Added array length support

Src/Newtonsoft.Json.Tests/Issues/Issue2688.cs

@@ -0,0 +1,115 @@
+#region License
+// Copyright (c) 2022 James Newton-King
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+#endregion
+
+using Newtonsoft.Json.Linq;
+
+#if DNXCORE50
+using Xunit;
+using Test = Xunit.FactAttribute;
+using Assert = Newtonsoft.Json.Tests.XUnitAssert;
+#else
+using NUnit.Framework;
+#endif
+
+namespace Newtonsoft.Json.Tests.Issues
+{
+    [TestFixture]
+    public class Issue2688
+    {
+        [Test]
+        public void ArrayLength()
+        {
+			string json = @"{
+	""firstName"": ""John"",
+	""lastName"": ""doe"",
+	""age"": 26,
+	""address"": {
+        ""streetAddress"": ""naist street"",
+		""city"": ""Nara"",
+		""postalCode"": ""630-0192""
+		},
+	""phoneNumbers"": [
+		{
+        ""type"": ""iPhone"",
+		""number"": ""0123-4567-8888""
+		},
+		{
+        ""type"": ""home"",
+		""number"": ""0123-4567-8910""
+		}
+		]
+	}";
+			JObject jobj = JObject.Parse(json);
+            string jsonPath = "$.phoneNumbers.length";
+            JToken token = jobj.SelectToken(jsonPath);
+            string count = token.ToString();
+            string expected = "2";
+            Assert.AreEqual(expected, count);
+        }
+
+		[Test]
+		public void ArrayLengthInBooleanExpression()
+		{
+			string json = @"{
+	""store"" : {
+		""book"" : [{
+				""category"" : ""reference"",
+				""author"" : ""Nigel Rees"",
+				""title"" : ""Sayings of the Century"",
+				""price"" : 8.68
+			}, {
+				""category"" : ""fiction"",
+				""author"" : ""Evelyn Waugh"",
+				""title"" : ""Sword of Honour"",
+				""price"" : 12.99
+			}, {
+				""category"" : ""fiction"",
+				""author"" : ""Herman Melville"",
+				""title"" : ""Moby Dick"",
+				""isbn"" : ""0-553-21311-3"",
+				""price"" : 2.56
+			}, {
+				""category"" : ""fiction"",
+				""author"" : ""J. R. R. Tolkien"",
+				""title"" : ""The Lord of the Rings"",
+				""isbn"" : ""0-395-19395-8"",
+				""price"" : 22.99
+			}
+		],
+		""bicycle"" : {
+				""color"" : ""red"",
+			""price"" : 19.95
+		}
+		}
+	}";
+			string jsonPath = "$.store.book[?(@.price < $.store.book.length)].author";
+			JObject jobj = JObject.Parse(json);
+			JToken token = jobj.SelectToken(jsonPath);
+			string actual = token.ToString();
+			string expected = "Herman Melville";
+			Assert.AreEqual(expected, actual);
+		}
+    }
+}

Src/Newtonsoft.Json/Linq/JArray.cs

@@ -41,6 +41,7 @@ namespace Newtonsoft.Json.Linq
     public partial class JArray : JContainer, IList<JToken>
     {
         private readonly List<JToken> _values = new List<JToken>();
+        static internal readonly string LengthProperty = "length";
 
         /// <summary>
         /// Gets the container's children tokens.

Src/Newtonsoft.Json/Linq/JsonPath/FieldFilter.cs

@@ -40,6 +40,10 @@ public override IEnumerable<JToken> ExecuteFilter(JToken root, IEnumerable<JToke
                         }
                     }
                 }
+                else if (Name == JArray.LengthProperty && t is JArray arr)
+                {
+                    yield return arr.Count;
+                }
                 else
                 {
                     if (settings?.ErrorWhenNoMatch ?? false)