Add structopt dependency in version 0.3.7

This patch series replaces argparse with structopt in the argument
handling code. As a first step, we need structopt as a dependency.

Import subrepo structopt/:structopt at efbdda4753592e27bc430fb01f7b9650b2f3174d
Import subrepo bitflags/:bitflags at 30668016aca6bd3b02c766e8347e0b4080d4c296
Import subrepo clap/:clap at 784524f7eb193e35f81082cc69454c8c21b948f7
Import subrepo heck/:heck at 093d56fbf001e1506e56dbfa38631d99b1066df1
Import subrepo proc-macro-error/:proc-macro-error at 6c4cfe79a622c5de8ae68557993542be46eacae2
Import subrepo proc-macro2/:proc-macro2 at d5d48eddca4566e5438e8a2cbed4a74e049544de
Import subrepo quote/:quote at 727436c6c137b20f0f34dde5d8fda2679b9747ad
Import subrepo rustversion/:rustversion at 0c5663313516263059ce9059ef81fc7a1cf655ca
Import subrepo syn-mid/:syn-mid at 5d3d85414a9e6674e1857ec22a87b96e04a6851a
Import subrepo syn/:syn at e87c27e87f6f4ef8919d0372bdb056d53ef0d8f3
Import subrepo textwrap/:textwrap at abcd618beae3f74841032aa5b53c1086b0a57ca2
Import subrepo unicode-segmentation/:unicode-segmentation at 637c9874c4fe0c205ff27787faf150a40295c6c3
Import subrepo unicode-width/:unicode-width at 3033826f8bf05e82724140a981d5941e48fce393
Import subrepo unicode-xid/:unicode-xid at 4baae9fffb156ba229665b972a9cd5991787ceb7

4 files changed, 3975 insertions, 0 deletions

diff --git a/proc-macro2/src/fallback.rs b/proc-macro2/src/fallback.rs
new file mode 100644
index 0000000..9762d3b
--- /dev/null
+++ b/proc-macro2/src/fallback.rs
@@ -0,0 +1,1458 @@
+#[cfg(span_locations)]
+use std::cell::RefCell;
+#[cfg(span_locations)]
+use std::cmp;
+use std::fmt;
+use std::iter;
+use std::ops::RangeBounds;
+#[cfg(procmacro2_semver_exempt)]
+use std::path::Path;
+use std::path::PathBuf;
+use std::str::FromStr;
+use std::vec;
+
+use crate::strnom::{block_comment, skip_whitespace, whitespace, word_break, Cursor, PResult};
+use crate::{Delimiter, Punct, Spacing, TokenTree};
+use unicode_xid::UnicodeXID;
+
+#[derive(Clone)]
+pub struct TokenStream {
+    inner: Vec<TokenTree>,
+}
+
+#[derive(Debug)]
+pub struct LexError;
+
+impl TokenStream {
+    pub fn new() -> TokenStream {
+        TokenStream { inner: Vec::new() }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.inner.len() == 0
+    }
+}
+
+#[cfg(span_locations)]
+fn get_cursor(src: &str) -> Cursor {
+    // Create a dummy file & add it to the source map
+    SOURCE_MAP.with(|cm| {
+        let mut cm = cm.borrow_mut();
+        let name = format!("<parsed string {}>", cm.files.len());
+        let span = cm.add_file(&name, src);
+        Cursor {
+            rest: src,
+            off: span.lo,
+        }
+    })
+}
+
+#[cfg(not(span_locations))]
+fn get_cursor(src: &str) -> Cursor {
+    Cursor { rest: src }
+}
+
+impl FromStr for TokenStream {
+    type Err = LexError;
+
+    fn from_str(src: &str) -> Result<TokenStream, LexError> {
+        // Create a dummy file & add it to the source map
+        let cursor = get_cursor(src);
+
+        match token_stream(cursor) {
+            Ok((input, output)) => {
+                if skip_whitespace(input).len() != 0 {
+                    Err(LexError)
+                } else {
+                    Ok(output)
+                }
+            }
+            Err(LexError) => Err(LexError),
+        }
+    }
+}
+
+impl fmt::Display for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut joint = false;
+        for (i, tt) in self.inner.iter().enumerate() {
+            if i != 0 && !joint {
+                write!(f, " ")?;
+            }
+            joint = false;
+            match *tt {
+                TokenTree::Group(ref tt) => {
+                    let (start, end) = match tt.delimiter() {
+                        Delimiter::Parenthesis => ("(", ")"),
+                        Delimiter::Brace => ("{", "}"),
+                        Delimiter::Bracket => ("[", "]"),
+                        Delimiter::None => ("", ""),
+                    };
+                    if tt.stream().into_iter().next().is_none() {
+                        write!(f, "{} {}", start, end)?
+                    } else {
+                        write!(f, "{} {} {}", start, tt.stream(), end)?
+                    }
+                }
+                TokenTree::Ident(ref tt) => write!(f, "{}", tt)?,
+                TokenTree::Punct(ref tt) => {
+                    write!(f, "{}", tt.as_char())?;
+                    match tt.spacing() {
+                        Spacing::Alone => {}
+                        Spacing::Joint => joint = true,
+                    }
+                }
+                TokenTree::Literal(ref tt) => write!(f, "{}", tt)?,
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl fmt::Debug for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("TokenStream ")?;
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+#[cfg(use_proc_macro)]
+impl From<proc_macro::TokenStream> for TokenStream {
+    fn from(inner: proc_macro::TokenStream) -> TokenStream {
+        inner
+            .to_string()
+            .parse()
+            .expect("compiler token stream parse failed")
+    }
+}
+
+#[cfg(use_proc_macro)]
+impl From<TokenStream> for proc_macro::TokenStream {
+    fn from(inner: TokenStream) -> proc_macro::TokenStream {
+        inner
+            .to_string()
+            .parse()
+            .expect("failed to parse to compiler tokens")
+    }
+}
+
+impl From<TokenTree> for TokenStream {
+    fn from(tree: TokenTree) -> TokenStream {
+        TokenStream { inner: vec![tree] }
+    }
+}
+
+impl iter::FromIterator<TokenTree> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenTree>>(streams: I) -> Self {
+        let mut v = Vec::new();
+
+        for token in streams.into_iter() {
+            v.push(token);
+        }
+
+        TokenStream { inner: v }
+    }
+}
+
+impl iter::FromIterator<TokenStream> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
+        let mut v = Vec::new();
+
+        for stream in streams.into_iter() {
+            v.extend(stream.inner);
+        }
+
+        TokenStream { inner: v }
+    }
+}
+
+impl Extend<TokenTree> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, streams: I) {
+        self.inner.extend(streams);
+    }
+}
+
+impl Extend<TokenStream> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
+        self.inner
+            .extend(streams.into_iter().flat_map(|stream| stream));
+    }
+}
+
+pub type TokenTreeIter = vec::IntoIter<TokenTree>;
+
+impl IntoIterator for TokenStream {
+    type Item = TokenTree;
+    type IntoIter = TokenTreeIter;
+
+    fn into_iter(self) -> TokenTreeIter {
+        self.inner.into_iter()
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+pub struct SourceFile {
+    path: PathBuf,
+}
+
+impl SourceFile {
+    /// Get the path to this source file as a string.
+    pub fn path(&self) -> PathBuf {
+        self.path.clone()
+    }
+
+    pub fn is_real(&self) -> bool {
+        // XXX(nika): Support real files in the future?
+        false
+    }
+}
+
+impl fmt::Debug for SourceFile {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("SourceFile")
+            .field("path", &self.path())
+            .field("is_real", &self.is_real())
+            .finish()
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct LineColumn {
+    pub line: usize,
+    pub column: usize,
+}
+
+#[cfg(span_locations)]
+thread_local! {
+    static SOURCE_MAP: RefCell<SourceMap> = RefCell::new(SourceMap {
+        // NOTE: We start with a single dummy file which all call_site() and
+        // def_site() spans reference.
+        files: vec![{
+            #[cfg(procmacro2_semver_exempt)]
+            {
+                FileInfo {
+                    name: "<unspecified>".to_owned(),
+                    span: Span { lo: 0, hi: 0 },
+                    lines: vec![0],
+                }
+            }
+
+            #[cfg(not(procmacro2_semver_exempt))]
+            {
+                FileInfo {
+                    span: Span { lo: 0, hi: 0 },
+                    lines: vec![0],
+                }
+            }
+        }],
+    });
+}
+
+#[cfg(span_locations)]
+struct FileInfo {
+    #[cfg(procmacro2_semver_exempt)]
+    name: String,
+    span: Span,
+    lines: Vec<usize>,
+}
+
+#[cfg(span_locations)]
+impl FileInfo {
+    fn offset_line_column(&self, offset: usize) -> LineColumn {
+        assert!(self.span_within(Span {
+            lo: offset as u32,
+            hi: offset as u32
+        }));
+        let offset = offset - self.span.lo as usize;
+        match self.lines.binary_search(&offset) {
+            Ok(found) => LineColumn {
+                line: found + 1,
+                column: 0,
+            },
+            Err(idx) => LineColumn {
+                line: idx,
+                column: offset - self.lines[idx - 1],
+            },
+        }
+    }
+
+    fn span_within(&self, span: Span) -> bool {
+        span.lo >= self.span.lo && span.hi <= self.span.hi
+    }
+}
+
+/// Computesthe offsets of each line in the given source string.
+#[cfg(span_locations)]
+fn lines_offsets(s: &str) -> Vec<usize> {
+    let mut lines = vec![0];
+    let mut prev = 0;
+    while let Some(len) = s[prev..].find('\n') {
+        prev += len + 1;
+        lines.push(prev);
+    }
+    lines
+}
+
+#[cfg(span_locations)]
+struct SourceMap {
+    files: Vec<FileInfo>,
+}
+
+#[cfg(span_locations)]
+impl SourceMap {
+    fn next_start_pos(&self) -> u32 {
+        // Add 1 so there's always space between files.
+        //
+        // We'll always have at least 1 file, as we initialize our files list
+        // with a dummy file.
+        self.files.last().unwrap().span.hi + 1
+    }
+
+    fn add_file(&mut self, name: &str, src: &str) -> Span {
+        let lines = lines_offsets(src);
+        let lo = self.next_start_pos();
+        // XXX(nika): Shouild we bother doing a checked cast or checked add here?
+        let span = Span {
+            lo,
+            hi: lo + (src.len() as u32),
+        };
+
+        #[cfg(procmacro2_semver_exempt)]
+        self.files.push(FileInfo {
+            name: name.to_owned(),
+            span,
+            lines,
+        });
+
+        #[cfg(not(procmacro2_semver_exempt))]
+        self.files.push(FileInfo { span, lines });
+        let _ = name;
+
+        span
+    }
+
+    fn fileinfo(&self, span: Span) -> &FileInfo {
+        for file in &self.files {
+            if file.span_within(span) {
+                return file;
+            }
+        }
+        panic!("Invalid span with no related FileInfo!");
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Span {
+    #[cfg(span_locations)]
+    lo: u32,
+    #[cfg(span_locations)]
+    hi: u32,
+}
+
+impl Span {
+    #[cfg(not(span_locations))]
+    pub fn call_site() -> Span {
+        Span {}
+    }
+
+    #[cfg(span_locations)]
+    pub fn call_site() -> Span {
+        Span { lo: 0, hi: 0 }
+    }
+
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn def_site() -> Span {
+        Span::call_site()
+    }
+
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn resolved_at(&self, _other: Span) -> Span {
+        // Stable spans consist only of line/column information, so
+        // `resolved_at` and `located_at` only select which span the
+        // caller wants line/column information from.
+        *self
+    }
+
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn located_at(&self, other: Span) -> Span {
+        other
+    }
+
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn source_file(&self) -> SourceFile {
+        SOURCE_MAP.with(|cm| {
+            let cm = cm.borrow();
+            let fi = cm.fileinfo(*self);
+            SourceFile {
+                path: Path::new(&fi.name).to_owned(),
+            }
+        })
+    }
+
+    #[cfg(span_locations)]
+    pub fn start(&self) -> LineColumn {
+        SOURCE_MAP.with(|cm| {
+            let cm = cm.borrow();
+            let fi = cm.fileinfo(*self);
+            fi.offset_line_column(self.lo as usize)
+        })
+    }
+
+    #[cfg(span_locations)]
+    pub fn end(&self) -> LineColumn {
+        SOURCE_MAP.with(|cm| {
+            let cm = cm.borrow();
+            let fi = cm.fileinfo(*self);
+            fi.offset_line_column(self.hi as usize)
+        })
+    }
+
+    #[cfg(not(span_locations))]
+    pub fn join(&self, _other: Span) -> Option<Span> {
+        Some(Span {})
+    }
+
+    #[cfg(span_locations)]
+    pub fn join(&self, other: Span) -> Option<Span> {
+        SOURCE_MAP.with(|cm| {
+            let cm = cm.borrow();
+            // If `other` is not within the same FileInfo as us, return None.
