Use our copy of RefCell for style data.

This allows removing `#![feature(as_unsafe_cell)]` in geckolib
and make progress towards #11815.

12 files changed, 481 insertions, 11 deletions

diff --git a/components/layout/lib.rs b/components/layout/lib.rs
index 12769808d50..e747993dd84 100644
--- a/components/layout/lib.rs
+++ b/components/layout/lib.rs
@@ -2,7 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#![feature(as_unsafe_cell)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(custom_derive)]
diff --git a/components/layout/wrapper.rs b/components/layout/wrapper.rs
index 6db7f8b7cc2..0f83454ab57 100644
--- a/components/layout/wrapper.rs
+++ b/components/layout/wrapper.rs
@@ -34,9 +34,9 @@ use core::nonzero::NonZero;
 use data::{LayoutDataFlags, PrivateLayoutData};
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutNode};
 use script_layout_interface::{OpaqueStyleAndLayoutData, PartialStyleAndLayoutData};
-use std::cell::{Ref, RefCell, RefMut};
 use style::computed_values::content::{self, ContentItem};
 use style::properties::ComputedValues;
+use style::refcell::{Ref, RefCell, RefMut};
 
 pub type NonOpaqueStyleAndLayoutData = *mut RefCell<PrivateLayoutData>;
 
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index e3c904d590b..fad57c499d3 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -92,7 +92,6 @@ use script_layout_interface::{OpaqueStyleAndLayoutData, PartialStyleAndLayoutDat
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
 use script_traits::{StackingContextScrollState, UntrustedNodeAddress};
 use std::borrow::ToOwned;
-use std::cell::RefCell;
 use std::collections::HashMap;
 use std::hash::BuildHasherDefault;
 use std::ops::{Deref, DerefMut};
@@ -108,6 +107,7 @@ use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaType};
 use style::parallel::WorkQueueData;
 use style::properties::ComputedValues;
+use style::refcell::RefCell;
 use style::selector_matching::USER_OR_USER_AGENT_STYLESHEETS;
 use style::servo::{SharedStyleContext, Stylesheet, Stylist};
 use style::stylesheets::CSSRuleIteratorExt;
diff --git a/components/script/layout_wrapper.rs b/components/script/layout_wrapper.rs
index 2fc6991310e..681fdab9c46 100644
--- a/components/script/layout_wrapper.rs
+++ b/components/script/layout_wrapper.rs
@@ -50,7 +50,6 @@ use script_layout_interface::{OpaqueStyleAndLayoutData, PartialStyleAndLayoutDat
 use selectors::matching::{DeclarationBlock, ElementFlags};
 use selectors::parser::{AttrSelector, NamespaceConstraint};
 use smallvec::VecLike;
-use std::cell::{Ref, RefCell, RefMut};
 use std::marker::PhantomData;
 use std::mem::{transmute, transmute_copy};
 use string_cache::{Atom, BorrowedAtom, BorrowedNamespace, Namespace};
@@ -60,6 +59,7 @@ use style::dom::{PresentationalHintsSynthetizer, OpaqueNode, TDocument, TElement
 use style::element_state::*;
 use style::properties::{ComputedValues, ServoComputedValues};
 use style::properties::{PropertyDeclaration, PropertyDeclarationBlock};
+use style::refcell::{Ref, RefCell, RefMut};
 use style::restyle_hints::ElementSnapshot;
 use style::selector_impl::{NonTSPseudoClass, ServoSelectorImpl};
 use style::servo::{PrivateStyleData, SharedStyleContext};
diff --git a/components/script_layout_interface/lib.rs b/components/script_layout_interface/lib.rs
index c2e06e3dcf7..805deb45349 100644
--- a/components/script_layout_interface/lib.rs
+++ b/components/script_layout_interface/lib.rs
@@ -52,7 +52,7 @@ use core::nonzero::NonZero;
 use ipc_channel::ipc::IpcSender;
 use libc::c_void;
 use restyle_damage::RestyleDamage;
-use std::cell::RefCell;
+use style::refcell::RefCell;
 use style::servo::PrivateStyleData;
 
 pub struct PartialStyleAndLayoutData {
diff --git a/components/script_layout_interface/wrapper_traits.rs b/components/script_layout_interface/wrapper_traits.rs
index 145f9dd067b..a816321ec28 100644
--- a/components/script_layout_interface/wrapper_traits.rs
+++ b/components/script_layout_interface/wrapper_traits.rs
@@ -10,13 +10,13 @@ use gfx_traits::{ByteIndex, LayerId, LayerType};
 use msg::constellation_msg::PipelineId;
