2 files changed, 637 insertions, 0 deletions
diff --git a/servo/components/style/gecko_string_cache/mod.rs b/servo/components/style/gecko_string_cache/mod.rs
new file mode 100644
index 0000000000..cb040390cf
--- /dev/null
+++ b/servo/components/style/gecko_string_cache/mod.rs
@@ -0,0 +1,532 @@
+/* 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/. */
+
+#![allow(unsafe_code)]
+// This is needed for the constants in atom_macro.rs, because we have some
+// atoms whose names differ only by case, e.g. datetime and dateTime.
+#![allow(non_upper_case_globals)]
+
+//! A drop-in replacement for string_cache, but backed by Gecko `nsAtom`s.
+
+use crate::gecko_bindings::bindings::Gecko_AddRefAtom;
+use crate::gecko_bindings::bindings::Gecko_Atomize;
+use crate::gecko_bindings::bindings::Gecko_Atomize16;
+use crate::gecko_bindings::bindings::Gecko_ReleaseAtom;
+use crate::gecko_bindings::structs::root::mozilla::detail::gGkAtoms;
+use crate::gecko_bindings::structs::root::mozilla::detail::kGkAtomsArrayOffset;
+use crate::gecko_bindings::structs::root::mozilla::detail::GkAtoms_Atoms_AtomsCount;
+use crate::gecko_bindings::structs::{nsAtom, nsDynamicAtom, nsStaticAtom};
+use nsstring::{nsAString, nsStr};
+use precomputed_hash::PrecomputedHash;
+use std::borrow::{Borrow, Cow};
+use std::char::{self, DecodeUtf16};
+use std::fmt::{self, Write};
+use std::hash::{Hash, Hasher};
+use std::iter::Cloned;
+use std::mem::{self, ManuallyDrop};
+use std::num::NonZeroUsize;
+use std::ops::Deref;
+use std::{slice, str};
+use style_traits::SpecifiedValueInfo;
+use to_shmem::{self, SharedMemoryBuilder, ToShmem};
+
+#[macro_use]
+#[allow(improper_ctypes, non_camel_case_types, missing_docs)]
+pub mod atom_macro {
+    include!(concat!(env!("OUT_DIR"), "/gecko/atom_macro.rs"));
+}
+
+#[macro_use]
+pub mod namespace;
+
+pub use self::namespace::{Namespace, WeakNamespace};
+
+/// A handle to a Gecko atom. This is a type that can represent either:
+///
+///  * A strong reference to a dynamic atom (an `nsAtom` pointer), in which case
+///    the `usize` just holds the pointer value.
+///
+///  * A byte offset from `gGkAtoms` to the `nsStaticAtom` object (shifted to
+///    the left one bit, and with the lower bit set to `1` to differentiate it
+///    from the above), so `(offset << 1 | 1)`.
+///
+#[derive(Eq, PartialEq)]
+#[repr(C)]
+pub struct Atom(NonZeroUsize);
+
+/// An atom *without* a strong reference.
+///
+/// Only usable as `&'a WeakAtom`,
+/// where `'a` is the lifetime of something that holds a strong reference to that atom.
+pub struct WeakAtom(nsAtom);
+
+/// The number of static atoms we have.
+const STATIC_ATOM_COUNT: usize = GkAtoms_Atoms_AtomsCount as usize;
+
+/// Returns the Gecko static atom array.
+///
+/// We have this rather than use rust-bindgen to generate
+/// mozilla::detail::gGkAtoms and then just reference gGkAtoms.mAtoms, so we
+/// avoid a problem with lld-link.exe on Windows.
+///
+/// https://bugzilla.mozilla.org/show_bug.cgi?id=1517685
+#[inline]
+fn static_atoms() -> &'static [nsStaticAtom; STATIC_ATOM_COUNT] {
+    unsafe {
+        let addr = &gGkAtoms as *const _ as usize + kGkAtomsArrayOffset as usize;
+        &*(addr as *const _)
+    }
+}
+
+/// Returns whether the specified address points to one of the nsStaticAtom
+/// objects in the Gecko static atom array.
