Allow omitting empty collections via DefaultValuesHandling

YamlDotNet.Test/Serialization/EmitDefaultValuesTests.cs

@@ -19,7 +19,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+using System.Collections.Generic;
 using System.ComponentModel;
+using System.Linq;
 using Xunit;
 using YamlDotNet.Serialization;
 
@@ -44,6 +46,20 @@ private class Model
             public int? ANullableNonZeroInteger => 1;
             [DefaultValue(2)] public int? ANullableNonZeroDefaultInteger => 2;
             [DefaultValue(2)] public int? ANullableNonZeroNonDefaultInteger => 1;
+
+            // Enumerables
+            public IList<int> ANullList => null;
+
+            public int[] AnEmptyArray => new int[0];
+            public IList<int> AnEmptyList => new List<int>();
+            public Dictionary<string, string> AnEmptyDictionary => new Dictionary<string, string>();
+            public IEnumerable<int> AnEmptyEnumerable => Enumerable.Empty<int>();
+
+            public string[] AnNonEmptyArray => new[] { "foo", "bar" };
+            public IList<int> AnNonEmptyList => new List<int> { 6, 9, 42 };
+            public IEnumerable<bool> ANonEmptyEnumerable => new[] { true, false };
+            public Dictionary<string, string> ANonEmptyDictionary => new Dictionary<string, string>() { { "foo", "bar" } };
+
         }
 
         [Fact]
@@ -74,12 +90,14 @@ public void All_default_values_and_nulls_are_emitted_when_no_configuration_is_pe
             Assert.Contains(nameof(Model.ANullableNonZeroNonDefaultInteger) + ':', yaml);
         }
 
-        [Fact]
-        public void Only_null_values_are_omitted_when_DefaultValuesHandling_is_OmitNull()
+        [Theory]
+        [InlineData(DefaultValuesHandling.OmitNull)]
+        [InlineData(DefaultValuesHandling.OmitNullOrEmpty)]
+        public void Only_null_values_are_omitted_when_DefaultValuesHandling_is_OmitNull(DefaultValuesHandling defaultValuesHandling)
         {
             // Arrange
             var sut = new SerializerBuilder()
-                .ConfigureDefaultValuesHandling(DefaultValuesHandling.OmitNull)
+                .ConfigureDefaultValuesHandling(defaultValuesHandling)
                 .Build();
 
             // Act
@@ -103,12 +121,14 @@ public void Only_null_values_are_omitted_when_DefaultValuesHandling_is_OmitNull(
             Assert.Contains(nameof(Model.ANullableNonZeroNonDefaultInteger) + ':', yaml);
         }
 
-        [Fact]
-        public void All_default_values_are_omitted_when_DefaultValuesHandling_is_OmitAll()
+        [Theory]
+        [InlineData(DefaultValuesHandling.OmitDefaults)]
+        [InlineData(DefaultValuesHandling.OmitDefaultsOrEmpty)]
+        public void All_default_values_are_omitted_when_DefaultValuesHandling_is_OmitDefaults(DefaultValuesHandling defaultValuesHandling)
         {
             // Arrange
             var sut = new SerializerBuilder()
-                .ConfigureDefaultValuesHandling(DefaultValuesHandling.OmitDefaults)
+                .ConfigureDefaultValuesHandling(defaultValuesHandling)
                 .Build();
 
             // Act
@@ -132,6 +152,33 @@ public void All_default_values_are_omitted_when_DefaultValuesHandling_is_OmitAll
             Assert.Contains(nameof(Model.ANullableNonZeroNonDefaultInteger) + ':', yaml);
         }
 
