[BUGFIX release] Don’t force invalidation of block param streams

[tomdale]

This commit removes the forced invalidation of block param streams on re-renders.

Previously, on re-renders, all block param streams were revalidated by calling notify() on them blindly.

While this often works, it creates a vector for light scopes to inadvertently invalidate their associated shadow scopes. In some cases, this leads to an infinite loop.

For example, imagine a component with the following template:

{{! app/templates/components/block-with-yield.hbs }}
{{yield danger}}

(Here danger is a property on the component.)

Now we invoke it:

{{#block-with-yield as |dangerBlockParam|}}
  {{dangerBlockParam}}
{{/block-with-yield}}

This works. The yielded block (light scope) receives a stream for the danger value. On re-renders, the stream is invalidated, but all that happens is the {{dangerBlockParam}} render node is dirtied again (which doesn’t matter, because we haven’t rendered and cleaned it yet).

However, imagine we change the component template to now display the same {{danger}} value:

{{! app/templates/components/block-with-yield.hbs }}
{{danger}}
{{yield danger}}

Now, when the block param stream is invalidated, it goes back and dirties the render node from the parent shadow scope. Because the component is dirtied, its {{yield}} helper is dirtied, causing the block param streams to be dirtied, and so on in an infinite loop.

This commit removes the forced invalidation, which I believe is unnecessary and probably left over from an earlier implementation. Specifically, if we are yielded a stream ({{yield danger}}), the stream should notify us of any changes to the value. Any downstream consumers of that stream will be notified correctly.

In the case of {{yield “hello”}} or some other primitive, we already wrap those values in a ProxyStream and call setSource when it changes, which has the effect of invalidating the stream anyway.

Closes #11519

[denzo]

This states that it has been merged into master. Does that mean it is available on the canary immediately?

[mmun]

@denzo Yes, usually a couple minutes after merging.