Bug 2024601 - patch 3 - Evaluate substitution functions in style query expression values. r=firefox-style-system-reviewers,emilio

jfkthame · jfkthame · commit d4728d9065d8 · 2026-04-01T00:04:54.000Z
This makes the examples with var(--foo, default) pass, as well as those with attr() that depend on the attribute lookup failing (so they use the default); actual attr lookups will require an AttributeTracker in the substitute() call. Differential Revision: https://phabricator.services.mozilla.com/D290904
diff --git a/servo/components/style/custom_properties.rs b/servo/components/style/custom_properties.rs
@@ -2392,6 +2392,7 @@ impl<'a> Substitution<'a> {
 }
 
 /// Result of var(), env(), and attr() substitution.
+#[derive(Debug)]
 pub struct SubstitutionResult<'a> {
     /// The resolved CSS string after substitution.
     pub css: Cow<'a, str>,
diff --git a/servo/components/style/queries/feature_expression.rs b/servo/components/style/queries/feature_expression.rs
@@ -8,7 +8,9 @@
 use super::feature::{Evaluator, QueryFeatureDescription};
 use super::feature::{FeatureFlags, KeywordDiscriminant};
 use crate::context::QuirksMode;
-use crate::custom_properties::VariableValue as CustomVariableValue;
+use crate::custom_properties::{
+    self, ComputedSubstitutionFunctions, VariableValue as CustomVariableValue,
+};
 use crate::derives::*;
 use crate::parser::{Parse, ParserContext};
 use crate::properties::CSSWideKeyword;
@@ -1016,6 +1018,25 @@ impl QueryStyleRange {
                     },
                 }
             },
+            QueryExpressionValue::Function(value) => {
+                let sub_funcs = ComputedSubstitutionFunctions::new(
+                    Some(context.inherited_custom_properties().clone()),
+                    None,
+                );
+                let stylist = context
+                    .builder
+                    .stylist
+                    .expect("container queries should have a stylist around");
+                let substituted = custom_properties::substitute(
+                    &value,
+                    &sub_funcs,
+                    stylist,
+                    context,
+                    &mut crate::dom::AttributeTracker::new_dummy(),
+                )
+                .ok()?;
+                Self::resolve_universal(&substituted.css, &value.url_data, context, visited_set)
+            },
             QueryExpressionValue::Length(v) => {
                 Some(Component::Length(v.to_computed_value(context)))
             },
diff --git a/testing/web-platform/meta/css/css-conditional/container-queries/query-evaluation-style.html.ini b/testing/web-platform/meta/css/css-conditional/container-queries/query-evaluation-style.html.ini
@@ -2,18 +2,3 @@
 
   [style(1px < attr(xyzzy type(<length>)) < 10px)]
     expected: FAIL
-
-  [style(1px < attr(plugh, 5px) < 10px)]
-    expected: FAIL
-
-  [style(1px < attr(plugh type(<length>), 5px) < 10px)]
-    expected: FAIL
-
-  [style(var(--unknown-prop, 20px) > 10px)]
-    expected: FAIL
-
-  [style(var(--prop, 5px) > 10px)]
-    expected: FAIL
-
-  [style(var(--length, 20px) < 10px)]
-    expected: FAIL

Original file line number	Diff line number	Diff line change
`@@ -2392,6 +2392,7 @@ impl<'a> Substitution<'a> {`
`2392`	`2392`	`}`
`2393`	`2393`
`2394`	`2394`	`/// Result of var(), env(), and attr() substitution.`
	`2395`	`+#[derive(Debug)]`
`2395`	`2396`	`pub struct SubstitutionResult<'a> {`
`2396`	`2397`	`/// The resolved CSS string after substitution.`
`2397`	`2398`	`pub css: Cow<'a, str>,`