Make duplicate key checking optional

Author: Chris Nussbaum

YamlDotNet.Test/Serialization/DeserializerTest.cs

@@ -284,7 +284,7 @@ public void DeserializeScalarEdgeCases(IConvertible value, Type type)
         }
 
         [Fact]
-        public void Deserialize_YamlWithDuplicateKeys_ThrowsYamlException()
+        public void DeserializeWithDuplicateKeyChecking_YamlWithDuplicateKeys_ThrowsYamlException()
         {
             var yaml = @"
 name: Jack
@@ -294,12 +294,30 @@ public void Deserialize_YamlWithDuplicateKeys_ThrowsYamlException()
 
             var sut = new DeserializerBuilder()
                 .WithNamingConvention(CamelCaseNamingConvention.Instance)
+                .WithDuplicateKeyChecking()
                 .Build();
 
             Action act = () => sut.Deserialize<Person>(yaml);
             act.ShouldThrow<YamlException>("Because there are duplicate name keys");
         }
 
+        [Fact]
+        public void DeserializeWithoutDuplicateKeyChecking_YamlWithDuplicateKeys_DoesNotThrowYamlException()
+        {
+            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.ShouldNotThrow<YamlException>("Because duplicate key checking is not enabled");
+        }
+
         public class Test
         {
             public string Value { get; set; }

YamlDotNet.Test/Serialization/SerializationTests.cs

@@ -1312,6 +1312,7 @@ public void IgnoreExtraPropertiesIfWantedNamingScheme()
                     "scratch: 'scratcher'",
                     "deleteScratch: false",
                     "notScratch: 9443",
+                    "notScratch: 192.168.1.30",
                     "mappedScratch:",
                     "- '/work/'"
                 );

YamlDotNet/Serialization/DeserializerBuilder.cs

@@ -47,6 +47,7 @@ public sealed class DeserializerBuilder : BuilderSkeleton<DeserializerBuilder>
         private readonly Dictionary<TagName, Type> tagMappings;
         private readonly Dictionary<Type, Type> typeMappings;
         private bool ignoreUnmatched;
+        private bool duplicateKeyChecking;
         private bool attemptUnknownTypeDeserialization;
 
         /// <summary>
@@ -85,7 +86,7 @@ public DeserializerBuilder()
                 { typeof(DictionaryNodeDeserializer), _ => new DictionaryNodeDeserializer(objectFactory.Value) },
                 { typeof(CollectionNodeDeserializer), _ => new CollectionNodeDeserializer(objectFactory.Value) },
                 { typeof(EnumerableNodeDeserializer), _ => new EnumerableNodeDeserializer() },
-                { typeof(ObjectNodeDeserializer), _ => new ObjectNodeDeserializer(objectFactory.Value, BuildTypeInspector(), ignoreUnmatched) }
+                { typeof(ObjectNodeDeserializer), _ => new ObjectNodeDeserializer(objectFactory.Value, BuildTypeInspector(), ignoreUnmatched, duplicateKeyChecking) }
             };
 
             nodeTypeResolverFactories = new LazyComponentRegistrationList<Nothing, INodeTypeResolver>
@@ -388,6 +389,16 @@ public DeserializerBuilder IgnoreUnmatchedProperties()
             return this;
         }
 
+        /// <summary>
+        /// Instructs the deserializer to check for duplicate keys and throw an exception if duplicate keys are found.
+        /// </summary>
+        /// <returns></returns>
+        public DeserializerBuilder WithDuplicateKeyChecking()
+        {
+            duplicateKeyChecking = true;
+            return this;
+        }
+
         /// <summary>
         /// Creates a new <see cref="Deserializer" /> according to the current configuration.
         /// </summary>

YamlDotNet/Serialization/NodeDeserializers/ObjectNodeDeserializer.cs

@@ -33,12 +33,14 @@ public sealed class ObjectNodeDeserializer : INodeDeserializer
         private readonly IObjectFactory objectFactory;
         private readonly ITypeInspector typeDescriptor;
         private readonly bool ignoreUnmatched;
+        private readonly bool duplicateKeyChecking;
 
-        public ObjectNodeDeserializer(IObjectFactory objectFactory, ITypeInspector typeDescriptor, bool ignoreUnmatched)
+        public ObjectNodeDeserializer(IObjectFactory objectFactory, ITypeInspector typeDescriptor, bool ignoreUnmatched, bool duplicateKeyChecking)
         {
             this.objectFactory = objectFactory ?? throw new ArgumentNullException(nameof(objectFactory));
             this.typeDescriptor = typeDescriptor ?? throw new ArgumentNullException(nameof(typeDescriptor));
             this.ignoreUnmatched = ignoreUnmatched;
+            this.duplicateKeyChecking = duplicateKeyChecking;
         }
 
         bool INodeDeserializer.Deserialize(IParser parser, Type expectedType, Func<IParser, Type, object?> nestedObjectDeserializer, out object? value)
@@ -57,9 +59,9 @@ bool INodeDeserializer.Deserialize(IParser parser, Type expectedType, Func<IPars
             while (!parser.TryConsume<MappingEnd>(out var _))
             {
                 var propertyName = parser.Consume<Scalar>();
-                if (consumedProperties.Contains(propertyName.Value))
+                if (duplicateKeyChecking && consumedProperties.Contains(propertyName.Value))
                 {
-                    throw new YamlException(propertyName.Start, propertyName.End, $"Encountered duplicate property {propertyName.Value}");
+                    throw new YamlException(propertyName.Start, propertyName.End, $"Encountered duplicate key {propertyName.Value}");
                 }
                 try
                 {