 use range::Range;
 use restyle_damage::RestyleDamage;
-use std::cell::{Ref, RefCell};
 use std::sync::Arc;
 use string_cache::{Atom, BorrowedAtom, BorrowedNamespace, Namespace};
 use style::computed_values::display;
 use style::dom::OpaqueNode;
 use style::dom::{PresentationalHintsSynthetizer, TNode};
 use style::properties::ServoComputedValues;
+use style::refcell::{Ref, RefCell};
 use style::selector_impl::{PseudoElement, PseudoElementCascadeType, ServoSelectorImpl};
 use style::servo::SharedStyleContext;
 use url::Url;
diff --git a/components/style/dom.rs b/components/style/dom.rs
index 7713cc1aa0a..573e02ff887 100644
--- a/components/style/dom.rs
+++ b/components/style/dom.rs
@@ -8,12 +8,12 @@ use context::SharedStyleContext;
 use data::PrivateStyleData;
 use element_state::ElementState;
 use properties::{ComputedValues, PropertyDeclaration, PropertyDeclarationBlock};
+use refcell::{Ref, RefMut};
 use restyle_hints::{ElementSnapshot, RESTYLE_DESCENDANTS, RESTYLE_LATER_SIBLINGS, RESTYLE_SELF, RestyleHint};
 use selector_impl::{ElementExt, SelectorImplExt};
 use selectors::Element;
 use selectors::matching::DeclarationBlock;
 use smallvec::VecLike;
-use std::cell::{Ref, RefMut};
 use std::ops::BitOr;
 use std::sync::Arc;
 use string_cache::{Atom, Namespace};
diff --git a/components/style/lib.rs b/components/style/lib.rs
index 28e2963f4ff..4d879e7584d 100644
--- a/components/style/lib.rs
+++ b/components/style/lib.rs
@@ -63,6 +63,7 @@ pub mod matching;
 pub mod media_queries;
 pub mod parallel;
 pub mod parser;
+pub mod refcell;
 pub mod restyle_hints;
 pub mod selector_impl;
 pub mod selector_matching;
diff --git a/components/style/refcell.rs b/components/style/refcell.rs
new file mode 100644
index 00000000000..f882c9ded7a
--- /dev/null
+++ b/components/style/refcell.rs
@@ -0,0 +1,461 @@
+// Copyright 2012-2014 The Rust Project Developers.
+// See http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A fork of std::cell::RefCell that makes `as_unsafe_cell` usable on stable Rust.
+//!
+//! FIXME(https://github.com/rust-lang/rust/issues/27708): Remove this when
+//! `std::cell::RefCell::as_unsafe_cell` is in Rust’s stable channel.
+
+#![allow(unsafe_code)]
+
+use std::cell::{UnsafeCell, Cell};
+use std::cmp::Ordering;
+use std::ops::{Deref, DerefMut};
+
+/// A fork of std::cell::RefCell that makes `as_unsafe_cell` usable on stable Rust.
+///
+/// FIXME(https://github.com/rust-lang/rust/issues/27708): Remove this when
+/// `std::cell::RefCell::as_unsafe_cell` is in Rust’s stable channel.
+pub struct RefCell<T: ?Sized> {
+    borrow: Cell<BorrowFlag>,
+    value: UnsafeCell<T>,
+}
+type BorrowFlag = usize;
+
+/// An enumeration of values returned from the `state` method on a `RefCell<T>`.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum BorrowState {
+    /// The cell is currently being read, there is at least one active `borrow`.
+    Reading,
+    /// The cell is currently being written to, there is an active `borrow_mut`.
+    Writing,
+    /// There are no outstanding borrows on this cell.
+    Unused,
+}
+
+// Values [1, MAX-1] represent the number of `Ref` active
+// (will not outgrow its range since `usize` is the size of the address space)
+const UNUSED: BorrowFlag = 0;
+const WRITING: BorrowFlag = !0;
+
+impl<T> RefCell<T> {
+    /// Creates a new `RefCell` containing `value`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::cell::RefCell;
+    ///
+    /// let c = RefCell::new(5);
+    /// ```
+    #[inline]
+    pub fn new(value: T) -> RefCell<T> {
+        RefCell {
+            value: UnsafeCell::new(value),
+            borrow: Cell::new(UNUSED),
+        }
+    }
+
+    /// Consumes the `RefCell`, returning the wrapped value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::cell::RefCell;
+    ///
+    /// let c = RefCell::new(5);
+    ///
+    /// let five = c.into_inner();
+    /// ```
+    #[inline]
+    pub fn into_inner(self) -> T {
+        // Since this function takes `self` (the `RefCell`) by value, the
+        // compiler statically verifies that it is not currently borrowed.
