feat: Remove default collection initialization for perf reasons (#2284)

* feat: use lazy get for collection initialization to reduce resource allocation

* chore: use Lazy<T> pattern; preserve null values

* chore: replicate for collections in other components

* chore: remove unnecessary usings

* fix: revert lazy initialization; remove collection initialization

* chore: initialize collections to prevent NREs

* chore: fix failing tests

* chore: revert changes

* chore: remove default collection initialization across all models; clean up and fix tests

* chore: clean up code; initialize collections where applicable

* chore: more cleanup

* chore: move assignment within the condition

* chore: replace interface with concrete type

* chore: simplify collection initialization

* Update src/Microsoft.OpenApi/Models/OpenApiPathItem.cs

Co-authored-by: Vincent Biret <vibiret@microsoft.com>

* chore: implement PR feedback

* chore: reverts casing change

---------

Co-authored-by: Vincent Biret <vibiret@microsoft.com>

Author: MaggieKimani1

README.md

@@ -55,7 +55,7 @@ var document = new OpenApiDocument
     {
         ["/pets"] = new OpenApiPathItem
         {
-            Operations = new Dictionary<HttpMethod, OpenApiOperation>
+            Operations = new()
             {
                 [HttpMethod.Get] = new OpenApiOperation
                 {

src/Microsoft.OpenApi.Hidi/Extensions/OpenApiExtensibleExtensions.cs

@@ -13,7 +13,7 @@ internal static class OpenApiExtensibleExtensions
         /// <param name="extensions">A dictionary of <see cref="IOpenApiExtension"/>.</param>
         /// <param name="extensionKey">The key corresponding to the <see cref="IOpenApiExtension"/>.</param>
         /// <returns>A <see cref="string"/> value matching the provided extensionKey. Return null when extensionKey is not found. </returns>
-        internal static string GetExtension(this IDictionary<string, IOpenApiExtension> extensions, string extensionKey)
+        internal static string GetExtension(this Dictionary<string, IOpenApiExtension> extensions, string extensionKey)
         {
             if (extensions.TryGetValue(extensionKey, out var value) && value is OpenApiAny { Node: JsonValue castValue } && castValue.TryGetValue<string>(out var stringValue))
             {

src/Microsoft.OpenApi.Hidi/Extensions/StringExtensions.cs

@@ -34,7 +34,7 @@ public static bool IsEquals(this string? target, string? searchValue, StringComp
         /// <param name="target">The target string to split by char. </param>
         /// <param name="separator">The char separator.</param>
         /// <returns>An <see cref="IList{String}"/> containing substrings.</returns>
-        public static IList<string> SplitByChar(this string target, char separator)
+        public static List<string> SplitByChar(this string target, char separator)
         {
             if (string.IsNullOrWhiteSpace(target))
             {

src/Microsoft.OpenApi.Hidi/Formatters/PowerShellFormatter.cs

@@ -77,7 +77,7 @@ public override void Visit(OpenApiOperation operation)
             // Order matters. Resolve operationId.
             operationId = RemoveHashSuffix(operationId);
             if (operationTypeExtension.IsEquals("action") || operationTypeExtension.IsEquals("function"))
-                operationId = RemoveKeyTypeSegment(operationId, operation.Parameters ?? new List<IOpenApiParameter>());
+                operationId = RemoveKeyTypeSegment(operationId, operation.Parameters ?? []);
             operationId = SingularizeAndDeduplicateOperationId(operationId.SplitByChar('.'));
             operationId = ResolveODataCastOperationId(operationId);
             operationId = ResolveByRefOperationId(operationId);
@@ -119,7 +119,7 @@ private static string ResolveODataCastOperationId(string operationId)
             return match.Success ? $"{match.Groups[1]}{match.Groups[2]}" : operationId;
         }
 
-        private static string SingularizeAndDeduplicateOperationId(IList<string> operationIdSegments)
+        private static string SingularizeAndDeduplicateOperationId(List<string> operationIdSegments)
         {
             var segmentsCount = operationIdSegments.Count;
             var lastSegmentIndex = segmentsCount - 1;
@@ -145,7 +145,7 @@ private static string RemoveHashSuffix(string operationId)
             return s_hashSuffixRegex.Match(operationId).Value;
         }
 
