ApiExplorer does not correctly populate parameters for IApiDescriptionGroupCollectionProvider when modelbinding is used

[statler]

ApiDescriptionProblem (2).zip

Describe the bug

When using [modelbinder] attribute, the ApiExplorer does not correctly populate for parameters of a controller method

To Reproduce

Populate the API Explorer for a parameter that uses [modelbinder]. Instead of the parameterDescriptions being enumerated in the ApiDescription as happened in .Net Core 2.2, the ApiDescription contains only the name of the parameter.

In the attached project, run it and put a breakpoint in the constructor of SampleDataController. The property group contains 2 items. The first uses modelbinding and has one parameter whereas the second directly maps to the bound model and has the expected 21.

Exceptions (if any)

None

Further technical details

• ASP.NET Core version 3.1
• Include the output of dotnet --info
• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version VS 19 (16.7.7)

[pranavkm]

@statler this is likely a dup of #4825. Model binding as opposed to input formatting uses a wire format that is tied to how MVC functions. It's a bit difficult to map that to a swagger spec. Custom binders make it more complex since the author of the binder has to describe the wire format to MVC.

For APIs, we would generally recommend using JSON as the wire format to get a reasonable Swagger experience. We'll continue using the linked issue to track further work here.