// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! A support library for macro authors when defining new macros.
//!
//! This library, provided by the standard distribution, provides the types
//! consumed in the interfaces of procedurally defined macro definitions such as
//! function-like macros `#[proc_macro]`, macro attributes `#[proc_macro_attribute]` and
//! custom derive attributes`#[proc_macro_derive]`.
//!
//! See [the book](../book/first-edition/procedural-macros.html) for more.

#![stable(feature = "proc_macro_lib", since = "1.15.0")]
#![deny(missing_docs)]
#![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/",
       html_playground_url = "https://play.rust-lang.org/",
       issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
       test(no_crate_inject, attr(deny(warnings))),
       test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]

#![feature(nll)]
#![feature(rustc_private)]
#![feature(staged_api)]
#![feature(lang_items)]
#![feature(optin_builtin_traits)]
#![feature(non_exhaustive)]

#![recursion_limit="256"]

extern crate syntax;
extern crate syntax_pos;
extern crate rustc_errors;
extern crate rustc_data_structures;

#[unstable(feature = "proc_macro_internals", issue = "27812")]
#[doc(hidden)]
pub mod rustc;

mod diagnostic;

#[unstable(feature = "proc_macro_diagnostic", issue = "54140")]
pub use diagnostic::{Diagnostic, Level, MultiSpan};

use std::ops::{Bound, RangeBounds};
use std::{ascii, fmt, iter};
use std::path::PathBuf;
use rustc_data_structures::sync::Lrc;
use std::str::FromStr;

use syntax::errors::DiagnosticBuilder;
use syntax::parse::{self, token};
use syntax::symbol::Symbol;
use syntax::tokenstream::{self, DelimSpan};
use syntax_pos::{Pos, FileName, BytePos};

/// The main type provided by this crate, representing an abstract stream of
/// tokens, or, more specifically, a sequence of token trees.
/// The type provide interfaces for iterating over those token trees and, conversely,
/// collecting a number of token trees into one stream.
///
/// This is both the input and output of `#[proc_macro]`, `#[proc_macro_attribute]`
/// and `#[proc_macro_derive]` definitions.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
#[derive(Clone)]
pub struct TokenStream(tokenstream::TokenStream);

#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Send for TokenStream {}
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Sync for TokenStream {}

/// Error returned from `TokenStream::from_str`.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
#[derive(Debug)]
pub struct LexError {
    _inner: (),
}

#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Send for LexError {}
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Sync for LexError {}

impl TokenStream {
    /// Returns an empty `TokenStream` containing no token trees.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new() -> TokenStream {
        TokenStream(tokenstream::TokenStream::empty())
    }

    /// Checks if this `TokenStream` is empty.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }
}

/// 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.
/// All tokens in the parsed stream get `Span::call_site()` spans.
///
/// NOTE: Some errors may cause panics instead of returning `LexError`. We reserve the right to
/// change these errors into `LexError`s later.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl FromStr for TokenStream {
    type Err = LexError;

    fn from_str(src: &str) -> Result<TokenStream, LexError> {
        __internal::with_sess(|sess, data| {
            Ok(__internal::token_stream_wrap(parse::parse_stream_from_source_str(
                FileName::ProcMacroSourceCode, src.to_string(), sess, Some(data.call_site.0)
            )))
        })
    }
}

/// 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.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl fmt::Display for TokenStream {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.0.fmt(f)
    }
}

/// Prints token in a form convenient for debugging.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
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()
    }
}

#[unstable(feature = "proc_macro_quote", issue = "54722")]
pub use quote::{quote, quote_span};

/// Creates a token stream containing a single token tree.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<TokenTree> for TokenStream {
    fn from(tree: TokenTree) -> TokenStream {
        TokenStream(tree.to_internal())
    }
}

/// Collects a number of token trees into a single stream.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl iter::FromIterator<TokenTree> for TokenStream {
    fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self {
        trees.into_iter().map(TokenStream::from).collect()
    }
}

/// A "flattening" operation on token streams, collects token trees
/// from multiple token streams into a single stream.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl iter::FromIterator<TokenStream> for TokenStream {
    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
        let mut builder = tokenstream::TokenStreamBuilder::new();
        for stream in streams {
            builder.push(stream.0);
        }
        TokenStream(builder.build())
    }
}

#[stable(feature = "token_stream_extend", since = "1.30.0")]
impl Extend<TokenTree> for TokenStream {
    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, trees: I) {
        self.extend(trees.into_iter().map(TokenStream::from));
    }
}

#[stable(feature = "token_stream_extend", since = "1.30.0")]
impl Extend<TokenStream> for TokenStream {
    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
        self.0.extend(streams.into_iter().map(|stream| stream.0));
    }
}

/// Public implementation details for the `TokenStream` type, such as iterators.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub mod token_stream {
    use syntax::tokenstream;
    use {TokenTree, TokenStream, Delimiter};

