectOption, parsedPath, this.ResourcePathNavigationSource, targetNavigationSource, elementTypeReference, generatedProperties);
 
+            if (isCount)
+            {
+                // Do we need to throw exception if orderBy and nested select expand are not null within /$count ?
+                return new PathCountSelectItem(new ODataSelectPath(selectedPath),
+                    this.NavigationSource,
+                    filter,
+                    search);
+            }
+
             return new PathSelectItem(new ODataSelectPath(selectedPath),
                 targetNavigationSource,
                 selectExpand,
@@ -953,8 +966,10 @@ private static BindingState CreateBindingState(ODataUriParserConfiguration confi
             return state;
         }
 
-        private static void VerifySelectedPath(SelectTermToken selectedToken)
+        private static void VerifySelectedPath(SelectTermToken selectedToken, bool enableCaseInsensitive, out bool isCount)
         {
+            isCount = false;
+            PathSegmentToken previous = null;
             PathSegmentToken current = selectedToken.PathToProperty;
             while (current != null)
             {
@@ -964,15 +979,39 @@ private static void VerifySelectedPath(SelectTermToken selectedToken)
                     throw new ODataException(Error.Format(SRResources.SelectExpandBinder_SystemTokenInSelect, current.Identifier));
                 }
 
+                // Be design, the "/$count" should be built using SystemToken, but now, ODL is using NonSystemToken.
+                // Shall we support "no-dollar sign"?
+                if (current.Identifier.Equals(UriQueryConstants.CountSegment, enableCaseInsensitive ? System.StringComparison.OrdinalIgnoreCase : System.StringComparison.Ordinal))
+                {
+                    if (current.NextToken != null)
+                    {
+                        throw new ODataException(Error.Format(SRResources.SelectExpandBinder_NoSegmentAllowedAfterDollarCount, current.NextToken.Identifier));
+                    }
+
+                    if (previous == null)
+                    {
+                        throw new ODataException(SRResources.SelectExpandBinder_NotAllowedDollarCountAsFirstSegment);
+                    }
+
+                    previous.NextToken = null; // Now remove the last "/$count" from the PathToProperty.
+                    isCount = true;
+                }
+
+                previous = current;
                 current = current.NextToken;
             }
         }
 
-        private static bool VerifySelectedNavigationProperty(IList<ODataPathSegment> selectedPath, SelectTermToken tokenIn)
+        private static bool VerifySelectedNavigationProperty(IList<ODataPathSegment> selectedPath, SelectTermToken tokenIn, bool isCount)
         {
             NavigationPropertySegment navPropSegment = selectedPath.LastOrDefault() as NavigationPropertySegment;
             if (navPropSegment != null)
             {
+                if (isCount)
+                {
+                    throw new ODataException(Error.Format(SRResources.SelectExpandBinder_NotAllowedDollarCountOnNavigationPropertyInDollarSelect, navPropSegment.NavigationProperty.Name));
+                }
+
                 // After navigation property, it's not allowed to nest query options
                 VerifyNoQueryOptionsNested(tokenIn, navPropSegment.Identifier);
 

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

@@ -136,11 +136,6 @@ private PathSegmentToken ParseSegment(PathSegmentToken previousSegment, bool all
                 }
             }
 
-            if (this.lexer.CurrentToken.Span.Equals(UriQueryConstants.CountSegment, StringComparison.Ordinal) && isSelect)
-            {
-                // $count is not allowed in $select e.g $select=NavProperty/$count
-                throw new ODataException(SRResources.ExpressionToken_DollarCountNotAllowedInSelect);
-            }
 
             ReadOnlySpan<char> propertyName;
 
@@ -170,6 +165,8 @@ private PathSegmentToken ParseSegment(PathSegmentToken previousSegment, bool all
                 this.lexer.NextToken();
             }
 
+            // By design, "/$count" or "/$ref" should return using SystemToken, but the existing implementation is using "NonSystemToken".
+            // So far, let's keep it unchanged.
             return new NonSystemToken(propertyName.ToString(), null, previousSegment);
         }
     }

