Auto merge of #17972 - heycam:ignore-existing, r=bholley

style: Allow styles to be computed ignoring existing element data.

From https://bugzilla.mozilla.org/show_bug.cgi?id=1384824.

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components/layout/query.rs

@@ -702,7 +702,7 @@ pub fn process_resolved_style_request<'a, N>(context: &LayoutContext,
         thread_local: &mut tlc,
     };
 
-    let styles = resolve_style(&mut context, element, RuleInclusion::All);
+    let styles = resolve_style(&mut context, element, RuleInclusion::All, false);
     let style = styles.primary();
     let longhand_id = match *property {
         PropertyId::Longhand(id) => id,

components/style/gecko/generated/bindings.rs

@@ -2827,7 +2827,8 @@ extern "C" {
                                     rule_inclusion: StyleRuleInclusion,
                                     snapshots:
                                         *const ServoElementSnapshotTable,
-                                    set: RawServoStyleSetBorrowed)
+                                    set: RawServoStyleSetBorrowed,
+                                    ignore_existing_styles: bool)
      -> ServoStyleContextStrong;
 }
 extern "C" {

components/style/properties/gecko.mako.rs

@@ -2181,7 +2181,7 @@ fn static_assert() {
     }
 
     pub fn set_font_family(&mut self, v: longhands::font_family::computed_value::T) {
-        use properties::longhands::font_family::computed_value::FontFamily;
+        use properties::longhands::font_family::computed_value::{FontFamily, FamilyNameSyntax};
 
         let list = &mut self.gecko.mFont.fontlist;
         unsafe { Gecko_FontFamilyList_Clear(list); }
@@ -2191,7 +2191,8 @@ fn static_assert() {
         for family in &v.0 {
             match *family {
                 FontFamily::FamilyName(ref f) => {
-                    unsafe { Gecko_FontFamilyList_AppendNamed(list, f.name.as_ptr(), f.quoted); }
+                    let quoted = matches!(f.syntax, FamilyNameSyntax::Quoted);
+                    unsafe { Gecko_FontFamilyList_AppendNamed(list, f.name.as_ptr(), quoted); }
                 }
                 FontFamily::Generic(ref name) => {
                     let (family_type, generic) = FontFamily::generic(name);
@@ -2222,7 +2223,7 @@ fn static_assert() {
     }
 
     pub fn clone_font_family(&self) -> longhands::font_family::computed_value::T {
-        use properties::longhands::font_family::computed_value::{FontFamily, FamilyName};
+        use properties::longhands::font_family::computed_value::{FontFamily, FamilyName, FamilyNameSyntax};
         use gecko_bindings::structs::FontFamilyType;
         use gecko_string_cache::Atom;
 
@@ -2235,13 +2236,16 @@ fn static_assert() {
                     FontFamilyType::eFamily_cursive => FontFamily::Generic(atom!("cursive")),
                     FontFamilyType::eFamily_fantasy => FontFamily::Generic(atom!("fantasy")),
                     FontFamilyType::eFamily_moz_fixed => FontFamily::Generic(Atom::from("-moz-fixed")),
-                    FontFamilyType::eFamily_named => FontFamily::FamilyName(FamilyName {
-                        name: (&*gecko_font_family_name.mName).into(),
-                        quoted: false
-                    }),
+                    FontFamilyType::eFamily_named => {
+                        let name = Atom::from(&*gecko_font_family_name.mName);
+                        FontFamily::FamilyName(FamilyName {
+                            name: name.clone(),
+                            syntax: FamilyNameSyntax::Identifiers(vec![name]),
+                        })
+                    },
                     FontFamilyType::eFamily_named_quoted => FontFamily::FamilyName(FamilyName {
                         name: (&*gecko_font_family_name.mName).into(),
-                        quoted: true
+                        syntax: FamilyNameSyntax::Quoted,
                     }),
                     x => panic!("Found unexpected font FontFamilyType: {:?}", x),
                 }

components/style/properties/longhand/font.mako.rs

@@ -96,7 +96,14 @@ macro_rules! impl_gecko_keyword_conversions {
         #[cfg_attr(feature = "servo", derive(HeapSizeOf, Deserialize, Serialize))]
         pub struct FamilyName {
             pub name: Atom,
-            pub quoted: bool,
+            pub syntax: FamilyNameSyntax,
+        }
+
+        #[derive(Debug, PartialEq, Eq, Clone, Hash)]
+        #[cfg_attr(feature = "servo", derive(HeapSizeOf, Deserialize, Serialize))]
+        pub enum FamilyNameSyntax {
+            Quoted,
+            Identifiers(Vec<Atom>),
         }
 
         impl FontFamily {
@@ -139,7 +146,7 @@ macro_rules! impl_gecko_keyword_conversions {
                 // quoted by default.
                 FontFamily::FamilyName(FamilyName {
                     name: input,
-                    quoted: true,
+                    syntax: FamilyNameSyntax::Quoted,
                 })
             }
 
