We have a huge Polymer 1.0 project with a few hundred elements and are wondering whats the best way to upgrade everything to 3.0. Should we upgrade to 2.0 first or directly go to 3.0? Also are there any good guides available as the Polymer documentation on this does not seem to be very good. Also there were tools promised for automatic upgrading but they are nowhere to be found, does anyone know about this?
there is polymer-modulizer to convert from Polymer 2.x to 3 directly
But as you are using polymer 1 then the conversion result will need a human review for sure.
One thing to mention that polymer 2 already supports the legacy elements style from polymer-1, so there is a chance that polymer-modulizer will be able to update the syntax to polymer 3 for polymer 1 elements too, but I have not tried that
Long story short, there is only one tool which is polymer-modulizer to convert Polymer 2.x to 3 and the tool will automate some repetitive tasks for you, but still, you need to fix some stuff manually, if polymer-modulizerfails to upgrade the project for you to the new syntax, then it is better to start thinking about refactoring to support polymer 3 manually
The official documentation about upgrading to polymer 3 can be found here