Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 984 insertions, 0 deletions

diff --git a/vendor/proc-macro2/src/wrapper.rs b/vendor/proc-macro2/src/wrapper.rs
new file mode 100644
index 000000000..750e156ff
--- /dev/null
+++ b/vendor/proc-macro2/src/wrapper.rs
@@ -0,0 +1,984 @@
+use crate::detection::inside_proc_macro;
+use crate::{fallback, Delimiter, Punct, Spacing, TokenTree};
+use std::fmt::{self, Debug, Display};
+use std::iter::FromIterator;
+use std::ops::RangeBounds;
+use std::panic;
+#[cfg(super_unstable)]
+use std::path::PathBuf;
+use std::str::FromStr;
+
+#[derive(Clone)]
+pub(crate) 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(crate) struct DeferredTokenStream {
+    stream: proc_macro::TokenStream,
+    extra: Vec<proc_macro::TokenTree>,
+}
+
+pub(crate) enum LexError {
+    Compiler(proc_macro::LexError),
+    Fallback(fallback::LexError),
+}
+
+impl LexError {
+    fn call_site() -> Self {
+        LexError::Fallback(fallback::LexError {
+            span: fallback::Span::call_site(),
+        })
+    }
+}
+
+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) {
+        // If-check provides a fast short circuit for the common case of `extra`
+        // being empty, which saves a round trip over the proc macro bridge.
+        // Improves macro expansion time in winrt by 6% in debug mode.
+        if !self.extra.is_empty() {
+            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() -> Self {
+        if inside_proc_macro() {
+            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 inside_proc_macro() {
+            Ok(TokenStream::Compiler(DeferredTokenStream::new(
+                proc_macro_parse(src)?,
+            )))
+        } else {
+            Ok(TokenStream::Fallback(src.parse()?))
+        }
+    }
+}
+
+// Work around https://github.com/rust-lang/rust/issues/58736.
+fn proc_macro_parse(src: &str) -> Result<proc_macro::TokenStream, LexError> {
+    let result = panic::catch_unwind(|| src.parse().map_err(LexError::Compiler));
+    result.unwrap_or_else(|_| Err(LexError::call_site()))
+}
+
+impl Display for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TokenStream::Compiler(tts) => Display::fmt(&tts.clone().into_token_stream(), f),
+            TokenStream::Fallback(tts) => Display::fmt(tts, 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 inside_proc_macro().
+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 punct = proc_macro::Punct::new(tt.as_char(), spacing);
+            punct.set_span(tt.span().inner.unwrap_nightly());
+            punct.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 inside_proc_macro() {
+            TokenStream::Compiler(DeferredTokenStream::new(into_compiler_token(token).into()))
+        } else {
+            TokenStream::Fallback(token.into())
+        }
+    }
+}
+
+impl FromIterator<TokenTree> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self {
+        if inside_proc_macro() {
+            TokenStream::Compiler(DeferredTokenStream::new(
+                trees.into_iter().map(into_compiler_token).collect(),
+            ))
+        } else {
+            TokenStream::Fallback(trees.into_iter().collect())
+        }
+    }
+}
+
+impl 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, stream: I) {
+        match self {
+            TokenStream::Compiler(tts) => {
+                // Here is the reason for DeferredTokenStream.
