872301 - enable ability to switch between longhand/shorthand behavior based on pref

Status: RESOLVED WONTFIX

(Core :: CSS Parsing and Computation, defect)

Description

[John Daggett (:jtd)]

The style/DOM system now has the ability to expose new CSS properties based on a pref.  For longhand properties this works just fine but it's tricky/non-trivial to do for a shorthand property.  I ran into this working on the new subproperties of font-variant that enable font features from the CSS3 Fonts spec.

Existing property: font-variant (longhand)

New properties: font-variant (shorthand!)
                font-variant-caps, font-variant-ligatures, etc. (longhand)

Maybe I'm missing an obvious way of doing this but I think at a minimum we need to adjust the macros to allow for a longhand/shorthand switch based on a pref, figure out what OM changes are needed and verify the testing infrastructure supports this (e.g. does property_database.js need additional structure or does the existing SpecialPowers.getBoolPref("layout.css.xxx.enabled") pattern suffice?).

This isn't the only example of this, switching a longhand property to a shorthand with more subproperty controls exists in other CSS3 specs.

Comment 1

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

We ended up not needing this to ship font-variant-*.

(For mask, we used a compile-time flag instead of run-time.)

Given the amount of work here, I'm inclined to wontfix this.