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fix(core): replace assertion with more intentional error #52234

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fix(core): replace assertion with more intentional error #52234

wants to merge 1 commit into from

Commits on Oct 27, 2023

  1. fix(core): replace assertion with more intentional error 

    Issue angular#50320 shows that in some cases, updating a signal that's a dependency
of a template during change detection of that template can have several
adverse effects. This can happen, for example, if the signal is set during
the lifecycle hook of a directive within the same template that reads the
signal.

This can cause a few things to happen:

* Straightforwardly, it can cause `ExpressionChanged` errors.
* Surprisingly, it can cause an assertion within the `ReactiveLViewConsumer`
  to fail.
* Very surprisingly, it can cause change detection for an `OnPush` component
  to stop working.

The root cause of these later behaviors is subtle, and is ultimately a
desync between the reactive graph and the view tree's notion of "dirty" for
a given view. This will be fixed with further work planned for change
detection to handle such updates directly. Until then, this commit improves
the DX through two changes:

1. The mechanism of "committing" `ReactiveLViewConsumer`s to a view is
   changed to use the `consumerOnSignalRead` hook from the reactive graph.
   This prevents the situation which required the assertion in the first
   place.

2. A `console.warn` warning is added when a view is marked dirty via a
   signal while it's still executing.

The warning informs users that they're pushing data against the direction of
change detection, risking `ExpressionChanged` or other issues. It's a
warning and not an error because the check is overly broad and captures
situations where the application would not actually break as a result, such
as if a `computed` marked the template dirty but still returned the same
value.
    @alxhub
    alxhub committed Oct 27, 2023
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