+            if !cm.fileinfo(*self).span_within(other) {
+                return None;
+            }
+            Some(Span {
+                lo: cmp::min(self.lo, other.lo),
+                hi: cmp::max(self.hi, other.hi),
+            })
+        })
+    }
+
+    #[cfg(not(span_locations))]
+    fn first_byte(self) -> Self {
+        self
+    }
+
+    #[cfg(span_locations)]
+    fn first_byte(self) -> Self {
+        Span {
+            lo: self.lo,
+            hi: cmp::min(self.lo.saturating_add(1), self.hi),
+        }
+    }
+
+    #[cfg(not(span_locations))]
+    fn last_byte(self) -> Self {
+        self
+    }
+
+    #[cfg(span_locations)]
+    fn last_byte(self) -> Self {
+        Span {
+            lo: cmp::max(self.hi.saturating_sub(1), self.lo),
+            hi: self.hi,
+        }
+    }
+}
+
+impl fmt::Debug for Span {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        #[cfg(procmacro2_semver_exempt)]
+        return write!(f, "bytes({}..{})", self.lo, self.hi);
+
+        #[cfg(not(procmacro2_semver_exempt))]
+        write!(f, "Span")
+    }
+}
+
+pub fn debug_span_field_if_nontrivial(debug: &mut fmt::DebugStruct, span: Span) {
+    if cfg!(procmacro2_semver_exempt) {
+        debug.field("span", &span);
+    }
+}
+
+#[derive(Clone)]
+pub struct Group {
+    delimiter: Delimiter,
+    stream: TokenStream,
+    span: Span,
+}
+
+impl Group {
+    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
+        Group {
+            delimiter,
+            stream,
+            span: Span::call_site(),
+        }
+    }
+
+    pub fn delimiter(&self) -> Delimiter {
+        self.delimiter
+    }
+
+    pub fn stream(&self) -> TokenStream {
+        self.stream.clone()
+    }
+
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    pub fn span_open(&self) -> Span {
+        self.span.first_byte()
+    }
+
+    pub fn span_close(&self) -> Span {
+        self.span.last_byte()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.span = span;
+    }
+}
+
+impl fmt::Display for Group {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let (left, right) = match self.delimiter {
+            Delimiter::Parenthesis => ("(", ")"),
+            Delimiter::Brace => ("{", "}"),
+            Delimiter::Bracket => ("[", "]"),
+            Delimiter::None => ("", ""),
+        };
+
+        f.write_str(left)?;
+        self.stream.fmt(f)?;
+        f.write_str(right)?;
+
+        Ok(())
+    }
+}
+
+impl fmt::Debug for Group {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        let mut debug = fmt.debug_struct("Group");
+        debug.field("delimiter", &self.delimiter);
+        debug.field("stream", &self.stream);
+        #[cfg(procmacro2_semver_exempt)]
+        debug.field("span", &self.span);
+        debug.finish()
+    }
+}
+
+#[derive(Clone)]
+pub struct Ident {
+    sym: String,
+    span: Span,
+    raw: bool,
+}
+
+impl Ident {
+    fn _new(string: &str, raw: bool, span: Span) -> Ident {
+        validate_ident(string);
+
+        Ident {
+            sym: string.to_owned(),
+            span,
+            raw,
+        }
+    }
+
+    pub fn new(string: &str, span: Span) -> Ident {
+        Ident::_new(string, false, span)
+    }
+
+    pub fn new_raw(string: &str, span: Span) -> Ident {
+        Ident::_new(string, true, span)
+    }
+
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.span = span;
+    }
+}
+
+fn is_ident_start(c: char) -> bool {
+    ('a' <= c && c <= 'z')
+        || ('A' <= c && c <= 'Z')
+        || c == '_'
+        || (c > '\x7f' && UnicodeXID::is_xid_start(c))
+}
+
+fn is_ident_continue(c: char) -> bool {
+    ('a' <= c && c <= 'z')
+        || ('A' <= c && c <= 'Z')
+        || c == '_'
+        || ('0' <= c && c <= '9')
+        || (c > '\x7f' && UnicodeXID::is_xid_continue(c))
+}
+
+fn validate_ident(string: &str) {
+    let validate = string;
+    if validate.is_empty() {
+        panic!("Ident is not allowed to be empty; use Option<Ident>");
+    }
+
+    if validate.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
+        panic!("Ident cannot be a number; use Literal instead");
+    }
+
+    fn ident_ok(string: &str) -> bool {
+        let mut chars = string.chars();
+        let first = chars.next().unwrap();
+        if !is_ident_start(first) {
+            return false;
+        }
+        for ch in chars {
+            if !is_ident_continue(ch) {
+                return false;
+            }
+        }
+        true
+    }
+
+    if !ident_ok(validate) {
+        panic!("{:?} is not a valid Ident", string);
+    }
+}
+
+impl PartialEq for Ident {
+    fn eq(&self, other: &Ident) -> bool {
+        self.sym == other.sym && self.raw == other.raw
+    }
+}
+
+impl<T> PartialEq<T> for Ident
+where
+    T: ?Sized + AsRef<str>,
+{
+    fn eq(&self, other: &T) -> bool {
+        let other = other.as_ref();
+        if self.raw {
+            other.starts_with("r#") && self.sym == other[2..]
+        } else {
+            self.sym == other
+        }
+    }
+}
+
+impl fmt::Display for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.raw {
+            "r#".fmt(f)?;
+        }
+        self.sym.fmt(f)
+    }
+}
+
+impl fmt::Debug for Ident {
+    // Ident(proc_macro), Ident(r#union)
+    #[cfg(not(procmacro2_semver_exempt))]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut debug = f.debug_tuple("Ident");
+        debug.field(&format_args!("{}", self));
+        debug.finish()
+    }
+
+    // Ident {
+    //     sym: proc_macro,
+    //     span: bytes(128..138)
+    // }
+    #[cfg(procmacro2_semver_exempt)]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut debug = f.debug_struct("Ident");
+        debug.field("sym", &format_args!("{}", self));
+        debug.field("span", &self.span);
+        debug.finish()
+    }
+}
+
+#[derive(Clone)]
+pub struct Literal {
+    text: String,
+    span: Span,
+}
+
+macro_rules! suffixed_numbers {
+    ($($name:ident => $kind:ident,)*) => ($(
+        pub fn $name(n: $kind) -> Literal {
+            Literal::_new(format!(concat!("{}", stringify!($kind)), n))
+        }
+    )*)
+}
+
+macro_rules! unsuffixed_numbers {
+    ($($name:ident => $kind:ident,)*) => ($(
+        pub fn $name(n: $kind) -> Literal {
+            Literal::_new(n.to_string())
+        }
+    )*)
+}
+
+impl Literal {
+    fn _new(text: String) -> Literal {
+        Literal {
+            text,
+            span: Span::call_site(),
+        }
+    }
+
+    suffixed_numbers! {
+        u8_suffixed => u8,
+        u16_suffixed => u16,
+        u32_suffixed => u32,
+        u64_suffixed => u64,
+        u128_suffixed => u128,
+        usize_suffixed => usize,
+        i8_suffixed => i8,
+        i16_suffixed => i16,
+        i32_suffixed => i32,
+        i64_suffixed => i64,
+        i128_suffixed => i128,
+        isize_suffixed => isize,
+
+        f32_suffixed => f32,
+        f64_suffixed => f64,
+    }
+
+    unsuffixed_numbers! {
+        u8_unsuffixed => u8,
+        u16_unsuffixed => u16,
+        u32_unsuffixed => u32,
+        u64_unsuffixed => u64,
+        u128_unsuffixed => u128,
+        usize_unsuffixed => usize,
+        i8_unsuffixed => i8,
+        i16_unsuffixed => i16,
+        i32_unsuffixed => i32,
+        i64_unsuffixed => i64,
+        i128_unsuffixed => i128,
+        isize_unsuffixed => isize,
+    }
+
+    pub fn f32_unsuffixed(f: f32) -> Literal {
+        let mut s = f.to_string();
+        if !s.contains(".") {
+            s.push_str(".0");
+        }
+        Literal::_new(s)
+    }
+
+    pub fn f64_unsuffixed(f: f64) -> Literal {
+        let mut s = f.to_string();
+        if !s.contains(".") {
+            s.push_str(".0");
+        }
+        Literal::_new(s)
+    }
+
+    pub fn string(t: &str) -> Literal {
+        let mut text = String::with_capacity(t.len() + 2);
+        text.push('"');
+        for c in t.chars() {
+            if c == '\'' {
+                // escape_default turns this into "\'" which is unnecessary.
+                text.push(c);
+            } else {
+                text.extend(c.escape_default());
+            }
+        }
+        text.push('"');
+        Literal::_new(text)
+    }
+
+    pub fn character(t: char) -> Literal {
+        let mut text = String::new();
+        text.push('\'');
+        if t == '"' {
+            // escape_default turns this into '\"' which is unnecessary.
+            text.push(t);
+        } else {
+            text.extend(t.escape_default());
+        }
+        text.push('\'');
+        Literal::_new(text)
+    }
+
+    pub fn byte_string(bytes: &[u8]) -> Literal {
+        let mut escaped = "b\"".to_string();
+        for b in bytes {
+            match *b {
+                b'\0' => escaped.push_str(r"\0"),
+                b'\t' => escaped.push_str(r"\t"),
+                b'\n' => escaped.push_str(r"\n"),
+                b'\r' => escaped.push_str(r"\r"),
+                b'"' => escaped.push_str("\\\""),
+                b'\\' => escaped.push_str("\\\\"),
+                b'\x20'..=b'\x7E' => escaped.push(*b as char),
+                _ => escaped.push_str(&format!("\\x{:02X}", b)),
+            }
+        }
+        escaped.push('"');
+        Literal::_new(escaped)
+    }
+
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.span = span;
+    }
+
+    pub fn subspan<R: RangeBounds<usize>>(&self, _range: R) -> Option<Span> {
+        None
+    }
+}
+
+impl fmt::Display for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.text.fmt(f)
+    }
+}
+
+impl fmt::Debug for Literal {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        let mut debug = fmt.debug_struct("Literal");
+        debug.field("lit", &format_args!("{}", self.text));
+        #[cfg(procmacro2_semver_exempt)]
+        debug.field("span", &self.span);
+        debug.finish()
+    }
+}
+
+fn token_stream(mut input: Cursor) -> PResult<TokenStream> {
+    let mut trees = Vec::new();
+    loop {
+        let input_no_ws = skip_whitespace(input);
+        if input_no_ws.rest.len() == 0 {
+            break;
+        }
+        if let Ok((a, tokens)) = doc_comment(input_no_ws) {
+            input = a;
+            trees.extend(tokens);
+            continue;
+        }
+
+        let (a, tt) = match token_tree(input_no_ws) {
+            Ok(p) => p,
+            Err(_) => break,
+        };
+        trees.push(tt);
+        input = a;
+    }
+    Ok((input, TokenStream { inner: trees }))
+}
+
+#[cfg(not(span_locations))]
+fn spanned<'a, T>(
+    input: Cursor<'a>,
+    f: fn(Cursor<'a>) -> PResult<'a, T>,
+) -> PResult<'a, (T, crate::Span)> {
+    let (a, b) = f(skip_whitespace(input))?;
+    Ok((a, ((b, crate::Span::_new_stable(Span::call_site())))))
+}
+
+#[cfg(span_locations)]
+fn spanned<'a, T>(
+    input: Cursor<'a>,
+    f: fn(Cursor<'a>) -> PResult<'a, T>,
+) -> PResult<'a, (T, crate::Span)> {
+    let input = skip_whitespace(input);
+    let lo = input.off;
+    let (a, b) = f(input)?;
+    let hi = a.off;
+    let span = crate::Span::_new_stable(Span { lo, hi });
+    Ok((a, (b, span)))
+}
+
+fn token_tree(input: Cursor) -> PResult<TokenTree> {
+    let (rest, (mut tt, span)) = spanned(input, token_kind)?;
+    tt.set_span(span);
+    Ok((rest, tt))
+}
+
+named!(token_kind -> TokenTree, alt!(
+    map!(group, |g| TokenTree::Group(crate::Group::_new_stable(g)))
+    |
+    map!(literal, |l| TokenTree::Literal(crate::Literal::_new_stable(l))) // must be before symbol
+    |
+    map!(op, TokenTree::Punct)
+    |
+    symbol_leading_ws
+));
+
+named!(group -> Group, alt!(
+    delimited!(
+        punct!("("),
+        token_stream,
+        punct!(")")
+    ) => { |ts| Group::new(Delimiter::Parenthesis, ts) }
+    |
+    delimited!(
+        punct!("["),
+        token_stream,
+        punct!("]")
+    ) => { |ts| Group::new(Delimiter::Bracket, ts) }
+    |
+    delimited!(
+        punct!("{"),
+        token_stream,
+        punct!("}")
+    ) => { |ts| Group::new(Delimiter::Brace, ts) }
+));
+
+fn symbol_leading_ws(input: Cursor) -> PResult<TokenTree> {
+    symbol(skip_whitespace(input))
+}
+
+fn symbol(input: Cursor) -> PResult<TokenTree> {
+    let raw = input.starts_with("r#");
+    let rest = input.advance((raw as usize) << 1);
+
+    let (rest, sym) = symbol_not_raw(rest)?;
+
+    if !raw {
+        let ident = crate::Ident::new(sym, crate::Span::call_site());
+        return Ok((rest, ident.into()));
+    }
+
+    if sym == "_" {
+        return Err(LexError);
+    }
+
+    let ident = crate::Ident::_new_raw(sym, crate::Span::call_site());
+    Ok((rest, ident.into()))
+}
+
+fn symbol_not_raw(input: Cursor) -> PResult<&str> {
+    let mut chars = input.char_indices();
+
+    match chars.next() {
+        Some((_, ch)) if is_ident_start(ch) => {}
+        _ => return Err(LexError),
+    }
+
+    let mut end = input.len();
+    for (i, ch) in chars {
+        if !is_ident_continue(ch) {
+            end = i;
+            break;
+        }
+    }
+
+    Ok((input.advance(end), &input.rest[..end]))
+}
+
+fn literal(input: Cursor) -> PResult<Literal> {
+    let input_no_ws = skip_whitespace(input);
+
+    match literal_nocapture(input_no_ws) {
+        Ok((a, ())) => {
+            let start = input.len() - input_no_ws.len();
+            let len = input_no_ws.len() - a.len();
+            let end = start + len;
+            Ok((a, Literal::_new(input.rest[start..end].to_string())))
+        }
+        Err(LexError) => Err(LexError),
+    }
+}
+
+named!(literal_nocapture -> (), alt!(
+    string
+    |
+    byte_string
+    |
+    byte
+    |
+    character
+    |
+    float
+    |
+    int
+));
+
+named!(string -> (), alt!(
+    quoted_string
+    |
+    preceded!(
+        punct!("r"),
+        raw_string
+    ) => { |_| () }
+));
+
+named!(quoted_string -> (), do_parse!(
+    punct!("\"") >>
+    cooked_string >>
+    tag!("\"") >>
+    option!(symbol_not_raw) >>
+    (())
+));
+
+fn cooked_string(input: Cursor) -> PResult<()> {
+    let mut chars = input.char_indices().peekable();
+    while let Some((byte_offset, ch)) = chars.next() {
+        match ch {
+            '"' => {
+                return Ok((input.advance(byte_offset), ()));
+            }
+            '\r' => {
+                if let Some((_, '\n')) = chars.next() {
+                    // ...
+                } else {
+                    break;
+                }
+            }
+            '\\' => match chars.next() {
+                Some((_, 'x')) => {
+                    if !backslash_x_char(&mut chars) {
+                        break;
+                    }
+                }
+                Some((_, 'n')) | Some((_, 'r')) | Some((_, 't')) | Some((_, '\\'))
+                | Some((_, '\'')) | Some((_, '"')) | Some((_, '0')) => {}
+                Some((_, 'u')) => {
+                    if !backslash_u(&mut chars) {
+                        break;
+                    }
+                }
+                Some((_, '\n')) | Some((_, '\r')) => {
+                    while let Some(&(_, ch)) = chars.peek() {
+                        if ch.is_whitespace() {
+                            chars.next();
+                        } else {
+                            break;
+                        }
+                    }
+                }
+                _ => break,
+            },
+            _ch => {}
+        }
+    }
+    Err(LexError)
+}
+
+named!(byte_string -> (), alt!(
+    delimited!(
+        punct!("b\""),
+        cooked_byte_string,
+        tag!("\"")
+    ) => { |_| () }
+    |
+    preceded!(
+        punct!("br"),
+        raw_string
+    ) => { |_| () }
+));
+
+fn cooked_byte_string(mut input: Cursor) -> PResult<()> {
+    let mut bytes = input.bytes().enumerate();
+    'outer: while let Some((offset, b)) = bytes.next() {
+        match b {
+            b'"' => {
+                return Ok((input.advance(offset), ()));
+            }
+            b'\r' => {
+                if let Some((_, b'\n')) = bytes.next() {
+                    // ...
