fix: parameter reference proxy design pattern implementation

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

@@ -7,6 +7,7 @@
 using Humanizer.Inflections;
 using Microsoft.OpenApi.Hidi.Extensions;
 using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Models.Interfaces;
 using Microsoft.OpenApi.Services;
 
 namespace Microsoft.OpenApi.Hidi.Formatters
@@ -69,13 +70,13 @@ public override void Visit(OpenApiOperation operation)
 
             var operationId = operation.OperationId;
             var operationTypeExtension = operation.Extensions?.GetExtension("x-ms-docs-operation-type");
-            if (operationTypeExtension.IsEquals("function"))
-                operation.Parameters = ResolveFunctionParameters(operation.Parameters ?? new List<OpenApiParameter>());
+            if (operationTypeExtension.IsEquals("function") && operation.Parameters is { Count :> 0})
+                ResolveFunctionParameters(operation.Parameters);
 
             // Order matters. Resolve operationId.
             operationId = RemoveHashSuffix(operationId);
             if (operationTypeExtension.IsEquals("action") || operationTypeExtension.IsEquals("function"))
-                operationId = RemoveKeyTypeSegment(operationId, operation.Parameters ?? new List<OpenApiParameter>());
+                operationId = RemoveKeyTypeSegment(operationId, operation.Parameters ?? new List<IOpenApiParameter>());
             operationId = SingularizeAndDeduplicateOperationId(operationId.SplitByChar('.'));
             operationId = ResolveODataCastOperationId(operationId);
             operationId = ResolveByRefOperationId(operationId);
@@ -143,7 +144,7 @@ private static string RemoveHashSuffix(string operationId)
             return s_hashSuffixRegex.Match(operationId).Value;
         }
 
-        private static string RemoveKeyTypeSegment(string operationId, IList<OpenApiParameter> parameters)
+        private static string RemoveKeyTypeSegment(string operationId, IList<IOpenApiParameter> parameters)
         {
             var segments = operationId.SplitByChar('.');
             foreach (var parameter in parameters)
@@ -157,9 +158,9 @@ private static string RemoveKeyTypeSegment(string operationId, IList<OpenApiPara
             return string.Join('.', segments);
         }
 
-        private static IList<OpenApiParameter> ResolveFunctionParameters(IList<OpenApiParameter> parameters)
+        private static void ResolveFunctionParameters(IList<IOpenApiParameter> parameters)
         {
-            foreach (var parameter in parameters.Where(static p => p.Content?.Any() ?? false))
+            foreach (var parameter in parameters.OfType<OpenApiParameter>().Where(static p => p.Content?.Any() ?? false))
             {
                 // Replace content with a schema object of type array
                 // for structured or collection-valued function parameters
@@ -173,7 +174,6 @@ private static IList<OpenApiParameter> ResolveFunctionParameters(IList<OpenApiPa
                     }
                 };
             }
-            return parameters;
         }
 
         private void AddAdditionalPropertiesToSchema(OpenApiSchema schema)

src/Microsoft.OpenApi.Hidi/StatsVisitor.cs

@@ -13,7 +13,7 @@ internal class StatsVisitor : OpenApiVisitorBase
     {
         public int ParameterCount { get; set; }
 
-        public override void Visit(OpenApiParameter parameter)
+        public override void Visit(IOpenApiParameter parameter)
         {
             ParameterCount++;
         }

src/Microsoft.OpenApi.Workbench/StatsVisitor.cs

@@ -13,7 +13,7 @@ internal class StatsVisitor : OpenApiVisitorBase
     {
         public int ParameterCount { get; set; }
 
-        public override void Visit(OpenApiParameter parameter)
+        public override void Visit(IOpenApiParameter parameter)
         {
             ParameterCount++;
         }