+        // Therefore the following assertion is just a `debug_assert!`.
+        debug_assert!(self.borrow.get() == UNUSED);
+        unsafe { self.value.into_inner() }
+    }
+}
+
+impl<T: ?Sized> RefCell<T> {
+    /// Query the current state of this `RefCell`
+    ///
+    /// The returned value can be dispatched on to determine if a call to
+    /// `borrow` or `borrow_mut` would succeed.
+    #[inline]
+    pub fn borrow_state(&self) -> BorrowState {
+        match self.borrow.get() {
+            WRITING => BorrowState::Writing,
+            UNUSED => BorrowState::Unused,
+            _ => BorrowState::Reading,
+        }
+    }
+
+    /// Immutably borrows the wrapped value.
+    ///
+    /// The borrow lasts until the returned `Ref` exits scope. Multiple
+    /// immutable borrows can be taken out at the same time.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is currently mutably borrowed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::cell::RefCell;
+    ///
+    /// let c = RefCell::new(5);
+    ///
+    /// let borrowed_five = c.borrow();
+    /// let borrowed_five2 = c.borrow();
+    /// ```
+    ///
+    /// An example of panic:
+    ///
+    /// ```
+    /// use std::cell::RefCell;
+    /// use std::thread;
+    ///
+    /// let result = thread::spawn(move || {
+    ///    let c = RefCell::new(5);
+    ///    let m = c.borrow_mut();
+    ///
+    ///    let b = c.borrow(); // this causes a panic
+    /// }).join();
+    ///
+    /// assert!(result.is_err());
+    /// ```
+    #[inline]
+    pub fn borrow(&self) -> Ref<T> {
+        match BorrowRef::new(&self.borrow) {
+            Some(b) => Ref {
+                value: unsafe { &*self.value.get() },
+                borrow: b,
+            },
+            None => panic!("RefCell<T> already mutably borrowed"),
+        }
+    }
+
+    /// Mutably borrows the wrapped value.
+    ///
+    /// The borrow lasts until the returned `RefMut` exits scope. The value
+    /// cannot be borrowed while this borrow is active.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is currently borrowed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::cell::RefCell;
+    ///
+    /// let c = RefCell::new(5);
+    ///
+    /// *c.borrow_mut() = 7;
+    ///
+    /// assert_eq!(*c.borrow(), 7);
+    /// ```
+    ///
+    /// An example of panic:
+    ///
+    /// ```
+    /// use std::cell::RefCell;
+    /// use std::thread;
+    ///
+    /// let result = thread::spawn(move || {
+    ///    let c = RefCell::new(5);
+    ///    let m = c.borrow();
+    ///
+    ///    let b = c.borrow_mut(); // this causes a panic
+    /// }).join();
+    ///
+    /// assert!(result.is_err());
+    /// ```
+    #[inline]
+    pub fn borrow_mut(&self) -> RefMut<T> {
+        match BorrowRefMut::new(&self.borrow) {
+            Some(b) => RefMut {
+                value: unsafe { &mut *self.value.get() },
+                borrow: b,
+            },
+            None => panic!("RefCell<T> already borrowed"),
+        }
+    }
+
+    /// Returns a reference to the underlying `UnsafeCell`.
+    ///
+    /// This can be used to circumvent `RefCell`'s safety checks.
+    ///
+    /// This function is `unsafe` because `UnsafeCell`'s field is public.
+    #[inline]
+    pub unsafe fn as_unsafe_cell(&self) -> &UnsafeCell<T> {
+        &self.value
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// This call borrows `RefCell` mutably (at compile-time) so there is no
+    /// need for dynamic checks.
