[1.x] Templatizer leaks instance <template> element and its dataHost onto prototype

[kevinpschaaf]

Description

The first time a template is "templatized", the reference to the <template> element instance is stored on the Templatized constructor's prototype, which is cached on the cached template content for any nested templates. This causes a leak not only of the template, but its dataHost reference, inadvertently causing a leak of potentially expensive elements all the way up the tree. The assumption is that once an element is detached and gc'ed, all dataHost references back up the tree to it are also gc'ed. This leak via the <template> element prevents proper gc from occurring.

Live Demo

http://jsbin.com/remilab/edit?html,console,output

Steps to Reproduce

Open jsBin

Expected Results

No reference to the template's dataHost is retained

Actual Results

After being removed, the instance element is retained via

    Polymer
      .telemetry
      .registrations
      .slice(-1)[0]
      ._notes[0]
      .templateContent
      ._ctor
      .prototype
      ._template
      .dataHost

Browsers Affected

All

Versions

• Polymer: v1.x

[kevinpschaaf]

The offending line looks to be here:

polymer/src/lib/template/templatizer.html

Line 201 in 9721433

archetype._template = template;

2.x does not appear to suffer from the same leak, as the <template> instance is stored on a subclass of the cached Templatized constructor each call to templatize, rather than the cached one directly:

polymer/lib/utils/templatize.html

Lines 518 to 522 in 9b3ca2c

	// Subclass base class and add reference for this specific template
	/** @private */
	let klass = class TemplateInstance extends baseClass {};
	klass.prototype._methodHost = findMethodHost(template);
	klass.prototype.__dataHost = template;

[TimvdLippe]

@kevinpschaaf I have updated your links to use permalinks to prevent linkrot and have nice in-lining of the corresponding source code

[TimvdLippe]

This has been fixed in #5102