feat: Remove default collection initialization for perf reasons

src/Microsoft.OpenApi/Models/OpenApiCallback.cs

@@ -13,17 +13,26 @@ namespace Microsoft.OpenApi.Models
     /// <summary>
     /// Callback Object: A map of possible out-of band callbacks related to the parent operation.
     /// </summary>
-    public class OpenApiCallback : IOpenApiReferenceable, IOpenApiExtensible, IOpenApiCallback
+    public class OpenApiCallback : IOpenApiExtensible, IOpenApiCallback
     {
+        private Lazy<Dictionary<RuntimeExpression, IOpenApiPathItem>>? _pathItems = new(() => []);
         /// <inheritdoc/>
-        public Dictionary<RuntimeExpression, IOpenApiPathItem>? PathItems { get; set; }
-            = [];
+        public Dictionary<RuntimeExpression, IOpenApiPathItem>? PathItems
+        {
+            get => _pathItems?.Value;
+            set => _pathItems = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
 
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor

src/Microsoft.OpenApi/Models/OpenApiComponents.cs

@@ -18,63 +18,115 @@
     /// </summary>
     public class OpenApiComponents : IOpenApiSerializable, IOpenApiExtensible
     {
+        private Lazy<IDictionary<string, IOpenApiSchema>>? _schemas = new(() => new Dictionary<string, IOpenApiSchema>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiSchema"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiSchema>? Schemas { get; set; } = new Dictionary<string, IOpenApiSchema>();
+        public IDictionary<string, IOpenApiSchema>? Schemas
+        {
+            get => _schemas?.Value;
+            set => _schemas = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiResponse>>? _responses = new(() => new Dictionary<string, IOpenApiResponse>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiResponse"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiResponse>? Responses { get; set; } = new Dictionary<string, IOpenApiResponse>();
+        public IDictionary<string, IOpenApiResponse>? Responses
+        {
+            get => _responses?.Value;
+            set => _responses = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiParameter>>? _parameters = new(() => new Dictionary<string, IOpenApiParameter>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiParameter"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiParameter>? Parameters { get; set; } =
-            new Dictionary<string, IOpenApiParameter>();
+        public IDictionary<string, IOpenApiParameter>? Parameters
+        {
+            get => _parameters?.Value;
+            set => _parameters = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiExample>>? _examples = new(() => new Dictionary<string, IOpenApiExample>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiExample"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiExample>? Examples { get; set; } = new Dictionary<string, IOpenApiExample>();
+        public IDictionary<string, IOpenApiExample>? Examples
+        {
+            get => _examples?.Value;
+            set => _examples = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiRequestBody>>? _requestBodies = new(() => new Dictionary<string, IOpenApiRequestBody>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiRequestBody"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiRequestBody>? RequestBodies { get; set; } =
-            new Dictionary<string, IOpenApiRequestBody>();
+        public IDictionary<string, IOpenApiRequestBody>? RequestBodies
+        {
+            get => _requestBodies?.Value;
+            set => _requestBodies = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiHeader>>? _headers = new(() => new Dictionary<string, IOpenApiHeader>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiHeader"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiHeader>? Headers { get; set; } = new Dictionary<string, IOpenApiHeader>();
+        public IDictionary<string, IOpenApiHeader>? Headers
+        {
+            get => _headers?.Value;
+            set => _headers = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiSecurityScheme>>? _securitySchemes = new(() => new Dictionary<string, IOpenApiSecurityScheme>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiSecurityScheme"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiSecurityScheme>? SecuritySchemes { get; set; } =
-            new Dictionary<string, IOpenApiSecurityScheme>();
+        public IDictionary<string, IOpenApiSecurityScheme>? SecuritySchemes
+        {
+            get => _securitySchemes?.Value;
+            set => _securitySchemes = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiLink>>? _links = new(() => new Dictionary<string, IOpenApiLink>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiLink"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiLink>? Links { get; set; } = new Dictionary<string, IOpenApiLink>();
+        public IDictionary<string, IOpenApiLink>? Links
+        {
+            get => _links?.Value;
+            set => _links = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiCallback>>? _callbacks = new(() => new Dictionary<string, IOpenApiCallback>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiCallback"/> Objects.
         /// </summary>
-        public IDictionary<string, IOpenApiCallback>? Callbacks { get; set; } = new Dictionary<string, IOpenApiCallback>();
+        public IDictionary<string, IOpenApiCallback>? Callbacks
+        {
+            get => _callbacks?.Value;
+            set => _callbacks = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiPathItem>>? _pathItems = new(() => new Dictionary<string, IOpenApiPathItem>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold reusable <see cref="IOpenApiPathItem"/> Object.
         /// </summary>
-        public IDictionary<string, IOpenApiPathItem>? PathItems { get; set; } = new Dictionary<string, IOpenApiPathItem>();
+        public IDictionary<string, IOpenApiPathItem>? PathItems
+        {
+            get => _pathItems?.Value;
+            set => _pathItems = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor
@@ -161,7 +213,7 @@
         /// <summary>
         /// Serialize <see cref="OpenApiComponents"/>.
         /// </summary>
         private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version,
             Action<IOpenApiWriter, IOpenApiSerializable> callback, Action<IOpenApiWriter, IOpenApiReferenceHolder> action)
         {
             // Serialize each referenceable object as full object without reference if the reference in the object points to itself.
@@ -320,7 +372,7 @@
         {
             var loops = writer.GetSettings().LoopDetector.Loops;
             writer.WriteStartObject();
             if (loops.TryGetValue(typeof(OpenApiSchema), out var schemas))
             {
                 writer.WriteOptionalMap(OpenApiConstants.Schemas, Schemas, callback);
             }