-        private static string RemoveKeyTypeSegment(string operationId, IList<IOpenApiParameter> parameters)
+        private static string RemoveKeyTypeSegment(string operationId, List<IOpenApiParameter> parameters)
         {
             var segments = operationId.SplitByChar('.');
             foreach (var parameter in parameters)
@@ -159,9 +159,9 @@ private static string RemoveKeyTypeSegment(string operationId, IList<IOpenApiPar
             return string.Join('.', segments);
         }
 
-        private static void ResolveFunctionParameters(IList<IOpenApiParameter> parameters)
+        private static void ResolveFunctionParameters(List<IOpenApiParameter> parameters)
         {
-            foreach (var parameter in parameters.OfType<OpenApiParameter>().Where(static p => p.Content?.Any() ?? false))
+            foreach (var parameter in parameters.OfType<OpenApiParameter>().Where(static p => p.Content?.Count > 0))
             {
                 // Replace content with a schema object of type array
                 // for structured or collection-valued function parameters

src/Microsoft.OpenApi.Hidi/StatsVisitor.cs

@@ -27,7 +27,7 @@ public override void Visit(IOpenApiSchema schema)
 
         public int HeaderCount { get; set; }
 
-        public override void Visit(IDictionary<string, IOpenApiHeader> headers)
+        public override void Visit(Dictionary<string, IOpenApiHeader> headers)
         {
             HeaderCount++;
         }

src/Microsoft.OpenApi.Workbench/StatsVisitor.cs

@@ -27,7 +27,7 @@ public override void Visit(IOpenApiSchema schema)
 
         public int HeaderCount { get; set; }
 
-        public override void Visit(IDictionary<string, IOpenApiHeader> headers)
+        public override void Visit(Dictionary<string, IOpenApiHeader> headers)
         {
             HeaderCount++;
         }

src/Microsoft.OpenApi/Extensions/OpenApiExtensibleExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Exceptions;
 using Microsoft.OpenApi.Interfaces;
 using Microsoft.OpenApi.Models;
@@ -32,10 +33,8 @@ public static void AddExtension<T>(this T element, string name, IOpenApiExtensio
                 throw new OpenApiException(string.Format(SRResource.ExtensionFieldNameMustBeginWithXDash, name));
             }
 
-            if (element.Extensions is not null)
-            {
-                element.Extensions[name] = Utils.CheckArgumentNull(any);
-            }            
+            element.Extensions ??= [];
+            element.Extensions[name] = Utils.CheckArgumentNull(any);
         }
     }
 }

src/Microsoft.OpenApi/Extensions/OpenApiServerExtensions.cs

@@ -21,7 +21,7 @@ public static class OpenApiServerExtensions
     ///   1. A substitution has no valid value in both the supplied dictionary and the default
     ///   2. A substitution's value is not available in the enum provided
     /// </exception>
-    public static string? ReplaceServerUrlVariables(this OpenApiServer server, IDictionary<string, string>? values = null)
+    public static string? ReplaceServerUrlVariables(this OpenApiServer server, Dictionary<string, string>? values = null)
     {
         var parsedUrl = server.Url;
         if (server.Variables is not null && parsedUrl is not null)

src/Microsoft.OpenApi/Interfaces/IMetadataContainer.cs

@@ -14,6 +14,6 @@ public interface IMetadataContainer
         /// <summary>
         /// A collection of properties associated with the current OpenAPI element.
         /// </summary>
-        IDictionary<string, object>? Metadata { get; set; }
+        Dictionary<string, object>? Metadata { get; set; }
     }
 }

src/Microsoft.OpenApi/Interfaces/IOpenApiExtensible.cs

@@ -13,6 +13,6 @@ public interface IOpenApiExtensible : IOpenApiElement
         /// <summary>
         /// Specification extensions.
         /// </summary>
-        IDictionary<string, IOpenApiExtension>? Extensions { get; set; }
+        Dictionary<string, IOpenApiExtension>? Extensions { get; set; }
     }
 }

src/Microsoft.OpenApi/Interfaces/IOpenApiReadOnlyExtensible.cs

@@ -10,6 +10,6 @@ public interface IOpenApiReadOnlyExtensible
     /// <summary>
     /// Specification extensions.
     /// </summary>
-    IDictionary<string, IOpenApiExtension>? Extensions { get; }
+    Dictionary<string, IOpenApiExtension>? Extensions { get; }
 
