Revert as many changes to selectors from upstream as possible (#31365)

This is part of the preparation for splitting stylo into a separate
crate. We have made various changes to selectors includings:

 1. Bumping the rust edition
 2. Fixing typos and updating links

In addition to reverting those changes, this PR pulls in some changes to
selectors we seem to have missed in the process of updates.

9 files changed, 58 insertions, 69 deletions

diff --git a/components/selectors/Cargo.toml b/components/selectors/Cargo.toml
index e1726a312cd..f447a18f4d5 100644
--- a/components/selectors/Cargo.toml
+++ b/components/selectors/Cargo.toml
@@ -9,7 +9,6 @@ readme = "README.md"
 keywords = ["css", "selectors"]
 license = "MPL-2.0"
 build = "build.rs"
-edition = "2018"
 
 [lib]
 name = "selectors"
diff --git a/components/selectors/README.md b/components/selectors/README.md
index ed30873a31f..dac4a7ff91a 100644
--- a/components/selectors/README.md
+++ b/components/selectors/README.md
@@ -1,11 +1,13 @@
 rust-selectors
 ==============
 
-* [Documentation](https://docs.rs/selectors)
+* [![Build Status](https://travis-ci.com/servo/rust-selectors.svg?branch=master)](
+  https://travis-ci.com/servo/rust-selectors)
+* [Documentation](https://docs.rs/selectors/)
 * [crates.io](https://crates.io/crates/selectors)
 
 CSS Selectors library for Rust.
-Includes parsing and serialization of selectors,
+Includes parsing and serilization of selectors,
 as well as matching against a generic tree of elements.
 Pseudo-elements and most pseudo-classes are generic as well.
 
diff --git a/components/selectors/attr.rs b/components/selectors/attr.rs
index ff4d2c561d6..e3122ea701e 100644
--- a/components/selectors/attr.rs
+++ b/components/selectors/attr.rs
@@ -5,19 +5,16 @@
 use crate::parser::SelectorImpl;
 use cssparser::ToCss;
 use std::fmt;
-#[cfg(feature = "shmem")]
-use to_shmem_derive::ToShmem;
 
-#[derive(Clone, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
-#[cfg_attr(feature = "shmem", shmem(no_bounds))]
+#[derive(Clone, Eq, PartialEq, ToShmem)]
+#[shmem(no_bounds)]
 pub struct AttrSelectorWithOptionalNamespace<Impl: SelectorImpl> {
-    #[cfg_attr(feature = "shmem", shmem(field_bound))]
+    #[shmem(field_bound)]
     pub namespace: Option<NamespaceConstraint<(Impl::NamespacePrefix, Impl::NamespaceUrl)>>,
-    #[cfg_attr(feature = "shmem", shmem(field_bound))]
+    #[shmem(field_bound)]
     pub local_name: Impl::LocalName,
     pub local_name_lower: Impl::LocalName,
-    #[cfg_attr(feature = "shmem", shmem(field_bound))]
+    #[shmem(field_bound)]
     pub operation: ParsedAttrSelectorOperation<Impl::AttrValue>,
 }
 
@@ -30,8 +27,7 @@ impl<Impl: SelectorImpl> AttrSelectorWithOptionalNamespace<Impl> {
     }
 }
 
-#[derive(Clone, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
+#[derive(Clone, Eq, PartialEq, ToShmem)]
 pub enum NamespaceConstraint<NamespaceUrl> {
     Any,
 
@@ -39,8 +35,7 @@ pub enum NamespaceConstraint<NamespaceUrl> {
     Specific(NamespaceUrl),
 }
 
-#[derive(Clone, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
+#[derive(Clone, Eq, PartialEq, ToShmem)]
 pub enum ParsedAttrSelectorOperation<AttrValue> {
     Exists,
     WithValue {
@@ -80,8 +75,7 @@ impl<AttrValue> AttrSelectorOperation<AttrValue> {
     }
 }
 