    /// 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)]
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub struct IntoIter {
        cursor: tokenstream::Cursor,
        stack: Vec<TokenTree>,
    }

    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    impl Iterator for IntoIter {
        type Item = TokenTree;

        fn next(&mut self) -> Option<TokenTree> {
            loop {
                let tree = self.stack.pop().or_else(|| {
                    let next = self.cursor.next_as_stream()?;
                    Some(TokenTree::from_internal(next, &mut self.stack))
                })?;
                // HACK: The condition "dummy span + group with empty delimiter" represents an AST
                // fragment approximately converted into a token stream. This may happen, for
                // example, with inputs to proc macro attributes, including derives. Such "groups"
                // need to flattened during iteration over stream's token trees.
                // Eventually this needs to be removed in favor of keeping original token trees
                // and not doing the roundtrip through AST.
                if tree.span().0.is_dummy() {
                    if let TokenTree::Group(ref group) = tree {
                        if group.delimiter() == Delimiter::None {
                            self.cursor.insert(group.stream.clone().0);
                            continue
                        }
                    }
                }
                return Some(tree);
            }
        }
    }

    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    impl IntoIterator for TokenStream {
        type Item = TokenTree;
        type IntoIter = IntoIter;

        fn into_iter(self) -> IntoIter {
            IntoIter { cursor: self.0.trees(), stack: Vec::new() }
        }
    }
}

/// `quote!(..)` accepts arbitrary tokens and expands into a `TokenStream` describing the input.
/// For example, `quote!(a + b)` will produce a expression, that, when evaluated, constructs
/// the `TokenStream` `[Ident("a"), Punct('+', Alone), Ident("b")]`.
///
/// Unquoting is done with `$`, and works by taking the single next ident as the unquoted term.
/// To quote `$` itself, use `$$`.
///
/// This is a dummy macro, the actual implementation is in `quote::quote`.`
#[unstable(feature = "proc_macro_quote", issue = "54722")]
#[macro_export]
macro_rules! quote { () => {} }

#[unstable(feature = "proc_macro_internals", issue = "27812")]
#[doc(hidden)]
mod quote;

/// A region of source code, along with macro expansion information.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
#[derive(Copy, Clone)]
pub struct Span(syntax_pos::Span);

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Span {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Span {}

macro_rules! diagnostic_method {
    ($name:ident, $level:expr) => (
        /// Create a new `Diagnostic` with the given `message` at the span
        /// `self`.
        #[unstable(feature = "proc_macro_diagnostic", issue = "54140")]
        pub fn $name<T: Into<String>>(self, message: T) -> Diagnostic {
            Diagnostic::spanned(self, $level, message)
        }
    )
}

impl Span {
    /// A span that resolves at the macro definition site.
    #[unstable(feature = "proc_macro_def_site", issue = "54724")]
    pub fn def_site() -> Span {
        ::__internal::with_sess(|_, data| data.def_site)
    }

    /// 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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn call_site() -> Span {
        ::__internal::with_sess(|_, data| data.call_site)
    }

    /// The original source file into which this span points.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn source_file(&self) -> SourceFile {
        SourceFile {
            source_file: __internal::lookup_char_pos(self.0.lo()).file,
        }
    }

    /// The `Span` for the tokens in the previous macro expansion from which
    /// `self` was generated from, if any.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn parent(&self) -> Option<Span> {
        self.0.parent().map(Span)
    }

    /// The span for the origin source code that `self` was generated from. If
    /// this `Span` wasn't generated from other macro expansions then the return
    /// value is the same as `*self`.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn source(&self) -> Span {
        Span(self.0.source_callsite())
    }

    /// Get the starting line/column in the source file for this span.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn start(&self) -> LineColumn {
        let loc = __internal::lookup_char_pos(self.0.lo());
        LineColumn {
            line: loc.line,
            column: loc.col.to_usize()
        }
    }

    /// Get the ending line/column in the source file for this span.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn end(&self) -> LineColumn {
        let loc = __internal::lookup_char_pos(self.0.hi());
        LineColumn {
            line: loc.line,
            column: loc.col.to_usize()
        }
    }

    /// Create a new span encompassing `self` and `other`.
    ///
    /// Returns `None` if `self` and `other` are from different files.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn join(&self, other: Span) -> Option<Span> {
        let self_loc = __internal::lookup_char_pos(self.0.lo());
        let other_loc = __internal::lookup_char_pos(other.0.lo());

        if self_loc.file.name != other_loc.file.name { return None }

        Some(Span(self.0.to(other.0)))
    }

    /// Creates a new span with the same line/column information as `self` but
    /// that resolves symbols as though it were at `other`.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn resolved_at(&self, other: Span) -> Span {
        Span(self.0.with_ctxt(other.0.ctxt()))
    }

