link-to assertion fail: property modified twice in a single render

ember-source: from 3.10.0 to 3.10.2 (I haven’t tried with other versions) ember-engines: from 0.7.2 to 0.8.2

Linking a property from a component or a controller to the @route of a <LinkTo> tag throws an assertion failed:

Assertion Failed: You modified “url” twice on [object Object] in a single render. It was rendered in “component:link-to” and modified in “component:link-to”. This was unreliable and slow in Ember 1.x and is no longer supported. See https://github.com/emberjs/ember.js/issues/13948 for more details.

This wasn’t an issue in prior versions of ember-engines.

Way to reproduce the error:

• create a new project
• add ember-engines 0.7.2
• create an in-repo-engine
• create an application controller inside the engine
• create a string property with value index (for example test)
• add a link-to component to the application.hbs (angle brackets or not)
• add this.test as route for the link-to component
• run the application

When visiting the application route of the engine, it will throw the exception. I don’t know if it can be relevant, but logging the property passed to the link-to component in the devtools, I saw that instead of being just the string index, link-to transforms it into a getter/setter.

[mydea]

Just noting this here, we also ran into this and were able to workaround this by passing the argument as readonly:

<LinkTo @route={{readonly this.dynamicRouteName}}>

It’s not ideal, but at least it works!

[thec0keman]

Looking into ember-router-helpers as a possible workaround… comes with a couple of caveats though:

1. That addon does not seem to support engines, so you have to use fully formed paths (and they generate full-app page loads)

2. Our engines have a lot of link-to’s… so this will be tedious.

The interesting thing is I think this is mostly tied to passing a bound attribute into the path property. So for example, when using the unbound helper to wrap the value:

= link-to (unbound myObject.path)

Then everything works. So it seems like the major issue here is when you pass bound objects into link-to, and ember-engines tries to prefix the engine name.