style: Correct style sharing handling for any element that considered `:has()` in selector matching

For any element that anchors a `:has()` selector (i.e. Matches a selector that
contains a `:has()` on its rightmost side), we prevent style sharing altogether,
as evaluation of the `:has()` selector is required in the first place to
determine style sharing.

On the other hand, any element matching a rule containing `:has()` without
anchoring it can do style sharing for siblings, but not cousins.

Differential Revision: https://phabricator.services.mozilla.com/D176836

1 files changed, 4 insertions, 1 deletions

diff --git a/components/style/properties/computed_value_flags.rs b/components/style/properties/computed_value_flags.rs
index 9b834efc222..d84311de084 100644
--- a/components/style/properties/computed_value_flags.rs
+++ b/components/style/properties/computed_value_flags.rs
@@ -118,6 +118,9 @@ bitflags! {
         /// A flag used to mark styles which have `container-type` of `size` or
         /// `inline-size`, or under one.
         const SELF_OR_ANCESTOR_HAS_SIZE_CONTAINER_TYPE = 1 << 23;
+
+        /// Whether the style evaluated any relative selector.
+        const CONSIDERED_RELATIVE_SELECTOR = 1 << 24;
     }
 }
 
@@ -150,7 +153,7 @@ impl ComputedValueFlags {
     /// Flags that are an input to the cascade.
     #[inline]
     fn cascade_input_flags() -> Self {
-        Self::USES_VIEWPORT_UNITS_ON_CONTAINER_QUERIES
+        Self::USES_VIEWPORT_UNITS_ON_CONTAINER_QUERIES | Self::CONSIDERED_RELATIVE_SELECTOR
     }
 
     /// Returns the flags that are always propagated to descendants.