    /// Creates a new span with the same name resolution behavior as `self` but
    /// with the line/column information of `other`.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn located_at(&self, other: Span) -> Span {
        other.resolved_at(*self)
    }

    /// Compares to spans to see if they're equal.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn eq(&self, other: &Span) -> bool {
        self.0 == other.0
    }

    diagnostic_method!(error, Level::Error);
    diagnostic_method!(warning, Level::Warning);
    diagnostic_method!(note, Level::Note);
    diagnostic_method!(help, Level::Help);
}

/// Prints a span in a form convenient for debugging.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Span {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{:?} bytes({}..{})",
               self.0.ctxt(),
               self.0.lo().0,
               self.0.hi().0)
    }
}

/// A line-column pair representing the start or end of a `Span`.
#[unstable(feature = "proc_macro_span", issue = "54725")]
#[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).
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub line: usize,
    /// The 0-indexed column (in UTF-8 characters) in the source file on which
    /// the span starts or ends (inclusive).
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub column: usize
}

#[unstable(feature = "proc_macro_span", issue = "54725")]
impl !Send for LineColumn {}
#[unstable(feature = "proc_macro_span", issue = "54725")]
impl !Sync for LineColumn {}

/// The source file of a given `Span`.
#[unstable(feature = "proc_macro_span", issue = "54725")]
#[derive(Clone)]
pub struct SourceFile {
    source_file: Lrc<syntax_pos::SourceFile>,
}

#[unstable(feature = "proc_macro_span", issue = "54725")]
impl !Send for SourceFile {}
#[unstable(feature = "proc_macro_span", issue = "54725")]
impl !Sync for SourceFile {}

impl SourceFile {
    /// Get the path to this source file.
    ///
    /// ### Note
    /// If the code span associated with this `SourceFile` was generated by an external macro, this
    /// 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
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn path(&self) -> PathBuf {
        match self.source_file.name {
            FileName::Real(ref path) => path.clone(),
            _ => PathBuf::from(self.source_file.name.to_string())
        }
    }

    /// Returns `true` if this source file is a real source file, and not generated by an external
    /// macro's expansion.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn is_real(&self) -> bool {
        // This is a hack until intercrate spans are implemented and we can have real source files
        // for spans generated in external macros.
        // https://github.com/rust-lang/rust/pull/43604#issuecomment-333334368
        self.source_file.is_real_file()
    }
}


#[unstable(feature = "proc_macro_span", issue = "54725")]
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()
    }
}

#[unstable(feature = "proc_macro_span", issue = "54725")]
impl PartialEq for SourceFile {
    fn eq(&self, other: &Self) -> bool {
        Lrc::ptr_eq(&self.source_file, &other.source_file)
    }
}

#[unstable(feature = "proc_macro_span", issue = "54725")]
impl Eq for SourceFile {}

/// A single token or a delimited sequence of token trees (e.g. `[1, (), ..]`).
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
#[derive(Clone)]
pub enum TokenTree {
    /// A token stream surrounded by bracket delimiters.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Group(
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        Group
    ),
    /// An identifier.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Ident(
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        Ident
    ),
    /// A single punctuation character (`+`, `,`, `$`, etc.).
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Punct(
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        Punct
    ),
    /// A literal character (`'a'`), string (`"hello"`), number (`2.3`), etc.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Literal(
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        Literal
    ),
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for TokenTree {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for TokenTree {}

impl TokenTree {
    /// Returns the span of this tree, delegating to the `span` method of
    /// the contained token or a delimited stream.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    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),
        }
    }
}

/// Prints token tree in a form convenient for debugging.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
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 tt) => tt.fmt(f),
            TokenTree::Ident(ref tt) => tt.fmt(f),
            TokenTree::Punct(ref tt) => tt.fmt(f),
            TokenTree::Literal(ref tt) => tt.fmt(f),
        }
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Group> for TokenTree {
    fn from(g: Group) -> TokenTree {
        TokenTree::Group(g)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Ident> for TokenTree {
    fn from(g: Ident) -> TokenTree {
        TokenTree::Ident(g)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Punct> for TokenTree {
    fn from(g: Punct) -> TokenTree {
        TokenTree::Punct(g)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
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.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
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),
        }
    }
}

/// A delimited token stream.
///
/// A `Group` internally contains a `TokenStream` which is surrounded by `Delimiter`s.
#[derive(Clone)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub struct Group {
    delimiter: Delimiter,
    stream: TokenStream,
    span: DelimSpan,
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Group {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Group {}

/// Describes how a sequence of token trees is delimited.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub enum Delimiter {
    /// `( ... )`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Parenthesis,
    /// `{ ... }`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Brace,
    /// `[ ... ]`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    None,
}

impl Group {
    /// 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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
        Group {
            delimiter: delimiter,
            stream: stream,
            span: DelimSpan::from_single(Span::call_site().0),
        }
    }