+                } else {
+                    break;
+                }
+            }
+            b'\\' => match bytes.next() {
+                Some((_, b'x')) => {
+                    if !backslash_x_byte(&mut bytes) {
+                        break;
+                    }
+                }
+                Some((_, b'n')) | Some((_, b'r')) | Some((_, b't')) | Some((_, b'\\'))
+                | Some((_, b'0')) | Some((_, b'\'')) | Some((_, b'"')) => {}
+                Some((newline, b'\n')) | Some((newline, b'\r')) => {
+                    let rest = input.advance(newline + 1);
+                    for (offset, ch) in rest.char_indices() {
+                        if !ch.is_whitespace() {
+                            input = rest.advance(offset);
+                            bytes = input.bytes().enumerate();
+                            continue 'outer;
+                        }
+                    }
+                    break;
+                }
+                _ => break,
+            },
+            b if b < 0x80 => {}
+            _ => break,
+        }
+    }
+    Err(LexError)
+}
+
+fn raw_string(input: Cursor) -> PResult<()> {
+    let mut chars = input.char_indices();
+    let mut n = 0;
+    while let Some((byte_offset, ch)) = chars.next() {
+        match ch {
+            '"' => {
+                n = byte_offset;
+                break;
+            }
+            '#' => {}
+            _ => return Err(LexError),
+        }
+    }
+    for (byte_offset, ch) in chars {
+        match ch {
+            '"' if input.advance(byte_offset + 1).starts_with(&input.rest[..n]) => {
+                let rest = input.advance(byte_offset + 1 + n);
+                return Ok((rest, ()));
+            }
+            '\r' => {}
+            _ => {}
+        }
+    }
+    Err(LexError)
+}
+
+named!(byte -> (), do_parse!(
+    punct!("b") >>
+    tag!("'") >>
+    cooked_byte >>
+    tag!("'") >>
+    (())
+));
+
+fn cooked_byte(input: Cursor) -> PResult<()> {
+    let mut bytes = input.bytes().enumerate();
+    let ok = match bytes.next().map(|(_, b)| b) {
+        Some(b'\\') => match bytes.next().map(|(_, b)| b) {
+            Some(b'x') => backslash_x_byte(&mut bytes),
+            Some(b'n') | Some(b'r') | Some(b't') | Some(b'\\') | Some(b'0') | Some(b'\'')
+            | Some(b'"') => true,
+            _ => false,
+        },
+        b => b.is_some(),
+    };
+    if ok {
+        match bytes.next() {
+            Some((offset, _)) => {
+                if input.chars().as_str().is_char_boundary(offset) {
+                    Ok((input.advance(offset), ()))
+                } else {
+                    Err(LexError)
+                }
+            }
+            None => Ok((input.advance(input.len()), ())),
+        }
+    } else {
+        Err(LexError)
+    }
+}
+
+named!(character -> (), do_parse!(
+    punct!("'") >>
+    cooked_char >>
+    tag!("'") >>
+    (())
+));
+
+fn cooked_char(input: Cursor) -> PResult<()> {
+    let mut chars = input.char_indices();
+    let ok = match chars.next().map(|(_, ch)| ch) {
+        Some('\\') => match chars.next().map(|(_, ch)| ch) {
+            Some('x') => backslash_x_char(&mut chars),
+            Some('u') => backslash_u(&mut chars),
+            Some('n') | Some('r') | Some('t') | Some('\\') | Some('0') | Some('\'') | Some('"') => {
+                true
+            }
+            _ => false,
+        },
+        ch => ch.is_some(),
+    };
+    if ok {
+        match chars.next() {
+            Some((idx, _)) => Ok((input.advance(idx), ())),
+            None => Ok((input.advance(input.len()), ())),
+        }
+    } else {
+        Err(LexError)
+    }
+}
+
+macro_rules! next_ch {
+    ($chars:ident @ $pat:pat $(| $rest:pat)*) => {
+        match $chars.next() {
+            Some((_, ch)) => match ch {
+                $pat $(| $rest)*  => ch,
+                _ => return false,
+            },
+            None => return false
+        }
+    };
+}
+
+fn backslash_x_char<I>(chars: &mut I) -> bool
+where
+    I: Iterator<Item = (usize, char)>,
+{
+    next_ch!(chars @ '0'..='7');
+    next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    true
+}
+
+fn backslash_x_byte<I>(chars: &mut I) -> bool
+where
+    I: Iterator<Item = (usize, u8)>,
+{
+    next_ch!(chars @ b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F');
+    next_ch!(chars @ b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F');
+    true
+}
+
+fn backslash_u<I>(chars: &mut I) -> bool
+where
+    I: Iterator<Item = (usize, char)>,
+{
+    next_ch!(chars @ '{');
+    next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    loop {
+        let c = next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F' | '_' | '}');
+        if c == '}' {
+            return true;
+        }
+    }
+}
+
+fn float(input: Cursor) -> PResult<()> {
+    let (mut rest, ()) = float_digits(input)?;
+    if let Some(ch) = rest.chars().next() {
+        if is_ident_start(ch) {
+            rest = symbol_not_raw(rest)?.0;
+        }
+    }
+    word_break(rest)
+}
+
+fn float_digits(input: Cursor) -> PResult<()> {
+    let mut chars = input.chars().peekable();
+    match chars.next() {
+        Some(ch) if ch >= '0' && ch <= '9' => {}
+        _ => return Err(LexError),
+    }
+
+    let mut len = 1;
+    let mut has_dot = false;
+    let mut has_exp = false;
+    while let Some(&ch) = chars.peek() {
+        match ch {
+            '0'..='9' | '_' => {
+                chars.next();
+                len += 1;
+            }
+            '.' => {
+                if has_dot {
+                    break;
+                }
+                chars.next();
+                if chars
+                    .peek()
+                    .map(|&ch| ch == '.' || is_ident_start(ch))
+                    .unwrap_or(false)
+                {
+                    return Err(LexError);
+                }
+                len += 1;
+                has_dot = true;
+            }
+            'e' | 'E' => {
+                chars.next();
+                len += 1;
+                has_exp = true;
+                break;
+            }
+            _ => break,
+        }
+    }
+
+    let rest = input.advance(len);
+    if !(has_dot || has_exp || rest.starts_with("f32") || rest.starts_with("f64")) {
+        return Err(LexError);
+    }
+
+    if has_exp {
+        let mut has_exp_value = false;
+        while let Some(&ch) = chars.peek() {
+            match ch {
+                '+' | '-' => {
+                    if has_exp_value {
+                        break;
+                    }
+                    chars.next();
+                    len += 1;
+                }
+                '0'..='9' => {
+                    chars.next();
+                    len += 1;
+                    has_exp_value = true;
+                }
+                '_' => {
+                    chars.next();
+                    len += 1;
+                }
+                _ => break,
+            }
+        }
+        if !has_exp_value {
+            return Err(LexError);
+        }
+    }
+
+    Ok((input.advance(len), ()))
+}
+
+fn int(input: Cursor) -> PResult<()> {
+    let (mut rest, ()) = digits(input)?;
+    if let Some(ch) = rest.chars().next() {
+        if is_ident_start(ch) {
+            rest = symbol_not_raw(rest)?.0;
+        }
+    }
+    word_break(rest)
+}
+
+fn digits(mut input: Cursor) -> PResult<()> {
+    let base = if input.starts_with("0x") {
+        input = input.advance(2);
+        16
+    } else if input.starts_with("0o") {
+        input = input.advance(2);
+        8
+    } else if input.starts_with("0b") {
+        input = input.advance(2);
+        2
+    } else {
+        10
+    };
+
+    let mut len = 0;
+    let mut empty = true;
+    for b in input.bytes() {
+        let digit = match b {
+            b'0'..=b'9' => (b - b'0') as u64,
+            b'a'..=b'f' => 10 + (b - b'a') as u64,
+            b'A'..=b'F' => 10 + (b - b'A') as u64,
+            b'_' => {
+                if empty && base == 10 {
+                    return Err(LexError);
+                }
+                len += 1;
+                continue;
+            }
+            _ => break,
+        };
+        if digit >= base {
+            return Err(LexError);
+        }
+        len += 1;
+        empty = false;
+    }
+    if empty {
+        Err(LexError)
+    } else {
+        Ok((input.advance(len), ()))
+    }
+}
+
+fn op(input: Cursor) -> PResult<Punct> {
+    let input = skip_whitespace(input);
+    match op_char(input) {
+        Ok((rest, '\'')) => {
+            symbol(rest)?;
+            Ok((rest, Punct::new('\'', Spacing::Joint)))
+        }
+        Ok((rest, ch)) => {
+            let kind = match op_char(rest) {
+                Ok(_) => Spacing::Joint,
+                Err(LexError) => Spacing::Alone,
+            };
+            Ok((rest, Punct::new(ch, kind)))
+        }
+        Err(LexError) => Err(LexError),
+    }
+}
+
+fn op_char(input: Cursor) -> PResult<char> {
+    if input.starts_with("//") || input.starts_with("/*") {
+        // Do not accept `/` of a comment as an op.
+        return Err(LexError);
+    }
+
+    let mut chars = input.chars();
+    let first = match chars.next() {
+        Some(ch) => ch,
+        None => {
+            return Err(LexError);
+        }
+    };
+    let recognized = "~!@#$%^&*-=+|;:,<.>/?'";
+    if recognized.contains(first) {
+        Ok((input.advance(first.len_utf8()), first))
+    } else {
+        Err(LexError)
+    }
+}
+
+fn doc_comment(input: Cursor) -> PResult<Vec<TokenTree>> {
+    let mut trees = Vec::new();
+    let (rest, ((comment, inner), span)) = spanned(input, doc_comment_contents)?;
+    trees.push(TokenTree::Punct(Punct::new('#', Spacing::Alone)));
+    if inner {
+        trees.push(Punct::new('!', Spacing::Alone).into());
+    }
+    let mut stream = vec![
+        TokenTree::Ident(crate::Ident::new("doc", span)),
+        TokenTree::Punct(Punct::new('=', Spacing::Alone)),
+        TokenTree::Literal(crate::Literal::string(comment)),
+    ];
+    for tt in stream.iter_mut() {
+        tt.set_span(span);
+    }
+    let group = Group::new(Delimiter::Bracket, stream.into_iter().collect());
+    trees.push(crate::Group::_new_stable(group).into());
+    for tt in trees.iter_mut() {
+        tt.set_span(span);
+    }
+    Ok((rest, trees))
+}
+
+named!(doc_comment_contents -> (&str, bool), alt!(
+    do_parse!(
+        punct!("//!") >>
+        s: take_until_newline_or_eof!() >>
+        ((s, true))
+    )
+    |
+    do_parse!(
+        option!(whitespace) >>
+        peek!(tag!("/*!")) >>
+        s: block_comment >>
+        ((s, true))
+    )
+    |
+    do_parse!(
+        punct!("///") >>
+        not!(tag!("/")) >>
+        s: take_until_newline_or_eof!() >>
+        ((s, false))
+    )
+    |
+    do_parse!(
+        option!(whitespace) >>
+        peek!(tuple!(tag!("/**"), not!(tag!("*")))) >>
+        s: block_comment >>
+        ((s, false))
+    )
+));
diff --git a/proc-macro2/src/lib.rs b/proc-macro2/src/lib.rs
new file mode 100644
index 0000000..bbfb375
--- /dev/null
+++ b/proc-macro2/src/lib.rs
@@ -0,0 +1,1199 @@
+//! A wrapper around the procedural macro API of the compiler's [`proc_macro`]
+//! crate. This library serves two purposes:
+//!
+//! [`proc_macro`]: https://doc.rust-lang.org/proc_macro/
+//!
+//! - **Bring proc-macro-like functionality to other contexts like build.rs and
+//!   main.rs.** Types from `proc_macro` are entirely specific to procedural
+//!   macros and cannot ever exist in code outside of a procedural macro.
+//!   Meanwhile `proc_macro2` types may exist anywhere including non-macro code.
+//!   By developing foundational libraries like [syn] and [quote] against
+//!   `proc_macro2` rather than `proc_macro`, the procedural macro ecosystem
+//!   becomes easily applicable to many other use cases and we avoid
+//!   reimplementing non-macro equivalents of those libraries.
+//!
+//! - **Make procedural macros unit testable.** As a consequence of being
+//!   specific to procedural macros, nothing that uses `proc_macro` can be
+//!   executed from a unit test. In order for helper libraries or components of
+//!   a macro to be testable in isolation, they must be implemented using
+//!   `proc_macro2`.
+//!
+//! [syn]: https://github.com/dtolnay/syn
+//! [quote]: https://github.com/dtolnay/quote
+//!
+//! # Usage
+//!
+//! The skeleton of a typical procedural macro typically looks like this:
+//!
+//! ```
+//! extern crate proc_macro;
+//!
+//! # const IGNORE: &str = stringify! {
+//! #[proc_macro_derive(MyDerive)]
+//! # };
+//! # #[cfg(wrap_proc_macro)]
+//! pub fn my_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+//!     let input = proc_macro2::TokenStream::from(input);
+//!
+//!     let output: proc_macro2::TokenStream = {
+//!         /* transform input */
+//!         # input
+//!     };
+//!
+//!     proc_macro::TokenStream::from(output)
+//! }
+//! ```
+//!
+//! If parsing with [Syn], you'll use [`parse_macro_input!`] instead to
+//! propagate parse errors correctly back to the compiler when parsing fails.
+//!
+//! [`parse_macro_input!`]: https://docs.rs/syn/1.0/syn/macro.parse_macro_input.html
+//!
+//! # Unstable features
+//!
+//! The default feature set of proc-macro2 tracks the most recent stable
+//! compiler API. Functionality in `proc_macro` that is not yet stable is not
+//! exposed by proc-macro2 by default.
+//!
+//! To opt into the additional APIs available in the most recent nightly
+//! compiler, the `procmacro2_semver_exempt` config flag must be passed to
+//! rustc. We will polyfill those nightly-only APIs back to Rust 1.31.0. As
+//! these are unstable APIs that track the nightly compiler, minor versions of
+//! proc-macro2 may make breaking changes to them at any time.
+//!
+//! ```sh
+//! RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo build
+//! ```
+//!
+//! Note that this must not only be done for your crate, but for any crate that
+//! depends on your crate. This infectious nature is intentional, as it serves
+//! as a reminder that you are outside of the normal semver guarantees.
+//!
+//! Semver exempt methods are marked as such in the proc-macro2 documentation.
+//!
+//! # Thread-Safety
+//!
+//! Most types in this crate are `!Sync` because the underlying compiler
+//! types make use of thread-local memory, meaning they cannot be accessed from
+//! a different thread.
+
+// Proc-macro2 types in rustdoc of other crates get linked to here.
+#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.7")]
+#![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
+#![cfg_attr(super_unstable, feature(proc_macro_raw_ident, proc_macro_def_site))]
+
+#[cfg(use_proc_macro)]
+extern crate proc_macro;
+
+use std::cmp::Ordering;
+use std::fmt;
+use std::hash::{Hash, Hasher};
+use std::iter::FromIterator;
+use std::marker;
+use std::ops::RangeBounds;
+#[cfg(procmacro2_semver_exempt)]
+use std::path::PathBuf;
+use std::rc::Rc;
+use std::str::FromStr;
+
+#[macro_use]
+mod strnom;
+mod fallback;
+
+#[cfg(not(wrap_proc_macro))]
+use crate::fallback as imp;
+#[path = "wrapper.rs"]
+#[cfg(wrap_proc_macro)]
+mod imp;
+
+/// An abstract stream of tokens, or more concretely a sequence of token trees.
