2020, not yet wired to the rest of layout.
This commit implements an object that handles the 10 rules in CSS 2.1:
https://www.w3.org/TR/CSS2/visuren.html#float-position
The implementation strategy is that of a persistent balanced binary search tree
of float bands. Binary search trees are commonly used for implementing float
positioning; e.g. by WebKit. Persistence enables each object that interacts
with floats to efficiently contain a snapshot of the float list at the time
that object was laid out. That way, incremental layout can invalidate and start
reflow at any point in a containing block.
This commit features extensive use of
[QuickCheck](https://github.com/BurntSushi/quickcheck) to ensure that the rules
of the CSS specification are followed.
Because this is not yet connected to layout, floats will not actually be laid
out in Web pages yet.
Note that unit tests as set up in Servo currently require types that they
access to be public. Therefore, some internal layout 2020 types that were
previously private have been made public. This is somewhat unfortunate.
Part of #25167.
Update parse_length to match spec
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There are a few canvas2d-related dependencies that haven't updated, but they
only use euclid internally so that's not blocking landing the rest of the
changes.
Given the size of this patch, I think it's useful to get this landed as-is.
Clipboard refactoring
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This PR removes clipboard handling from the constellation. Instead, now embedder handles it.
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ISSUE-20455: introduce stronger types for textinput indexing
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Added two new types:
- ByteOffset
- UTF16CodeUnitOffset
I've replaced any instance of `usize` that would be better represented by one or the other of these. I also updated any downstream code, including the unit tests for `textinput.rs`. Along the way, I tried to add or edit comments to better reflect my understanding of this file - happy to revisit if I have misrepresented anything.
I did not end up finding any places where types were very obviously being mixed, as the issue description suggested I should do... LMK if I should re-audit the file for that (might need a bit of guidance)!
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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.