-#[derive(Clone, Copy, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
+#[derive(Clone, Copy, Eq, PartialEq, ToShmem)]
 pub enum AttrSelectorOperator {
     Equal,
     Includes,
@@ -146,8 +140,7 @@ impl AttrSelectorOperator {
 /// The definition of whitespace per CSS Selectors Level 3 § 4.
 pub static SELECTOR_WHITESPACE: &[char] = &[' ', '\t', '\n', '\r', '\x0C'];
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, ToShmem)]
 pub enum ParsedCaseSensitivity {
     /// 's' was specified.
     ExplicitCaseSensitive,
diff --git a/components/selectors/build.rs b/components/selectors/build.rs
index a4b07b3d430..c5c3803991e 100644
--- a/components/selectors/build.rs
+++ b/components/selectors/build.rs
@@ -2,6 +2,8 @@
  * 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/. */
 
+extern crate phf_codegen;
+
 use std::env;
 use std::fs::File;
 use std::io::{BufWriter, Write};
diff --git a/components/selectors/builder.rs b/components/selectors/builder.rs
index 3539032b35e..63a6323c532 100644
--- a/components/selectors/builder.rs
+++ b/components/selectors/builder.rs
@@ -19,16 +19,12 @@
 
 use crate::parser::{Combinator, Component, RelativeSelector, Selector, SelectorImpl};
 use crate::sink::Push;
-use bitflags::bitflags;
-use derive_more::{Add, AddAssign};
 use servo_arc::{Arc, HeaderWithLength, ThinArc};
 use smallvec::{self, SmallVec};
 use std::cmp;
 use std::iter;
 use std::ptr;
 use std::slice;
-#[cfg(feature = "shmem")]
-use to_shmem_derive::ToShmem;
 
 /// Top-level SelectorBuilder struct. This should be stack-allocated by the
 /// consumer and never moved (because it contains a lot of inline data that
@@ -182,8 +178,7 @@ fn split_from_end<T>(s: &[T], at: usize) -> (&[T], &[T]) {
 
 bitflags! {
     /// Flags that indicate at which point of parsing a selector are we.
-    #[derive(Default)]
-    #[cfg_attr(feature = "shmem", derive(ToShmem))]
+    #[derive(Default, ToShmem)]
     pub (crate) struct SelectorFlags : u8 {
         const HAS_PSEUDO = 1 << 0;
         const HAS_SLOTTED = 1 << 1;
@@ -192,8 +187,7 @@ bitflags! {
     }
 }
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, ToShmem)]
 pub struct SpecificityAndFlags {
     /// There are two free bits here, since we use ten bits for each specificity
     /// kind (id, class, element).
diff --git a/components/selectors/lib.rs b/components/selectors/lib.rs
index 17f81c535b6..d71d3c84876 100644
--- a/components/selectors/lib.rs
+++ b/components/selectors/lib.rs
@@ -5,6 +5,25 @@
 // Make |cargo bench| work.
 #![cfg_attr(feature = "bench", feature(test))]
 
+#[macro_use]
+extern crate bitflags;
+#[macro_use]
+extern crate cssparser;
+#[macro_use]
+extern crate debug_unreachable;
+#[macro_use]
+extern crate derive_more;
+extern crate fxhash;
+#[macro_use]
+extern crate log;
+extern crate phf;
+extern crate precomputed_hash;
+extern crate servo_arc;
+extern crate smallvec;
+extern crate to_shmem;
+#[macro_use]
+extern crate to_shmem_derive;
+
 pub mod attr;
 pub mod bloom;
 mod builder;
diff --git a/components/selectors/matching.rs b/components/selectors/matching.rs
index 05704923b60..83bc878797a 100644
--- a/components/selectors/matching.rs
+++ b/components/selectors/matching.rs
@@ -15,8 +15,6 @@ use crate::parser::{
 };
 use crate::tree::Element;
 use bitflags::bitflags;
-use debug_unreachable::debug_unreachable;
-use log::debug;
 use smallvec::SmallVec;
 use std::borrow::Borrow;
 use std::iter;
diff --git a/components/selectors/parser.rs b/components/selectors/parser.rs
index f9017b95b9b..2c44da8018e 100644
--- a/components/selectors/parser.rs
+++ b/components/selectors/parser.rs
@@ -14,21 +14,17 @@ use crate::sink::Push;
 use crate::visitor::SelectorListKind;
 pub use crate::visitor::SelectorVisitor;
 use bitflags::bitflags;
-use cssparser::{match_ignore_ascii_case, parse_nth};
+use cssparser::parse_nth;
 use cssparser::{BasicParseError, BasicParseErrorKind, ParseError, ParseErrorKind};
 use cssparser::{CowRcStr, Delimiter, SourceLocation};
 use cssparser::{Parser as CssParser, ToCss, Token};
-use debug_unreachable::debug_unreachable;
 use precomputed_hash::PrecomputedHash;
 use servo_arc::{HeaderWithLength, ThinArc, UniqueArc};
-use size_of_test::size_of_test;
 use smallvec::SmallVec;
 use std::borrow::{Borrow, Cow};
 use std::fmt::{self, Debug};
 use std::iter::Rev;
 use std::slice;
-#[cfg(feature = "shmem")]
-use to_shmem_derive::ToShmem;
 
