CSHARP-1660: added support for both bytes and codepoint variant.

Author: craiggwilson

src/MongoDB.Driver/Linq/Translators/AggregateLanguageTranslator.cs

@@ -814,7 +814,11 @@ private bool TryTranslateStringMemberAccess(MemberExpression node, out BsonValue
             switch (node.Member.Name)
             {
                 case "Length":
-                    result = new BsonDocument("$strLenCP", field);
+                    var name = _stringTranslationMode == AggregateStringTranslationMode.CodePoints ?
+                        "$strLenCP" :
+                        "$strLenBytes";
+
+                    result = new BsonDocument(name, field);
                     return true;
             }
 
@@ -1123,11 +1127,9 @@ private bool TryTranslateStringMethodCall(MethodCallExpression node, out BsonVal
                 case "Substring":
                     if (node.Arguments.Count == 2)
                     {
-                        var name = "$substr";
-                        if (_stringTranslationMode == AggregateStringTranslationMode.CodePoints)
-                        {
-                            name = "$substrCP";
-                        }
+                        var name = _stringTranslationMode == AggregateStringTranslationMode.CodePoints ?
+                            "$substrCP" :
+                            "$substr";
                         result = new BsonDocument(name, new BsonArray(new[]
                             {
                                 field,

tests/MongoDB.Driver.Tests/Linq/Translators/AggregateProjectTranslatorTests.cs

@@ -1165,12 +1165,24 @@ public void Should_translate_select_with_an_anonymous_type_then_where_to_map_the
         }
 
         [SkippableFact]
-        public void Should_translate_string_length()
+        public void Should_translate_strLenBytes()
         {
             RequireServer.Where(minimumVersion: "3.3.4");
 
             var result = Project(x => new { Result = x.A.Length });
 
+            result.Projection.Should().Be("{ Result: { \"$strLenBytes\": \"$A\" }, _id: 0 }");
+
+            result.Value.Result.Should().Be(7);
+        }
+
+        [SkippableFact]
+        public void Should_translate_strLenCP()
+        {
+            RequireServer.Where(minimumVersion: "3.3.4");
+
+            var result = Project(x => new { Result = x.A.Length }, __codePointTranslationOptions);
+
             result.Projection.Should().Be("{ Result: { \"$strLenCP\": \"$A\" }, _id: 0 }");
 
             result.Value.Result.Should().Be(7);