legacy-data-mixin: not applied to TemplatizerInstances

[kevinpschaaf]

Description

When using the legacy-data-mixin.html to assist in identifying observers/computed functions that may need additional undefined checks due to changes in the undefined rule when porting from 1.x to 2.x, the mixin does not apply to TemplatizerInstaces created by dom-if and dom-repeat. As such, computed bindings in those nested templates will not properly warn on undefined arguments.

Note that this was fixed in the 2.x branch as noted here, and just needs porting to the 3.x branch.

Live Demo

See repross in #5266 (comment).

Browsers Affected

All

Versions

• Polymer: v3.x