This includes a `size_of` regression for a few DOM types,
due to https://github.com/rust-lang/rust/pull/58623 which replaces the
implementation of `HashMap` in the standard library to Hashbrown.
Although `size_of<HashMap>` grows, it’s not obvious how total memory usage
is going to be impacted: Hashbrown only has one `u8` instead of one `usize`
of overhead per hash table bucket for storing (part of) a hash,
and so might allocate less memory itself.
Hashbrown also typically has better run time performance:
https://github.com/rust-lang/hashbrown#performance
Still, I’ve filed https://github.com/rust-lang/hashbrown/issues/69
about potentially reducing the `size_of<HashMap>` regression.
Implement custom element reactions
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Initial work for implementing custom element reactions: https://html.spec.whatwg.org/multipage/custom-elements.html#custom-element-reactions
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This allows us to have ensure_data() and clear_data() functions on the TElement
trait, instead of hacking around it adding methods in random traits.
This also allows us to do some further cleanup, which I'd rather do in a
followup.
This will go back down soonish when NonZero stablizes and we can use it in
StyleArc, which I expect will be long before the memory overhead here matters.
This patch does a number of things, unfortunately all at once:
* Hoists a large subset of the layout wrapper functionality into the style system.
* Merges TElementAttributes into the newly-created TElement.
* Reorganizes LayoutData by style vs layout, and removes LayoutDataShared.
* Simplifies the API for borrowing style/layout data.
There's still more to do to make the style system usable standalone, but
this is a good start.
There is now an inclusive_descendants_version field of each node, which
increases each time the node, or any of its descendants, is dirtied.
This can be used for cache invalidation, by caching a version number
and comparting the current version number against the cached version number.
After rebasing, this suddenly became a problem again, even though there's no actual size increase here
(we're shrinking NodeFlags by 1 byte, and adding 1 byte of EventState). Moving the NodeFlags to the end
of Node and the EventState bits to the beginning of Element doesn't seem to helper either.
This is probably a padding issue that's worth investigating at some point, but given the level
of churn in this code it doesn't seem worth it to fuss to much over this right now.
