Per spec, the initial containing block (ICB) should have the size of the
viewport. We have only done this for the width until now, since we had
no way to express scrollable overflow.
This patch adds Layout::Box::m_overflow_data, an optional struct that
can hold on to information about a box's overflow. Then we have BFC
set the ICB up with some scrollable overflow instead of sizing it to fit
its content vertically.
This fixes a number of broken layouts where correctness depends on
having the appropriate ICB height.
Apparently it's not only replaced elements that can have intrinsic
sizes, so let's move this concept from ReplacedBox to Box. To avoid
bloating Box, we make the accessors virtual.
Note there are a couple of type differences between the spec and the IDL
file added in this commit. For example, we will need to support a type
of Variant to handle spec types such as "(double or sequence<double>)".
But for now, this allows web pages to construct an IntersectionObserver
with any valid type.
Since FFC is only ever run() on the flex container, we can assume (but
verify) that the run box is the flex container and use an accessor
throughout. The end result: less parameter passing.
Determining the available main and cross space is now done by a separate
function. The signature is a little bit hairy since this function
computes some things that are used by subsequent algorithm steps.
Factoring can definitely be improved further.
Per css-sizing-3:
Additionally, the size of the containing block of an absolutely
positioned element is always definite with respect to that element.
As I understand this, it doesn't mean that all absolutely positioned
boxes have definite size, but that the containing block of an absolutely
positioned descendant has definite size from the perspective of the
descendant.
Since style update is driven by Document, moving a node with dirty style
from one document to another means that we have to schedule a style
update in the new document.
If we had a scheduled update of either of these kind, make sure to
cancel it after performing an update. Otherwise we might do a redundant
second update with the same results.
This could happen if something schedules an async layout, and before it
can happen, something requires a sync layout, which we do right away.
This paves the way for the rejectionhandled and unhandledrejection
events.
It's also used by core-js (in browsers, at least) to check whether
Promise needs to be polyfilled, so adding it should allow more websites
to leverage LibJS's native Promise implementation :^)
When computing whether whitespace should be collapsed or not, we have to
consider empty fragments, since <br> will produce an empty fragment to
force a line break.
LineBox::is_empty_or_ends_in_whitespace() is amended to look at the
length of the last fragment, and return true if it is 0.
