Implemented CSHARP-313. Give a more useful error message when attempting to write a scalar value to the root of a BSON document.

Bson/IO/BsonWriter.cs

@@ -746,8 +746,24 @@ namespace MongoDB.Bson.IO {
             string methodName,
             params BsonWriterState[] validStates
         ) {
+            string message;
+            if (state == BsonWriterState.Initial || state == BsonWriterState.ScopeDocument || state == BsonWriterState.Done) {
+                if (!methodName.StartsWith("End") && methodName != "WriteName") {
+                    var typeName = methodName.Substring(5);
+                    if (typeName.StartsWith("Start")) { 
+                        typeName = typeName.Substring(5);
+                    }
+                    var article = "A";
+                    if (new char[] { 'A', 'E', 'I', 'O', 'U' }.Contains(typeName[0])) {
+                        article = "An";
+                    }
+                    message = string.Format("{0} {1} value cannot be written to the root level of a BSON document.", article, typeName);
+                    throw new InvalidOperationException(message);
+                }
+            }
+
             var validStatesString = string.Join(" or ", validStates.Select(s => s.ToString()).ToArray());
-            var message = string.Format("{0} can only be called when State is {1}, not when State is {2}", methodName, validStatesString, state);
+            message = string.Format("{0} can only be called when State is {1}, not when State is {2}", methodName, validStatesString, state);
             throw new InvalidOperationException(message);
         }
         #endregion

BsonUnitTests/BsonUnitTests.csproj

@@ -131,6 +131,7 @@
     <Compile Include="Jira\CSharp276Tests.cs" />
     <Compile Include="Jira\CSharp293Tests.cs" />
     <Compile Include="Jira\CSharp311Tests.cs" />
+    <Compile Include="Jira\CSharp313Tests.cs" />
     <Compile Include="Jira\CSharp70Tests.cs" />
     <Compile Include="Jira\CSharp71Tests.cs" />
     <Compile Include="Jira\CSharp74Tests.cs" />

BsonUnitTests/Jira/CSharp313Tests.cs

@@ -0,0 +1,60 @@
+/* Copyright 2010-2011 10gen 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;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Bson.Serialization.Options;
+
+namespace MongoDB.BsonUnitTests.Jira {
+    [TestFixture]
+    public class CSharp313Tests {
+        private static object[] scalarValues = new object[] {
+            new BsonBinaryData(new byte[] { 1, 2, 3 }),
+            true,
+            DateTime.UtcNow,
+            1.2,
+            1,
+            1L,
+            new BsonJavaScript("this.x == 1"),
+            new BsonJavaScriptWithScope("this.x == y", new BsonDocument("y", 1)),
+            BsonMaxKey.Value,
+            BsonMinKey.Value,
+            BsonNull.Value,
+            ObjectId.GenerateNewId(),
+            new BsonRegularExpression("abc"),
+            new BsonArray { 1, 2 },
+            "abc",
+            BsonSymbol.Create("abc"),
+            new BsonTimestamp(1234L),
+            BsonUndefined.Value
+        };
+
+        [Test]
+        public void TestStringToBson() {
+            foreach (var scalarValue in scalarValues) {
+                Assert.Throws<InvalidOperationException>(() => { var bson = scalarValue.ToBson(); });
+                Assert.Throws<InvalidOperationException>(() => { var bson = scalarValue.ToBsonDocument(); });
+            }
+        }
+    }
+}