Bug 1865810 - [css-properties-values-api] Recompute initial values when viewport changes r=firefox-style-system-reviewers,emilio

If the initial values of custom property registrations contain viewport
units, changing the viewport will result in recomputing the initial
values.

Differential Revision: https://phabricator.services.mozilla.com/D194668

servo/components/style/custom_properties.rs

@@ -864,9 +864,17 @@ pub struct CustomPropertiesBuilder<'a, 'b: 'a> {
 impl<'a, 'b: 'a> CustomPropertiesBuilder<'a, 'b> {
     /// Create a new builder, inheriting from a given custom properties map.
     pub fn new(stylist: &'a Stylist, computed_context: &'a computed::Context<'b>) -> Self {
+        let is_root_element = computed_context.is_root_element();
+
         let inherited = computed_context.inherited_custom_properties();
         let initial_values = stylist.get_custom_property_initial_values();
-        let is_root_element = computed_context.is_root_element();
+
+        // Reuse flags from computing registered custom properties initial values, such as whether
+        // they depend on viewport units.
+        computed_context
+            .style()
+            .add_flags(stylist.get_custom_property_initial_values_flags());
+
         Self {
             seen: PrecomputedHashSet::default(),
             reverted: Default::default(),

servo/ports/geckolib/glue.rs

@@ -21,6 +21,7 @@ use std::os::raw::c_void;
 use std::ptr;
 use style::color::mix::ColorInterpolationMethod;
 use style::color::{AbsoluteColor, ColorSpace};
+use style::computed_value_flags::ComputedValueFlags;
 use style::context::ThreadLocalStyleContext;
 use style::context::{CascadeInputs, QuirksMode, SharedStyleContext, StyleContext};
 use style::counter_style;
@@ -8547,8 +8548,9 @@ pub unsafe extern "C" fn Servo_InvalidateForViewportUnits(
     root: &RawGeckoElement,
     dynamic_only: bool,
 ) {
-    let document_data = document_style.borrow();
-    let device = document_data.stylist.device();
+    let mut document_data = document_style.borrow_mut();
+    let ref mut stylist = document_data.stylist;
+    let device = stylist.device();
 
     if !device.used_viewport_size() {
         return;
@@ -8558,6 +8560,14 @@ pub unsafe extern "C" fn Servo_InvalidateForViewportUnits(
         return;
     }
 
+    // If the viewport changed, then initial values containing viewport units need to be recomputed.
+    if stylist
+        .get_custom_property_initial_values_flags()
+        .intersects(ComputedValueFlags::USES_VIEWPORT_UNITS)
+    {
+        stylist.rebuild_initial_values_for_custom_properties();
+    }
+
     if style::invalidation::viewport_units::invalidate(GeckoElement(root)) {
         // The invalidation machinery propagates the bits up, but we still need
         // to tell the Gecko restyle root machinery about it.

testing/web-platform/meta/css/css-properties-values-api/at-property-viewport-units-dynamic.html.ini

@@ -1,3 +0,0 @@
-[at-property-viewport-units-dynamic.html]
-  [@property: viewport units in initial value (dynamic)]
-    expected: FAIL