Auto merge of #18373 - canaltinova:font-feature-vals, r=xidorn

Don't unnecessarily construct gfxFontFeatureValueSet

This is reviewed by xidorn in bugzilla.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1394551](https://bugzilla.mozilla.org/show_bug.cgi?id=1394551)

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---
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components/style/gecko/generated/bindings.rs

@@ -913,6 +913,10 @@ extern "C" {
 extern "C" {
     pub fn Gecko_nsFont_Destroy(dst: *mut nsFont);
 }
+extern "C" {
+    pub fn Gecko_ConstructFontFeatureValueSet()
+     -> *mut gfxFontFeatureValueSet;
+}
 extern "C" {
     pub fn Gecko_AppendFeatureValueHashEntry(value_set:
                                                  *mut gfxFontFeatureValueSet,
@@ -2047,10 +2051,8 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_StyleSet_BuildFontFeatureValueSet(set:
-                                                       RawServoStyleSetBorrowed,
-                                                   list:
-                                                       *mut gfxFontFeatureValueSet)
-     -> bool;
+                                                       RawServoStyleSetBorrowed)
+     -> *mut gfxFontFeatureValueSet;
 }
 extern "C" {
     pub fn Servo_StyleSet_ResolveForDeclarations(set:

components/style/stylesheets/font_feature_values_rule.rs

@@ -210,7 +210,7 @@ impl<'a, 'b, 'i, T> DeclarationParser<'i> for FFVDeclarationsParser<'a, 'b, T>
                        -> Result<(), ParseError<'i>> {
         let value = input.parse_entirely(|i| T::parse(self.context, i))?;
         let new = FFVDeclaration {
-            name: Atom::from(&*name).to_ascii_lowercase(),
+            name: Atom::from(&*name),
             value: value,
         };
         update_or_push(&mut self.declarations, new);

ports/geckolib/glue.rs

@@ -47,6 +47,7 @@ use style::gecko_bindings::bindings::{ServoCssRulesBorrowed, ServoCssRulesStrong
 use style::gecko_bindings::bindings::{nsACString, nsAString, nsCSSPropertyIDSetBorrowedMut};
 use style::gecko_bindings::bindings::Gecko_AddPropertyToSet;
 use style::gecko_bindings::bindings::Gecko_AppendPropertyValuePair;
+use style::gecko_bindings::bindings::Gecko_ConstructFontFeatureValueSet;
 use style::gecko_bindings::bindings::Gecko_GetOrCreateFinalKeyframe;
 use style::gecko_bindings::bindings::Gecko_GetOrCreateInitialKeyframe;
 use style::gecko_bindings::bindings::Gecko_GetOrCreateKeyframeAtStart;
@@ -3560,26 +3561,30 @@ pub extern "C" fn Servo_StyleSet_GetCounterStyleRule(raw_data: RawServoStyleSetB
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleSet_BuildFontFeatureValueSet(
-  raw_data: RawServoStyleSetBorrowed,
-  set: *mut gfxFontFeatureValueSet
-) -> bool {
+  raw_data: RawServoStyleSetBorrowed) -> *mut gfxFontFeatureValueSet {
     let data = PerDocumentStyleData::from_ffi(raw_data).borrow();
 
     let global_style_data = &*GLOBAL_STYLE_DATA;
     let guard = global_style_data.shared_lock.read();
 
+    let has_rule = data.extra_style_data
+                  .iter_origins()
+                  .any(|(d, _)| !d.font_feature_values.is_empty());
+
+    if !has_rule {
+      return ptr::null_mut();
+    }
+
     let font_feature_values_iter = data.extra_style_data
         .iter_origins_rev()
         .flat_map(|(d, _)| d.font_feature_values.iter());
 
-    let mut any_rule = false;
+    let set = unsafe { Gecko_ConstructFontFeatureValueSet() };
     for src in font_feature_values_iter {
-        any_rule = true;
         let rule = src.read_with(&guard);
         rule.set_at_rules(set);
     }
-
-    any_rule
+    set
 }
 
 #[no_mangle]