+        [Theory]
+        [InlineData(DefaultValuesHandling.OmitNullOrEmpty)]
+        [InlineData(DefaultValuesHandling.OmitDefaultsOrEmpty)]
+        public void Empty_enumerables_are_omitted_when_DefaultValuesHandling_is_OmitDefaultsOrEmpty(DefaultValuesHandling defaultValuesHandling)
+        {
+            // Arrange
+            var sut = new SerializerBuilder()
+                .ConfigureDefaultValuesHandling(DefaultValuesHandling.OmitDefaultsOrEmpty)
+                .Build();
+
+            // Act
+            var yaml = sut.Serialize(new Model());
+
+            // Assert enumerables
+            Assert.DoesNotContain(nameof(Model.ANullList) + ':', yaml);
+
+            Assert.DoesNotContain(nameof(Model.AnEmptyArray) + ':', yaml);
+            Assert.DoesNotContain(nameof(Model.AnEmptyList) + ':', yaml);
+            Assert.DoesNotContain(nameof(Model.AnEmptyDictionary) + ':', yaml);
+            Assert.DoesNotContain(nameof(Model.AnEmptyEnumerable) + ':', yaml);
+
+            Assert.Contains(nameof(Model.AnNonEmptyArray) + ':', yaml);
+            Assert.Contains(nameof(Model.AnNonEmptyList) + ':', yaml);
+            Assert.Contains(nameof(Model.ANonEmptyEnumerable) + ':', yaml);
+            Assert.Contains(nameof(Model.ANonEmptyDictionary) + ':', yaml);
+        }
+
         [Fact]
         public void YamlMember_overrides_default_value_handling()
         {

YamlDotNet/Serialization/DefaultValuesHandling.cs

@@ -36,9 +36,19 @@ public enum DefaultValuesHandling
         /// </summary>
         OmitNull,
 
+        /// <summary>
+        /// More relaxed than OmitNull - omits null values and also collections/arrays/enumerations that are empty.
+        /// </summary>
+        OmitNullOrEmpty,
+
         /// <summary>
         /// Specifies that properties that that contain their default value, either default(T) or the value specified in DefaultValueAttribute are to be omitted. 
         /// </summary>
         OmitDefaults,
+
+        /// <summary>
+        /// More relaxed than OmitDefaults - omits default values and also collections/arrays/enumerations that are empty.
+        /// </summary>
+        OmitDefaultsOrEmpty,
     }
 }

YamlDotNet/Serialization/NodeTypeResolvers/MappingNodeTypeResolver.cs

@@ -31,7 +31,10 @@ public class MappingNodeTypeResolver : INodeTypeResolver
 
         public MappingNodeTypeResolver(IDictionary<Type, Type> mappings)
         {
-            if (mappings == null) throw new ArgumentNullException(nameof(mappings));
+            if (mappings == null)
+            {
+                throw new ArgumentNullException(nameof(mappings));
+            }
 
             foreach (var pair in mappings)
             {

YamlDotNet/Serialization/ObjectGraphVisitors/DefaultValuesObjectGraphVisitor.cs

@@ -20,6 +20,7 @@
 // SOFTWARE.
 
 using System;
+using System.Collections;
 using System.ComponentModel;
 using YamlDotNet.Core;
 
@@ -58,13 +59,29 @@ public override bool EnterMapping(IPropertyDescriptor key, IObjectDescriptor val
                     }
                     break;
 
+                case DefaultValuesHandling.OmitNullOrEmpty:
+                    if (value.Value is IEnumerable enumerable && !enumerable.GetEnumerator().MoveNext())
+                    {
+                        return false;
+                    }
+
+                    goto case DefaultValuesHandling.OmitNull;
+
                 case DefaultValuesHandling.OmitDefaults:
                     var defaultValue = key.GetCustomAttribute<DefaultValueAttribute>()?.Value ?? GetDefault(key.Type);
                     if (Equals(value.Value, defaultValue))
                     {
                         return false;
                     }
                     break;
+
+                case DefaultValuesHandling.OmitDefaultsOrEmpty:
+                    if (value.Value is IEnumerable ienumerable && !ienumerable.GetEnumerator().MoveNext())
+                    {
+                        return false;
+                    }
+
+                    goto case DefaultValuesHandling.OmitDefaults;
             }
 
             return base.EnterMapping(key, value, context);