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; }
     }
 }