Dep collection not paused during first invocation of immediate watchers, leading to unnecessary re-render

[delaneyb]

Version

2.6.11

Reproduction link

https://jsfiddle.net/gyejmL14/32/

Steps to reproduce

Press the button "change value of testKey".

What is expected?

No components should be updated

What is actually happening?

The root components render function is being run again.

During component-a's creation, the immediate watcher for testKey is invoked without a pushTarget(). At this point the updateComponent() of the parent is still the Dep.target. Everything accessed within the immediate watcher is then collected as a dependency of the parents updateComponent watcher. When the button is then pressed, this triggers an unnecessary update of the Root component.