+                for token in stream {
+                    tts.extra.push(into_compiler_token(token));
+                }
+            }
+            TokenStream::Fallback(tts) => tts.extend(stream),
+        }
+    }
+}
+
+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(TokenStream::unwrap_nightly));
+            }
+            TokenStream::Fallback(tts) => {
+                tts.extend(streams.into_iter().map(TokenStream::unwrap_stable));
+            }
+        }
+    }
+}
+
+impl Debug for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            TokenStream::Compiler(tts) => Debug::fmt(&tts.clone().into_token_stream(), f),
+            TokenStream::Fallback(tts) => Debug::fmt(tts, f),
+        }
+    }
+}
+
+impl LexError {
+    pub(crate) fn span(&self) -> Span {
+        match self {
+            LexError::Compiler(_) => Span::call_site(),
+            LexError::Fallback(e) => Span::Fallback(e.span()),
+        }
+    }
+}
+
+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 Debug for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            LexError::Compiler(e) => Debug::fmt(e, f),
+            LexError::Fallback(e) => Debug::fmt(e, f),
+        }
+    }
+}
+
+impl Display for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            #[cfg(not(no_lexerror_display))]
+            LexError::Compiler(e) => Display::fmt(e, f),
+            #[cfg(no_lexerror_display)]
+            LexError::Compiler(_e) => Display::fmt(
+                &fallback::LexError {
+                    span: fallback::Span::call_site(),
+                },
+                f,
+            ),
+            LexError::Fallback(e) => Display::fmt(e, f),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) 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 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(crate) 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 Debug for SourceFile {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            SourceFile::Compiler(a) => Debug::fmt(a, f),
+            SourceFile::Fallback(a) => Debug::fmt(a, f),
+        }
+    }
+}
+
+#[cfg(any(super_unstable, feature = "span-locations"))]
+pub(crate) struct LineColumn {
+    pub line: usize,
+    pub column: usize,
+}
+
+#[derive(Copy, Clone)]
+pub(crate) enum Span {
+    Compiler(proc_macro::Span),
+    Fallback(fallback::Span),
+}
+
+impl Span {
+    pub fn call_site() -> Self {
+        if inside_proc_macro() {
+            Span::Compiler(proc_macro::Span::call_site())
+        } else {
+            Span::Fallback(fallback::Span::call_site())
+        }
+    }
+
+    #[cfg(not(no_hygiene))]
+    pub fn mixed_site() -> Self {
+        if inside_proc_macro() {
+            Span::Compiler(proc_macro::Span::mixed_site())
+        } else {
+            Span::Fallback(fallback::Span::mixed_site())
+        }
+    }
+
+    #[cfg(super_unstable)]
+    pub fn def_site() -> Self {
+        if inside_proc_macro() {
+            Span::Compiler(proc_macro::Span::def_site())
+        } else {
+            Span::Fallback(fallback::Span::def_site())
+        }
+    }
+
+    pub fn resolved_at(&self, other: Span) -> Span {
+        match (self, other) {
+            #[cfg(not(no_hygiene))]
+            (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.resolved_at(b)),
+
+            // Name resolution affects semantics, but location is only cosmetic
+            #[cfg(no_hygiene)]
+            (Span::Compiler(_), Span::Compiler(_)) => other,
+
+            (Span::Fallback(a), Span::Fallback(b)) => Span::Fallback(a.resolved_at(b)),
+            _ => mismatch(),
+        }
+    }
+
+    pub fn located_at(&self, other: Span) -> Span {
+        match (self, other) {
+            #[cfg(not(no_hygiene))]
+            (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.located_at(b)),
+
+            // Name resolution affects semantics, but location is only cosmetic
+            #[cfg(no_hygiene)]
+            (Span::Compiler(_), Span::Compiler(_)) => *self,
+
+            (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 Debug for Span {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Span::Compiler(s) => Debug::fmt(s, f),
+            Span::Fallback(s) => Debug::fmt(s, f),
+        }
+    }
+}
+
+pub(crate) 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(crate) enum Group {
+    Compiler(proc_macro::Group),
+    Fallback(fallback::Group),
+}
+
+impl Group {
+    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Self {
+        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(not(no_group_open_close))]
+            Group::Compiler(g) => Span::Compiler(g.span_open()),
+            #[cfg(no_group_open_close)]
+            Group::Compiler(g) => Span::Compiler(g.span()),
+            Group::Fallback(g) => Span::Fallback(g.span_open()),
+        }
+    }
+
+    pub fn span_close(&self) -> Span {
+        match self {
+            #[cfg(not(no_group_open_close))]
+            Group::Compiler(g) => Span::Compiler(g.span_close()),
+            #[cfg(no_group_open_close)]
+            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 Display for Group {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Group::Compiler(group) => Display::fmt(group, formatter),
+            Group::Fallback(group) => Display::fmt(group, formatter),
+        }
+    }
+}
+
+impl Debug for Group {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Group::Compiler(group) => Debug::fmt(group, formatter),
+            Group::Fallback(group) => Debug::fmt(group, formatter),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) enum Ident {
+    Compiler(proc_macro::Ident),
+    Fallback(fallback::Ident),
+}
+
+impl Ident {
+    pub fn new(string: &str, span: Span) -> Self {
+        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) -> Self {
+        match span {
+            #[cfg(not(no_ident_new_raw))]
+            Span::Compiler(s) => Ident::Compiler(proc_macro::Ident::new_raw(string, s)),
+            #[cfg(no_ident_new_raw)]
+            Span::Compiler(s) => {
+                let _ = proc_macro::Ident::new(string, s);
+                // At this point the un-r#-prefixed string is known to be a
+                // valid identifier. Try to produce a valid raw identifier by
+                // running the `TokenStream` parser, and unwrapping the first
+                // token as an `Ident`.