+///
+/// This type provides interfaces for iterating over token trees and for
+/// collecting token trees into one stream.
+///
+/// Token stream is both the input and output of `#[proc_macro]`,
+/// `#[proc_macro_attribute]` and `#[proc_macro_derive]` definitions.
+#[derive(Clone)]
+pub struct TokenStream {
+    inner: imp::TokenStream,
+    _marker: marker::PhantomData<Rc<()>>,
+}
+
+/// Error returned from `TokenStream::from_str`.
+pub struct LexError {
+    inner: imp::LexError,
+    _marker: marker::PhantomData<Rc<()>>,
+}
+
+impl TokenStream {
+    fn _new(inner: imp::TokenStream) -> TokenStream {
+        TokenStream {
+            inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
+    fn _new_stable(inner: fallback::TokenStream) -> TokenStream {
+        TokenStream {
+            inner: inner.into(),
+            _marker: marker::PhantomData,
+        }
+    }
+
+    /// Returns an empty `TokenStream` containing no token trees.
+    pub fn new() -> TokenStream {
+        TokenStream::_new(imp::TokenStream::new())
+    }
+
+    /// Checks if this `TokenStream` is empty.
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+}
+
+/// `TokenStream::default()` returns an empty stream,
+/// i.e. this is equivalent with `TokenStream::new()`.
+impl Default for TokenStream {
+    fn default() -> Self {
+        TokenStream::new()
+    }
+}
+
+/// Attempts to break the string into tokens and parse those tokens into a token
+/// stream.
+///
+/// May fail for a number of reasons, for example, if the string contains
+/// unbalanced delimiters or characters not existing in the language.
+///
+/// NOTE: Some errors may cause panics instead of returning `LexError`. We
+/// reserve the right to change these errors into `LexError`s later.
+impl FromStr for TokenStream {
+    type Err = LexError;
+
+    fn from_str(src: &str) -> Result<TokenStream, LexError> {
+        let e = src.parse().map_err(|e| LexError {
+            inner: e,
+            _marker: marker::PhantomData,
+        })?;
+        Ok(TokenStream::_new(e))
+    }
+}
+
+#[cfg(use_proc_macro)]
+impl From<proc_macro::TokenStream> for TokenStream {
+    fn from(inner: proc_macro::TokenStream) -> TokenStream {
+        TokenStream::_new(inner.into())
+    }
+}
+
+#[cfg(use_proc_macro)]
+impl From<TokenStream> for proc_macro::TokenStream {
+    fn from(inner: TokenStream) -> proc_macro::TokenStream {
+        inner.inner.into()
+    }
+}
+
+impl From<TokenTree> for TokenStream {
+    fn from(token: TokenTree) -> Self {
+        TokenStream::_new(imp::TokenStream::from(token))
+    }
+}
+
+impl Extend<TokenTree> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, streams: I) {
+        self.inner.extend(streams)
+    }
+}
+
+impl Extend<TokenStream> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
+        self.inner
+            .extend(streams.into_iter().map(|stream| stream.inner))
+    }
+}
+
+/// Collects a number of token trees into a single stream.
+impl FromIterator<TokenTree> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenTree>>(streams: I) -> Self {
+        TokenStream::_new(streams.into_iter().collect())
+    }
+}
+impl FromIterator<TokenStream> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
+        TokenStream::_new(streams.into_iter().map(|i| i.inner).collect())
+    }
+}
+
+/// Prints the token stream as a string that is supposed to be losslessly
+/// convertible back into the same token stream (modulo spans), except for
+/// possibly `TokenTree::Group`s with `Delimiter::None` delimiters and negative
+/// numeric literals.
+impl fmt::Display for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// Prints token in a form convenient for debugging.
+impl fmt::Debug for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::Debug for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// The source file of a given `Span`.
+///
+/// This type is semver exempt and not exposed by default.
+#[cfg(procmacro2_semver_exempt)]
+#[derive(Clone, PartialEq, Eq)]
+pub struct SourceFile {
+    inner: imp::SourceFile,
+    _marker: marker::PhantomData<Rc<()>>,
+}
+
+#[cfg(procmacro2_semver_exempt)]
+impl SourceFile {
+    fn _new(inner: imp::SourceFile) -> Self {
+        SourceFile {
+            inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
+    /// Get the path to this source file.
+    ///
+    /// ### Note
+    ///
+    /// If the code span associated with this `SourceFile` was generated by an
+    /// external macro, this may not be an actual path on the filesystem. Use
+    /// [`is_real`] to check.
+    ///
+    /// Also note that even if `is_real` returns `true`, if
+    /// `--remap-path-prefix` was passed on the command line, the path as given
+    /// may not actually be valid.
+    ///
+    /// [`is_real`]: #method.is_real
+    pub fn path(&self) -> PathBuf {
+        self.inner.path()
+    }
+
+    /// Returns `true` if this source file is a real source file, and not
+    /// generated by an external macro's expansion.
+    pub fn is_real(&self) -> bool {
+        self.inner.is_real()
+    }
+}
+
+#[cfg(procmacro2_semver_exempt)]
+impl fmt::Debug for SourceFile {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// A line-column pair representing the start or end of a `Span`.
+///
+/// This type is semver exempt and not exposed by default.
+#[cfg(span_locations)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct LineColumn {
+    /// The 1-indexed line in the source file on which the span starts or ends
+    /// (inclusive).
+    pub line: usize,
+    /// The 0-indexed column (in UTF-8 characters) in the source file on which
+    /// the span starts or ends (inclusive).
+    pub column: usize,
+}
+
+/// A region of source code, along with macro expansion information.
+#[derive(Copy, Clone)]
+pub struct Span {
+    inner: imp::Span,
+    _marker: marker::PhantomData<Rc<()>>,
+}
+
+impl Span {
+    fn _new(inner: imp::Span) -> Span {
+        Span {
+            inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
+    fn _new_stable(inner: fallback::Span) -> Span {
+        Span {
+            inner: inner.into(),
+            _marker: marker::PhantomData,
+        }
+    }
+
+    /// The span of the invocation of the current procedural macro.
+    ///
+    /// Identifiers created with this span will be resolved as if they were
+    /// written directly at the macro call location (call-site hygiene) and
+    /// other code at the macro call site will be able to refer to them as well.
+    pub fn call_site() -> Span {
+        Span::_new(imp::Span::call_site())
+    }
+
+    /// A span that resolves at the macro definition site.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn def_site() -> Span {
+        Span::_new(imp::Span::def_site())
+    }
+
+    /// Creates a new span with the same line/column information as `self` but
+    /// that resolves symbols as though it were at `other`.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn resolved_at(&self, other: Span) -> Span {
+        Span::_new(self.inner.resolved_at(other.inner))
+    }
+
+    /// Creates a new span with the same name resolution behavior as `self` but
+    /// with the line/column information of `other`.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn located_at(&self, other: Span) -> Span {
+        Span::_new(self.inner.located_at(other.inner))
+    }
+
+    /// Convert `proc_macro2::Span` to `proc_macro::Span`.
+    ///
+    /// This method is available when building with a nightly compiler, or when
+    /// building with rustc 1.29+ *without* semver exempt features.
+    ///
+    /// # Panics
+    ///
+    /// Panics if called from outside of a procedural macro. Unlike
+    /// `proc_macro2::Span`, the `proc_macro::Span` type can only exist within
+    /// the context of a procedural macro invocation.
+    #[cfg(wrap_proc_macro)]
+    pub fn unwrap(self) -> proc_macro::Span {
+        self.inner.unwrap()
+    }
+
+    // Soft deprecated. Please use Span::unwrap.
+    #[cfg(wrap_proc_macro)]
+    #[doc(hidden)]
+    pub fn unstable(self) -> proc_macro::Span {
+        self.unwrap()
+    }
+
+    /// The original source file into which this span points.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn source_file(&self) -> SourceFile {
+        SourceFile::_new(self.inner.source_file())
+    }
+
+    /// Get the starting line/column in the source file for this span.
+    ///
+    /// This method requires the `"span-locations"` feature to be enabled.
+    #[cfg(span_locations)]
+    pub fn start(&self) -> LineColumn {
+        let imp::LineColumn { line, column } = self.inner.start();
+        LineColumn { line, column }
+    }
+
+    /// Get the ending line/column in the source file for this span.
+    ///
+    /// This method requires the `"span-locations"` feature to be enabled.
+    #[cfg(span_locations)]
+    pub fn end(&self) -> LineColumn {
+        let imp::LineColumn { line, column } = self.inner.end();
+        LineColumn { line, column }
+    }
+
+    /// Create a new span encompassing `self` and `other`.
+    ///
+    /// Returns `None` if `self` and `other` are from different files.
+    ///
+    /// Warning: the underlying [`proc_macro::Span::join`] method is
+    /// nightly-only. When called from within a procedural macro not using a
+    /// nightly compiler, this method will always return `None`.
+    ///
+    /// [`proc_macro::Span::join`]: https://doc.rust-lang.org/proc_macro/struct.Span.html#method.join
+    pub fn join(&self, other: Span) -> Option<Span> {
+        self.inner.join(other.inner).map(Span::_new)
+    }
+
+    /// Compares two spans to see if they're equal.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn eq(&self, other: &Span) -> bool {
+        self.inner.eq(&other.inner)
+    }
+}
+
+/// Prints a span in a form convenient for debugging.
+impl fmt::Debug for Span {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// A single token or a delimited sequence of token trees (e.g. `[1, (), ..]`).
+#[derive(Clone)]
+pub enum TokenTree {
+    /// A token stream surrounded by bracket delimiters.
+    Group(Group),
+    /// An identifier.
+    Ident(Ident),
+    /// A single punctuation character (`+`, `,`, `$`, etc.).
+    Punct(Punct),
+    /// A literal character (`'a'`), string (`"hello"`), number (`2.3`), etc.
+    Literal(Literal),
+}
+
+impl TokenTree {
+    /// Returns the span of this tree, delegating to the `span` method of
+    /// the contained token or a delimited stream.
+    pub fn span(&self) -> Span {
+        match *self {
+            TokenTree::Group(ref t) => t.span(),
+            TokenTree::Ident(ref t) => t.span(),
+            TokenTree::Punct(ref t) => t.span(),
+            TokenTree::Literal(ref t) => t.span(),
+        }
+    }
+
+    /// Configures the span for *only this token*.
+    ///
+    /// Note that if this token is a `Group` then this method will not configure
+    /// the span of each of the internal tokens, this will simply delegate to
+    /// the `set_span` method of each variant.
+    pub fn set_span(&mut self, span: Span) {
+        match *self {
+            TokenTree::Group(ref mut t) => t.set_span(span),
+            TokenTree::Ident(ref mut t) => t.set_span(span),
+            TokenTree::Punct(ref mut t) => t.set_span(span),
+            TokenTree::Literal(ref mut t) => t.set_span(span),
+        }
+    }
+}
+
+impl From<Group> for TokenTree {
+    fn from(g: Group) -> TokenTree {
+        TokenTree::Group(g)
+    }
+}
+
+impl From<Ident> for TokenTree {
+    fn from(g: Ident) -> TokenTree {
+        TokenTree::Ident(g)
+    }
+}
+
+impl From<Punct> for TokenTree {
+    fn from(g: Punct) -> TokenTree {
+        TokenTree::Punct(g)
+    }
+}
+
+impl From<Literal> for TokenTree {
+    fn from(g: Literal) -> TokenTree {
+        TokenTree::Literal(g)
+    }
+}
+
+/// Prints the token tree as a string that is supposed to be losslessly
+/// convertible back into the same token tree (modulo spans), except for
+/// possibly `TokenTree::Group`s with `Delimiter::None` delimiters and negative
+/// numeric literals.
+impl fmt::Display for TokenTree {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            TokenTree::Group(ref t) => t.fmt(f),
+            TokenTree::Ident(ref t) => t.fmt(f),
+            TokenTree::Punct(ref t) => t.fmt(f),
+            TokenTree::Literal(ref t) => t.fmt(f),
+        }
+    }
+}
+
+/// Prints token tree in a form convenient for debugging.
+impl fmt::Debug for TokenTree {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // Each of these has the name in the struct type in the derived debug,
+        // so don't bother with an extra layer of indirection
+        match *self {
+            TokenTree::Group(ref t) => t.fmt(f),
+            TokenTree::Ident(ref t) => {
+                let mut debug = f.debug_struct("Ident");
+                debug.field("sym", &format_args!("{}", t));
+                imp::debug_span_field_if_nontrivial(&mut debug, t.span().inner);
+                debug.finish()
+            }
+            TokenTree::Punct(ref t) => t.fmt(f),
+            TokenTree::Literal(ref t) => t.fmt(f),
+        }
+    }
+}
+
+/// A delimited token stream.
+///
+/// A `Group` internally contains a `TokenStream` which is surrounded by
+/// `Delimiter`s.
+#[derive(Clone)]
+pub struct Group {
+    inner: imp::Group,
+}
+
+/// Describes how a sequence of token trees is delimited.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum Delimiter {
+    /// `( ... )`
+    Parenthesis,
+    /// `{ ... }`
+    Brace,
+    /// `[ ... ]`
+    Bracket,
+    /// `Ø ... Ø`
+    ///
+    /// An implicit delimiter, that may, for example, appear around tokens
+    /// coming from a "macro variable" `$var`. It is important to preserve
+    /// operator priorities in cases like `$var * 3` where `$var` is `1 + 2`.
+    /// Implicit delimiters may not survive roundtrip of a token stream through
+    /// a string.
+    None,
+}
+
+impl Group {
+    fn _new(inner: imp::Group) -> Self {
+        Group { inner }
+    }
+
+    fn _new_stable(inner: fallback::Group) -> Self {
+        Group {
+            inner: inner.into(),
+        }
+    }
+
+    /// Creates a new `Group` with the given delimiter and token stream.
+    ///
+    /// This constructor will set the span for this group to
+    /// `Span::call_site()`. To change the span you can use the `set_span`
+    /// method below.
+    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
+        Group {
+            inner: imp::Group::new(delimiter, stream.inner),
+        }
+    }
+
+    /// Returns the delimiter of this `Group`
+    pub fn delimiter(&self) -> Delimiter {
+        self.inner.delimiter()
+    }
+
+    /// Returns the `TokenStream` of tokens that are delimited in this `Group`.
+    ///
+    /// Note that the returned token stream does not include the delimiter
+    /// returned above.
+    pub fn stream(&self) -> TokenStream {
+        TokenStream::_new(self.inner.stream())
+    }
+
+    /// Returns the span for the delimiters of this token stream, spanning the
+    /// entire `Group`.
