IEdmModel.ConvertToOpenApi() throws System.InvalidOperationException when having dollar-count similar path in controller

[ra-design]

I have a Count() operation in an ODataController. When I call ConvertToOpenApi on the IEdmModel a System.InvalidOperationException: 'Collection was modified; enumeration operation may not execute.' is thrown ( in src/Microsoft.OpenApi.OData.Reader/Edm/ODataPathProvider.cs).

Assemblies affected

occurs at least in:

• Microsoft.OpenApi.OData 1.7.4
• Microsoft.OpenApi.OData 2.0.0 preview 8

Steps to reproduce

In an ODataController, add a dollar-count-similar operation, eg:

[HttpGet]
[Description("Shows the total count of entities")]
public async Task<IActionResult> Count()
{
    return await CountEntities();
}

Add the function to the ODataConventionModelBuilder, eg: builder.EntityType<Entity>().Collection.Function(nameof(EntitiesController.Count)).Returns<int>();

Create the IEdmModel and call

var edmModel = odataBuilder.GetEdmModel();
var document = edmModel.ConvertToOpenApi();

Expected result

The OpenApiDocument gets created.

Actual result

System.InvalidOperationException: 'Collection was modified; enumeration operation may not execute.' Following the StackTrace the reason is: AppendBoundOperationOnNavigationSourcePath() has a foreach on IList<ODataPath>, which calls AppendPath(newPath);, which results in a modification of the paths, if a dollar-count-similar path is found, hence resulting in the InvalidOperationException.

Additional detail

Creating a copy of the collection before iterating over it in ODataPathProvider.cs L950 would work in my use-case, but keeps the $count and Count() operations in the openapi specification. Don't know if that is a problem.

foreach (var subPath in value.ToList())
...

As a workaround - not using dollar-similar-paths in your OData operations removes the issue as well ;)