DOMMatrix.to_string() throws exceptions if any of its values are
non-finite. This ends up affecting CSSStyleValue because its subclass
CSSTransformValue (which is about to be added) serializes
CSSTransformComponents, and one of those is CSSMatrixComponent, which
calls DOMMatrix.to_string().
This is all quite unfortunate, and because at the time the spec for
DOMMatrix was written, CSS couldn't represent NaN or infinity. That's
no longer true, so I'm hoping the spec can be updated and this can be
reverted. https://github.com/w3c/fxtf-drafts/issues/611
What I thought was a spec issue was actually a combination of my own
misunderstanding and a bug in our IDL generator. With that bug fixed, I
can correct this to how it is in the spec.
Reifying the result gets quite ad-hoc. Firstly because "parse a
component value" produces a ComponentValue, not a full StyleValue like
we need for math functions. And second, because not all math functions
can be reified as a CSSNumericValue:
Besides the fact that I haven't implemented CalculatedStyleValue
reification at all yet, there are a lot of math functions with no
corresponding CSSMathValue in the spec yet. If the calculation tree
contains any of those, the best we can do is reify as a CSSStyleValue,
and that isn't a valid return value from CSSNumericValue.parse(). So, I
made us throw a SyntaxError in those cases. This seems to match
Chrome's behaviour. Spec issue:
https://github.com/w3c/css-houdini-drafts/issues/1090