src/Microsoft.OpenApi/Models/OpenApiContact.cs

@@ -29,10 +29,15 @@ public class OpenApiContact : IOpenApiSerializable, IOpenApiExtensible
         /// </summary>
         public string? Email { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor

src/Microsoft.OpenApi/Models/OpenApiDiscriminator.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
+using System;
 using System.Collections.Generic;
 using Microsoft.OpenApi.Interfaces;
 using Microsoft.OpenApi.Writers;
@@ -17,15 +18,25 @@ public class OpenApiDiscriminator : IOpenApiSerializable, IOpenApiExtensible
         /// </summary>
         public string? PropertyName { get; set; }
 
+        private Lazy<IDictionary<string, string>>? _mapping = new(() => new Dictionary<string, string>(StringComparer.Ordinal));
         /// <summary>
         /// An object to hold mappings between payload values and schema names or references.
         /// </summary>
-        public IDictionary<string, string>? Mapping { get; set; } = new Dictionary<string, string>();
+        public IDictionary<string, string>? Mapping
+        {   
+            get => _mapping?.Value;
+            set => _mapping = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -48,33 +48,47 @@
         /// </summary>
         public Uri? JsonSchemaDialect { get; set; }
 
+        private Lazy<IList<OpenApiServer>>? _servers = new(() => []);
         /// <summary>
         /// An array of Server Objects, which provide connectivity information to a target server.
         /// </summary>
-        public IList<OpenApiServer>? Servers { get; set; } = new List<OpenApiServer>();
+        public IList<OpenApiServer>? Servers
+        {
+            get => _servers?.Value;
+            set => _servers = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// REQUIRED. The available paths and operations for the API.
         /// </summary>
         public OpenApiPaths Paths { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiPathItem>>? _webhooks = new(() => new Dictionary<string, IOpenApiPathItem>(StringComparer.Ordinal));
         /// <summary>
         /// The incoming webhooks that MAY be received as part of this API and that the API consumer MAY choose to implement.
         /// A map of requests initiated other than by an API call, for example by an out of band registration. 
         /// The key name is a unique string to refer to each webhook, while the (optionally referenced) Path Item Object describes a request that may be initiated by the API provider and the expected responses
         /// </summary>
-        public IDictionary<string, IOpenApiPathItem>? Webhooks { get; set; } = new Dictionary<string, IOpenApiPathItem>();
+        public IDictionary<string, IOpenApiPathItem>? Webhooks
+        {
+            get => _webhooks?.Value;
+            set => _webhooks = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// An element to hold various schemas for the specification.
         /// </summary>
         public OpenApiComponents? Components { get; set; }
 
+        private Lazy<IList<OpenApiSecurityRequirement>>? _security = new(() => []);
         /// <summary>
         /// A declaration of which security mechanisms can be used across the API.
         /// </summary>
-        public IList<OpenApiSecurityRequirement>? Security { get; set; } =
-            new List<OpenApiSecurityRequirement>();
+        public IList<OpenApiSecurityRequirement>? Security
+        {
+            get => _security?.Value;
+            set => _security = value is null ? null : new(() => value);
+        }
 
         private HashSet<OpenApiTag>? _tags;
         /// <summary>
@@ -103,10 +117,15 @@
         /// </summary>
         public OpenApiExternalDocs? ExternalDocs { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <inheritdoc />
         public IDictionary<string, object>? Metadata { get; set; }
@@ -268,7 +287,7 @@
         /// <summary>
         /// Serialize <see cref="OpenApiDocument"/> to OpenAPI object V2.0.
         /// </summary>
         public void SerializeAsV2(IOpenApiWriter writer)
         {
             Utils.CheckArgumentNull(writer);
 
