Fix parameter serialization - Style doesn't respect the default value

src/Microsoft.OpenApi/Models/OpenApiParameter.cs

@@ -16,6 +16,7 @@ namespace Microsoft.OpenApi.Models
     public class OpenApiParameter : IOpenApiSerializable, IOpenApiReferenceable, IEffective<OpenApiParameter>, IOpenApiExtensible
     {
         private bool? _explode;
+        public ParameterStyle? _style;
 
         /// <summary>
         /// Indicates if object is populated with data or is just a reference to the data
@@ -73,7 +74,11 @@ public class OpenApiParameter : IOpenApiSerializable, IOpenApiReferenceable, IEf
         /// Default values (based on value of in): for query - form; for path - simple; for header - simple;
         /// for cookie - form.
         /// </summary>
-        public ParameterStyle? Style { get; set; }
+        public ParameterStyle? Style
+        { 
+            get => _style ?? SetDefaultStyleValue();
+            set => _style = value;
+        }
 
         /// <summary>
         /// When this is true, parameter values of type array or object generate separate parameters
@@ -396,6 +401,20 @@ public void SerializeAsV2WithoutReference(IOpenApiWriter writer)
             writer.WriteEndObject();
         }
 
+        private ParameterStyle? SetDefaultStyleValue()
+        {
+            Style = In switch
+            {
+                ParameterLocation.Query => (ParameterStyle?)ParameterStyle.Form,
+                ParameterLocation.Header => (ParameterStyle?)ParameterStyle.Simple,
+                ParameterLocation.Path => (ParameterStyle?)ParameterStyle.Simple,
+                ParameterLocation.Cookie => (ParameterStyle?)ParameterStyle.Form,
+                _ => (ParameterStyle?)ParameterStyle.Simple,
+            };
+
+            return Style;
+        }
+
     }
 
     /// <summary>

test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.SerializeAdvancedDocumentAsV2JsonWorks_produceTerseOutput=False.verified.txt

@@ -38,14 +38,16 @@
             "type": "array",
             "items": {
               "type": "string"
-            }
+            },
+            "collectionFormat": "multi"
           },
           {
             "in": "query",
             "name": "limit",
             "description": "maximum number of results to return",
             "type": "integer",
-            "format": "int32"
+            "format": "int32",
+            "collectionFormat": "multi"
           }
         ],
         "responses": {

test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.SerializeAdvancedDocumentAsV2JsonWorks_produceTerseOutput=True.verified.txt

