Bug 1865332 - Expose MozTransform in CSSStyleDeclaration unconditiona…

…lly. r=jwatt Shipping CSS zoom requires to remove -moz-transform from stylesheets. That's generally fine, however we've seen a bunch of regressions due to sites doing broken feature detection in JS (see bugs mentioned in the patch). It seems like exposing MozTransform in CSSStyleDeclaration is a requirement, for some large amount of pages. The hypothesis here is that setting both MozTransform and zoom using JS is uncommon. We could expose it conditionally, with some sort of reverse origin trial or what not but, given the amount of regressions only on Nightly and that this is harmless if you do proper feature detection, I think I'd rather expose it unconditionally, rather than playing whack-a-mole fixing pages after the fact. We could play whack-a-mole with pages that use zoom and -moz-transform, if needed in the future, which seems like a safer path forward. Note that this change currently only affects behavior on Nightly, because on other release channels -moz-transform is enabled right now. Differential Revision: https://phabricator.services.mozilla.com/D194006
dothq · Nov 19, 2023 · 5bbdc56 · 5bbdc56
1 parent 0fbcd96
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diff --git a/dom/bindings/GenerateCSS2PropertiesWebIDL.py b/dom/bindings/GenerateCSS2PropertiesWebIDL.py
@@ -50,7 +50,9 @@ def generate(output, idlFilename, dataFile):
             # a function instead of checking the pref directly.
             if p.method == "BackdropFilter":
                 extendedAttrs.append('Func="nsCSSProps::IsBackdropFilterAvailable"')
-            else:
+            # MozTransform accessor is generated regardless, for compatibility,
+            # see bug 1861828, 1865332, 1860424, 1864970, 1865332.
+            elif p.method != "MozTransform":
                 extendedAttrs.append('Pref="%s"' % p.pref)
 
         def add_extra_accessors(p):

diff --git a/testing/web-platform/mozilla/tests/css/cssom/moz-transform-exists.html b/testing/web-platform/mozilla/tests/css/cssom/moz-transform-exists.html
@@ -0,0 +1,15 @@
+<!doctype html>
+<title>CSS Test: MozTransform exists in Gecko for compat reasons</title>
+<meta charset="utf-8">
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:[email protected]">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+test(function() {
+  let el = document.documentElement;
+  assert_true("MozTransform" in el.style, "MozTransform exists");
+  el.style.MozTransform = "scale(1)";
+  assert_not_equals(el.MozTransform, "", "MozTransform sets the value");
+  assert_equals(el.transform, el.MozTransform, "MozTransform is an alias of transform");
+});
+</script>