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe {
+            &mut *self.value.get()
+        }
+    }
+}
+
+unsafe impl<T: ?Sized> Send for RefCell<T> where T: Send {}
+
+impl<T: Clone> Clone for RefCell<T> {
+    #[inline]
+    fn clone(&self) -> RefCell<T> {
+        RefCell::new(self.borrow().clone())
+    }
+}
+
+impl<T: Default> Default for RefCell<T> {
+    #[inline]
+    fn default() -> RefCell<T> {
+        RefCell::new(Default::default())
+    }
+}
+
+impl<T: ?Sized + PartialEq> PartialEq for RefCell<T> {
+    #[inline]
+    fn eq(&self, other: &RefCell<T>) -> bool {
+        *self.borrow() == *other.borrow()
+    }
+}
+
+impl<T: ?Sized + Eq> Eq for RefCell<T> {}
+
+impl<T: ?Sized + PartialOrd> PartialOrd for RefCell<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &RefCell<T>) -> Option<Ordering> {
+        self.borrow().partial_cmp(&*other.borrow())
+    }
+
+    #[inline]
+    fn lt(&self, other: &RefCell<T>) -> bool {
+        *self.borrow() < *other.borrow()
+    }
+
+    #[inline]
+    fn le(&self, other: &RefCell<T>) -> bool {
+        *self.borrow() <= *other.borrow()
+    }
+
+    #[inline]
+    fn gt(&self, other: &RefCell<T>) -> bool {
+        *self.borrow() > *other.borrow()
+    }
+
+    #[inline]
+    fn ge(&self, other: &RefCell<T>) -> bool {
+        *self.borrow() >= *other.borrow()
+    }
+}
+
+impl<T: ?Sized + Ord> Ord for RefCell<T> {
+    #[inline]
+    fn cmp(&self, other: &RefCell<T>) -> Ordering {
+        self.borrow().cmp(&*other.borrow())
+    }
+}
+
+struct BorrowRef<'b> {
+    borrow: &'b Cell<BorrowFlag>,
+}
+
+impl<'b> BorrowRef<'b> {
+    #[inline]
+    fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRef<'b>> {
+        match borrow.get() {
+            WRITING => None,
+            b => {
+                borrow.set(b + 1);
+                Some(BorrowRef { borrow: borrow })
+            },
+        }
+    }
+}
+
+impl<'b> Drop for BorrowRef<'b> {
+    #[inline]
+    fn drop(&mut self) {
+        let borrow = self.borrow.get();
+        debug_assert!(borrow != WRITING && borrow != UNUSED);
+        self.borrow.set(borrow - 1);
+    }
+}
+
+impl<'b> Clone for BorrowRef<'b> {
+    #[inline]
+    fn clone(&self) -> BorrowRef<'b> {
+        // Since this Ref exists, we know the borrow flag
+        // is not set to WRITING.
+        let borrow = self.borrow.get();
+        debug_assert!(borrow != UNUSED);
+        // Prevent the borrow counter from overflowing.
+        assert!(borrow != WRITING);
+        self.borrow.set(borrow + 1);
+        BorrowRef { borrow: self.borrow }
+    }
+}
+
+/// Wraps a borrowed reference to a value in a `RefCell` box.
+/// A wrapper type for an immutably borrowed value from a `RefCell<T>`.
+///
+/// See the [module-level documentation](index.html) for more.
+pub struct Ref<'b, T: ?Sized + 'b> {
+    value: &'b T,
+    borrow: BorrowRef<'b>,
+}
+
+impl<'b, T: ?Sized> Deref for Ref<'b, T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        self.value
+    }
+}
+
+impl<'b, T: ?Sized> Ref<'b, T> {
+    /// Copies a `Ref`.
+    ///
+    /// The `RefCell` is already immutably borrowed, so this cannot fail.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `Ref::clone(...)`.  A `Clone` implementation or a method would interfere
+    /// with the widespread use of `r.borrow().clone()` to clone the contents of
+    /// a `RefCell`.
+    #[inline]
+    pub fn clone(orig: &Ref<'b, T>) -> Ref<'b, T> {
+        Ref {
+            value: orig.value,
+            borrow: orig.borrow.clone(),
+        }
+    }
+
+    /// Make a new `Ref` for a component of the borrowed data.
+    ///
+    /// The `RefCell` is already immutably borrowed, so this cannot fail.
+    ///
+    /// This is an associated function that needs to be used as `Ref::map(...)`.
+    /// A method would interfere with methods of the same name on the contents
+    /// of a `RefCell` used through `Deref`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use std::cell::{RefCell, Ref};
+    ///
+    /// let c = RefCell::new((5, 'b'));
+    /// let b1: Ref<(u32, char)> = c.borrow();
+    /// let b2: Ref<u32> = Ref::map(b1, |t| &t.0);
+    /// assert_eq!(*b2, 5)
+    /// ```
+    #[inline]
+    pub fn map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Ref<'b, U>
+        where F: FnOnce(&T) -> &U
+    {
+        Ref {
+            value: f(orig.value),
+            borrow: orig.borrow,
+        }
+    }
+}
+
+impl<'b, T: ?Sized> RefMut<'b, T> {
+    /// Make a new `RefMut` for a component of the borrowed data, e.g. an enum
+    /// variant.