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

@@ -0,0 +1,86 @@
+//---------------------------------------------------------------------
+// <copyright file="PathCountSelectItem.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>
+    /// Class to represent $select=collectionProperty/$count.
+    /// </summary>
+    public sealed class PathCountSelectItem : SelectItem
+    {
+        /// <summary>
+        /// Initializes a new <see cref="PathCountSelectItem"/>.
+        /// </summary>
+        /// <param name="selectedPath">The selected path.</param>
+        public PathCountSelectItem(ODataSelectPath selectedPath)
+            : this(selectedPath, null, null, null)
+        { }
+
+        /// <summary>
+        /// Initializes a new <see cref="PathCountSelectItem"/>.
+        /// </summary>
+        /// <param name="selectedPath">The selected path.</param>
+        /// <param name="navigationSource">The navigation source for this select item.</param>
+        /// <param name="filter">A filter clause for this select (can be null).</param>
+        /// <param name="search">A search clause for this select (can be null).</param>
+        public PathCountSelectItem(ODataSelectPath selectedPath,
+            IEdmNavigationSource navigationSource,
+            FilterClause filter,
+            SearchClause search)
+        {
+            ExceptionUtils.CheckArgumentNotNull(selectedPath, "selectedPath");
+
+            SelectedPath = selectedPath;
+            NavigationSource = navigationSource;
+            Filter = filter;
+            Search = search;
+        }
+
+        /// <summary>
+        /// Gets the selected path.
+        /// </summary>
+        public ODataSelectPath SelectedPath { get; }
+
+        /// <summary>
+        /// Gets the navigation source for this select level.
+        /// </summary>
+        public IEdmNavigationSource NavigationSource { get; }
+
+        /// <summary>
+        /// The filter clause for this select level.
+        /// </summary>
+        public FilterClause Filter { get; }
+
+        /// <summary>
+        /// Gets the search clause for this select level.
+        /// </summary>
+        public SearchClause Search { get; }
+
+        /// <summary>
+        /// Translate using a <see cref="SelectItemTranslator{T}"/>.
+        /// </summary>
+        /// <typeparam name="T">Type that the translator will return after visiting this item.</typeparam>
+        /// <param name="translator">An implementation of the translator interface.</param>
+        /// <returns>An object whose type is determined by the type parameter of the translator.</returns>
+        /// <exception cref="System.ArgumentNullException">Throws if the input translator is null.</exception>
+        public override T TranslateWith<T>(SelectItemTranslator<T> translator)
+        {
+            return translator.Translate(this);
+        }
+
+        /// <summary>
+        /// Handle using a <see cref="SelectItemHandler"/>.
+        /// </summary>
+        /// <param name="handler">An implementation of the handler interface.</param>
+        /// <exception cref="System.ArgumentNullException">Throws if the input handler is null.</exception>
+        public override void HandleWith(SelectItemHandler handler)
+        {
+            handler.Handle(this);
+        }
+    }
+}

src/Microsoft.OData.Core/UriParser/Visitors/SelectItemHandler.cs

@@ -22,6 +22,15 @@ public virtual void Handle(WildcardSelectItem item)
             throw new NotImplementedException();
         }
 
+        /// <summary>
+        /// Handle a PathCountSelectItem
+        /// </summary>
+        /// <param name="item">the item to Handle</param>
+        public virtual void Handle(PathCountSelectItem item)
+        {
+            throw new NotImplementedException();
+        }
+
         /// <summary>
         /// Handle a PathSelectItem
         /// </summary>

src/Microsoft.OData.Core/UriParser/Visitors/SelectItemTranslator.cs

@@ -34,6 +34,16 @@ public virtual T Translate(PathSelectItem item)
             throw new NotImplementedException();
         }
 
+        /// <summary>
+        /// Translate a PathCountSelectItem
+        /// </summary>
+        /// <param name="item">the item to Translate</param>
+        /// <returns>Defined by the implementer</returns>
+        public virtual T Translate(PathCountSelectItem item)
+        {
+            throw new NotImplementedException();
+        }
+
         /// <summary>
         /// Translate a ContainerQualifiedWildcardSelectItem
         /// </summary>