@@ -420,7 +439,7 @@
             return server.ReplaceServerUrlVariables(new Dictionary<string, string>(0));
         }
 
         private static void WriteHostInfoV2(IOpenApiWriter writer, IList<OpenApiServer>? servers)
         {
             if (servers == null || !servers.Any())
             {
@@ -489,7 +508,7 @@
                 // schemes
                 writer.WriteOptionalCollection(OpenApiConstants.Schemes, schemes, (w, s) => 
                 {
                     if(!string.IsNullOrEmpty(s) && s is not null)
                     {
                         w.WriteValue(s);
                     }
@@ -574,7 +593,7 @@
             }
             else
             {
                 string relativePath = OpenApiConstants.ComponentsSegment + reference.Type.GetDisplayName() + "/" + id;
 
                 uriLocation = useExternal
                     ? Workspace?.GetDocumentId(reference.ExternalResource)?.OriginalString + relativePath

src/Microsoft.OpenApi/Models/OpenApiEncoding.cs

@@ -22,10 +22,15 @@ public class OpenApiEncoding : IOpenApiSerializable, IOpenApiExtensible
         /// </summary>
         public string? ContentType { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiHeader>>? _headers = new(() => new Dictionary<string, IOpenApiHeader>());
         /// <summary>
         /// A map allowing additional information to be provided as headers.
         /// </summary>
-        public IDictionary<string, IOpenApiHeader>? Headers { get; set; } = new Dictionary<string, IOpenApiHeader>();
+        public IDictionary<string, IOpenApiHeader>? Headers
+        {
+            get => _headers?.Value;
+            set => _headers = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Describes how a specific property value will be serialized depending on its type.
@@ -49,10 +54,15 @@ public class OpenApiEncoding : IOpenApiSerializable, IOpenApiExtensible
         /// </summary>
         public bool? AllowReserved { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor

src/Microsoft.OpenApi/Models/OpenApiExample.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
+using System;
 using System.Collections.Generic;
 using System.Text.Json.Nodes;
 using Microsoft.OpenApi.Helpers;
@@ -13,7 +14,7 @@ namespace Microsoft.OpenApi.Models
     /// <summary>
     /// Example Object.
     /// </summary>
-    public class OpenApiExample : IOpenApiReferenceable, IOpenApiExtensible, IOpenApiExample
+    public class OpenApiExample : IOpenApiExtensible, IOpenApiExample
     {
         /// <inheritdoc/>
         public string? Summary { get; set; }
@@ -27,8 +28,13 @@ public class OpenApiExample : IOpenApiReferenceable, IOpenApiExtensible, IOpenAp
         /// <inheritdoc/>
         public JsonNode? Value { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <inheritdoc/>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor

src/Microsoft.OpenApi/Models/OpenApiExternalDocs.cs

@@ -23,10 +23,15 @@ public class OpenApiExternalDocs : IOpenApiSerializable, IOpenApiExtensible
         /// </summary>
         public Uri? Url { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor

src/Microsoft.OpenApi/Models/OpenApiHeader.cs

@@ -46,14 +46,29 @@ public class OpenApiHeader : IOpenApiHeader, IOpenApiExtensible
         /// <inheritdoc/>
         public JsonNode? Example { get; set; }
 
+        private Lazy<IDictionary<string, IOpenApiExample>>? _examples = new(() => new Dictionary<string, IOpenApiExample>(StringComparer.Ordinal));
         /// <inheritdoc/>
-        public IDictionary<string, IOpenApiExample>? Examples { get; set; } = new Dictionary<string, IOpenApiExample>();
+        public IDictionary<string, IOpenApiExample>? Examples
+        {
+            get => _examples?.Value;
+            set => _examples = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, OpenApiMediaType>>? _content = new(() => new Dictionary<string, OpenApiMediaType>(StringComparer.Ordinal));
         /// <inheritdoc/>
-        public IDictionary<string, OpenApiMediaType>? Content { get; set; } = new Dictionary<string, OpenApiMediaType>();
+        public IDictionary<string, OpenApiMediaType>? Content
+        {
+            get => _content?.Value;
+            set => _content = value is null ? null : new(() => value);
+        }
 
+        private Lazy<IDictionary<string, IOpenApiExtension>>? _extensions = new(() => new Dictionary<string, IOpenApiExtension>(StringComparer.Ordinal));
         /// <inheritdoc/>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions
+        {
+            get => _extensions?.Value;
+            set => _extensions = value is null ? null : new(() => value);
+        }
 
         /// <summary>
         /// Parameter-less constructor