+    ///
+    /// ```text
+    /// pub fn span(&self) -> Span {
+    ///            ^^^^^^^
+    /// ```
+    pub fn span(&self) -> Span {
+        Span::_new(self.inner.span())
+    }
+
+    /// Returns the span pointing to the opening delimiter of this group.
+    ///
+    /// ```text
+    /// pub fn span_open(&self) -> Span {
+    ///                 ^
+    /// ```
+    pub fn span_open(&self) -> Span {
+        Span::_new(self.inner.span_open())
+    }
+
+    /// Returns the span pointing to the closing delimiter of this group.
+    ///
+    /// ```text
+    /// pub fn span_close(&self) -> Span {
+    ///                        ^
+    /// ```
+    pub fn span_close(&self) -> Span {
+        Span::_new(self.inner.span_close())
+    }
+
+    /// Configures the span for this `Group`'s delimiters, but not its internal
+    /// tokens.
+    ///
+    /// This method will **not** set the span of all the internal tokens spanned
+    /// by this group, but rather it will only set the span of the delimiter
+    /// tokens at the level of the `Group`.
+    pub fn set_span(&mut self, span: Span) {
+        self.inner.set_span(span.inner)
+    }
+}
+
+/// Prints the group as a string that should be losslessly convertible back
+/// into the same group (modulo spans), except for possibly `TokenTree::Group`s
+/// with `Delimiter::None` delimiters.
+impl fmt::Display for Group {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.inner, formatter)
+    }
+}
+
+impl fmt::Debug for Group {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.inner, formatter)
+    }
+}
+
+/// An `Punct` is an single punctuation character like `+`, `-` or `#`.
+///
+/// Multicharacter operators like `+=` are represented as two instances of
+/// `Punct` with different forms of `Spacing` returned.
+#[derive(Clone)]
+pub struct Punct {
+    op: char,
+    spacing: Spacing,
+    span: Span,
+}
+
+/// Whether an `Punct` is followed immediately by another `Punct` or followed by
+/// another token or whitespace.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum Spacing {
+    /// E.g. `+` is `Alone` in `+ =`, `+ident` or `+()`.
+    Alone,
+    /// E.g. `+` is `Joint` in `+=` or `'` is `Joint` in `'#`.
+    ///
+    /// Additionally, single quote `'` can join with identifiers to form
+    /// lifetimes `'ident`.
+    Joint,
+}
+
+impl Punct {
+    /// Creates a new `Punct` from the given character and spacing.
+    ///
+    /// The `ch` argument must be a valid punctuation character permitted by the
+    /// language, otherwise the function will panic.
+    ///
+    /// The returned `Punct` will have the default span of `Span::call_site()`
+    /// which can be further configured with the `set_span` method below.
+    pub fn new(op: char, spacing: Spacing) -> Punct {
+        Punct {
+            op,
+            spacing,
+            span: Span::call_site(),
+        }
+    }
+
+    /// Returns the value of this punctuation character as `char`.
+    pub fn as_char(&self) -> char {
+        self.op
+    }
+
+    /// Returns the spacing of this punctuation character, indicating whether
+    /// it's immediately followed by another `Punct` in the token stream, so
+    /// they can potentially be combined into a multicharacter operator
+    /// (`Joint`), or it's followed by some other token or whitespace (`Alone`)
+    /// so the operator has certainly ended.
+    pub fn spacing(&self) -> Spacing {
+        self.spacing
+    }
+
+    /// Returns the span for this punctuation character.
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    /// Configure the span for this punctuation character.
+    pub fn set_span(&mut self, span: Span) {
+        self.span = span;
+    }
+}
+
+/// Prints the punctuation character as a string that should be losslessly
+/// convertible back into the same character.
+impl fmt::Display for Punct {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.op.fmt(f)
+    }
+}
+
+impl fmt::Debug for Punct {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        let mut debug = fmt.debug_struct("Punct");
+        debug.field("op", &self.op);
+        debug.field("spacing", &self.spacing);
+        imp::debug_span_field_if_nontrivial(&mut debug, self.span.inner);
+        debug.finish()
+    }
+}
+
+/// A word of Rust code, which may be a keyword or legal variable name.
+///
+/// An identifier consists of at least one Unicode code point, the first of
+/// which has the XID_Start property and the rest of which have the XID_Continue
+/// property.
+///
+/// - The empty string is not an identifier. Use `Option<Ident>`.
+/// - A lifetime is not an identifier. Use `syn::Lifetime` instead.
+///
+/// An identifier constructed with `Ident::new` is permitted to be a Rust
+/// keyword, though parsing one through its [`Parse`] implementation rejects
+/// Rust keywords. Use `input.call(Ident::parse_any)` when parsing to match the
+/// behaviour of `Ident::new`.
+///
+/// [`Parse`]: https://docs.rs/syn/1.0/syn/parse/trait.Parse.html
+///
+/// # Examples
+///
+/// A new ident can be created from a string using the `Ident::new` function.
+/// A span must be provided explicitly which governs the name resolution
+/// behavior of the resulting identifier.
+///
+/// ```
+/// use proc_macro2::{Ident, Span};
+///
+/// fn main() {
+///     let call_ident = Ident::new("calligraphy", Span::call_site());
+///
+///     println!("{}", call_ident);
+/// }
+/// ```
+///
+/// An ident can be interpolated into a token stream using the `quote!` macro.
+///
+/// ```
+/// use proc_macro2::{Ident, Span};
+/// use quote::quote;
+///
+/// fn main() {
+///     let ident = Ident::new("demo", Span::call_site());
+///
+///     // Create a variable binding whose name is this ident.
+///     let expanded = quote! { let #ident = 10; };
+///
+///     // Create a variable binding with a slightly different name.
+///     let temp_ident = Ident::new(&format!("new_{}", ident), Span::call_site());
+///     let expanded = quote! { let #temp_ident = 10; };
+/// }
+/// ```
+///
+/// A string representation of the ident is available through the `to_string()`
+/// method.
+///
+/// ```
+/// # use proc_macro2::{Ident, Span};
+/// #
+/// # let ident = Ident::new("another_identifier", Span::call_site());
+/// #
+/// // Examine the ident as a string.
+/// let ident_string = ident.to_string();
+/// if ident_string.len() > 60 {
+///     println!("Very long identifier: {}", ident_string)
+/// }
+/// ```
+#[derive(Clone)]
+pub struct Ident {
+    inner: imp::Ident,
+    _marker: marker::PhantomData<Rc<()>>,
+}
+
+impl Ident {
+    fn _new(inner: imp::Ident) -> Ident {
+        Ident {
+            inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
+    /// Creates a new `Ident` with the given `string` as well as the specified
+    /// `span`.
+    ///
+    /// The `string` argument must be a valid identifier permitted by the
+    /// language, otherwise the function will panic.
+    ///
+    /// Note that `span`, currently in rustc, configures the hygiene information
+    /// for this identifier.
+    ///
+    /// As of this time `Span::call_site()` explicitly opts-in to "call-site"
+    /// hygiene meaning that identifiers created with this span will be resolved
+    /// as if they were written directly at the location of the macro call, and
+    /// other code at the macro call site will be able to refer to them as well.
+    ///
+    /// Later spans like `Span::def_site()` will allow to opt-in to
+    /// "definition-site" hygiene meaning that identifiers created with this
+    /// span will be resolved at the location of the macro definition and other
+    /// code at the macro call site will not be able to refer to them.
+    ///
+    /// Due to the current importance of hygiene this constructor, unlike other
+    /// tokens, requires a `Span` to be specified at construction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the input string is neither a keyword nor a legal variable
+    /// name. If you are not sure whether the string contains an identifier and
+    /// need to handle an error case, use
+    /// <a href="https://docs.rs/syn/1.0/syn/fn.parse_str.html"><code
+    ///   style="padding-right:0;">syn::parse_str</code></a><code
+    ///   style="padding-left:0;">::&lt;Ident&gt;</code>
+    /// rather than `Ident::new`.
+    pub fn new(string: &str, span: Span) -> Ident {
+        Ident::_new(imp::Ident::new(string, span.inner))
+    }
+
+    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`).
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn new_raw(string: &str, span: Span) -> Ident {
+        Ident::_new_raw(string, span)
+    }
+
+    fn _new_raw(string: &str, span: Span) -> Ident {
+        Ident::_new(imp::Ident::new_raw(string, span.inner))
+    }
+
+    /// Returns the span of this `Ident`.
+    pub fn span(&self) -> Span {
+        Span::_new(self.inner.span())
+    }
+
+    /// Configures the span of this `Ident`, possibly changing its hygiene
+    /// context.
+    pub fn set_span(&mut self, span: Span) {
+        self.inner.set_span(span.inner);
+    }
+}
+
+impl PartialEq for Ident {
+    fn eq(&self, other: &Ident) -> bool {
+        self.inner == other.inner
+    }
+}
+
+impl<T> PartialEq<T> for Ident
+where
+    T: ?Sized + AsRef<str>,
+{
+    fn eq(&self, other: &T) -> bool {
+        self.inner == other
+    }
+}
+
+impl Eq for Ident {}
+
+impl PartialOrd for Ident {
+    fn partial_cmp(&self, other: &Ident) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Ident {
+    fn cmp(&self, other: &Ident) -> Ordering {
+        self.to_string().cmp(&other.to_string())
+    }
+}
+
+impl Hash for Ident {
+    fn hash<H: Hasher>(&self, hasher: &mut H) {
+        self.to_string().hash(hasher)
+    }
+}
+
+/// Prints the identifier as a string that should be losslessly convertible back
+/// into the same identifier.
+impl fmt::Display for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::Debug for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// A literal string (`"hello"`), byte string (`b"hello"`), character (`'a'`),
+/// byte character (`b'a'`), an integer or floating point number with or without
+/// a suffix (`1`, `1u8`, `2.3`, `2.3f32`).
+///
+/// Boolean literals like `true` and `false` do not belong here, they are
+/// `Ident`s.
+#[derive(Clone)]
+pub struct Literal {
+    inner: imp::Literal,
+    _marker: marker::PhantomData<Rc<()>>,
+}
+
+macro_rules! suffixed_int_literals {
+    ($($name:ident => $kind:ident,)*) => ($(
+        /// Creates a new suffixed integer literal with the specified value.
+        ///
+        /// This function will create an integer like `1u32` where the integer
+        /// value specified is the first part of the token and the integral is
+        /// also suffixed at the end. Literals created from negative numbers may
+        /// not survive rountrips through `TokenStream` or strings and may be
+        /// broken into two tokens (`-` and positive literal).
+        ///
+        /// Literals created through this method have the `Span::call_site()`
+        /// span by default, which can be configured with the `set_span` method
+        /// below.
+        pub fn $name(n: $kind) -> Literal {
+            Literal::_new(imp::Literal::$name(n))
+        }
+    )*)
+}
+
+macro_rules! unsuffixed_int_literals {
+    ($($name:ident => $kind:ident,)*) => ($(
+        /// Creates a new unsuffixed integer literal with the specified value.
+        ///
+        /// This function will create an integer like `1` where the integer
+        /// value specified is the first part of the token. No suffix is
+        /// specified on this token, meaning that invocations like
+        /// `Literal::i8_unsuffixed(1)` are equivalent to
+        /// `Literal::u32_unsuffixed(1)`. Literals created from negative numbers
+        /// may not survive rountrips through `TokenStream` or strings and may
+        /// be broken into two tokens (`-` and positive literal).
+        ///
+        /// Literals created through this method have the `Span::call_site()`
+        /// span by default, which can be configured with the `set_span` method
+        /// below.
+        pub fn $name(n: $kind) -> Literal {
+            Literal::_new(imp::Literal::$name(n))
+        }
+    )*)
+}
+
+impl Literal {
+    fn _new(inner: imp::Literal) -> Literal {
+        Literal {
+            inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
+    fn _new_stable(inner: fallback::Literal) -> Literal {
+        Literal {
+            inner: inner.into(),
+            _marker: marker::PhantomData,
+        }
+    }
+
+    suffixed_int_literals! {
+        u8_suffixed => u8,
+        u16_suffixed => u16,
+        u32_suffixed => u32,
+        u64_suffixed => u64,
+        u128_suffixed => u128,
+        usize_suffixed => usize,
+        i8_suffixed => i8,
+        i16_suffixed => i16,
+        i32_suffixed => i32,
+        i64_suffixed => i64,
+        i128_suffixed => i128,
+        isize_suffixed => isize,
+    }
+
+    unsuffixed_int_literals! {
+        u8_unsuffixed => u8,
+        u16_unsuffixed => u16,
+        u32_unsuffixed => u32,
+        u64_unsuffixed => u64,
+        u128_unsuffixed => u128,
+        usize_unsuffixed => usize,
+        i8_unsuffixed => i8,
+        i16_unsuffixed => i16,
+        i32_unsuffixed => i32,
+        i64_unsuffixed => i64,
+        i128_unsuffixed => i128,
+        isize_unsuffixed => isize,
+    }
+
+    /// Creates a new unsuffixed floating-point literal.
+    ///
+    /// This constructor is similar to those like `Literal::i8_unsuffixed` where
+    /// the float's value is emitted directly into the token but no suffix is
+    /// used, so it may be inferred to be a `f64` later in the compiler.
+    /// Literals created from negative numbers may not survive rountrips through
+    /// `TokenStream` or strings and may be broken into two tokens (`-` and
+    /// positive literal).
+    ///
+    /// # Panics
+    ///
+    /// This function requires that the specified float is finite, for example
+    /// if it is infinity or NaN this function will panic.
+    pub fn f64_unsuffixed(f: f64) -> Literal {
+        assert!(f.is_finite());
+        Literal::_new(imp::Literal::f64_unsuffixed(f))
+    }
+
+    /// Creates a new suffixed floating-point literal.
+    ///
+    /// This constructor will create a literal like `1.0f64` where the value
+    /// specified is the preceding part of the token and `f64` is the suffix of
+    /// the token. This token will always be inferred to be an `f64` in the
+    /// compiler. Literals created from negative numbers may not survive
+    /// rountrips through `TokenStream` or strings and may be broken into two
+    /// tokens (`-` and positive literal).
+    ///
+    /// # Panics
+    ///
+    /// This function requires that the specified float is finite, for example
+    /// if it is infinity or NaN this function will panic.
+    pub fn f64_suffixed(f: f64) -> Literal {
+        assert!(f.is_finite());
+        Literal::_new(imp::Literal::f64_suffixed(f))
+    }
+
+    /// Creates a new unsuffixed floating-point literal.
+    ///
+    /// This constructor is similar to those like `Literal::i8_unsuffixed` where
+    /// the float's value is emitted directly into the token but no suffix is
+    /// used, so it may be inferred to be a `f64` later in the compiler.
+    /// Literals created from negative numbers may not survive rountrips through
+    /// `TokenStream` or strings and may be broken into two tokens (`-` and
+    /// positive literal).
+    ///
+    /// # Panics
+    ///
+    /// This function requires that the specified float is finite, for example
+    /// if it is infinity or NaN this function will panic.
