fix: address PR feedback on UnevaluatedProperties implementation

- Simplify copy constructor using pattern matching
- Add V3.2 deserialization support for UnevaluatedPropertiesSchema
- Add test for default value (no property set, defaults to true)
- Emit as x-jsonschema-unevaluatedProperties extension for versions < 3.1
- Add comprehensive tests for extension serialization in V2 and V3.0
- Add V3.2 deserialization tests

Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

Author: Copilot

src/Microsoft.OpenApi/Models/OpenApiSchema.cs

@@ -280,9 +280,9 @@ internal OpenApiSchema(IOpenApiSchema schema)
             DynamicRef = schema.DynamicRef ?? DynamicRef;
             Definitions = schema.Definitions != null ? new Dictionary<string, IOpenApiSchema>(schema.Definitions) : null;
             UnevaluatedProperties = schema.UnevaluatedProperties;
-            if (schema is IOpenApiSchemaWithUnevaluatedProperties schemaWithUnevaluated)
+            if (schema is IOpenApiSchemaWithUnevaluatedProperties { UnevaluatedPropertiesSchema: { } unevaluatedSchema })
             {
-                UnevaluatedPropertiesSchema = schemaWithUnevaluated.UnevaluatedPropertiesSchema?.CreateShallowCopy();
+                UnevaluatedPropertiesSchema = unevaluatedSchema.CreateShallowCopy();
             }
             ExclusiveMaximum = schema.ExclusiveMaximum ?? ExclusiveMaximum;
             ExclusiveMinimum = schema.ExclusiveMinimum ?? ExclusiveMinimum;
@@ -539,9 +539,29 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // deprecated
             writer.WriteProperty(OpenApiConstants.Deprecated, Deprecated, false);
 
+            // For versions < 3.1, write unevaluatedProperties as an extension
+            if (version < OpenApiSpecVersion.OpenApi3_1)
+            {
+                // Write UnevaluatedPropertiesSchema as extension if present
+                if (UnevaluatedPropertiesSchema is not null)
+                {
+                    writer.WriteOptionalObject(
+                        "x-jsonschema-unevaluatedProperties",
+                        UnevaluatedPropertiesSchema,
+                        callback);
+                }
+                // Write boolean false as extension if explicitly set to false
+                else if (!UnevaluatedProperties)
+                {
+                    writer.WritePropertyName("x-jsonschema-unevaluatedProperties");
+                    writer.WriteValue(false);
+                }
+            }
+
             // extensions
             writer.WriteExtensions(Extensions, version);
 
+
             // Unrecognized keywords
             if (UnrecognizedKeywords is not null && UnrecognizedKeywords.Any())
             {
@@ -795,6 +815,21 @@ private void SerializeAsV2(
             // x-nullable extension
             SerializeNullable(writer, OpenApiSpecVersion.OpenApi2_0);
 
+            // Write UnevaluatedPropertiesSchema as extension if present
+            if (UnevaluatedPropertiesSchema is not null)
+            {
+                writer.WriteOptionalObject(
+                    "x-jsonschema-unevaluatedProperties",
+                    UnevaluatedPropertiesSchema,
+                    (w, s) => s.SerializeAsV2(w));
+            }
+            // Write boolean false as extension if explicitly set to false
+            else if (!UnevaluatedProperties)
+            {
+                writer.WritePropertyName("x-jsonschema-unevaluatedProperties");
+                writer.WriteValue(false);
+            }
+
             // extensions
             writer.WriteExtensions(Extensions, OpenApiSpecVersion.OpenApi2_0);
 