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

@@ -0,0 +1,106 @@
+using System.Collections.Generic;
+using System.Text.Json.Nodes;
+using Microsoft.OpenApi.Interfaces;
+
+namespace Microsoft.OpenApi.Models.Interfaces;
+
+/// <summary>
+/// Defines the base properties for the example object.
+/// This interface is provided for type assertions but should not be implemented by package consumers beyond automatic mocking.
+/// </summary>
+public interface IOpenApiParameter : IOpenApiDescribedElement, IOpenApiSerializable, IOpenApiReadOnlyExtensible
+{
+    /// <summary>
+    /// REQUIRED. The name of the parameter. Parameter names are case sensitive.
+    /// If in is "path", the name field MUST correspond to the associated path segment from the path field in the Paths Object.
+    /// If in is "header" and the name field is "Accept", "Content-Type" or "Authorization", the parameter definition SHALL be ignored.
+    /// For all other cases, the name corresponds to the parameter name used by the in property.
+    /// </summary>
+    public string Name { get; }
+
+    /// <summary>
+    /// REQUIRED. The location of the parameter.
+    /// Possible values are "query", "header", "path" or "cookie".
+    /// </summary>
+    public ParameterLocation? In { get; }
+
+    /// <summary>
+    /// Determines whether this parameter is mandatory.
+    /// If the parameter location is "path", this property is REQUIRED and its value MUST be true.
+    /// Otherwise, the property MAY be included and its default value is false.
+    /// </summary>
+    public bool Required { get; }
+
+    /// <summary>
+    /// Specifies that a parameter is deprecated and SHOULD be transitioned out of usage.
+    /// </summary>
+    public bool Deprecated { get; }
+
+    /// <summary>
+    /// Sets the ability to pass empty-valued parameters.
+    /// This is valid only for query parameters and allows sending a parameter with an empty value.
+    /// Default value is false.
+    /// If style is used, and if behavior is n/a (cannot be serialized),
+    /// the value of allowEmptyValue SHALL be ignored.
+    /// </summary>
+    public bool AllowEmptyValue { get; }
+
+    /// <summary>
+    /// Describes how the parameter value will be serialized depending on the type of the parameter value.
+    /// Default values (based on value of in): for query - form; for path - simple; for header - simple;
+    /// for cookie - form.
+    /// </summary>
+    public ParameterStyle? Style { get; }
+
+    /// <summary>
+    /// When this is true, parameter values of type array or object generate separate parameters
+    /// for each value of the array or key-value pair of the map.
+    /// For other types of parameters this property has no effect.
+    /// When style is form, the default value is true.
+    /// For all other styles, the default value is false.
+    /// </summary>
+    public bool Explode { get; }
+
+    /// <summary>
+    /// Determines whether the parameter value SHOULD allow reserved characters,
+    /// as defined by RFC3986 :/?#[]@!$&amp;'()*+,;= to be included without percent-encoding.
+    /// This property only applies to parameters with an in value of query.
+    /// The default value is false.
+    /// </summary>
+    public bool AllowReserved { get; }
+
+    /// <summary>
+    /// The schema defining the type used for the parameter.
+    /// </summary>
+    public OpenApiSchema Schema { get; }
+
+    /// <summary>
+    /// Examples of the media type. Each example SHOULD contain a value
+    /// in the correct format as specified in the parameter encoding.
+    /// The examples object is mutually exclusive of the example object.
+    /// 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; }
+
+    /// <summary>
+    /// Example of the media type. The example SHOULD match the specified schema and encoding properties
+    /// if present. The example object is mutually exclusive of the examples object.
+    /// Furthermore, if referencing a schema which contains an example,
+    /// the example value SHALL override the example provided by the schema.
+    /// To represent examples of media types that cannot naturally be represented in JSON or YAML,
+    /// a string value can contain the example with escaping where necessary.
+    /// </summary>
+    public JsonNode Example { get; }
+
+    /// <summary>
+    /// A map containing the representations for the parameter.
+    /// The key is the media type and the value describes it.
+    /// The map MUST only contain one entry.
+    /// For more complex scenarios, the content property can define the media type and schema of the parameter.
+    /// A parameter MUST contain either a schema property, or a content property, but not both.
+    /// 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; }    
+}

src/Microsoft.OpenApi/Models/OpenApiComponents.cs

@@ -28,10 +28,10 @@ public class OpenApiComponents : IOpenApiSerializable, IOpenApiExtensible
         public IDictionary<string, OpenApiResponse>? Responses { get; set; } = new Dictionary<string, OpenApiResponse>();
 