+    pub fn f32_unsuffixed(f: f32) -> Literal {
+        assert!(f.is_finite());
+        Literal::_new(imp::Literal::f32_unsuffixed(f))
+    }
+
+    /// Creates a new suffixed floating-point literal.
+    ///
+    /// This constructor will create a literal like `1.0f32` where the value
+    /// specified is the preceding part of the token and `f32` is the suffix of
+    /// the token. This token will always be inferred to be an `f32` in the
+    /// compiler. Literals created from negative numbers may not survive
+    /// rountrips through `TokenStream` or strings and may be broken into two
+    /// tokens (`-` and positive literal).
+    ///
+    /// # Panics
+    ///
+    /// This function requires that the specified float is finite, for example
+    /// if it is infinity or NaN this function will panic.
+    pub fn f32_suffixed(f: f32) -> Literal {
+        assert!(f.is_finite());
+        Literal::_new(imp::Literal::f32_suffixed(f))
+    }
+
+    /// String literal.
+    pub fn string(string: &str) -> Literal {
+        Literal::_new(imp::Literal::string(string))
+    }
+
+    /// Character literal.
+    pub fn character(ch: char) -> Literal {
+        Literal::_new(imp::Literal::character(ch))
+    }
+
+    /// Byte string literal.
+    pub fn byte_string(s: &[u8]) -> Literal {
+        Literal::_new(imp::Literal::byte_string(s))
+    }
+
+    /// Returns the span encompassing this literal.
+    pub fn span(&self) -> Span {
+        Span::_new(self.inner.span())
+    }
+
+    /// Configures the span associated for this literal.
+    pub fn set_span(&mut self, span: Span) {
+        self.inner.set_span(span.inner);
+    }
+
+    /// Returns a `Span` that is a subset of `self.span()` containing only
+    /// the source bytes in range `range`. Returns `None` if the would-be
+    /// trimmed span is outside the bounds of `self`.
+    ///
+    /// Warning: the underlying [`proc_macro::Literal::subspan`] method is
+    /// nightly-only. When called from within a procedural macro not using a
+    /// nightly compiler, this method will always return `None`.
+    ///
+    /// [`proc_macro::Literal::subspan`]: https://doc.rust-lang.org/proc_macro/struct.Literal.html#method.subspan
+    pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
+        self.inner.subspan(range).map(Span::_new)
+    }
+}
+
+impl fmt::Debug for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::Display for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+/// Public implementation details for the `TokenStream` type, such as iterators.
+pub mod token_stream {
+    use std::fmt;
+    use std::marker;
+    use std::rc::Rc;
+
+    pub use crate::TokenStream;
+    use crate::{imp, TokenTree};
+
+    /// An iterator over `TokenStream`'s `TokenTree`s.
+    ///
+    /// The iteration is "shallow", e.g. the iterator doesn't recurse into
+    /// delimited groups, and returns whole groups as token trees.
+    #[derive(Clone)]
+    pub struct IntoIter {
+        inner: imp::TokenTreeIter,
+        _marker: marker::PhantomData<Rc<()>>,
+    }
+
+    impl Iterator for IntoIter {
+        type Item = TokenTree;
+
+        fn next(&mut self) -> Option<TokenTree> {
+            self.inner.next()
+        }
+    }
+
+    impl fmt::Debug for IntoIter {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            self.inner.fmt(f)
+        }
+    }
+
+    impl IntoIterator for TokenStream {
+        type Item = TokenTree;
+        type IntoIter = IntoIter;
+
+        fn into_iter(self) -> IntoIter {
+            IntoIter {
+                inner: self.inner.into_iter(),
+                _marker: marker::PhantomData,
+            }
+        }
+    }
+}
diff --git a/proc-macro2/src/strnom.rs b/proc-macro2/src/strnom.rs
new file mode 100644
index 0000000..eb7d0b8
--- /dev/null
+++ b/proc-macro2/src/strnom.rs
@@ -0,0 +1,391 @@
+//! Adapted from [`nom`](https://github.com/Geal/nom).
+
+use crate::fallback::LexError;
+use std::str::{Bytes, CharIndices, Chars};
+use unicode_xid::UnicodeXID;
+
+#[derive(Copy, Clone, Eq, PartialEq)]
+pub struct Cursor<'a> {
+    pub rest: &'a str,
+    #[cfg(span_locations)]
+    pub off: u32,
+}
+
+impl<'a> Cursor<'a> {
+    #[cfg(not(span_locations))]
+    pub fn advance(&self, amt: usize) -> Cursor<'a> {
+        Cursor {
+            rest: &self.rest[amt..],
+        }
+    }
+    #[cfg(span_locations)]
+    pub fn advance(&self, amt: usize) -> Cursor<'a> {
+        Cursor {
+            rest: &self.rest[amt..],
+            off: self.off + (amt as u32),
+        }
+    }
+
+    pub fn find(&self, p: char) -> Option<usize> {
+        self.rest.find(p)
+    }
+
+    pub fn starts_with(&self, s: &str) -> bool {
+        self.rest.starts_with(s)
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.rest.is_empty()
+    }
+
+    pub fn len(&self) -> usize {
+        self.rest.len()
+    }
+
+    pub fn as_bytes(&self) -> &'a [u8] {
+        self.rest.as_bytes()
+    }
+
+    pub fn bytes(&self) -> Bytes<'a> {
+        self.rest.bytes()
+    }
+
+    pub fn chars(&self) -> Chars<'a> {
+        self.rest.chars()
+    }
+
+    pub fn char_indices(&self) -> CharIndices<'a> {
+        self.rest.char_indices()
+    }
+}
+
+pub type PResult<'a, O> = Result<(Cursor<'a>, O), LexError>;
+
+pub fn whitespace(input: Cursor) -> PResult<()> {
+    if input.is_empty() {
+        return Err(LexError);
+    }
+
+    let bytes = input.as_bytes();
+    let mut i = 0;
+    while i < bytes.len() {
+        let s = input.advance(i);
+        if bytes[i] == b'/' {
+            if s.starts_with("//")
+                && (!s.starts_with("///") || s.starts_with("////"))
+                && !s.starts_with("//!")
+            {
+                if let Some(len) = s.find('\n') {
+                    i += len + 1;
+                    continue;
+                }
+                break;
+            } else if s.starts_with("/**/") {
+                i += 4;
+                continue;
+            } else if s.starts_with("/*")
+                && (!s.starts_with("/**") || s.starts_with("/***"))
+                && !s.starts_with("/*!")
+            {
+                let (_, com) = block_comment(s)?;
+                i += com.len();
+                continue;
+            }
+        }
+        match bytes[i] {
+            b' ' | 0x09..=0x0d => {
+                i += 1;
+                continue;
+            }
+            b if b <= 0x7f => {}
+            _ => {
+                let ch = s.chars().next().unwrap();
+                if is_whitespace(ch) {
+                    i += ch.len_utf8();
+                    continue;
+                }
+            }
+        }
+        return if i > 0 { Ok((s, ())) } else { Err(LexError) };
+    }
+    Ok((input.advance(input.len()), ()))
+}
+
+pub fn block_comment(input: Cursor) -> PResult<&str> {
+    if !input.starts_with("/*") {
+        return Err(LexError);
+    }
+
+    let mut depth = 0;
+    let bytes = input.as_bytes();
+    let mut i = 0;
+    let upper = bytes.len() - 1;
+    while i < upper {
+        if bytes[i] == b'/' && bytes[i + 1] == b'*' {
+            depth += 1;
+            i += 1; // eat '*'
+        } else if bytes[i] == b'*' && bytes[i + 1] == b'/' {
+            depth -= 1;
+            if depth == 0 {
+                return Ok((input.advance(i + 2), &input.rest[..i + 2]));
+            }
+            i += 1; // eat '/'
+        }
+        i += 1;
+    }
+    Err(LexError)
+}
+
+pub fn skip_whitespace(input: Cursor) -> Cursor {
+    match whitespace(input) {
+        Ok((rest, _)) => rest,
+        Err(LexError) => input,
+    }
+}
+
+fn is_whitespace(ch: char) -> bool {
+    // Rust treats left-to-right mark and right-to-left mark as whitespace
+    ch.is_whitespace() || ch == '\u{200e}' || ch == '\u{200f}'
+}
+
+pub fn word_break(input: Cursor) -> PResult<()> {
+    match input.chars().next() {
+        Some(ch) if UnicodeXID::is_xid_continue(ch) => Err(LexError),
+        Some(_) | None => Ok((input, ())),
+    }
+}
+
+macro_rules! named {
+    ($name:ident -> $o:ty, $submac:ident!( $($args:tt)* )) => {
+        fn $name<'a>(i: Cursor<'a>) -> $crate::strnom::PResult<'a, $o> {
+            $submac!(i, $($args)*)
+        }
+    };
+}
+
+macro_rules! alt {
+    ($i:expr, $e:ident | $($rest:tt)*) => {
+        alt!($i, call!($e) | $($rest)*)
+    };
+
+    ($i:expr, $subrule:ident!( $($args:tt)*) | $($rest:tt)*) => {
+        match $subrule!($i, $($args)*) {
+            res @ Ok(_) => res,
+            _ => alt!($i, $($rest)*)
+        }
+    };
+
+    ($i:expr, $subrule:ident!( $($args:tt)* ) => { $gen:expr } | $($rest:tt)+) => {
+        match $subrule!($i, $($args)*) {
+            Ok((i, o)) => Ok((i, $gen(o))),
+            Err(LexError) => alt!($i, $($rest)*)
+        }
+    };
+
+    ($i:expr, $e:ident => { $gen:expr } | $($rest:tt)*) => {
+        alt!($i, call!($e) => { $gen } | $($rest)*)
+    };
+
+    ($i:expr, $e:ident => { $gen:expr }) => {
+        alt!($i, call!($e) => { $gen })
+    };
+
+    ($i:expr, $subrule:ident!( $($args:tt)* ) => { $gen:expr }) => {
+        match $subrule!($i, $($args)*) {
+            Ok((i, o)) => Ok((i, $gen(o))),
+            Err(LexError) => Err(LexError),
+        }
+    };
+
+    ($i:expr, $e:ident) => {
+        alt!($i, call!($e))
+    };
+
+    ($i:expr, $subrule:ident!( $($args:tt)*)) => {
+        $subrule!($i, $($args)*)
+    };
+}
+
+macro_rules! do_parse {
+    ($i:expr, ( $($rest:expr),* )) => {
+        Ok(($i, ( $($rest),* )))
+    };
+
+    ($i:expr, $e:ident >> $($rest:tt)*) => {
+        do_parse!($i, call!($e) >> $($rest)*)
+    };
+
+    ($i:expr, $submac:ident!( $($args:tt)* ) >> $($rest:tt)*) => {
+        match $submac!($i, $($args)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i, _)) => do_parse!(i, $($rest)*),
+        }
+    };
+
+    ($i:expr, $field:ident : $e:ident >> $($rest:tt)*) => {
+        do_parse!($i, $field: call!($e) >> $($rest)*)
+    };
+
+    ($i:expr, $field:ident : $submac:ident!( $($args:tt)* ) >> $($rest:tt)*) => {
+        match $submac!($i, $($args)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i, o)) => {
+                let $field = o;
+                do_parse!(i, $($rest)*)
+            },
+        }
+    };
+}
+
+macro_rules! peek {
+    ($i:expr, $submac:ident!( $($args:tt)* )) => {
+        match $submac!($i, $($args)*) {
+            Ok((_, o)) => Ok(($i, o)),
+            Err(LexError) => Err(LexError),
+        }
+    };
+}
+
+macro_rules! call {
+    ($i:expr, $fun:expr $(, $args:expr)*) => {
+        $fun($i $(, $args)*)
+    };
+}
+
+macro_rules! option {
+    ($i:expr, $f:expr) => {
+        match $f($i) {
+            Ok((i, o)) => Ok((i, Some(o))),
+            Err(LexError) => Ok(($i, None)),
+        }
+    };
+}
+
+macro_rules! take_until_newline_or_eof {
+    ($i:expr,) => {{
+        if $i.len() == 0 {
+            Ok(($i, ""))
+        } else {
+            match $i.find('\n') {
+                Some(i) => Ok(($i.advance(i), &$i.rest[..i])),
+                None => Ok(($i.advance($i.len()), &$i.rest[..$i.len()])),
+            }
+        }
+    }};
+}
+
+macro_rules! tuple {
+    ($i:expr, $($rest:tt)*) => {
+        tuple_parser!($i, (), $($rest)*)
+    };
+}
+
+/// Do not use directly. Use `tuple!`.
+macro_rules! tuple_parser {
+    ($i:expr, ($($parsed:tt),*), $e:ident, $($rest:tt)*) => {
+        tuple_parser!($i, ($($parsed),*), call!($e), $($rest)*)
+    };
+
+    ($i:expr, (), $submac:ident!( $($args:tt)* ), $($rest:tt)*) => {
+        match $submac!($i, $($args)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i, o)) => tuple_parser!(i, (o), $($rest)*),
+        }
+    };
+
+    ($i:expr, ($($parsed:tt)*), $submac:ident!( $($args:tt)* ), $($rest:tt)*) => {
+        match $submac!($i, $($args)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i, o)) => tuple_parser!(i, ($($parsed)* , o), $($rest)*),
+        }
+    };
+
+    ($i:expr, ($($parsed:tt),*), $e:ident) => {
+        tuple_parser!($i, ($($parsed),*), call!($e))
+    };
+
+    ($i:expr, (), $submac:ident!( $($args:tt)* )) => {
+        $submac!($i, $($args)*)
+    };
+
+    ($i:expr, ($($parsed:expr),*), $submac:ident!( $($args:tt)* )) => {
+        match $submac!($i, $($args)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i, o)) => Ok((i, ($($parsed),*, o)))
+        }
+    };
+
+    ($i:expr, ($($parsed:expr),*)) => {
+        Ok(($i, ($($parsed),*)))
+    };
+}
+
+macro_rules! not {
+    ($i:expr, $submac:ident!( $($args:tt)* )) => {
+        match $submac!($i, $($args)*) {
+            Ok((_, _)) => Err(LexError),
+            Err(LexError) => Ok(($i, ())),
+        }
+    };
+}
+
+macro_rules! tag {
+    ($i:expr, $tag:expr) => {
+        if $i.starts_with($tag) {
+            Ok(($i.advance($tag.len()), &$i.rest[..$tag.len()]))
+        } else {
+            Err(LexError)
+        }
+    };
+}
+
+macro_rules! punct {
+    ($i:expr, $punct:expr) => {
+        $crate::strnom::punct($i, $punct)
+    };
+}
+
+/// Do not use directly. Use `punct!`.
