CSHARP-2708: Verify that string.IsNullOrEmpty with or without null coalescing argument works in LINQ3.

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/LinqProviderAdapterV3.cs

@@ -117,6 +117,7 @@ internal override BsonDocument TranslateExpressionToFilter<TDocument>(
         {
             var context = TranslationContext.Create(expression, documentSerializer);
             var filter = ExpressionToFilterTranslator.TranslateLambda(context, expression, documentSerializer);
+            filter = AstSimplifier.SimplifyAndConvert(filter);
 
             return filter.Render().AsBsonDocument;
         }

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp2708Tests.cs

@@ -0,0 +1,132 @@
+/* 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.Linq;
+using MongoDB.Driver.Linq;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp2708Tests
+    {
+        [Fact]
+        public void IsNullOrEmpty_in_aggregate_match_should_work()
+        {
+            var collection = GetCollection();
+            var subject = collection.Aggregate();
+
+            var aggregate = subject.Match(x => string.IsNullOrEmpty(x.S));
+
+            var stages = Linq3TestHelpers.Translate(collection, aggregate);
+            var expectedStages = new[]
+            {
+                "{ $match : { S : { $in : [null, ''] } } }"
+            };
+            Linq3TestHelpers.AssertStages(stages, expectedStages);
+        }
+
+        [Fact]
+        public void IsNullOrEmpty_with_null_coalescing_operator_in_aggregate_match_should_work()
+        {
+            var collection = GetCollection();
+            var subject = collection.Aggregate();
+
+            var aggregate = subject.Match(x => string.IsNullOrEmpty(x.S ?? ""));
+
+            var stages = Linq3TestHelpers.Translate(collection, aggregate);
+            var expectedStages = new[]
+            {
+                "{ $match : { $expr : { $in : [{ $ifNull : ['$S', ''] }, [null, '']] } } }" // requires use of $expr
+            };
+            Linq3TestHelpers.AssertStages(stages, expectedStages);
+        }
+
+        [Fact]
+        public void Null_coalescing_operator_in_aggregate_project_should_work()
+        {
+            var collection = GetCollection();
+            var subject = collection.Aggregate();
+
+            var aggregate = subject.Project(x => x.S ?? "");
+
+            var stages = Linq3TestHelpers.Translate(collection, aggregate);
+            var expectedStages = new[]
+            {
+                "{ $project : { _v : { $ifNull : ['$S', ''] }, _id : 0  } }"
+            };
+            Linq3TestHelpers.AssertStages(stages, expectedStages);
+        }
+
+        [Fact]
+        public void Null_coalescing_operator_in_queryable_select_should_work()
+        {
+            var collection = GetCollection();
+            var subject = collection.AsQueryable();
+
+            var queryable = subject.Select(x => x.S ?? "");
+
+            var stages = Linq3TestHelpers.Translate(collection, queryable);
+            var expectedStages = new[]
+            {
+                "{ $project : { _v : { $ifNull : ['$S', ''] }, _id : 0  } }"
+            };
+            Linq3TestHelpers.AssertStages(stages, expectedStages);
+        }
+
+        [Fact]
+        public void IsNullOrEmpty_in_queryable_where_should_work()
+        {
+            var collection = GetCollection();
+            var subject = collection.AsQueryable();
+
+            var queryable = subject.Where(x => string.IsNullOrEmpty(x.S));
+
+            var stages = Linq3TestHelpers.Translate(collection, queryable);
+            var expectedStages = new[]
+            {
+                "{ $match : { S : { $in : [null, ''] } } }"
+            };
+            Linq3TestHelpers.AssertStages(stages, expectedStages);
+        }
+
+        [Fact]
+        public void IsNullOrEmpty_with_null_coalescing_operator_in_queryable_where_should_work()
+        {
+            var collection = GetCollection();
+            var subject = collection.AsQueryable();
+
+            var queryable = subject.Where(x => string.IsNullOrEmpty(x.S ?? ""));
+
+            var stages = Linq3TestHelpers.Translate(collection, queryable);
+            var expectedStages = new[]
+            {
+                "{ $match : { $expr : { $in : [{ $ifNull : ['$S', ''] }, [null, '']] } } }" // requires use of $expr
+            };
+            Linq3TestHelpers.AssertStages(stages, expectedStages);
+        }
+
+        private IMongoCollection<C> GetCollection()
+        {
+            var client = DriverTestConfiguration.Linq3Client;
+            var database = client.GetDatabase("foo");
+            return database.GetCollection<C>("foo");
+        }
+
+        private class C
+        {
+            public string S { get; set; }
+        }
+    }
+}