 /// A trait that represents a pseudo-element.
 pub trait PseudoElement: Sized + ToCss {
@@ -168,8 +164,6 @@ impl SelectorParsingState {
 
 pub type SelectorParseError<'i> = ParseError<'i, SelectorParseErrorKind<'i>>;
 
-size_of_test!(SelectorParseError, 48);
-
 #[derive(Clone, Debug, PartialEq)]
 pub enum SelectorParseErrorKind<'i> {
     NoQualifiedNameInAttributeSelector(Token<'i>),
@@ -194,8 +188,6 @@ pub enum SelectorParseErrorKind<'i> {
     ClassNeedsIdent(Token<'i>),
 }
 
-size_of_test!(SelectorParseErrorKind, 40);
-
 macro_rules! with_all_bounds {
     (
         [ $( $InSelector: tt )* ]
@@ -298,9 +290,6 @@ pub trait Parser<'i> {
         true
     }
 
-    /// Parses non-tree-structural pseudo-classes. Tree structural pseudo-classes,
-    /// like `:first-child`, are built into this library.
-    ///
     /// This function can return an "Err" pseudo-element in order to support CSS2.1
     /// pseudo-elements.
     fn parse_non_ts_pseudo_class(
@@ -363,11 +352,10 @@ pub trait Parser<'i> {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
-#[cfg_attr(feature = "shmem", shmem(no_bounds))]
+#[derive(Clone, Debug, Eq, PartialEq, ToShmem)]
+#[shmem(no_bounds)]
 pub struct SelectorList<Impl: SelectorImpl>(
-    #[cfg_attr(feature = "shmem", shmem(field_bound))] pub SmallVec<[Selector<Impl>; 1]>,
+    #[shmem(field_bound)] pub SmallVec<[Selector<Impl>; 1]>,
 );
 
 /// Whether or not we're using forgiving parsing mode
@@ -643,12 +631,10 @@ pub fn namespace_empty_string<Impl: SelectorImpl>() -> Impl::NamespaceUrl {
 ///
 /// This reordering doesn't change the semantics of selector matching, and we
 /// handle it in to_css to make it invisible to serialization.
-#[derive(Clone, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
-#[cfg_attr(feature = "shmem", shmem(no_bounds))]
+#[derive(Clone, Eq, PartialEq, ToShmem)]
+#[shmem(no_bounds)]
 pub struct Selector<Impl: SelectorImpl>(
-    #[cfg_attr(feature = "shmem", shmem(field_bound))]
-    ThinArc<SpecificityAndFlags, Component<Impl>>,
+    #[shmem(field_bound)] ThinArc<SpecificityAndFlags, Component<Impl>>,
 );
 
 impl<Impl: SelectorImpl> Selector<Impl> {
@@ -1299,8 +1285,7 @@ impl<'a, Impl: SelectorImpl> Iterator for AncestorIter<'a, Impl> {
     }
 }
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, ToShmem)]
 pub enum Combinator {
     Child,        //  >
     Descendant,   // space
@@ -1541,10 +1526,10 @@ impl CombinatorComposition {
         for combinator in CombinatorIter::new(inner_selector.iter_skip_relative_selector_anchor()) {
             match combinator {
                 Combinator::Descendant | Combinator::Child => {
-                    result.insert(CombinatorComposition::DESCENDANTS);
+                    result.insert(Self::DESCENDANTS);
                 },
                 Combinator::NextSibling | Combinator::LaterSibling => {
-                    result.insert(CombinatorComposition::SIBLINGS);
+                    result.insert(Self::SIBLINGS);
                 },
                 Combinator::Part | Combinator::PseudoElement | Combinator::SlotAssignment => {
                     continue
@@ -1637,17 +1622,16 @@ impl<Impl: SelectorImpl> RelativeSelector<Impl> {
 /// optimal packing and cache performance, see [1].
 ///
 /// [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1357973
-#[derive(Clone, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
-#[cfg_attr(feature = "shmem", shmem(no_bounds))]
+#[derive(Clone, Eq, PartialEq, ToShmem)]
+#[shmem(no_bounds)]
 pub enum Component<Impl: SelectorImpl> {
     LocalName(LocalName<Impl>),
 