+pub fn punct<'a>(input: Cursor<'a>, token: &'static str) -> PResult<'a, &'a str> {
+    let input = skip_whitespace(input);
+    if input.starts_with(token) {
+        Ok((input.advance(token.len()), token))
+    } else {
+        Err(LexError)
+    }
+}
+
+macro_rules! preceded {
+    ($i:expr, $submac:ident!( $($args:tt)* ), $submac2:ident!( $($args2:tt)* )) => {
+        match tuple!($i, $submac!($($args)*), $submac2!($($args2)*)) {
+            Ok((remaining, (_, o))) => Ok((remaining, o)),
+            Err(LexError) => Err(LexError),
+        }
+    };
+
+    ($i:expr, $submac:ident!( $($args:tt)* ), $g:expr) => {
+        preceded!($i, $submac!($($args)*), call!($g))
+    };
+}
+
+macro_rules! delimited {
+    ($i:expr, $submac:ident!( $($args:tt)* ), $($rest:tt)+) => {
+        match tuple_parser!($i, (), $submac!($($args)*), $($rest)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i1, (_, o, _))) => Ok((i1, o))
+        }
+    };
+}
+
+macro_rules! map {
+    ($i:expr, $submac:ident!( $($args:tt)* ), $g:expr) => {
+        match $submac!($i, $($args)*) {
+            Err(LexError) => Err(LexError),
+            Ok((i, o)) => Ok((i, call!(o, $g)))
+        }
+    };
+
+    ($i:expr, $f:expr, $g:expr) => {
+        map!($i, call!($f), $g)
+    };
+}
diff --git a/proc-macro2/src/wrapper.rs b/proc-macro2/src/wrapper.rs
new file mode 100644
index 0000000..552b938
--- /dev/null
+++ b/proc-macro2/src/wrapper.rs
@@ -0,0 +1,927 @@
+use std::fmt;
+use std::iter;
+use std::ops::RangeBounds;
+use std::panic::{self, PanicInfo};
+#[cfg(super_unstable)]
+use std::path::PathBuf;
+use std::str::FromStr;
+
+use crate::{fallback, Delimiter, Punct, Spacing, TokenTree};
+
+#[derive(Clone)]
+pub enum TokenStream {
+    Compiler(DeferredTokenStream),
+    Fallback(fallback::TokenStream),
+}
+
+// Work around https://github.com/rust-lang/rust/issues/65080.
+// In `impl Extend<TokenTree> for TokenStream` which is used heavily by quote,
+// we hold on to the appended tokens and do proc_macro::TokenStream::extend as
+// late as possible to batch together consecutive uses of the Extend impl.
+#[derive(Clone)]
+pub struct DeferredTokenStream {
+    stream: proc_macro::TokenStream,
+    extra: Vec<proc_macro::TokenTree>,
+}
+
+pub enum LexError {
+    Compiler(proc_macro::LexError),
+    Fallback(fallback::LexError),
+}
+
+fn nightly_works() -> bool {
+    use std::sync::atomic::*;
+    use std::sync::Once;
+
+    static WORKS: AtomicUsize = AtomicUsize::new(0);
+    static INIT: Once = Once::new();
+
+    match WORKS.load(Ordering::SeqCst) {
+        1 => return false,
+        2 => return true,
+        _ => {}
+    }
+
+    // Swap in a null panic hook to avoid printing "thread panicked" to stderr,
+    // then use catch_unwind to determine whether the compiler's proc_macro is
+    // working. When proc-macro2 is used from outside of a procedural macro all
+    // of the proc_macro crate's APIs currently panic.
+    //
+    // The Once is to prevent the possibility of this ordering:
+    //
+    //     thread 1 calls take_hook, gets the user's original hook
+    //     thread 1 calls set_hook with the null hook
+    //     thread 2 calls take_hook, thinks null hook is the original hook
+    //     thread 2 calls set_hook with the null hook
+    //     thread 1 calls set_hook with the actual original hook
+    //     thread 2 calls set_hook with what it thinks is the original hook
+    //
+    // in which the user's hook has been lost.
+    //
+    // There is still a race condition where a panic in a different thread can
+    // happen during the interval that the user's original panic hook is
+    // unregistered such that their hook is incorrectly not called. This is
+    // sufficiently unlikely and less bad than printing panic messages to stderr
+    // on correct use of this crate. Maybe there is a libstd feature request
+    // here. For now, if a user needs to guarantee that this failure mode does
+    // not occur, they need to call e.g. `proc_macro2::Span::call_site()` from
+    // the main thread before launching any other threads.
+    INIT.call_once(|| {
+        type PanicHook = dyn Fn(&PanicInfo) + Sync + Send + 'static;
+
+        let null_hook: Box<PanicHook> = Box::new(|_panic_info| { /* ignore */ });
+        let sanity_check = &*null_hook as *const PanicHook;
+        let original_hook = panic::take_hook();
+        panic::set_hook(null_hook);
+
+        let works = panic::catch_unwind(|| proc_macro::Span::call_site()).is_ok();
+        WORKS.store(works as usize + 1, Ordering::SeqCst);
+
+        let hopefully_null_hook = panic::take_hook();
+        panic::set_hook(original_hook);
+        if sanity_check != &*hopefully_null_hook {
+            panic!("observed race condition in proc_macro2::nightly_works");
+        }
+    });
+    nightly_works()
+}
+
+fn mismatch() -> ! {
+    panic!("stable/nightly mismatch")
+}
+
+impl DeferredTokenStream {
+    fn new(stream: proc_macro::TokenStream) -> Self {
+        DeferredTokenStream {
+            stream,
+            extra: Vec::new(),
+        }
+    }
+
+    fn is_empty(&self) -> bool {
+        self.stream.is_empty() && self.extra.is_empty()
+    }
+
+    fn evaluate_now(&mut self) {
+        self.stream.extend(self.extra.drain(..));
+    }
+
+    fn into_token_stream(mut self) -> proc_macro::TokenStream {
+        self.evaluate_now();
+        self.stream
+    }
+}
+
+impl TokenStream {
+    pub fn new() -> TokenStream {
+        if nightly_works() {
+            TokenStream::Compiler(DeferredTokenStream::new(proc_macro::TokenStream::new()))
+        } else {
+            TokenStream::Fallback(fallback::TokenStream::new())
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        match self {
+            TokenStream::Compiler(tts) => tts.is_empty(),
+            TokenStream::Fallback(tts) => tts.is_empty(),
+        }
+    }
+
+    fn unwrap_nightly(self) -> proc_macro::TokenStream {
+        match self {
+            TokenStream::Compiler(s) => s.into_token_stream(),
+            TokenStream::Fallback(_) => mismatch(),
+        }
+    }
+
+    fn unwrap_stable(self) -> fallback::TokenStream {
+        match self {
+            TokenStream::Compiler(_) => mismatch(),
+            TokenStream::Fallback(s) => s,
+        }
+    }
+}
+
+impl FromStr for TokenStream {
+    type Err = LexError;
+
+    fn from_str(src: &str) -> Result<TokenStream, LexError> {
+        if nightly_works() {
+            Ok(TokenStream::Compiler(DeferredTokenStream::new(
+                src.parse()?,
+            )))
+        } else {
+            Ok(TokenStream::Fallback(src.parse()?))
+        }
+    }
+}
+
+impl fmt::Display for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TokenStream::Compiler(tts) => tts.clone().into_token_stream().fmt(f),
+            TokenStream::Fallback(tts) => tts.fmt(f),
+        }
+    }
+}
+
+impl From<proc_macro::TokenStream> for TokenStream {
+    fn from(inner: proc_macro::TokenStream) -> TokenStream {
+        TokenStream::Compiler(DeferredTokenStream::new(inner))
+    }
+}
+
+impl From<TokenStream> for proc_macro::TokenStream {
+    fn from(inner: TokenStream) -> proc_macro::TokenStream {
+        match inner {
+            TokenStream::Compiler(inner) => inner.into_token_stream(),
+            TokenStream::Fallback(inner) => inner.to_string().parse().unwrap(),
+        }
+    }
+}
+
+impl From<fallback::TokenStream> for TokenStream {
+    fn from(inner: fallback::TokenStream) -> TokenStream {
+        TokenStream::Fallback(inner)
+    }
+}
+
+// Assumes nightly_works().
+fn into_compiler_token(token: TokenTree) -> proc_macro::TokenTree {
+    match token {
+        TokenTree::Group(tt) => tt.inner.unwrap_nightly().into(),
+        TokenTree::Punct(tt) => {
+            let spacing = match tt.spacing() {
+                Spacing::Joint => proc_macro::Spacing::Joint,
+                Spacing::Alone => proc_macro::Spacing::Alone,
+            };
+            let mut op = proc_macro::Punct::new(tt.as_char(), spacing);
+            op.set_span(tt.span().inner.unwrap_nightly());
+            op.into()
+        }
+        TokenTree::Ident(tt) => tt.inner.unwrap_nightly().into(),
+        TokenTree::Literal(tt) => tt.inner.unwrap_nightly().into(),
+    }
+}
+
+impl From<TokenTree> for TokenStream {
+    fn from(token: TokenTree) -> TokenStream {
+        if nightly_works() {
+            TokenStream::Compiler(DeferredTokenStream::new(into_compiler_token(token).into()))
+        } else {
+            TokenStream::Fallback(token.into())
+        }
+    }
+}
+
+impl iter::FromIterator<TokenTree> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self {
+        if nightly_works() {
+            TokenStream::Compiler(DeferredTokenStream::new(
+                trees.into_iter().map(into_compiler_token).collect(),
+            ))
+        } else {
+            TokenStream::Fallback(trees.into_iter().collect())
+        }
+    }
+}
+
+impl iter::FromIterator<TokenStream> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
+        let mut streams = streams.into_iter();
+        match streams.next() {
+            Some(TokenStream::Compiler(mut first)) => {
+                first.evaluate_now();
+                first.stream.extend(streams.map(|s| match s {
+                    TokenStream::Compiler(s) => s.into_token_stream(),
+                    TokenStream::Fallback(_) => mismatch(),
+                }));
+                TokenStream::Compiler(first)
+            }
+            Some(TokenStream::Fallback(mut first)) => {
+                first.extend(streams.map(|s| match s {
+                    TokenStream::Fallback(s) => s,
+                    TokenStream::Compiler(_) => mismatch(),
+                }));
+                TokenStream::Fallback(first)
+            }
+            None => TokenStream::new(),
+        }
+    }
+}
+
+impl Extend<TokenTree> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, streams: I) {
+        match self {
+            TokenStream::Compiler(tts) => {
+                // Here is the reason for DeferredTokenStream.
+                tts.extra
+                    .extend(streams.into_iter().map(into_compiler_token));
+            }
+            TokenStream::Fallback(tts) => tts.extend(streams),
+        }
+    }
+}
+
+impl Extend<TokenStream> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
+        match self {
+            TokenStream::Compiler(tts) => {
+                tts.evaluate_now();
+                tts.stream
+                    .extend(streams.into_iter().map(|stream| stream.unwrap_nightly()));
+            }
+            TokenStream::Fallback(tts) => {
+                tts.extend(streams.into_iter().map(|stream| stream.unwrap_stable()));
+            }
+        }
+    }
+}
+
+impl fmt::Debug for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TokenStream::Compiler(tts) => tts.clone().into_token_stream().fmt(f),
+            TokenStream::Fallback(tts) => tts.fmt(f),
+        }
+    }
+}
+
+impl From<proc_macro::LexError> for LexError {
+    fn from(e: proc_macro::LexError) -> LexError {
+        LexError::Compiler(e)
+    }
+}
+
+impl From<fallback::LexError> for LexError {
+    fn from(e: fallback::LexError) -> LexError {
+        LexError::Fallback(e)
+    }
+}
+
+impl fmt::Debug for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            LexError::Compiler(e) => e.fmt(f),
+            LexError::Fallback(e) => e.fmt(f),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum TokenTreeIter {
+    Compiler(proc_macro::token_stream::IntoIter),
+    Fallback(fallback::TokenTreeIter),
+}
+
+impl IntoIterator for TokenStream {
+    type Item = TokenTree;
+    type IntoIter = TokenTreeIter;
+
+    fn into_iter(self) -> TokenTreeIter {
+        match self {
+            TokenStream::Compiler(tts) => {
+                TokenTreeIter::Compiler(tts.into_token_stream().into_iter())
+            }
+            TokenStream::Fallback(tts) => TokenTreeIter::Fallback(tts.into_iter()),
+        }
+    }
+}
+
+impl Iterator for TokenTreeIter {
+    type Item = TokenTree;
+
+    fn next(&mut self) -> Option<TokenTree> {
+        let token = match self {
+            TokenTreeIter::Compiler(iter) => iter.next()?,
+            TokenTreeIter::Fallback(iter) => return iter.next(),
+        };
+        Some(match token {
+            proc_macro::TokenTree::Group(tt) => crate::Group::_new(Group::Compiler(tt)).into(),
+            proc_macro::TokenTree::Punct(tt) => {
+                let spacing = match tt.spacing() {
+                    proc_macro::Spacing::Joint => Spacing::Joint,
+                    proc_macro::Spacing::Alone => Spacing::Alone,
+                };
+                let mut o = Punct::new(tt.as_char(), spacing);
+                o.set_span(crate::Span::_new(Span::Compiler(tt.span())));
+                o.into()
+            }
+            proc_macro::TokenTree::Ident(s) => crate::Ident::_new(Ident::Compiler(s)).into(),
+            proc_macro::TokenTree::Literal(l) => crate::Literal::_new(Literal::Compiler(l)).into(),
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self {
+            TokenTreeIter::Compiler(tts) => tts.size_hint(),
+            TokenTreeIter::Fallback(tts) => tts.size_hint(),
+        }
+    }
+}
+
+impl fmt::Debug for TokenTreeIter {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("TokenTreeIter").finish()
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+#[cfg(super_unstable)]
+pub enum SourceFile {
+    Compiler(proc_macro::SourceFile),
+    Fallback(fallback::SourceFile),
+}
+
+#[cfg(super_unstable)]
+impl SourceFile {
+    fn nightly(sf: proc_macro::SourceFile) -> Self {
+        SourceFile::Compiler(sf)
+    }
+
+    /// Get the path to this source file as a string.
