Web API: API Explorer Fails with API Version Parameter

[commonsensesoftware]

Symptoms

When defining a controller action with a model bound API version, public IHttpActionResult Get( ApiVersion version ), which is versioned by URL segment with the ApiVersionRouteConstraint, API exploration throws an exception.

Analysis

A model bound ApiVersion parameter may be reported as ApiParamaterSource.Unknown. When part of the URL path, a placeholder is required to expand the path and evaluate the template. The only appears to affect versioning by URL segment and when including a model bound ApiVersion parameter.