Fix StackOverflowException in DescriptionOperationFilter if a type ha…

[DerAtro]

The DescriptionOperationFilter could cause a StackOverflowException due to circular calls of the recursive UpdateDescriptions() method. This happens if the used type for an operation parameter or response (in SwaggerResponseAttribute) has a property with its own type defined (see 'SelfReferencingTypeObject' in commit) and this property has a DescriptionAttribute defined - the value descriptions of the very same Schema would be updated again and again until the StackOverflowException is thrown.
A check has been added in UpdateDescription() if the Schema of the current type has already been updated with the descriptions, avoiding multiple/infinite updates.
I've also added a new type 'SelfReferencingTypeObjectResponse' holding the 'SelfReferencingTypeObject' and a controller method to illustrate/verify the issue.

[mattfrear]

Hi, sorry for the delay. This PR flew under my radar and I haven't done anything with this repo for a long time.
Most of it got ported to the .NET Core version at Swashbuckle.AspNetCore.Filters, and I deprecated the DescriptionOperationFilter from the .NET Core version, I can't remember why, probably because the same thing can be accomplished with XML comments.

I'll have a look at this some time soon.

[mattfrear]

When I wrote the DescriptionOperationFilter in 2017, I didn't know that Swashbuckle itself has a way to add Descriptions - by using XML comments. It's poorly documented here: https://github.com/domaindrivendev/Swashbuckle.WebApi#including-xml-comments

I just tested it, and it works like this:

        /// <summary>
        /// Their age, in years
        /// </summary>
        public int Age { get; set; }

        [Description("The first name of the person")] // this uses my filter
        public string FirstName { get; set; }

results in:

This is why I deprecated the DescriptionOperationFilter from my Swashbuckle.AspNetCore.Filters package, as it isn't needed.
My preference would be to do the same to the DescriptionOperationFilter here.

My question for you is: can you use XML comments to annotate your properties? Is there a good reason to keep my DescriptionOperationFilter?

[mattfrear]

I have removed the DescriptionOperationFilter from Swashbuckle.Examples 4.0.0.