@@ -1 +1 @@
-{"swagger":"2.0","info":{"title":"Swagger Petstore (Simple)","description":"A sample API that uses a petstore as an example to demonstrate features in the swagger-2.0 specification","termsOfService":"http://helloreverb.com/terms/","contact":{"name":"Swagger API team","url":"http://swagger.io","email":"[email protected]"},"license":{"name":"MIT","url":"http://opensource.org/licenses/MIT"},"version":"1.0.0"},"host":"petstore.swagger.io","basePath":"/api","schemes":["http"],"paths":{"/pets":{"get":{"description":"Returns all pets from the system that the user has access to","operationId":"findPets","produces":["application/json","application/xml","text/html"],"parameters":[{"in":"query","name":"tags","description":"tags to filter by","type":"array","items":{"type":"string"}},{"in":"query","name":"limit","description":"maximum number of results to return","type":"integer","format":"int32"}],"responses":{"200":{"description":"pet response","schema":{"type":"array","items":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}}},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}},"post":{"description":"Creates a new pet in the store.  Duplicates are allowed","operationId":"addPet","consumes":["application/json"],"produces":["application/json","text/html"],"parameters":[{"in":"body","name":"body","description":"Pet to add to the store","required":true,"schema":{"required":["name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}}],"responses":{"200":{"description":"pet response","schema":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}}},"/pets/{id}":{"get":{"description":"Returns a user based on a single ID, if the user does not have access to the pet","operationId":"findPetById","produces":["application/json","application/xml","text/html"],"parameters":[{"in":"path","name":"id","description":"ID of pet to fetch","required":true,"type":"integer","format":"int64"}],"responses":{"200":{"description":"pet response","schema":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}},"delete":{"description":"deletes a single pet based on the ID supplied","operationId":"deletePet","produces":["text/html"],"parameters":[{"in":"path","name":"id","description":"ID of pet to delete","required":true,"type":"integer","format":"int64"}],"responses":{"204":{"description":"pet deleted"},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}}}},"definitions":{"pet":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}},"newPet":{"required":["name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}},"errorModel":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}
+{"swagger":"2.0","info":{"title":"Swagger Petstore (Simple)","description":"A sample API that uses a petstore as an example to demonstrate features in the swagger-2.0 specification","termsOfService":"http://helloreverb.com/terms/","contact":{"name":"Swagger API team","url":"http://swagger.io","email":"[email protected]"},"license":{"name":"MIT","url":"http://opensource.org/licenses/MIT"},"version":"1.0.0"},"host":"petstore.swagger.io","basePath":"/api","schemes":["http"],"paths":{"/pets":{"get":{"description":"Returns all pets from the system that the user has access to","operationId":"findPets","produces":["application/json","application/xml","text/html"],"parameters":[{"in":"query","name":"tags","description":"tags to filter by","type":"array","items":{"type":"string"},"collectionFormat":"multi"},{"in":"query","name":"limit","description":"maximum number of results to return","type":"integer","format":"int32","collectionFormat":"multi"}],"responses":{"200":{"description":"pet response","schema":{"type":"array","items":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}}},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}},"post":{"description":"Creates a new pet in the store.  Duplicates are allowed","operationId":"addPet","consumes":["application/json"],"produces":["application/json","text/html"],"parameters":[{"in":"body","name":"body","description":"Pet to add to the store","required":true,"schema":{"required":["name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}}],"responses":{"200":{"description":"pet response","schema":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}}},"/pets/{id}":{"get":{"description":"Returns a user based on a single ID, if the user does not have access to the pet","operationId":"findPetById","produces":["application/json","application/xml","text/html"],"parameters":[{"in":"path","name":"id","description":"ID of pet to fetch","required":true,"type":"integer","format":"int64"}],"responses":{"200":{"description":"pet response","schema":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}}},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}},"delete":{"description":"deletes a single pet based on the ID supplied","operationId":"deletePet","produces":["text/html"],"parameters":[{"in":"path","name":"id","description":"ID of pet to delete","required":true,"type":"integer","format":"int64"}],"responses":{"204":{"description":"pet deleted"},"4XX":{"description":"unexpected client error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}},"5XX":{"description":"unexpected server error","schema":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}}}},"definitions":{"pet":{"required":["id","name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}},"newPet":{"required":["name"],"type":"object","properties":{"id":{"format":"int64","type":"integer"},"name":{"type":"string"},"tag":{"type":"string"}}},"errorModel":{"required":["code","message"],"type":"object","properties":{"code":{"format":"int32","type":"integer"},"message":{"type":"string"}}}}}

test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.SerializeAdvancedDocumentAsV3JsonWorks_produceTerseOutput=False.verified.txt

@@ -30,6 +30,7 @@
             "name": "tags",
             "in": "query",
             "description": "tags to filter by",
+            "style": "form",
             "schema": {
               "type": "array",
               "items": {
@@ -41,6 +42,7 @@
             "name": "limit",
             "in": "query",
             "description": "maximum number of results to return",
+            "style": "form",
             "schema": {
               "type": "integer",
               "format": "int32"
@@ -264,6 +266,7 @@
             "in": "path",
             "description": "ID of pet to fetch",
             "required": true,
+            "style": "simple",
             "schema": {
               "type": "integer",
               "format": "int64"
@@ -375,6 +378,7 @@
             "in": "path",
             "description": "ID of pet to delete",
             "required": true,
+            "style": "simple",
             "schema": {
               "type": "integer",
               "format": "int64"