Throw an exception on duplicate keys

Author: Chris Nussbaum

YamlDotNet.Test/Serialization/DeserializerTest.cs

@@ -24,6 +24,7 @@
 using System.Linq;
 using FluentAssertions;
 using Xunit;
+using YamlDotNet.Core;
 using YamlDotNet.Serialization;
 using YamlDotNet.Serialization.NamingConventions;
 
@@ -216,7 +217,6 @@ public void NewLinesInKeys()
             Assert.Equal($"value\na\nb", dictionary.First().Value);
         }
 
-        
         [Theory]
         [InlineData(".nan", System.Single.NaN)]
         [InlineData(".NaN", System.Single.NaN)]
@@ -283,6 +283,23 @@ public void DeserializeScalarEdgeCases(IConvertible value, Type type)
             result.Should().Be(value);
         }
 
+        [Fact]
+        public void Deserialize_YamlWithDuplicateKeys_ThrowsYamlException()
+        {
+            var yaml = @"
+name: Jack
+momentOfBirth: 1983-04-21T20:21:03.0041599Z
+name: Jake
+";
+
+            var sut = new DeserializerBuilder()
+                .WithNamingConvention(CamelCaseNamingConvention.Instance)
+                .Build();
+
+            Action act = () => sut.Deserialize<Person>(yaml);
+            act.ShouldThrow<YamlException>("Because there are duplicate name keys");
+        }
+
         public class Test
         {
             public string Value { get; set; }

YamlDotNet/Serialization/NodeDeserializers/ObjectNodeDeserializer.cs

@@ -20,6 +20,7 @@
 // SOFTWARE.
 
 using System;
+using System.Collections.Generic;
 using System.Runtime.Serialization;
 using YamlDotNet.Core;
 using YamlDotNet.Core.Events;
@@ -52,11 +53,17 @@ bool INodeDeserializer.Deserialize(IParser parser, Type expectedType, Func<IPars
             var implementationType = Nullable.GetUnderlyingType(expectedType) ?? expectedType;
 
             value = objectFactory.Create(implementationType);
+            var consumedProperties = new List<string>();
             while (!parser.TryConsume<MappingEnd>(out var _))
             {
                 var propertyName = parser.Consume<Scalar>();
+                if (consumedProperties.Contains(propertyName.Value))
+                {
+                    throw new YamlException(propertyName.Start, propertyName.End, $"Encountered duplicate property {propertyName.Value}");
+                }
                 try
                 {
+                    consumedProperties.Add(propertyName.Value);
                     var property = typeDescriptor.GetProperty(implementationType, null, propertyName.Value, ignoreUnmatched);
                     if (property == null)
                     {