1 files changed, 247 insertions, 0 deletions
diff --git a/servo/components/style/stylesheets/origin.rs b/servo/components/style/stylesheets/origin.rs
new file mode 100644
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+++ b/servo/components/style/stylesheets/origin.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+//! [CSS cascade origins](https://drafts.csswg.org/css-cascade/#cascading-origins).
+
+use std::marker::PhantomData;
+use std::ops::BitOrAssign;
+
+/// Each style rule has an origin, which determines where it enters the cascade.
+///
+/// <https://drafts.csswg.org/css-cascade/#cascading-origins>
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToShmem, PartialOrd, Ord)]
+#[repr(u8)]
+pub enum Origin {
+    /// <https://drafts.csswg.org/css-cascade/#cascade-origin-user-agent>
+    UserAgent = 0x1,
+
+    /// <https://drafts.csswg.org/css-cascade/#cascade-origin-user>
+    User = 0x2,
+
+    /// <https://drafts.csswg.org/css-cascade/#cascade-origin-author>
+    Author = 0x4,
+}
+
+impl Origin {
+    /// Returns an origin that goes in order for `index`.
+    ///
+    /// This is used for iterating across origins.
+    fn from_index(index: i8) -> Option<Self> {
+        Some(match index {
+            0 => Origin::Author,
+            1 => Origin::User,
+            2 => Origin::UserAgent,
+            _ => return None,
+        })
+    }
+
+    fn to_index(self) -> i8 {
+        match self {
+            Origin::Author => 0,
+            Origin::User => 1,
+            Origin::UserAgent => 2,
+        }
+    }
+
+    /// Returns an iterator from this origin, towards all the less specific
+    /// origins. So for `UserAgent`, it'd iterate through all origins.
+    #[inline]
+    pub fn following_including(self) -> OriginSetIterator {
+        OriginSetIterator {
+            set: OriginSet::ORIGIN_USER | OriginSet::ORIGIN_AUTHOR | OriginSet::ORIGIN_USER_AGENT,
+            cur: self.to_index(),
+            rev: true,
+        }
+    }
+}
+
+bitflags! {
+    /// A set of origins. This is equivalent to Gecko's OriginFlags.
+    #[derive(MallocSizeOf)]
+    pub struct OriginSet: u8 {
+        /// <https://drafts.csswg.org/css-cascade/#cascade-origin-user-agent>
+        const ORIGIN_USER_AGENT = Origin::UserAgent as u8;
+        /// <https://drafts.csswg.org/css-cascade/#cascade-origin-user>
+        const ORIGIN_USER = Origin::User as u8;
+        /// <https://drafts.csswg.org/css-cascade/#cascade-origin-author>
+        const ORIGIN_AUTHOR = Origin::Author as u8;
+    }
+}
+
+impl OriginSet {
+    /// Returns an iterator over the origins present in this `OriginSet`.
+    ///
+    /// See the `OriginSet` documentation for information about the order
+    /// origins are iterated.
+    pub fn iter(&self) -> OriginSetIterator {
+        OriginSetIterator {
+            set: *self,
+            cur: 0,
+            rev: false,
+        }
+    }
+}
+
+impl From<Origin> for OriginSet {
+    fn from(origin: Origin) -> Self {
+        Self::from_bits_truncate(origin as u8)
+    }
+}
+
+impl BitOrAssign<Origin> for OriginSet {
+    fn bitor_assign(&mut self, origin: Origin) {
+        *self |= OriginSet::from(origin);
+    }
+}
+
+/// Iterates over the origins present in an `OriginSet`, in order from
+/// highest priority (author) to lower (user agent).
+#[derive(Clone)]
+pub struct OriginSetIterator {
+    set: OriginSet,
+    cur: i8,
+    rev: bool,
+}
+
+impl Iterator for OriginSetIterator {
+    type Item = Origin;
+
+    fn next(&mut self) -> Option<Origin> {
+        loop {
+            let origin = Origin::from_index(self.cur)?;
+
+            if self.rev {
+                self.cur -= 1;
+            } else {
+                self.cur += 1;
+            }
+
+            if self.set.contains(origin.into()) {
+                return Some(origin);
+            }
+        }
+    }
+}
+
+/// An object that stores a `T` for each origin of the CSS cascade.