 }

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiHeader.cs

@@ -55,11 +55,11 @@ public interface IOpenApiHeader : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// <summary>
     /// Examples of the media type.
     /// </summary>
-    public IDictionary<string, IOpenApiExample>? Examples { get; }
+    public Dictionary<string, IOpenApiExample>? Examples { get; }
 
     /// <summary>
     /// A map containing the representations for the header.
     /// </summary>
-    public IDictionary<string, OpenApiMediaType>? Content { get; }
+    public Dictionary<string, OpenApiMediaType>? Content { get; }
 
 }

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiLink.cs

@@ -24,7 +24,7 @@ public interface IOpenApiLink : IOpenApiDescribedElement, IOpenApiReadOnlyExtens
     /// <summary>
     /// A map representing parameters to pass to an operation as specified with operationId or identified via operationRef.
     /// </summary>
-    public IDictionary<string, RuntimeExpressionAnyWrapper>? Parameters { get; }
+    public Dictionary<string, RuntimeExpressionAnyWrapper>? Parameters { get; }
 
     /// <summary>
     /// A literal value or {expression} to use as a request body when calling the target operation.

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiParameter.cs

@@ -81,7 +81,7 @@ public interface IOpenApiParameter : IOpenApiDescribedElement, IOpenApiReadOnlyE
     /// Furthermore, if referencing a schema which contains an example,
     /// the examples value SHALL override the example provided by the schema.
     /// </summary>
-    public IDictionary<string, IOpenApiExample>? Examples { get; }
+    public Dictionary<string, IOpenApiExample>? Examples { get; }
 
     /// <summary>
     /// Example of the media type. The example SHOULD match the specified schema and encoding properties
@@ -102,5 +102,5 @@ public interface IOpenApiParameter : IOpenApiDescribedElement, IOpenApiReadOnlyE
     /// When example or examples are provided in conjunction with the schema object,
     /// the example MUST follow the prescribed serialization strategy for the parameter.
     /// </summary>
-    public IDictionary<string, OpenApiMediaType>? Content { get; }    
+    public Dictionary<string, OpenApiMediaType>? Content { get; }    
 }

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiPathItem.cs

@@ -14,16 +14,16 @@ public interface IOpenApiPathItem : IOpenApiDescribedElement, IOpenApiSummarized
     /// <summary>
     /// Gets the definition of operations on this path.
     /// </summary>
-    public IDictionary<HttpMethod, OpenApiOperation>? Operations { get; }
+    public Dictionary<HttpMethod, OpenApiOperation>? Operations { get; }
 
     /// <summary>
     /// An alternative server array to service all operations in this path.
     /// </summary>
-    public IList<OpenApiServer>? Servers { get; }
+    public List<OpenApiServer>? Servers { get; }
 
     /// <summary>
     /// A list of parameters that are applicable for all the operations described under this path.
     /// These parameters can be overridden at the operation level, but cannot be removed there.
     /// </summary>
-    public IList<IOpenApiParameter>? Parameters { get; }
+    public List<IOpenApiParameter>? Parameters { get; }
 }

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiRequestBody.cs

@@ -19,7 +19,7 @@ public interface IOpenApiRequestBody : IOpenApiDescribedElement, IOpenApiReadOnl
     /// REQUIRED. The content of the request body. The key is a media type or media type range and the value describes it.
     /// For requests that match multiple keys, only the most specific key is applicable. e.g. text/plain overrides text/*
     /// </summary>
-    public IDictionary<string, OpenApiMediaType>? Content { get; }
+    public Dictionary<string, OpenApiMediaType>? Content { get; }
     /// <summary>
     /// Converts the request body to a body parameter in preparation for a v2 serialization.
     /// </summary>

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiResponse.cs

@@ -12,18 +12,18 @@ public interface IOpenApiResponse : IOpenApiDescribedElement, IOpenApiReadOnlyEx
     /// <summary>
     /// Maps a header name to its definition.
     /// </summary>
-    public IDictionary<string, IOpenApiHeader>? Headers { get; }
+    public Dictionary<string, IOpenApiHeader>? Headers { get; }
 
     /// <summary>
     /// A map containing descriptions of potential response payloads.
     /// The key is a media type or media type range and the value describes it.
     /// </summary>
-    public IDictionary<string, OpenApiMediaType>? Content { get; }
+    public Dictionary<string, OpenApiMediaType>? Content { get; }
 
