Previously, has_scrollable_overflow was a purely geometric check, true
whenever content extended beyond the padding box regardless of the
overflow property. This caused unnecessary scroll frame allocation for
boxes with `overflow:visible`.
Per CSS Overflow 3, scrollable overflow is only defined for scroll
containers (overflow: auto/hidden/scroll). Gate the flag on
`is_scroll_container()` so that only actual scroll containers get scroll
frames assigned.
Inline nodes in our layout tree have a position, so let's show it. By
centralizing the logic for this, block nodes now lose their redundant
'content-size' dump info which is already part of the box model dump.
This exposed a few bugs which caused the following tests to behave
incorrectly:
- `tab-size-text-wrap.html`: This previously relied on a bug where we
incorrectly treated `white-space: pre` as allowing text wrapping. The
fix here is to implement the text-wrap CSS shorthand property.
- `execCommand-preserveWhitespace.html`: We don't correctly serialize
shorthand properties. This is covered by an existing FIXME in
`CSSStyleProperties::serialized()`
- `white-space-shorthand.html`: The last 5 subtests here fail as we
don't correctly handle shorthand properties in
`CSSStyleProperties::remove_property()`. This is covered by an
existing FIXME in said function.
Browsers such as Chrome and Firefox apply an arbitrary scale to the
current font size if `normal` is used for `line-height`. Firefox uses
1.2 while Chrome uses 1.15. Let's go with the latter for now, it's
relatively easy to change if we ever want to go back on that decision.
This also requires updating the expectations for a lot of layout tests.
The upside of this is that it's a bit easier to compare our layout
results to other browsers', especially Chrome.
When setting `font-family: monospace;` in CSS, we have to interpret
the keyword font sizes (small, medium, large, etc) as slightly smaller
for historical reasons. Normally the medium font size is 16px, but
for monospace it's 13px.
The way this needs to behave is extremely strange:
When encountering `font-family: monospace`, we have to go back and
replay the CSS cascade as if the medium font size had been 13px all
along. Otherwise relative values like 2em/200%/etc could have gotten
lost in the inheritance chain.
We implement this in a fairly naive way by explicitly checking for
`font-family: monospace` (note: it has to be *exactly* like that,
it can't be `font-family: monospace, Courier` or similar.)
When encountered, we simply walk the element ancestors and re-run the
cascade for the font-size property. This is clumsy and inefficient,
but it does work for the common cases.
Other browsers do more elaborate things that we should eventually care
about as well, such as user-configurable font settings, per-language
behavior, etc. For now, this is just something that allows us to handle
more WPT tests where things fall apart due to unexpected font sizes.
To learn more about the wonders of font-size, see this blog post:
https://manishearth.github.io/blog/2017/08/10/font-size-an-unexpectedly-complex-css-property/
The reason we were keeping track of the pre-shaping buffer was to know
where we had tab characters in the input. This is a very strange way of
doing that, but since it broke the web, let's patch it up quickly.
Follow-up to #1870 which broke text layout on many web pages.
This fixes a browser crash as experienced on Wikipedia when encountering
the ≠ entity. As a side-effect, this also affects some tab-align and
-wrap tests.
