800983 - Expose a way to get computed style taking only UA and user sheets into account (getDefaultComputedStyle)

Status: RESOLVED FIXED

(Core :: DOM: CSS Object Model, defect)

Description

[Boris Zbarsky [:bzbarsky]]

I'm going to call this getDefaultComputedStyle.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Attachment: Expose a getter for default computed style. alternative implementation strategy is to add "default-only"

versions of ResolveStyleFor and ResolvePseudoElementStyle and then
modify FileRules to support those, or use a cut-down custom version of
FileRules for them.  That would be faster, but more complicated on the
style set side.  We can always make that switch if we need to, I guess.

Comment 2

[Boris Zbarsky [:bzbarsky]]

Oh, an open question is whether preshints should be counted as "default" style or not.  Either way is easy to implement.  For now I did not include them.  This is generally OK, modulo things like @hidden, for which we treat them as preshints but the spec technically treats them as UA rules or something.

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Comment on attachment 670868 [details] [diff] [review]
Expose a getter for default computed style.   alternative implementation strategy is to add "default-only"

Could you:

 (1) replace the boolean with an enum (with useful names for the values)?

 (2) append to an array, and then either (a) reverse into another array (preferably with SetCapacity first) or (b) add a Reverse method to nsTArray and use nsTArray<nsCOMPtr<nsIStyleRule> >

?

r=dbaron with that

Comment 4

[Boris Zbarsky [:bzbarsky]]

For #2, I did a combination, because knowing that I have an nsTArray of nsCOMPtr means I can reverse without refcounting like so:

    for (uint32_t i = 0, length = rules.Length(), stop = length / 2;
         i < stop; ++i) {
      rules[i].swap(rules[length - i - 1]);
    }

Comment 5

[Boris Zbarsky [:bzbarsky]]

Oh, and I can't use the enum in nsGlobalWindow function signatures, unfortunately, because I can't include nsComputedDOMStyle.h in nsGlobalWindow.h due to include hell.  :(

Comment 6

[Boris Zbarsky [:bzbarsky]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/fd12a2c69e93

Comment 7

[Boris Zbarsky [:bzbarsky]]

I wrote some docs at https://developer.mozilla.org/en-US/docs/DOM/window.getDefaultComputedStyle

Comment 8

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/fd12a2c69e93