Rack middleware is not called when using scope with interpolation

[ahx]

Scenario

There seems to be a problem when adding a middleware inside a scope block with interpolation. Here is an example:

scope 'i' do
  scope ':tenant_id' do
    use LogTenantIdMiddleware

    get 'foo' do
      "Hello, world #{params[:tenant_id]}"
     end
  end
end

Problem

GET "/i/42/foo"

• LogTenantIdMiddleware is not called
• Responds with status 200, "Hello, world 42"

GET "/i/:tenant_id/foo"

• LogTenantIdMiddleware is called
• Responds with status 200, "Hello, world :tenant_id"

Example

Here is a gist with a demo app to illustrate the issue.