+#[inline]
+fn valid_static_atom_addr(addr: usize) -> bool {
+    unsafe {
+        let atoms = static_atoms();
+        let start = atoms.as_ptr();
+        let end = atoms.get_unchecked(STATIC_ATOM_COUNT) as *const _;
+        let in_range = addr >= start as usize && addr < end as usize;
+        let aligned = addr % mem::align_of::<nsStaticAtom>() == 0;
+        in_range && aligned
+    }
+}
+
+impl Deref for Atom {
+    type Target = WeakAtom;
+
+    #[inline]
+    fn deref(&self) -> &WeakAtom {
+        unsafe {
+            let addr = if self.is_static() {
+                (&gGkAtoms as *const _ as usize) + (self.0.get() >> 1)
+            } else {
+                self.0.get()
+            };
+            debug_assert!(!self.is_static() || valid_static_atom_addr(addr));
+            WeakAtom::new(addr as *const nsAtom)
+        }
+    }
+}
+
+impl PrecomputedHash for Atom {
+    #[inline]
+    fn precomputed_hash(&self) -> u32 {
+        self.get_hash()
+    }
+}
+
+impl Borrow<WeakAtom> for Atom {
+    #[inline]
+    fn borrow(&self) -> &WeakAtom {
+        self
+    }
+}
+
+impl ToShmem for Atom {
+    fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> to_shmem::Result<Self> {
+        if !self.is_static() {
+            return Err(format!(
+                "ToShmem failed for Atom: must be a static atom: {}",
+                self
+            ));
+        }
+
+        Ok(ManuallyDrop::new(Atom(self.0)))
+    }
+}
+
+impl Eq for WeakAtom {}
+impl PartialEq for WeakAtom {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        let weak: *const WeakAtom = self;
+        let other: *const WeakAtom = other;
+        weak == other
+    }
+}
+
+impl PartialEq<Atom> for WeakAtom {
+    #[inline]
+    fn eq(&self, other: &Atom) -> bool {
+        self == &**other
+    }
+}
+
+unsafe impl Send for Atom {}
+unsafe impl Sync for Atom {}
+unsafe impl Sync for WeakAtom {}
+
+impl WeakAtom {
+    /// Construct a `WeakAtom` from a raw `nsAtom`.
+    #[inline]
+    pub unsafe fn new<'a>(atom: *const nsAtom) -> &'a mut Self {
+        &mut *(atom as *mut WeakAtom)
+    }
+
+    /// Clone this atom, bumping the refcount if the atom is not static.
+    #[inline]
+    pub fn clone(&self) -> Atom {
+        unsafe { Atom::from_raw(self.as_ptr()) }
+    }
+
+    /// Get the atom hash.
+    #[inline]
+    pub fn get_hash(&self) -> u32 {
+        self.0.mHash
+    }
+
+    /// Get the atom as a slice of utf-16 chars.
+    #[inline]
+    pub fn as_slice(&self) -> &[u16] {
+        let string = if self.is_static() {
+            let atom_ptr = self.as_ptr() as *const nsStaticAtom;
+            let string_offset = unsafe { (*atom_ptr).mStringOffset };
+            let string_offset = -(string_offset as isize);
+            let u8_ptr = atom_ptr as *const u8;
+            // It is safe to use offset() here because both addresses are within
+            // the same struct, e.g. mozilla::detail::gGkAtoms.
+            unsafe { u8_ptr.offset(string_offset) as *const u16 }
+        } else {
+            let atom_ptr = self.as_ptr() as *const nsDynamicAtom;
+            // Dynamic atom chars are stored at the end of the object.
+            unsafe { atom_ptr.offset(1) as *const u16 }
+        };
+        unsafe { slice::from_raw_parts(string, self.len() as usize) }
+    }
+
+    // NOTE: don't expose this, since it's slow, and easy to be misused.
+    fn chars(&self) -> DecodeUtf16<Cloned<slice::Iter<u16>>> {
+        char::decode_utf16(self.as_slice().iter().cloned())
+    }
+
+    /// Execute `cb` with the string that this atom represents.
+    ///
+    /// Find alternatives to this function when possible, please, since it's
+    /// pretty slow.
+    pub fn with_str<F, Output>(&self, cb: F) -> Output
+    where
+        F: FnOnce(&str) -> Output,
+    {
+        let mut buffer = mem::MaybeUninit::<[u8; 64]>::uninit();
+        let buffer = unsafe { &mut *buffer.as_mut_ptr() };
+
+        // The total string length in utf16 is going to be less than or equal
+        // the slice length (each utf16 character is going to take at least one
+        // and at most 2 items in the utf16 slice).