-    ID(#[cfg_attr(feature = "shmem", shmem(field_bound))] Impl::Identifier),
-    Class(#[cfg_attr(feature = "shmem", shmem(field_bound))] Impl::Identifier),
+    ID(#[shmem(field_bound)] Impl::Identifier),
+    Class(#[shmem(field_bound)] Impl::Identifier),
 
     AttributeInNoNamespaceExists {
-        #[cfg_attr(feature = "shmem", shmem(field_bound))]
+        #[shmem(field_bound)]
         local_name: Impl::LocalName,
         local_name_lower: Impl::LocalName,
     },
@@ -1655,7 +1639,7 @@ pub enum Component<Impl: SelectorImpl> {
     AttributeInNoNamespace {
         local_name: Impl::LocalName,
         operator: AttrSelectorOperator,
-        #[cfg_attr(feature = "shmem", shmem(field_bound))]
+        #[shmem(field_bound)]
         value: Impl::AttrValue,
         case_sensitivity: ParsedCaseSensitivity,
     },
@@ -1680,7 +1664,7 @@ pub enum Component<Impl: SelectorImpl> {
     ParentSelector,
     Nth(NthSelectorData),
     NthOf(NthOfSelectorData<Impl>),
-    NonTSPseudoClass(#[cfg_attr(feature = "shmem", shmem(field_bound))] Impl::NonTSPseudoClass),
+    NonTSPseudoClass(#[shmem(field_bound)] Impl::NonTSPseudoClass),
     /// The ::slotted() pseudo-element:
     ///
     /// https://drafts.csswg.org/css-scoping/#slotted-pseudo
@@ -1695,7 +1679,7 @@ pub enum Component<Impl: SelectorImpl> {
     Slotted(Selector<Impl>),
     /// The `::part` pseudo-element.
     ///   https://drafts.csswg.org/css-shadow-parts/#part
-    Part(#[cfg_attr(feature = "shmem", shmem(field_bound))] Box<[Impl::Identifier]>),
+    Part(#[shmem(field_bound)] Box<[Impl::Identifier]>),
     /// The `:host` pseudo-class:
     ///
     /// https://drafts.csswg.org/css-scoping/#host-selector
@@ -1726,7 +1710,7 @@ pub enum Component<Impl: SelectorImpl> {
     /// Same comment as above re. the argument.
     Has(Box<[RelativeSelector<Impl>]>),
     /// An implementation-dependent pseudo-element selector.
-    PseudoElement(#[cfg_attr(feature = "shmem", shmem(field_bound))] Impl::PseudoElement),
+    PseudoElement(#[shmem(field_bound)] Impl::PseudoElement),
 
     Combinator(Combinator),
 
@@ -1886,11 +1870,10 @@ impl<Impl: SelectorImpl> Component<Impl> {
     }
 }
 
-#[derive(Clone, Eq, PartialEq)]
-#[cfg_attr(feature = "shmem", derive(ToShmem))]
-#[cfg_attr(feature = "shmem", shmem(no_bounds))]
+#[derive(Clone, Eq, PartialEq, ToShmem)]
+#[shmem(no_bounds)]
 pub struct LocalName<Impl: SelectorImpl> {
-    #[cfg_attr(feature = "shmem", shmem(field_bound))]
+    #[shmem(field_bound)]
     pub name: Impl::LocalName,
     pub lower_name: Impl::LocalName,
 }
diff --git a/components/selectors/visitor.rs b/components/selectors/visitor.rs
index 8b9e3ac3966..785c12813a6 100644
--- a/components/selectors/visitor.rs
+++ b/components/selectors/visitor.rs
@@ -8,7 +8,6 @@
 
 use crate::attr::NamespaceConstraint;
 use crate::parser::{Combinator, Component, Selector, SelectorImpl};
-use bitflags::bitflags;
 
 /// A trait to visit selector properties.
 ///