+    ///
+    /// The `RefCell` is already mutably borrowed, so this cannot fail.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `RefMut::map(...)`.  A method would interfere with methods of the same
+    /// name on the contents of a `RefCell` used through `Deref`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use std::cell::{RefCell, RefMut};
+    ///
+    /// let c = RefCell::new((5, 'b'));
+    /// {
+    ///     let b1: RefMut<(u32, char)> = c.borrow_mut();
+    ///     let mut b2: RefMut<u32> = RefMut::map(b1, |t| &mut t.0);
+    ///     assert_eq!(*b2, 5);
+    ///     *b2 = 42;
+    /// }
+    /// assert_eq!(*c.borrow(), (42, 'b'));
+    /// ```
+    #[inline]
+    pub fn map<U: ?Sized, F>(orig: RefMut<'b, T>, f: F) -> RefMut<'b, U>
+        where F: FnOnce(&mut T) -> &mut U
+    {
+        RefMut {
+            value: f(orig.value),
+            borrow: orig.borrow,
+        }
+    }
+}
+
+struct BorrowRefMut<'b> {
+    borrow: &'b Cell<BorrowFlag>,
+}
+
+impl<'b> Drop for BorrowRefMut<'b> {
+    #[inline]
+    fn drop(&mut self) {
+        let borrow = self.borrow.get();
+        debug_assert!(borrow == WRITING);
+        self.borrow.set(UNUSED);
+    }
+}
+
+impl<'b> BorrowRefMut<'b> {
+    #[inline]
+    fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRefMut<'b>> {
+        match borrow.get() {
+            UNUSED => {
+                borrow.set(WRITING);
+                Some(BorrowRefMut { borrow: borrow })
+            },
+            _ => None,
+        }
+    }
+}
+
+/// A wrapper type for a mutably borrowed value from a `RefCell<T>`.
+///
+/// See the [module-level documentation](index.html) for more.
+pub struct RefMut<'b, T: ?Sized + 'b> {
+    value: &'b mut T,
+    borrow: BorrowRefMut<'b>,
+}
+
+impl<'b, T: ?Sized> Deref for RefMut<'b, T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        self.value
+    }
+}
+
+impl<'b, T: ?Sized> DerefMut for RefMut<'b, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        self.value
+    }
+}
diff --git a/ports/geckolib/lib.rs b/ports/geckolib/lib.rs
index 96b4580216a..cedf344568f 100644
--- a/ports/geckolib/lib.rs
+++ b/ports/geckolib/lib.rs
@@ -2,8 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#![feature(as_unsafe_cell)]
-
 extern crate app_units;
 #[macro_use]
 extern crate cssparser;
diff --git a/ports/geckolib/wrapper.rs b/ports/geckolib/wrapper.rs
index 2e497f04f9e..016a33fa811 100644
--- a/ports/geckolib/wrapper.rs
+++ b/ports/geckolib/wrapper.rs
@@ -28,7 +28,6 @@ use selectors::Element;
 use selectors::matching::DeclarationBlock;
 use selectors::parser::{AttrSelector, NamespaceConstraint};
 use smallvec::VecLike;
-use std::cell::{Ref, RefCell, RefMut};
 use std::marker::PhantomData;
 use std::ops::BitOr;
 use std::ptr;
@@ -46,6 +45,7 @@ use style::parser::ParserContextExtraData;
 #[allow(unused_imports)] // Used in commented-out code.
 use style::properties::parse_style_attribute;
 use style::properties::{PropertyDeclaration, PropertyDeclarationBlock};
+use style::refcell::{Ref, RefCell, RefMut};
 use style::restyle_hints::ElementSnapshot;
 use style::selector_impl::ElementExt;
 #[allow(unused_imports)] // Used in commented-out code.
diff --git a/python/tidy/servo_tidy/licenseck.py b/python/tidy/servo_tidy/licenseck.py
index a67713b4421..ce5fdee075d 100644
--- a/python/tidy/servo_tidy/licenseck.py
+++ b/python/tidy/servo_tidy/licenseck.py
@@ -69,5 +69,16 @@ licenses = [
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-"""
+""",
+
+"""\
+// Copyright 2012-2014 The Rust Project Developers.
+// See http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+""",
 ]  # noqa: Indicate to flake8 that we do not want to check indentation here