test/Microsoft.OpenApi.Readers.Tests/V31Tests/OpenApiSchemaTests.cs

@@ -815,5 +815,34 @@ public void ParseSchemaWithUnevaluatedPropertiesComplexSchema()
             // Assert
             Assert.Equivalent(expected, actual);
         }
+
+        [Fact]
+        public void ParseSchemaWithoutUnevaluatedPropertiesDefaultsToTrue()
+        {
+            // Arrange - no unevaluatedProperties property should default to true (allow all)
+            var schema = @"{
+  ""type"": ""object"",
+  ""properties"": {
+    ""name"": { ""type"": ""string"" }
+  }
+}";
+
+            var expected = new OpenApiSchema()
+            {
+                Type = JsonSchemaType.Object,
+                Properties = new Dictionary<string, IOpenApiSchema>
+                {
+                    ["name"] = new OpenApiSchema { Type = JsonSchemaType.String }
+                },
+                UnevaluatedProperties = true // Default value
+            };
+
+            // Act
+            var actual = OpenApiModelFactory.Parse<OpenApiSchema>(schema, OpenApiSpecVersion.OpenApi3_1, new(), out _);
+
+            // Assert
+            Assert.Equivalent(expected, actual);
+            Assert.True(actual.UnevaluatedProperties); // Explicitly verify the default
+        }
     }
 }

test/Microsoft.OpenApi.Tests/Models/OpenApiSchemaTests.cs

@@ -1234,10 +1234,10 @@ public async Task SerializeUnevaluatedPropertiesSchemaTakesPrecedenceOverBoolean
         [Theory]
         [InlineData(OpenApiSpecVersion.OpenApi2_0)]
         [InlineData(OpenApiSpecVersion.OpenApi3_0)]
-        public async Task SerializeUnevaluatedPropertiesNotEmittedInEarlierVersions(OpenApiSpecVersion version)
+        public async Task SerializeUnevaluatedPropertiesAsExtensionInEarlierVersions(OpenApiSpecVersion version)
         {
-            var expected = @"{ }";
-            // Given - UnevaluatedProperties should not be emitted in versions < 3.1
+            var expected = @"{ ""x-jsonschema-unevaluatedProperties"": false }";
+            // Given - UnevaluatedProperties should be emitted as extension in versions < 3.1
             var schema = new OpenApiSchema
             {
                 UnevaluatedProperties = false
@@ -1250,6 +1250,47 @@ public async Task SerializeUnevaluatedPropertiesNotEmittedInEarlierVersions(Open
             Assert.True(JsonNode.DeepEquals(JsonNode.Parse(expected), JsonNode.Parse(actual)));
         }
 
+        [Theory]
+        [InlineData(OpenApiSpecVersion.OpenApi2_0)]
+        [InlineData(OpenApiSpecVersion.OpenApi3_0)]
+        public async Task SerializeUnevaluatedPropertiesSchemaAsExtensionInEarlierVersions(OpenApiSpecVersion version)
+        {
+            var expected = @"{ ""x-jsonschema-unevaluatedProperties"": { ""type"": ""string"" } }";
+            // Given - UnevaluatedPropertiesSchema should be emitted as extension in versions < 3.1
+            var schema = new OpenApiSchema
+            {
+                UnevaluatedPropertiesSchema = new OpenApiSchema
+                {
+                    Type = JsonSchemaType.String
+                }
+            };
+
+            // When
+            var actual = await schema.SerializeAsJsonAsync(version);
+
+            // Then
+            Assert.True(JsonNode.DeepEquals(JsonNode.Parse(expected), JsonNode.Parse(actual)));
+        }
+
+        [Theory]
+        [InlineData(OpenApiSpecVersion.OpenApi2_0)]
+        [InlineData(OpenApiSpecVersion.OpenApi3_0)]
+        public async Task SerializeUnevaluatedPropertiesTrueNotEmittedInEarlierVersions(OpenApiSpecVersion version)
+        {
+            var expected = @"{ }";
+            // Given - UnevaluatedProperties true (default) should not be emitted even as extension
+            var schema = new OpenApiSchema
+            {
+                UnevaluatedProperties = true
+            };
+
+            // When
+            var actual = await schema.SerializeAsJsonAsync(version);
+
+            // Then
+            Assert.True(JsonNode.DeepEquals(JsonNode.Parse(expected), JsonNode.Parse(actual)));
+        }
+
         internal class SchemaVisitor : OpenApiVisitorBase
         {
             public List<string> Titles = new();