         /// <summary>
-        /// An object to hold reusable <see cref="OpenApiParameter"/> Objects.
+        /// An object to hold reusable <see cref="IOpenApiParameter"/> Objects.
         /// </summary>
-        public IDictionary<string, OpenApiParameter>? Parameters { get; set; } =
-            new Dictionary<string, OpenApiParameter>();
+        public IDictionary<string, IOpenApiParameter>? Parameters { get; set; } =
+            new Dictionary<string, IOpenApiParameter>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiExample"/> Objects.
@@ -87,7 +87,7 @@ public OpenApiComponents(OpenApiComponents? components)
         {
             Schemas = components?.Schemas != null ? new Dictionary<string, OpenApiSchema>(components.Schemas) : null;
             Responses = components?.Responses != null ? new Dictionary<string, OpenApiResponse>(components.Responses) : null;
-            Parameters = components?.Parameters != null ? new Dictionary<string, OpenApiParameter>(components.Parameters) : null;
+            Parameters = components?.Parameters != null ? new Dictionary<string, IOpenApiParameter>(components.Parameters) : null;
             Examples = components?.Examples != null ? new Dictionary<string, IOpenApiExample>(components.Examples) : null;
             RequestBodies = components?.RequestBodies != null ? new Dictionary<string, OpenApiRequestBody>(components.RequestBodies) : null;
             Headers = components?.Headers != null ? new Dictionary<string, IOpenApiHeader>(components.Headers) : null;

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -277,8 +277,8 @@ public void SerializeAsV2(IOpenApiWriter writer)
 
                 // parameters
                 var parameters = Components?.Parameters != null
-                    ? new Dictionary<string, OpenApiParameter>(Components.Parameters)
-                    : new Dictionary<string, OpenApiParameter>();
+                    ? new Dictionary<string, IOpenApiParameter>(Components.Parameters)
+                    : [];
 
                 if (Components?.RequestBodies != null)
                 {
@@ -592,7 +592,7 @@ public bool AddComponent<T>(string id, T componentToRegister)
                     Components.Schemas.Add(id, openApiSchema);
                     break;
                 case OpenApiParameter openApiParameter:
-                    Components.Parameters ??= new Dictionary<string, OpenApiParameter>();
+                    Components.Parameters ??= new Dictionary<string, IOpenApiParameter>();
                     Components.Parameters.Add(id, openApiParameter);
                     break;
                 case OpenApiResponse openApiResponse:

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -58,7 +58,7 @@ public class OpenApiOperation : IOpenApiSerializable, IOpenApiExtensible, IOpenA
         /// The list MUST NOT include duplicated parameters. A unique parameter is defined by a combination of a name and location.
         /// The list can use the Reference Object to link to parameters that are defined at the OpenAPI Object's components/parameters.
         /// </summary>
-        public IList<OpenApiParameter>? Parameters { get; set; } = new List<OpenApiParameter>();
+        public IList<IOpenApiParameter>? Parameters { get; set; } = [];
 
         /// <summary>
         /// The request body applicable for this operation.
@@ -127,7 +127,7 @@ public OpenApiOperation(OpenApiOperation? operation)
             Description = operation?.Description ?? Description;
             ExternalDocs = operation?.ExternalDocs != null ? new(operation?.ExternalDocs) : null;
             OperationId = operation?.OperationId ?? OperationId;
-            Parameters = operation?.Parameters != null ? new List<OpenApiParameter>(operation.Parameters) : null;
+            Parameters = operation?.Parameters != null ? new List<IOpenApiParameter>(operation.Parameters) : null;
             RequestBody = operation?.RequestBody != null ? new(operation?.RequestBody) : null;
             Responses = operation?.Responses != null ? new(operation?.Responses) : null;
             Callbacks = operation?.Callbacks != null ? new Dictionary<string, IOpenApiCallback>(operation.Callbacks) : null;
@@ -235,7 +235,7 @@ public void SerializeAsV2(IOpenApiWriter writer)
             // operationId
             writer.WriteProperty(OpenApiConstants.OperationId, OperationId);
 
-            List<OpenApiParameter> parameters;
+            List<IOpenApiParameter> parameters;
             if (Parameters == null)
             {
                 parameters = [];