+        //
+        // Each of those characters will take at most four bytes in the utf8
+        // one. Thus if the slice is less than 64 / 4 (16) we can guarantee that
+        // we'll decode it in place.
+        let owned_string;
+        let len = self.len();
+        let utf8_slice = if len <= 16 {
+            let mut total_len = 0;
+
+            for c in self.chars() {
+                let c = c.unwrap_or(char::REPLACEMENT_CHARACTER);
+                let utf8_len = c.encode_utf8(&mut buffer[total_len..]).len();
+                total_len += utf8_len;
+            }
+
+            let slice = unsafe { str::from_utf8_unchecked(&buffer[..total_len]) };
+            debug_assert_eq!(slice, String::from_utf16_lossy(self.as_slice()));
+            slice
+        } else {
+            owned_string = String::from_utf16_lossy(self.as_slice());
+            &*owned_string
+        };
+
+        cb(utf8_slice)
+    }
+
+    /// Returns whether this atom is static.
+    #[inline]
+    pub fn is_static(&self) -> bool {
+        self.0.mIsStatic() != 0
+    }
+
+    /// Returns whether this atom is ascii lowercase.
+    #[inline]
+    fn is_ascii_lowercase(&self) -> bool {
+        self.0.mIsAsciiLowercase() != 0
+    }
+
+    /// Returns the length of the atom string.
+    #[inline]
+    pub fn len(&self) -> u32 {
+        self.0.mLength()
+    }
+
+    /// Returns whether this atom is the empty string.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Returns the atom as a mutable pointer.
+    #[inline]
+    pub fn as_ptr(&self) -> *mut nsAtom {
+        let const_ptr: *const nsAtom = &self.0;
+        const_ptr as *mut nsAtom
+    }
+
+    /// Convert this atom to ASCII lower-case
+    pub fn to_ascii_lowercase(&self) -> Atom {
+        if self.is_ascii_lowercase() {
+            return self.clone();
+        }
+
+        let slice = self.as_slice();
+        let mut buffer = mem::MaybeUninit::<[u16; 64]>::uninit();
+        let buffer = unsafe { &mut *buffer.as_mut_ptr() };
+        let mut vec;
+        let mutable_slice = if let Some(buffer_prefix) = buffer.get_mut(..slice.len()) {
+            buffer_prefix.copy_from_slice(slice);
+            buffer_prefix
+        } else {
+            vec = slice.to_vec();
+            &mut vec
+        };
+        for char16 in &mut *mutable_slice {
+            if *char16 <= 0x7F {
+                *char16 = (*char16 as u8).to_ascii_lowercase() as u16
+            }
+        }
+        Atom::from(&*mutable_slice)
+    }
+
+    /// Return whether two atoms are ASCII-case-insensitive matches
+    #[inline]
+    pub fn eq_ignore_ascii_case(&self, other: &Self) -> bool {
+        if self == other {
+            return true;
+        }
+
+        // If we know both atoms are ascii-lowercase, then we can stick with
+        // pointer equality.
+        if self.is_ascii_lowercase() && other.is_ascii_lowercase() {
+            debug_assert!(!self.eq_ignore_ascii_case_slow(other));
+            return false;
+        }
+
+        self.eq_ignore_ascii_case_slow(other)
+    }
+
+    fn eq_ignore_ascii_case_slow(&self, other: &Self) -> bool {
+        let a = self.as_slice();
+        let b = other.as_slice();
+
+        if a.len() != b.len() {
+            return false;
+        }
+
+        a.iter().zip(b).all(|(&a16, &b16)| {
+            if a16 <= 0x7F && b16 <= 0x7F {
+                (a16 as u8).eq_ignore_ascii_case(&(b16 as u8))
+            } else {
+                a16 == b16
+            }
+        })
+    }
+}
+
+impl fmt::Debug for WeakAtom {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        write!(w, "Gecko WeakAtom({:p}, {})", self, self)
+    }
+}
+
+impl fmt::Display for WeakAtom {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        for c in self.chars() {
+            w.write_char(c.unwrap_or(char::REPLACEMENT_CHARACTER))?
