Empty session with _simple_filters

[remibernard]

There is a huge caveat when using the _simple_filters scope query parameter. If the scope we wish to update with _simple_filters does not exist yet (with an empty session, for example) the filters will be placed in the default scope (default_scope_name). This is very rarely what is desired since this default is rarely used.

For example, a simple filtering URL like /userfiles?_simple_filters=1&data_provider_id=1 will create a userfiles#index scope instead of the expected userfiles one (if there is no userfiles scope yet) and the specified filters wont be applied, as the controller expects its scope to be userfiles, not userfiles#index.

view_scopes.rb:1235:

if (simple = params['_simple_filters'])
      # Determine which scope to update
      known      = (current_session['scopes'] ||= {})
      controller = params[:controller].to_s.downcase
      name   = simple     if known.has_key?(simple)
      name ||= controller if known.has_key?(controller)
      name ||= default_scope_name
# ...

Unfortunately, there is no way to know at that point in update_session_scopes where to place the given filters if the session does not contain either the parameter (simple) or the controller name (controller). This issue notably only concerns the first request made; on subsequent requests, the controller will have set up its scope and name ||= controller if known.has_key?(controller) will correctly assign the desired scope name.

Underlying cause of aces/cbrain-apis#5