Polymer 3.3.0 breaks Flow

See the detailed explanation what’s going on here: https://github.com/vaadin/flow/issues/5966#issuecomment-507232485

There are things to do:

• make a quick fix for PolymerTemplate class which allows to avoid unnecessary shadowRoot creation. That will fix immediately a lot of cases (along with beverage) .
• understand what to do with attachShadow method . This is Element API and it may be called by the app developer explicitly. In case of Polymer element it may cause the same issue as we have now. Most likely there is no need to create a shadow root for polymer element at all so this method can be no-op. But it should be possible to add something to the shadow root. And since it may be not available at the attachShadow call we should postpone somehow operations with shadow root when it becomes available. This is true for polymer elements. For other elements there should not be changes I believe.

It can be just a bug in Polymer 3.3.0 : it doesn’t reuse the existing shadow root.

Feel free to create a separate ticket for shadow root only issue.

[pleku]

I’ve bumped the priority - I hope we’ll get to this in this / next week.

[denis-anisimov]

PR: https://github.com/vaadin/flow/pull/6889

It makes a workaround for Polymer 3.3.0 in its current state. There still may be an issue if you are using attachShadowRoot Element API method. This is not fixed: this should be fixed on Polymer side (see the ticket above). So since Polymer 3.3.0 is not really ready I didn’t switch Polymer version. It’s still 3.2.0 (hardcoded). But I’ve added a parameter which can be used :

• in dev mode devmode.polymer.version parameter can be used in a deployment config to specify the polymer version (or vaadin.devmode.polymer.version as a system property )
• polymerVersion config parameter for maven plugin. You may specify a value via this property if you build the project production.

Tested with beverage: it works without problems.