+        }
+        Ok(())
+    }
+}
+
+#[inline]
+unsafe fn make_handle(ptr: *const nsAtom) -> NonZeroUsize {
+    debug_assert!(!ptr.is_null());
+    if !WeakAtom::new(ptr).is_static() {
+        NonZeroUsize::new_unchecked(ptr as usize)
+    } else {
+        make_static_handle(ptr as *mut nsStaticAtom)
+    }
+}
+
+#[inline]
+unsafe fn make_static_handle(ptr: *const nsStaticAtom) -> NonZeroUsize {
+    // FIXME(heycam): Use offset_from once it's stabilized.
+    // https://github.com/rust-lang/rust/issues/41079
+    debug_assert!(valid_static_atom_addr(ptr as usize));
+    let base = &gGkAtoms as *const _;
+    let offset = ptr as usize - base as usize;
+    NonZeroUsize::new_unchecked((offset << 1) | 1)
+}
+
+impl Atom {
+    #[inline]
+    fn is_static(&self) -> bool {
+        self.0.get() & 1 == 1
+    }
+
+    /// Execute a callback with the atom represented by `ptr`.
+    pub unsafe fn with<F, R>(ptr: *const nsAtom, callback: F) -> R
+    where
+        F: FnOnce(&Atom) -> R,
+    {
+        let atom = Atom(make_handle(ptr as *mut nsAtom));
+        let ret = callback(&atom);
+        mem::forget(atom);
+        ret
+    }
+
+    /// Creates a static atom from its index in the static atom table, without
+    /// checking.
+    #[inline]
+    pub const unsafe fn from_index_unchecked(index: u16) -> Self {
+        // FIXME(emilio): No support for debug_assert! in const fn for now. Note
+        // that violating this invariant will debug-assert in the `Deref` impl
+        // though.
+        //
+        // debug_assert!((index as usize) < STATIC_ATOM_COUNT);
+        let offset =
+            (index as usize) * std::mem::size_of::<nsStaticAtom>() + kGkAtomsArrayOffset as usize;
+        Atom(NonZeroUsize::new_unchecked((offset << 1) | 1))
+    }
+
+    /// Creates an atom from an atom pointer.
+    #[inline(always)]
+    pub unsafe fn from_raw(ptr: *mut nsAtom) -> Self {
+        let atom = Atom(make_handle(ptr));
+        if !atom.is_static() {
+            Gecko_AddRefAtom(ptr);
+        }
+        atom
+    }
+
+    /// Creates an atom from an atom pointer that has already had AddRef
+    /// called on it. This may be a static or dynamic atom.
+    #[inline]
+    pub unsafe fn from_addrefed(ptr: *mut nsAtom) -> Self {
+        assert!(!ptr.is_null());
+        Atom(make_handle(ptr))
+    }
+
+    /// Convert this atom into an addrefed nsAtom pointer.
+    #[inline]
+    pub fn into_addrefed(self) -> *mut nsAtom {
+        let ptr = self.as_ptr();
+        mem::forget(self);
+        ptr
+    }
+}
+
+impl Hash for Atom {
+    fn hash<H>(&self, state: &mut H)
+    where
+        H: Hasher,
+    {
+        state.write_u32(self.get_hash());
+    }
+}
+
+impl Hash for WeakAtom {
+    fn hash<H>(&self, state: &mut H)
+    where
+        H: Hasher,
+    {
+        state.write_u32(self.get_hash());
+    }
+}
+
+impl Clone for Atom {
+    #[inline(always)]
+    fn clone(&self) -> Atom {
+        unsafe {
+            let atom = Atom(self.0);
+            if !atom.is_static() {
+                Gecko_AddRefAtom(atom.as_ptr());
+            }
+            atom
+        }
+    }
+}
+
+impl Drop for Atom {
+    #[inline]
+    fn drop(&mut self) {
+        if !self.is_static() {
+            unsafe {
+                Gecko_ReleaseAtom(self.as_ptr());
+            }
+        }
+    }
+}
+
+impl Default for Atom {
+    #[inline]
+    fn default() -> Self {
+        atom!("")
+    }
+}
+
+impl fmt::Debug for Atom {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        write!(w, "Atom(0x{:08x}, {})", self.0, self)
+    }
+}
+
+impl fmt::Display for Atom {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        self.deref().fmt(w)
