AsParameters throwing error on cast when showing the Description with EnableAnnotations

[jgarciadelanoceda]

This fixes an issue shown when investigating #2658. Not sure if this fixes it all.

Tested with the project WebApi, if you do not apply the GetCustomAttributes to GetCustomAttribute change then you will see an error on the SwaggerUi based on a Cast.

As the SwaggerParameter is an attribute that only can be set once per property there is no issue on the change
I have studied if inserting a test in Swashbuckle.AspNetCore.Annotations.Test, but the existing test are hitting this change, so I think there is no need to add it(In fact I have not seen a test using MinimalApi approach)

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@@            Coverage Diff             @@
##           master    #2962      +/-   ##
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+ Coverage   90.28%   90.34%   +0.06%     
==========================================
  Files          72       72              
  Lines        2840     2839       -1     
  Branches      446      446              
==========================================
+ Hits         2564     2565       +1     
+ Misses        276      274       -2     

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[martincostello]

What is the stack trace of the exception that occurs without this change? Odd that one works but "first of possibly many" doesn't.

[jgarciadelanoceda]

It's a thing that is only happening for MinimalApi when the property has a SwaggerParameterAttribute on it. I think the problem is right here:

It is not able to cast the array of Attributes to a Ienumerable of SwaggerParameterAttribute. Since the SwaggerParamterAttribute can only be applied once for each parameter then there is no problem in adding it

The stackTrace is this one:

Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
      Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Failed to generate Operation for action - HTTP: POST /fruit/{id}. See inner exception
       ---> System.InvalidCastException: Unable to cast object of type 'System.Attribute[]' to type 'System.Collections.Generic.IEnumerable`1[Swashbuckle.AspNetCore.Annotations.SwaggerParameterAttribute]'.
         at System.Reflection.CustomAttributeExtensions.GetCustomAttributes[T](ParameterInfo element)
         at Swashbuckle.AspNetCore.Annotations.AnnotationsParameterFilter.ApplyParamAnnotations(OpenApiParameter parameter, ParameterInfo parameterInfo) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.Annotations\AnnotationsParameterFilter.cs:line 34
         at Swashbuckle.AspNetCore.Annotations.AnnotationsParameterFilter.Apply(OpenApiParameter parameter, ParameterFilterContext context) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.Annotations\AnnotationsParameterFilter.cs:line 18
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParameterAsync(ApiParameterDescription apiParameter, SchemaRepository schemaRepository) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 599
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParametersAsync(ApiDescription apiDescription, SchemaRepository schemaRespository, Func`3 parameterGenerator) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 490
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParametersAsync(ApiDescription apiDescription, SchemaRepository schemaRespository) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 508
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(ApiDescription apiDescription, SchemaRepository schemaRepository, Func`3 parametersGenerator, Func`3 bodyGenerator, Func`3 applyFilters) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 322
         --- End of inner exception stack trace ---
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(ApiDescription apiDescription, SchemaRepository schemaRepository, Func`3 parametersGenerator, Func`3 bodyGenerator, Func`3 applyFilters) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 345
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(ApiDescription apiDescription, SchemaRepository schemaRepository) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 373
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationsAsync(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 268
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePathsAsync(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository, Func`3 operationsGenerator) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 207
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePathsAsync(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 229
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerAsync(String documentName, String host, String basePath) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.SwaggerGen\SwaggerGenerator\SwaggerGenerator.cs:line 56
         at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider) in C:\Git\Github\Swashbuckle.AspNetCore\src\Swashbuckle.AspNetCore.Swagger\SwaggerMiddleware.cs:line 64
         at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

[jgarciadelanoceda]

It's strange indeed!, because for Controller parameters this does not happen.