     /// <summary>
     /// A map of operations links that can be followed from the response.
     /// The key of the map is a short name for the link,
     /// following the naming constraints of the names for Component Objects.
     /// </summary>
-    public IDictionary<string, IOpenApiLink>? Links { get; }
+    public Dictionary<string, IOpenApiLink>? Links { get; }
 }

src/Microsoft.OpenApi/Models/Interfaces/IOpenApiSchema.cs

@@ -35,7 +35,7 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// <summary>
     /// $vocabulary- used in meta-schemas to identify the vocabularies available for use in schemas described by that meta-schema.
     /// </summary>
-    public IDictionary<string, bool>? Vocabulary { get; }
+    public Dictionary<string, bool>? Vocabulary { get; }
 
     /// <summary>
     /// $dynamicRef - an applicator that allows for deferring the full resolution until runtime, at which point it is resolved each time it is encountered while evaluating an instance
@@ -51,7 +51,7 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// $defs - reserves a location for schema authors to inline re-usable JSON Schemas into a more general schema. 
     /// The keyword does not directly affect the validation result
     /// </summary>
-    public IDictionary<string, IOpenApiSchema>? Definitions { get; }
+    public Dictionary<string, IOpenApiSchema>? Definitions { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
@@ -144,19 +144,19 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
     /// Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
     /// </summary>
-    public IList<IOpenApiSchema>? AllOf { get; }
+    public List<IOpenApiSchema>? AllOf { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
     /// Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
     /// </summary>
-    public IList<IOpenApiSchema>? OneOf { get; }
+    public List<IOpenApiSchema>? OneOf { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
     /// Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
     /// </summary>
-    public IList<IOpenApiSchema>? AnyOf { get; }
+    public List<IOpenApiSchema>? AnyOf { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
@@ -167,7 +167,7 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
     /// </summary>
-    public ISet<string>? Required { get; }
+    public HashSet<string>? Required { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
@@ -195,7 +195,7 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
     /// Property definitions MUST be a Schema Object and not a standard JSON Schema (inline or referenced).
     /// </summary>
-    public IDictionary<string, IOpenApiSchema>? Properties { get; }
+    public Dictionary<string, IOpenApiSchema>? Properties { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
@@ -204,7 +204,7 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// egular expression dialect. Each property value of this object MUST be an object, and each object MUST 
     /// be a valid Schema Object not a standard JSON Schema.
     /// </summary>
-    public IDictionary<string, IOpenApiSchema>? PatternProperties { get; }
+    public Dictionary<string, IOpenApiSchema>? PatternProperties { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
@@ -246,12 +246,12 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// To represent examples that cannot be naturally represented in JSON or YAML, 
     /// a list of values can be used to contain the examples with escaping where necessary.
     /// </summary>
-    public IList<JsonNode>? Examples { get; }
+    public List<JsonNode>? Examples { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
     /// </summary>
-    public IList<JsonNode>? Enum { get; }
+    public List<JsonNode>? Enum { get; }
 
     /// <summary>
     /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
@@ -278,16 +278,16 @@ public interface IOpenApiSchema : IOpenApiDescribedElement, IOpenApiReadOnlyExte
     /// <summary>
     /// This object stores any unrecognized keywords found in the schema.
     /// </summary>
-    public IDictionary<string, JsonNode>? UnrecognizedKeywords { get; }
+    public Dictionary<string, JsonNode>? UnrecognizedKeywords { get; }
 
     /// <summary>
     /// Any annotation to attach to the schema to be used by the application.
     /// Annotations are NOT (de)serialized with the schema and can be used for custom properties.
     /// </summary>
-    public IDictionary<string, object>? Annotations { get; }
+    public Dictionary<string, object>? Annotations { get; }
 
     /// <summary>
     /// Follow JSON Schema definition:https://json-schema.org/draft/2020-12/json-schema-validation#section-6.5.4
     /// </summary>
-    public IDictionary<string, ISet<string>>? DependentRequired { get; }
+    public Dictionary<string, HashSet<string>>? DependentRequired { get; }
 }

src/Microsoft.OpenApi/Models/OpenApiCallback.cs

@@ -13,17 +13,16 @@ 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
     {
         /// <inheritdoc/>
         public Dictionary<RuntimeExpression, IOpenApiPathItem>? PathItems { get; set; }
-            = [];
 
 
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public Dictionary<string, IOpenApiExtension>? Extensions { get; set; }
 
         /// <summary>
         /// Parameter-less constructor