Previously we would generate the calculation context based on the
current value parsing context. The main problem with this was that
contexts were defined per property by default and had to be overriden
per component value using "special" contexts, which was easy to forget.
We now generate the calculation context per component value in the
relevant `parse_foo_value` methods.
The new failures in `typed_arithmetic.html` are because we no longer
treat percentages as resolving to their property-level type when
computing what the resolved type of a calculation is i.e. when we are
parsing the `<number>` portion of `line-height` we treat percentages as
raw percentages, not lengths. This brings us in line with WebKit but no
longer with Chrome and WPT, I am not sure what the correct behavior is.
The definition of syntax in the "css-properties-values-api" spec (which
is used for the `@property/syntax` descriptor) is slightly different
from the definition of `<syntax>` in the "css-values" spec (which we
implement) in that it limits literal idents to exclusively
`<custom-ident>`s (i.e. not CSS-wide keywords or "default").
`<custom-ident>`s are also case-sensitive so that behavior is
implemented for syntax matching here as well
Previously we would consider an alternative syntax child to be a match
as long as parsing produced a value, even if there were trailing tokens
(which would later invalidate it within `parse_with_a_syntax`). This
meant that we wouldn't consider later alternatives which may actually
produce a valid match.
This reverts 0e3487b9ab.
Back when I made that change, I thought we could make our StyleValue
classes match the typed-om definitions directly. However, they have
different requirements. Typed-om types need to be mutable and GCed,
whereas StyleValues are immutable and ideally wouldn't require a JS VM.
While I was already making such a cataclysmic change, I've moved it into
the StyleValues directory, because it *not* being there has bothered me
for a long time. 😅
`<syntax>` is a limited subset of the "value definition syntax" used in
CSS specs. It's used for `@property`'s `syntax` descriptor, and for the
`type()` function in `attr()`.
