style: Implement parsing of the page property

Differential Revision: https://phabricator.services.mozilla.com/D131531

components/style/properties/counted_unknown_properties.py

@@ -38,7 +38,6 @@ COUNTED_UNKNOWN_PROPERTIES = [
     "-webkit-writing-mode",
     "baseline-shift",
     "-webkit-hyphenate-character",
-    "page",
     "-webkit-highlight",
     "background-repeat-x",
     "-webkit-padding-end",

components/style/properties/longhands/page.mako.rs

@@ -19,3 +19,13 @@ ${helpers.predefined_type(
     animation_value_type="none",
     rule_types_allowed=PAGE_RULE,
 )}
+
+${helpers.predefined_type(
+    "page",
+    "PageName",
+    "computed::PageName::auto()",
+    engines="gecko",
+    gecko_pref="layout.css.named-pages.enabled",
+    spec="https://drafts.csswg.org/css-page-3/#using-named-pages",
+    animation_value_type="discrete",
+)}

components/style/values/computed/mod.rs

@@ -72,7 +72,7 @@ pub use self::list::ListStyleType;
 pub use self::list::Quotes;
 pub use self::motion::{OffsetPath, OffsetRotate};
 pub use self::outline::OutlineStyle;
-pub use self::page::{Orientation, PageSize, PaperSize};
+pub use self::page::{Orientation, PageName, PageSize, PaperSize};
 pub use self::percentage::{NonNegativePercentage, Percentage};
 pub use self::position::AspectRatio;
 pub use self::position::{

components/style/values/computed/page.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-//! Computed @page at-rule properties
+//! Computed @page at-rule properties and named-page style properties
 
 use crate::values::computed::length::NonNegativeLength;
 use crate::values::computed::{Context, ToComputedValue};
@@ -13,6 +13,7 @@ use crate::values::specified::page as specified;
 pub use generics::page::GenericPageSize;
 pub use generics::page::Orientation;
 pub use generics::page::PaperSize;
+pub use specified::PageName;
 
 /// Computed value of the @page size descriptor
 ///

components/style/values/specified/mod.rs

@@ -69,7 +69,7 @@ pub use self::list::ListStyleType;
 pub use self::list::Quotes;
 pub use self::motion::{OffsetPath, OffsetRotate};
 pub use self::outline::OutlineStyle;
-pub use self::page::{Orientation, PageSize, PaperSize};
+pub use self::page::{Orientation, PageName, PageSize, PaperSize};
 pub use self::percentage::{NonNegativePercentage, Percentage};
 pub use self::position::AspectRatio;
 pub use self::position::{

components/style/values/specified/page.rs

@@ -2,10 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-//! Specified @page at-rule properties
+//! Specified @page at-rule properties and named-page style properties
 
 use crate::parser::{Parse, ParserContext};
-use crate::values::generics;
+use crate::values::{generics, CustomIdent};
 use crate::values::generics::size::Size2D;
 use crate::values::specified::length::NonNegativeLength;
 use cssparser::Parser;
@@ -46,3 +46,43 @@ impl Parse for PageSize {
         Ok(PageSize::Auto)
     }
 }
+
+/// Page name value.
+///
+/// https://drafts.csswg.org/css-page-3/#using-named-pages
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToComputedValue, ToResolvedValue, ToShmem)]
+#[repr(C, u8)]
+pub enum PageName {
+    /// `auto` value.
+    Auto,
+    /// Page name value
+    PageName(CustomIdent),
+}
+
+impl Parse for PageName {
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        let ident = input.expect_ident()?;
+        Ok(match_ignore_ascii_case! { ident,
+            "auto" => PageName::auto(),
+            _ => PageName::PageName(CustomIdent::from_ident(location, ident, &[])?),
+        })
+    }
+}
+
+impl PageName {
+    /// `auto` value.
+    #[inline]
+    pub fn auto() -> Self {
+        PageName::Auto
+    }
+
+    /// Whether this is the `auto` value.
+    #[inline]
+    pub fn is_auto(&self) -> bool {
+        matches!(*self, PageName::Auto)
+    }
+}