+#[derive(Debug, Default, MallocSizeOf)]
+pub struct PerOrigin<T> {
+    /// Data for `Origin::UserAgent`.
+    pub user_agent: T,
+
+    /// Data for `Origin::User`.
+    pub user: T,
+
+    /// Data for `Origin::Author`.
+    pub author: T,
+}
+
+impl<T> PerOrigin<T> {
+    /// Returns a reference to the per-origin data for the specified origin.
+    #[inline]
+    pub fn borrow_for_origin(&self, origin: &Origin) -> &T {
+        match *origin {
+            Origin::UserAgent => &self.user_agent,
+            Origin::User => &self.user,
+            Origin::Author => &self.author,
+        }
+    }
+
+    /// Returns a mutable reference to the per-origin data for the specified
+    /// origin.
+    #[inline]
+    pub fn borrow_mut_for_origin(&mut self, origin: &Origin) -> &mut T {
+        match *origin {
+            Origin::UserAgent => &mut self.user_agent,
+            Origin::User => &mut self.user,
+            Origin::Author => &mut self.author,
+        }
+    }
+
+    /// Iterates over references to per-origin extra style data, from highest
+    /// level (author) to lowest (user agent).
+    pub fn iter_origins(&self) -> PerOriginIter<T> {
+        PerOriginIter {
+            data: &self,
+            cur: 0,
+            rev: false,
+        }
+    }
+
+    /// Iterates over references to per-origin extra style data, from lowest
+    /// level (user agent) to highest (author).
+    pub fn iter_origins_rev(&self) -> PerOriginIter<T> {
+        PerOriginIter {
+            data: &self,
+            cur: 2,
+            rev: true,
+        }
+    }
+
+    /// Iterates over mutable references to per-origin extra style data, from
+    /// highest level (author) to lowest (user agent).
+    pub fn iter_mut_origins(&mut self) -> PerOriginIterMut<T> {
+        PerOriginIterMut {
+            data: self,
+            cur: 0,
+            _marker: PhantomData,
+        }
+    }
+}
+
+/// Iterator over `PerOrigin<T>`, from highest level (author) to lowest
+/// (user agent).
+///
+/// We rely on this specific order for correctly looking up @font-face,
+/// @counter-style and @keyframes rules.
+pub struct PerOriginIter<'a, T: 'a> {
+    data: &'a PerOrigin<T>,
+    cur: i8,
+    rev: bool,
+}
+
+impl<'a, T> Iterator for PerOriginIter<'a, T>
+where
+    T: 'a,
+{
+    type Item = (&'a T, Origin);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let origin = Origin::from_index(self.cur)?;
+
+        self.cur += if self.rev { -1 } else { 1 };
+
+        Some((self.data.borrow_for_origin(&origin), origin))
+    }
+}
+
+/// Like `PerOriginIter<T>`, but iterates over mutable references to the
+/// per-origin data.
+///
+/// We must use unsafe code here since it's not possible for the borrow
+/// checker to know that we are safely returning a different reference
+/// each time from `next()`.
+pub struct PerOriginIterMut<'a, T: 'a> {
+    data: *mut PerOrigin<T>,
+    cur: i8,
+    _marker: PhantomData<&'a mut PerOrigin<T>>,
+}
+
+impl<'a, T> Iterator for PerOriginIterMut<'a, T>
+where
+    T: 'a,
+{
+    type Item = (&'a mut T, Origin);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let origin = Origin::from_index(self.cur)?;
+
+        self.cur += 1;
+
+        Some((
+            unsafe { (*self.data).borrow_mut_for_origin(&origin) },
+            origin,
+        ))
+    }
+}