+    }
+}
+
+impl<'a> From<&'a str> for Atom {
+    #[inline]
+    fn from(string: &str) -> Atom {
+        debug_assert!(string.len() <= u32::max_value() as usize);
+        unsafe {
+            Atom::from_addrefed(Gecko_Atomize(
+                string.as_ptr() as *const _,
+                string.len() as u32,
+            ))
+        }
+    }
+}
+
+impl<'a> From<&'a [u16]> for Atom {
+    #[inline]
+    fn from(slice: &[u16]) -> Atom {
+        Atom::from(&*nsStr::from(slice))
+    }
+}
+
+impl<'a> From<&'a nsAString> for Atom {
+    #[inline]
+    fn from(string: &nsAString) -> Atom {
+        unsafe { Atom::from_addrefed(Gecko_Atomize16(string)) }
+    }
+}
+
+impl<'a> From<Cow<'a, str>> for Atom {
+    #[inline]
+    fn from(string: Cow<'a, str>) -> Atom {
+        Atom::from(&*string)
+    }
+}
+
+impl From<String> for Atom {
+    #[inline]
+    fn from(string: String) -> Atom {
+        Atom::from(&*string)
+    }
+}
+
+malloc_size_of_is_0!(Atom);
+
+impl SpecifiedValueInfo for Atom {}
diff --git a/servo/components/style/gecko_string_cache/namespace.rs b/servo/components/style/gecko_string_cache/namespace.rs
new file mode 100644
index 0000000000..d9745b9e21
--- /dev/null
+++ b/servo/components/style/gecko_string_cache/namespace.rs
@@ -0,0 +1,105 @@
+/* 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/. */
+
+//! A type to represent a namespace.
+
+use crate::gecko_bindings::structs::nsAtom;
+use crate::string_cache::{Atom, WeakAtom};
+use precomputed_hash::PrecomputedHash;
+use std::borrow::Borrow;
+use std::fmt;
+use std::ops::Deref;
+
+/// In Gecko namespaces are just regular atoms, so this is a simple macro to
+/// forward one macro to the other.
+#[macro_export]
+macro_rules! ns {
+    () => {
+        $crate::string_cache::Namespace(atom!(""))
+    };
+    ($s:tt) => {
+        $crate::string_cache::Namespace(atom!($s))
+    };
+}
+
+/// A Gecko namespace is just a wrapped atom.
+#[derive(
+    Clone,
+    Debug,
+    Default,
+    Eq,
+    Hash,
+    MallocSizeOf,
+    PartialEq,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(transparent)]
+pub struct Namespace(pub Atom);
+
+impl PrecomputedHash for Namespace {
+    #[inline]
+    fn precomputed_hash(&self) -> u32 {
+        self.0.precomputed_hash()
+    }
+}
+
+/// A Gecko WeakNamespace is a wrapped WeakAtom.
+#[derive(Deref, Hash)]
+pub struct WeakNamespace(WeakAtom);
+
+impl Deref for Namespace {
+    type Target = WeakNamespace;
+
+    #[inline]
+    fn deref(&self) -> &WeakNamespace {
+        let weak: *const WeakAtom = &*self.0;
+        unsafe { &*(weak as *const WeakNamespace) }
+    }
+}
+
+impl<'a> From<&'a str> for Namespace {
+    fn from(s: &'a str) -> Self {
+        Namespace(Atom::from(s))
+    }
+}
+
+impl fmt::Display for Namespace {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        self.0.fmt(w)
+    }
+}
+
+impl Borrow<WeakNamespace> for Namespace {
+    #[inline]
+    fn borrow(&self) -> &WeakNamespace {
+        self
+    }
+}
+
+impl WeakNamespace {
+    /// Trivially construct a WeakNamespace.
+    #[inline]
+    pub unsafe fn new<'a>(atom: *mut nsAtom) -> &'a Self {
+        &*(atom as *const WeakNamespace)
+    }
+
+    /// Clone this WeakNamespace to obtain a strong reference to the same
+    /// underlying namespace.
+    #[inline]
+    pub fn clone(&self) -> Namespace {
+        Namespace(self.0.clone())
+    }
+}
+
+impl Eq for WeakNamespace {}
+impl PartialEq for WeakNamespace {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        let weak: *const WeakNamespace = self;
+        let other: *const WeakNamespace = other;
+        weak == other
+    }
+}