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[BUGFIX][FEAT][Tracked Properties] Adds Arg Proxy Feature Flag #17835

Merged
merged 2 commits into from
Apr 22, 2019
Merged

[BUGFIX][FEAT][Tracked Properties] Adds Arg Proxy Feature Flag #17835

merged 2 commits into from
Apr 22, 2019

Commits on Apr 22, 2019

  1. add unstable args test

    Chris Garrett committed Apr 22, 2019
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  2. [BUGFIX] Adds Arg Proxy feature for tracked properties 

    Currently, we pass a captured snapshot of arguments to the custom
component manager and expect users to update their `args` and trigger
notifications, dirtying any getters that rely on `args`. This is
problematic for a few reasons:

1. It's fundamentally less efficient, since every getter on a component
   will invalidate any time _any_ of the arguments on the component
   changes. This may not be a huge deal in most components, but it could
   be problematic at scale.
2. Upstream components will currently rerender if anything changes
   downstream of them.

The second problem is more of an issue here. The crux of the issue is
that as we are rendering, we must somehow dirty the `args` object in
order for getters to invalidate. Currently, there are two ways of doing
this:

1. Dirtying the tag and bumping the global revision count. This results
   in the component itself being dirtied, which causes arguments to be
   assigned again on the next render, which dirties everything again.
2. Setting the argument's tag to `CURRENT_TAG`, as we do in Glimmer.js.
   This always returns the _latest_ revision though, which means that we
   are _always_ dirty.

This issue can crop up in many forms and leads to infinite rerender bugs
when it does.

The solution proposed here is to instead use a Proxy (or an object with
manually defined getters on platforms which do not support Proxy) to
wrap `args`. This allows us to directly access the references that
represent the arguments, and push their tags onto the autotrack stack as
accessed. Everything entangles properly, and we only rerender or
recalculate a getter when needed.

Alternatively, we could add a way to set the `args` tag to _exactly_
the current revision as the component is rendering. This would solve the
problems of upstream invalidations, but would not solve the issue of all
getters on a component invalidating each render.
    Chris Garrett committed Apr 22, 2019
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