Bug 1865065 - Do not apply content-visibility to frames with NS_FRAME_SVG_LAYOUT set. r=emilio,firefox-style-system-reviewers

The CSS containment spec [1] indicates that `content-visibility` applies
to "elements for which size containment can apply" and additionally
(1) "in the case of SVG2, the `contain` property only applies to `<svg>`
elements that have an associated CSS layout box".
(2) "size containment has no effect" for misc cases on CSS boxes.

Currently, we properly do (1) (via the NS_FRAME_SVG_LAYOUT flag)
and (2) (via the `PrecludesSizeContainmentOrContentVisibilityWithFrame`)
for size containment, but only exclude the latter for
`content-visibility`. This patch makes sure also do (1) and update
comments to refer to relevant text from the spec.

Differential Revision: https://phabricator.services.mozilla.com/D194995

layout/style/nsStyleStruct.cpp

@@ -3494,8 +3494,22 @@ nscoord StyleCalcLengthPercentage::Resolve(nscoord aBasis,
 
 bool nsStyleDisplay::PrecludesSizeContainmentOrContentVisibilityWithFrame(
     const nsIFrame& aFrame) const {
-  // Note: The spec for size containment says it should have no effect on
-  // non-atomic, inline-level boxes.
+  // The spec says that in the case of SVG, the contain property only applies
+  // to <svg> elements that have an associated CSS layout box.
+  // https://drafts.csswg.org/css-contain/#contain-property
+  // Internal SVG elements do not use the standard CSS box model, and wouldn't
+  // be affected by size containment. By disabling it we prevent them from
+  // becoming query containers for size features.
+  if (aFrame.HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    return true;
+  }
+
+  // Note: The spec for size containment says it should have no effect
+  // - on non-atomic, inline-level boxes.
+  // - on internal ruby boxes.
+  // - if inner display type is table.
+  // - on internal table boxes.
+  // https://drafts.csswg.org/css-contain/#containment-size
   bool isNonReplacedInline = aFrame.IsLineParticipant() && !aFrame.IsReplaced();
   return isNonReplacedInline || IsInternalRubyDisplayType() ||
          DisplayInside() == mozilla::StyleDisplayInside::Table ||
@@ -3513,13 +3527,6 @@ ContainSizeAxes nsStyleDisplay::GetContainSizeAxes(
     return ContainSizeAxes(false, false);
   }
 
-  // Internal SVG elements do not use the standard CSS box model, and wouldn't
-  // be affected by size containment. By disabling it we prevent them from
-  // becoming query containers for size features.
-  if (aFrame.HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
-    return ContainSizeAxes(false, false);
-  }
-
   // https://drafts.csswg.org/css-contain-2/#content-visibility
   // If this content skips its content via content-visibility, it always has
   // size containment.
@@ -3538,6 +3545,8 @@ StyleContentVisibility nsStyleDisplay::ContentVisibility(
   if (MOZ_LIKELY(mContentVisibility == StyleContentVisibility::Visible)) {
     return StyleContentVisibility::Visible;
   }
+  // content-visibility applies to elements for which size containment applies.
+  // https://drafts.csswg.org/css-contain/#content-visibility
   if (PrecludesSizeContainmentOrContentVisibilityWithFrame(aFrame)) {
     return StyleContentVisibility::Visible;
   }

testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-on-g.html.ini

@@ -1,2 +0,0 @@
-[content-visibility-on-g.html]
-  expected: FAIL