@@ -148,10 +155,14 @@ macro_rules! impl_gecko_keyword_conversions {
                 if let Ok(value) = input.try(|i| i.expect_string_cloned()) {
                     return Ok(FontFamily::FamilyName(FamilyName {
                         name: Atom::from(&*value),
-                        quoted: true,
+                        syntax: FamilyNameSyntax::Quoted,
                     }))
                 }
+
+                let mut identifiers = vec![];
+
                 let first_ident = input.expect_ident()?.clone();
+                identifiers.push(Atom::from(&*first_ident));
 
                 // FIXME(bholley): The fast thing to do here would be to look up the
                 // string (as lowercase) in the static atoms table. We don't have an
@@ -188,14 +199,16 @@ macro_rules! impl_gecko_keyword_conversions {
                     let ident = input.expect_ident()?;
                     value.push_str(" ");
                     value.push_str(&ident);
+                    identifiers.push(Atom::from(&*ident.clone()));
                 }
                 while let Ok(ident) = input.try(|i| i.expect_ident_cloned()) {
                     value.push_str(" ");
                     value.push_str(&ident);
+                    identifiers.push(Atom::from(&*ident));
                 }
                 Ok(FontFamily::FamilyName(FamilyName {
                     name: Atom::from(value),
-                    quoted: false,
+                    syntax: FamilyNameSyntax::Identifiers(identifiers),
                 }))
             }
 
@@ -229,12 +242,23 @@ macro_rules! impl_gecko_keyword_conversions {
 
         impl ToCss for FamilyName {
             fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-                if self.quoted {
-                    dest.write_char('"')?;
-                    write!(CssStringWriter::new(dest), "{}", self.name)?;
-                    dest.write_char('"')
-                } else {
-                    serialize_identifier(&*self.name.to_string(), dest)
+                match self.syntax {
+                    FamilyNameSyntax::Quoted => {
+                        dest.write_char('"')?;
+                        write!(CssStringWriter::new(dest), "{}", self.name)?;
+                        dest.write_char('"')
+                    }
+                    FamilyNameSyntax::Identifiers(ref identifiers) => {
+                        let mut first = true;
+                        for identifier in identifiers {
+                            if !first {
+                                dest.write_char(' ')?;
+                            }
+                            serialize_identifier(&*identifier.to_string(), dest)?;
+                            first = false;
+                        }
+                        Ok(())
+                    }
                 }
             }
         }
@@ -2508,7 +2532,7 @@ ${helpers.single_keyword("-moz-math-variant",
                     use properties::longhands::font_family::computed_value::*;
                     FontFamily::FamilyName(FamilyName {
                         name: (&*font.mName).into(),
-                        quoted: true
+                        syntax: FamilyNameSyntax::Quoted,
                     })
                 }).collect::<Vec<_>>();
                 let weight = longhands::font_weight::computed_value::T::from_gecko_weight(system.weight);

components/style/traversal.rs

@@ -391,6 +391,7 @@ pub fn resolve_style<E>(
     context: &mut StyleContext<E>,
     element: E,
     rule_inclusion: RuleInclusion,
+    ignore_existing_style: bool,
 ) -> ElementStyles
 where
     E: TElement,
@@ -398,6 +399,7 @@ where
     use style_resolver::StyleResolverForElement;
 
     debug_assert!(rule_inclusion == RuleInclusion::DefaultOnly ||
+                  ignore_existing_style ||
                   element.borrow_data().map_or(true, |d| !d.has_styles()),
                   "Why are we here?");
     let mut ancestors_requiring_style_resolution = SmallVec::<[E; 16]>::new();
@@ -408,7 +410,7 @@ where
     let mut style = None;
     let mut ancestor = element.traversal_parent();
     while let Some(current) = ancestor {
-        if rule_inclusion == RuleInclusion::All {
+        if rule_inclusion == RuleInclusion::All && !ignore_existing_style {
             if let Some(data) = current.borrow_data() {
                 if let Some(ancestor_style) = data.styles.get_primary() {
                     style = Some(ancestor_style.clone());