+                let raw_prefixed = format!("r#{}", string);
+                if let Ok(ts) = raw_prefixed.parse::<proc_macro::TokenStream>() {
+                    let mut iter = ts.into_iter();
+                    if let (Some(proc_macro::TokenTree::Ident(mut id)), None) =
+                        (iter.next(), iter.next())
+                    {
+                        id.set_span(s);
+                        return Ident::Compiler(id);
+                    }
+                }
+                panic!("not allowed as a raw identifier: `{}`", raw_prefixed)
+            }
+            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 Display for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Ident::Compiler(t) => Display::fmt(t, f),
+            Ident::Fallback(t) => Display::fmt(t, f),
+        }
+    }
+}
+
+impl Debug for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Ident::Compiler(t) => Debug::fmt(t, f),
+            Ident::Fallback(t) => Debug::fmt(t, f),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) enum Literal {
+    Compiler(proc_macro::Literal),
+    Fallback(fallback::Literal),
+}
+
+macro_rules! suffixed_numbers {
+    ($($name:ident => $kind:ident,)*) => ($(
+        pub fn $name(n: $kind) -> Literal {
+            if inside_proc_macro() {
+                Literal::Compiler(proc_macro::Literal::$name(n))
+            } else {
+                Literal::Fallback(fallback::Literal::$name(n))
+            }
+        }
+    )*)
+}
+
+macro_rules! unsuffixed_integers {
+    ($($name:ident => $kind:ident,)*) => ($(
+        pub fn $name(n: $kind) -> Literal {
+            if inside_proc_macro() {
+                Literal::Compiler(proc_macro::Literal::$name(n))
+            } else {
+                Literal::Fallback(fallback::Literal::$name(n))
+            }
+        }
+    )*)
+}
+
+impl Literal {
+    pub unsafe fn from_str_unchecked(repr: &str) -> Self {
+        if inside_proc_macro() {
+            Literal::Compiler(compiler_literal_from_str(repr).expect("invalid literal"))
+        } else {
+            Literal::Fallback(fallback::Literal::from_str_unchecked(repr))
+        }
+    }
+
+    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 inside_proc_macro() {
+            Literal::Compiler(proc_macro::Literal::f32_unsuffixed(f))
+        } else {
+            Literal::Fallback(fallback::Literal::f32_unsuffixed(f))
+        }
+    }
+
+    pub fn f64_unsuffixed(f: f64) -> Literal {
+        if inside_proc_macro() {
+            Literal::Compiler(proc_macro::Literal::f64_unsuffixed(f))
+        } else {
+            Literal::Fallback(fallback::Literal::f64_unsuffixed(f))
+        }
+    }
+
+    pub fn string(t: &str) -> Literal {
+        if inside_proc_macro() {
+            Literal::Compiler(proc_macro::Literal::string(t))
+        } else {
+            Literal::Fallback(fallback::Literal::string(t))
+        }
+    }
+
+    pub fn character(t: char) -> Literal {
+        if inside_proc_macro() {
+            Literal::Compiler(proc_macro::Literal::character(t))
+        } else {
+            Literal::Fallback(fallback::Literal::character(t))
+        }
+    }
+
+    pub fn byte_string(bytes: &[u8]) -> Literal {
+        if inside_proc_macro() {
+            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 FromStr for Literal {
+    type Err = LexError;
+
+    fn from_str(repr: &str) -> Result<Self, Self::Err> {
+        if inside_proc_macro() {
+            compiler_literal_from_str(repr).map(Literal::Compiler)
+        } else {
+            let literal = fallback::Literal::from_str(repr)?;
+            Ok(Literal::Fallback(literal))
+        }
+    }
+}
+
+fn compiler_literal_from_str(repr: &str) -> Result<proc_macro::Literal, LexError> {
+    #[cfg(not(no_literal_from_str))]
+    {
+        proc_macro::Literal::from_str(repr).map_err(LexError::Compiler)
+    }
+    #[cfg(no_literal_from_str)]
+    {
+        let tokens = proc_macro_parse(repr)?;
+        let mut iter = tokens.into_iter();
+        if let (Some(proc_macro::TokenTree::Literal(literal)), None) = (iter.next(), iter.next()) {
+            if literal.to_string().len() == repr.len() {
+                return Ok(literal);
+            }
+        }
+        Err(LexError::call_site())
+    }
+}
+
+impl Display for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Literal::Compiler(t) => Display::fmt(t, f),
+            Literal::Fallback(t) => Display::fmt(t, f),
+        }
+    }
+}
+
+impl Debug for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Literal::Compiler(t) => Debug::fmt(t, f),
+            Literal::Fallback(t) => Debug::fmt(t, f),
+        }
+    }
+}