CSHARP-4592: Support indexer for IDictionary (as well as Dictionary).

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/Misc/TypeExtensions.cs

@@ -216,6 +216,12 @@ public static bool IsValueTuple(this Type type)
 
         public static bool TryGetIDictionaryGenericInterface(this Type type, out Type idictionaryGenericInterface)
         {
+            if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(IDictionary<,>))
+            {
+                idictionaryGenericInterface = type;
+                return true;
+            }
+
             foreach (var interfaceType in type.GetInterfaces())
             {
                 if (interfaceType.IsGenericType && interfaceType.GetGenericTypeDefinition() == typeof(IDictionary<,>))

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp4592Tests.cs

@@ -0,0 +1,67 @@
+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System.Collections.Generic;
+using System.Linq;
+using FluentAssertions;
+using MongoDB.Driver.Linq;
+using MongoDB.TestHelpers.XunitExtensions;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp4592Tests : Linq3IntegrationTest
+    {
+        [Theory]
+        [ParameterAttributeData]
+        public void Project_dictionary_value_should_work(
+            [Values(LinqProvider.V2, LinqProvider.V3)] LinqProvider linqProvider)
+        {
+            var collection = CreateCollection(linqProvider);
+
+            var queryable = collection.AsQueryable()
+                .Select(x => x.Dict["test"]);
+
+            var stages = Translate(collection, queryable);
+            if (linqProvider == LinqProvider.V2)
+            {
+                AssertStages(stages, "{ $project : { test : '$Dict.test', _id : 0 } }"); // LINQ2 translates slightly differently
+            }
+            else
+            {
+                AssertStages(stages, "{ $project : { _v : '$Dict.test', _id : 0 } }");
+            }
+
+            var results = queryable.ToList();
+            results.Should().Equal(3, 0); // missing values deserialize as 0
+        }
+
+        private IMongoCollection<ExampleClass> CreateCollection(LinqProvider linqProvider)
+        {
+            var collection = GetCollection<ExampleClass>("test", linqProvider);
+            CreateCollection(
+                collection,
+                new ExampleClass { Id = 1, Dict = new Dictionary<string, int> { ["test"] = 3 } },
+                new ExampleClass { Id = 2, Dict = new Dictionary<string, int> { ["a"] = 4 } });
+            return collection;
+        }
+
+        private class ExampleClass
+        {
+            public int Id { get; set; }
+            public IDictionary<string, int> Dict { get; set; }
+        }
+    }
+}