Sort required properties of schemas

Restore sorting of `required` in schemas.

Author: martincostello

src/Swashbuckle.AspNetCore.Annotations/AnnotationsSchemaFilter.cs

@@ -112,9 +112,9 @@ private static void ApplySchemaAttribute(IOpenApiSchema schema, SwaggerSchemaAtt
             }
         }
 
-        if (schemaAttribute.Required is { } required)
+        if (schemaAttribute.Required is { Length: > 1 } required)
         {
-            concrete.Required = [.. required];
+            concrete.Required = [.. new SortedSet<string>(required)];
         }
 
         if (schemaAttribute.Title is { } title)

src/Swashbuckle.AspNetCore.SwaggerGen/SwaggerGenerator/SwaggerGenerator.cs

@@ -70,7 +70,7 @@ public async Task<OpenApiDocument> GetSwaggerAsync(
             filter.Apply(document, filterContext);
         }
 
-        SortSchemas(document);
+        SortDocument(document);
 
         return document;
     }
@@ -102,7 +102,7 @@ public OpenApiDocument GetSwagger(string documentName, string host = null, strin
                 filter.Apply(document, filterContext);
             }
 
-            SortSchemas(document);
+            SortDocument(document);
 
             return document;
         }
@@ -129,11 +129,24 @@ public OpenApiDocument GetSwagger(string documentName, string host = null, strin
 
     public IList<string> GetDocumentNames() => [.. _options.SwaggerDocs.Keys];
 
-    private void SortSchemas(OpenApiDocument document)
+    private void SortDocument(OpenApiDocument document)
     {
         document.Components.Schemas =
             new SortedDictionary<string, IOpenApiSchema>(document.Components.Schemas, _options.SchemaComparer)
             .ToDictionary((k) => k.Key, (v) => v.Value);
+
+        foreach (var schema in document.Components.Schemas.Values)
+        {
+            SortSchemas(schema);
+        }
+
+        static void SortSchemas(IOpenApiSchema schema)
+        {
+            if (schema is OpenApiSchema { Required.Count: > 1 } concrete)
+            {
+                concrete.Required = [.. new SortedSet<string>(concrete.Required)];
+            }
+        }
     }
 
     private (DocumentFilterContext, OpenApiDocument) GetSwaggerDocumentWithoutPaths(string documentName, string host = null, string basePath = null)