+    pub fn path(&self) -> PathBuf {
+        match self {
+            SourceFile::Compiler(a) => a.path(),
+            SourceFile::Fallback(a) => a.path(),
+        }
+    }
+
+    pub fn is_real(&self) -> bool {
+        match self {
+            SourceFile::Compiler(a) => a.is_real(),
+            SourceFile::Fallback(a) => a.is_real(),
+        }
+    }
+}
+
+#[cfg(super_unstable)]
+impl fmt::Debug for SourceFile {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            SourceFile::Compiler(a) => a.fmt(f),
+            SourceFile::Fallback(a) => a.fmt(f),
+        }
+    }
+}
+
+#[cfg(any(super_unstable, feature = "span-locations"))]
+pub struct LineColumn {
+    pub line: usize,
+    pub column: usize,
+}
+
+#[derive(Copy, Clone)]
+pub enum Span {
+    Compiler(proc_macro::Span),
+    Fallback(fallback::Span),
+}
+
+impl Span {
+    pub fn call_site() -> Span {
+        if nightly_works() {
+            Span::Compiler(proc_macro::Span::call_site())
+        } else {
+            Span::Fallback(fallback::Span::call_site())
+        }
+    }
+
+    #[cfg(super_unstable)]
+    pub fn def_site() -> Span {
+        if nightly_works() {
+            Span::Compiler(proc_macro::Span::def_site())
+        } else {
+            Span::Fallback(fallback::Span::def_site())
+        }
+    }
+
+    #[cfg(super_unstable)]
+    pub fn resolved_at(&self, other: Span) -> Span {
+        match (self, other) {
+            (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.resolved_at(b)),
+            (Span::Fallback(a), Span::Fallback(b)) => Span::Fallback(a.resolved_at(b)),
+            _ => mismatch(),
+        }
+    }
+
+    #[cfg(super_unstable)]
+    pub fn located_at(&self, other: Span) -> Span {
+        match (self, other) {
+            (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.located_at(b)),
+            (Span::Fallback(a), Span::Fallback(b)) => Span::Fallback(a.located_at(b)),
+            _ => mismatch(),
+        }
+    }
+
+    pub fn unwrap(self) -> proc_macro::Span {
+        match self {
+            Span::Compiler(s) => s,
+            Span::Fallback(_) => panic!("proc_macro::Span is only available in procedural macros"),
+        }
+    }
+
+    #[cfg(super_unstable)]
+    pub fn source_file(&self) -> SourceFile {
+        match self {
+            Span::Compiler(s) => SourceFile::nightly(s.source_file()),
+            Span::Fallback(s) => SourceFile::Fallback(s.source_file()),
+        }
+    }
+
+    #[cfg(any(super_unstable, feature = "span-locations"))]
+    pub fn start(&self) -> LineColumn {
+        match self {
+            #[cfg(proc_macro_span)]
+            Span::Compiler(s) => {
+                let proc_macro::LineColumn { line, column } = s.start();
+                LineColumn { line, column }
+            }
+            #[cfg(not(proc_macro_span))]
+            Span::Compiler(_) => LineColumn { line: 0, column: 0 },
+            Span::Fallback(s) => {
+                let fallback::LineColumn { line, column } = s.start();
+                LineColumn { line, column }
+            }
+        }
+    }
+
+    #[cfg(any(super_unstable, feature = "span-locations"))]
+    pub fn end(&self) -> LineColumn {
+        match self {
+            #[cfg(proc_macro_span)]
+            Span::Compiler(s) => {
+                let proc_macro::LineColumn { line, column } = s.end();
+                LineColumn { line, column }
+            }
+            #[cfg(not(proc_macro_span))]
+            Span::Compiler(_) => LineColumn { line: 0, column: 0 },
+            Span::Fallback(s) => {
+                let fallback::LineColumn { line, column } = s.end();
+                LineColumn { line, column }
+            }
+        }
+    }
+
+    pub fn join(&self, other: Span) -> Option<Span> {
+        let ret = match (self, other) {
+            #[cfg(proc_macro_span)]
+            (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.join(b)?),
+            (Span::Fallback(a), Span::Fallback(b)) => Span::Fallback(a.join(b)?),
+            _ => return None,
+        };
+        Some(ret)
+    }
+
+    #[cfg(super_unstable)]
+    pub fn eq(&self, other: &Span) -> bool {
+        match (self, other) {
+            (Span::Compiler(a), Span::Compiler(b)) => a.eq(b),
+            (Span::Fallback(a), Span::Fallback(b)) => a.eq(b),
+            _ => false,
+        }
+    }
+
+    fn unwrap_nightly(self) -> proc_macro::Span {
+        match self {
+            Span::Compiler(s) => s,
+            Span::Fallback(_) => mismatch(),
+        }
+    }
+}
+
+impl From<proc_macro::Span> for crate::Span {
+    fn from(proc_span: proc_macro::Span) -> crate::Span {
+        crate::Span::_new(Span::Compiler(proc_span))
+    }
+}
+
+impl From<fallback::Span> for Span {
+    fn from(inner: fallback::Span) -> Span {
+        Span::Fallback(inner)
+    }
+}
+
+impl fmt::Debug for Span {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Span::Compiler(s) => s.fmt(f),
+            Span::Fallback(s) => s.fmt(f),
+        }
+    }
+}
+
+pub fn debug_span_field_if_nontrivial(debug: &mut fmt::DebugStruct, span: Span) {
+    match span {
+        Span::Compiler(s) => {
+            debug.field("span", &s);
+        }
+        Span::Fallback(s) => fallback::debug_span_field_if_nontrivial(debug, s),
+    }
+}
+
+#[derive(Clone)]
+pub enum Group {
+    Compiler(proc_macro::Group),
+    Fallback(fallback::Group),
+}
+
+impl Group {
+    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
+        match stream {
+            TokenStream::Compiler(tts) => {
+                let delimiter = match delimiter {
+                    Delimiter::Parenthesis => proc_macro::Delimiter::Parenthesis,
+                    Delimiter::Bracket => proc_macro::Delimiter::Bracket,
+                    Delimiter::Brace => proc_macro::Delimiter::Brace,
+                    Delimiter::None => proc_macro::Delimiter::None,
+                };
+                Group::Compiler(proc_macro::Group::new(delimiter, tts.into_token_stream()))
+            }
+            TokenStream::Fallback(stream) => {
+                Group::Fallback(fallback::Group::new(delimiter, stream))
+            }
+        }
+    }
+
+    pub fn delimiter(&self) -> Delimiter {
+        match self {
+            Group::Compiler(g) => match g.delimiter() {
+                proc_macro::Delimiter::Parenthesis => Delimiter::Parenthesis,
+                proc_macro::Delimiter::Bracket => Delimiter::Bracket,
+                proc_macro::Delimiter::Brace => Delimiter::Brace,
+                proc_macro::Delimiter::None => Delimiter::None,
+            },
+            Group::Fallback(g) => g.delimiter(),
+        }
+    }
+
+    pub fn stream(&self) -> TokenStream {
+        match self {
+            Group::Compiler(g) => TokenStream::Compiler(DeferredTokenStream::new(g.stream())),
+            Group::Fallback(g) => TokenStream::Fallback(g.stream()),
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        match self {
+            Group::Compiler(g) => Span::Compiler(g.span()),
+            Group::Fallback(g) => Span::Fallback(g.span()),
+        }
+    }
+
+    pub fn span_open(&self) -> Span {
+        match self {
+            #[cfg(proc_macro_span)]
+            Group::Compiler(g) => Span::Compiler(g.span_open()),
+            #[cfg(not(proc_macro_span))]
+            Group::Compiler(g) => Span::Compiler(g.span()),
+            Group::Fallback(g) => Span::Fallback(g.span_open()),
+        }
+    }
+
+    pub fn span_close(&self) -> Span {
+        match self {
+            #[cfg(proc_macro_span)]
+            Group::Compiler(g) => Span::Compiler(g.span_close()),
+            #[cfg(not(proc_macro_span))]
+            Group::Compiler(g) => Span::Compiler(g.span()),
+            Group::Fallback(g) => Span::Fallback(g.span_close()),
+        }
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        match (self, span) {
+            (Group::Compiler(g), Span::Compiler(s)) => g.set_span(s),
+            (Group::Fallback(g), Span::Fallback(s)) => g.set_span(s),
+            _ => mismatch(),
+        }
+    }
+
+    fn unwrap_nightly(self) -> proc_macro::Group {
+        match self {
+            Group::Compiler(g) => g,
+            Group::Fallback(_) => mismatch(),
+        }
+    }
+}
+
+impl From<fallback::Group> for Group {
+    fn from(g: fallback::Group) -> Self {
+        Group::Fallback(g)
+    }
+}
+
+impl fmt::Display for Group {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Group::Compiler(group) => group.fmt(formatter),
+            Group::Fallback(group) => group.fmt(formatter),
+        }
+    }
+}
+
+impl fmt::Debug for Group {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Group::Compiler(group) => group.fmt(formatter),
+            Group::Fallback(group) => group.fmt(formatter),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum Ident {
+    Compiler(proc_macro::Ident),
+    Fallback(fallback::Ident),
+}
+
+impl Ident {
+    pub fn new(string: &str, span: Span) -> Ident {
+        match span {
+            Span::Compiler(s) => Ident::Compiler(proc_macro::Ident::new(string, s)),
+            Span::Fallback(s) => Ident::Fallback(fallback::Ident::new(string, s)),
+        }
+    }
+
+    pub fn new_raw(string: &str, span: Span) -> Ident {
+        match span {
+            Span::Compiler(s) => {
+                let p: proc_macro::TokenStream = string.parse().unwrap();
+                let ident = match p.into_iter().next() {
+                    Some(proc_macro::TokenTree::Ident(mut i)) => {
+                        i.set_span(s);
+                        i
+                    }
+                    _ => panic!(),
+                };
+                Ident::Compiler(ident)
+            }
+            Span::Fallback(s) => Ident::Fallback(fallback::Ident::new_raw(string, s)),
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        match self {
+            Ident::Compiler(t) => Span::Compiler(t.span()),
+            Ident::Fallback(t) => Span::Fallback(t.span()),
+        }
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        match (self, span) {
+            (Ident::Compiler(t), Span::Compiler(s)) => t.set_span(s),
+            (Ident::Fallback(t), Span::Fallback(s)) => t.set_span(s),
+            _ => mismatch(),
+        }
+    }
+
+    fn unwrap_nightly(self) -> proc_macro::Ident {
+        match self {
+            Ident::Compiler(s) => s,
+            Ident::Fallback(_) => mismatch(),
+        }
+    }
+}
+
+impl PartialEq for Ident {
+    fn eq(&self, other: &Ident) -> bool {
+        match (self, other) {
+            (Ident::Compiler(t), Ident::Compiler(o)) => t.to_string() == o.to_string(),
+            (Ident::Fallback(t), Ident::Fallback(o)) => t == o,
+            _ => mismatch(),
+        }
+    }
+}
+
+impl<T> PartialEq<T> for Ident
+where
+    T: ?Sized + AsRef<str>,
+{
+    fn eq(&self, other: &T) -> bool {
+        let other = other.as_ref();
+        match self {
+            Ident::Compiler(t) => t.to_string() == other,
+            Ident::Fallback(t) => t == other,
+        }
+    }
+}
+
+impl fmt::Display for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Ident::Compiler(t) => t.fmt(f),
+            Ident::Fallback(t) => t.fmt(f),
+        }
+    }
+}
+
+impl fmt::Debug for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Ident::Compiler(t) => t.fmt(f),
+            Ident::Fallback(t) => t.fmt(f),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum Literal {
+    Compiler(proc_macro::Literal),
+    Fallback(fallback::Literal),
+}
+
+macro_rules! suffixed_numbers {
+    ($($name:ident => $kind:ident,)*) => ($(
+        pub fn $name(n: $kind) -> Literal {
+            if nightly_works() {
+                Literal::Compiler(proc_macro::Literal::$name(n))
+            } else {
+                Literal::Fallback(fallback::Literal::$name(n))
+            }
+        }
+    )*)
+}
+
+macro_rules! unsuffixed_integers {
+    ($($name:ident => $kind:ident,)*) => ($(
+        pub fn $name(n: $kind) -> Literal {
+            if nightly_works() {
+                Literal::Compiler(proc_macro::Literal::$name(n))
+            } else {
+                Literal::Fallback(fallback::Literal::$name(n))
+            }
+        }
+    )*)
+}
+
+impl Literal {
+    suffixed_numbers! {
+        u8_suffixed => u8,
+        u16_suffixed => u16,
+        u32_suffixed => u32,
+        u64_suffixed => u64,
+        u128_suffixed => u128,
+        usize_suffixed => usize,
+        i8_suffixed => i8,
+        i16_suffixed => i16,
+        i32_suffixed => i32,
+        i64_suffixed => i64,
+        i128_suffixed => i128,
+        isize_suffixed => isize,
+
+        f32_suffixed => f32,
+        f64_suffixed => f64,
+    }
+
+    unsuffixed_integers! {
+        u8_unsuffixed => u8,
+        u16_unsuffixed => u16,
+        u32_unsuffixed => u32,
+        u64_unsuffixed => u64,
+        u128_unsuffixed => u128,
+        usize_unsuffixed => usize,
+        i8_unsuffixed => i8,
+        i16_unsuffixed => i16,
+        i32_unsuffixed => i32,
+        i64_unsuffixed => i64,
+        i128_unsuffixed => i128,
+        isize_unsuffixed => isize,
+    }
+
+    pub fn f32_unsuffixed(f: f32) -> Literal {
+        if nightly_works() {
+            Literal::Compiler(proc_macro::Literal::f32_unsuffixed(f))
+        } else {
+            Literal::Fallback(fallback::Literal::f32_unsuffixed(f))
+        }
+    }
+
+    pub fn f64_unsuffixed(f: f64) -> Literal {
+        if nightly_works() {
+            Literal::Compiler(proc_macro::Literal::f64_unsuffixed(f))
+        } else {
+            Literal::Fallback(fallback::Literal::f64_unsuffixed(f))
+        }
+    }
+
+    pub fn string(t: &str) -> Literal {
+        if nightly_works() {
+            Literal::Compiler(proc_macro::Literal::string(t))
+        } else {
+            Literal::Fallback(fallback::Literal::string(t))
+        }
+    }
+
+    pub fn character(t: char) -> Literal {
+        if nightly_works() {
+            Literal::Compiler(proc_macro::Literal::character(t))
+        } else {
+            Literal::Fallback(fallback::Literal::character(t))
+        }
+    }
+
+    pub fn byte_string(bytes: &[u8]) -> Literal {
+        if nightly_works() {
+            Literal::Compiler(proc_macro::Literal::byte_string(bytes))
+        } else {
+            Literal::Fallback(fallback::Literal::byte_string(bytes))
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        match self {
+            Literal::Compiler(lit) => Span::Compiler(lit.span()),
+            Literal::Fallback(lit) => Span::Fallback(lit.span()),
+        }
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        match (self, span) {
+            (Literal::Compiler(lit), Span::Compiler(s)) => lit.set_span(s),
+            (Literal::Fallback(lit), Span::Fallback(s)) => lit.set_span(s),
+            _ => mismatch(),
+        }
+    }
+
+    pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
+        match self {
+            #[cfg(proc_macro_span)]
+            Literal::Compiler(lit) => lit.subspan(range).map(Span::Compiler),
+            #[cfg(not(proc_macro_span))]
+            Literal::Compiler(_lit) => None,
+            Literal::Fallback(lit) => lit.subspan(range).map(Span::Fallback),
+        }
+    }
+
+    fn unwrap_nightly(self) -> proc_macro::Literal {
+        match self {
+            Literal::Compiler(s) => s,
+            Literal::Fallback(_) => mismatch(),
+        }
+    }
+}
+
+impl From<fallback::Literal> for Literal {
+    fn from(s: fallback::Literal) -> Literal {
+        Literal::Fallback(s)
+    }
+}
+
+impl fmt::Display for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Literal::Compiler(t) => t.fmt(f),
+            Literal::Fallback(t) => t.fmt(f),
+        }
+    }
+}
+
+impl fmt::Debug for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Literal::Compiler(t) => t.fmt(f),
+            Literal::Fallback(t) => t.fmt(f),
+        }
+    }
+}