    /// Returns the delimiter of this `Group`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn delimiter(&self) -> Delimiter {
        self.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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn stream(&self) -> TokenStream {
        self.stream.clone()
    }

    /// Returns the span for the delimiters of this token stream, spanning the
    /// entire `Group`.
    ///
    /// ```text
    /// pub fn span(&self) -> Span {
    ///            ^^^^^^^
    /// ```
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        Span(self.span.entire())
    }

    /// Returns the span pointing to the opening delimiter of this group.
    ///
    /// ```text
    /// pub fn span_open(&self) -> Span {
    ///                 ^
    /// ```
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn span_open(&self) -> Span {
        Span(self.span.open)
    }

    /// Returns the span pointing to the closing delimiter of this group.
    ///
    /// ```text
    /// pub fn span_close(&self) -> Span {
    ///                        ^
    /// ```
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn span_close(&self) -> Span {
        Span(self.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`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.span = DelimSpan::from_single(span.0);
    }
}

/// 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.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Group {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        TokenStream::from(TokenTree::from(self.clone())).fmt(f)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Group {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Group")
            .field("delimiter", &self.delimiter())
            .field("stream", &self.stream())
            .field("span", &self.span())
            .finish()
    }
}

/// An `Punct` is an single punctuation character like `+`, `-` or `#`.
///
/// Multi-character operators like `+=` are represented as two instances of `Punct` with different
/// forms of `Spacing` returned.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
#[derive(Clone)]
pub struct Punct {
    ch: char,
    spacing: Spacing,
    span: Span,
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Punct {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Punct {}

/// Whether an `Punct` is followed immediately by another `Punct` or
/// followed by another token or whitespace.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub enum Spacing {
    /// E.g. `+` is `Alone` in `+ =`, `+ident` or `+()`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Alone,
    /// E.g. `+` is `Joint` in `+=` or `'#`.
    /// Additionally, single quote `'` can join with identifiers to form lifetimes `'ident`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new(ch: char, spacing: Spacing) -> Punct {
        const LEGAL_CHARS: &[char] = &['=', '<', '>', '!', '~', '+', '-', '*', '/', '%', '^',
                                       '&', '|', '@', '.', ',', ';', ':', '#', '$', '?', '\''];
        if !LEGAL_CHARS.contains(&ch) {
            panic!("unsupported character `{:?}`", ch)
        }
        Punct {
            ch: ch,
            spacing: spacing,
            span: Span::call_site(),
        }
    }

    /// Returns the value of this punctuation character as `char`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn as_char(&self) -> char {
        self.ch
    }

    /// 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 multi-character operator (`Joint`), or it's followed by some other token or whitespace
    /// (`Alone`) so the operator has certainly ended.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn spacing(&self) -> Spacing {
        self.spacing
    }

    /// Returns the span for this punctuation character.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        self.span
    }

    /// Configure the span for this punctuation character.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    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.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Punct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        TokenStream::from(TokenTree::from(self.clone())).fmt(f)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Punct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Punct")
            .field("ch", &self.as_char())
            .field("spacing", &self.spacing())
            .field("span", &self.span())
            .finish()
    }
}

/// An identifier (`ident`).
#[derive(Clone)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub struct Ident {
    sym: Symbol,
    span: Span,
    is_raw: bool,
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Ident {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Ident {}

impl Ident {
    fn is_valid(string: &str) -> bool {
        let mut chars = string.chars();
        if let Some(start) = chars.next() {
            (start == '_' || start.is_xid_start())
                && chars.all(|cont| cont == '_' || cont.is_xid_continue())
        } else {
            false
        }
    }

    /// 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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new(string: &str, span: Span) -> Ident {
        if !Ident::is_valid(string) {
            panic!("`{:?}` is not a valid identifier", string)
        }
        Ident::new_maybe_raw(string, span, false)
    }

    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`).
    #[unstable(feature = "proc_macro_raw_ident", issue = "54723")]
    pub fn new_raw(string: &str, span: Span) -> Ident {
        if !Ident::is_valid(string) {
            panic!("`{:?}` is not a valid identifier", string)
        }
        Ident::new_maybe_raw(string, span, true)
    }

    /// Returns the span of this `Ident`, encompassing the entire string returned
    /// by `as_str`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        self.span
    }

    /// Configures the span of this `Ident`, possibly changing its hygiene context.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.span = span;
    }
}

/// Prints the identifier as a string that should be losslessly convertible
/// back into the same identifier.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Ident {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        TokenStream::from(TokenTree::from(self.clone())).fmt(f)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Ident {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Ident")
            .field("ident", &self.to_string())
            .field("span", &self.span())
            .finish()
    }
}

/// 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.
// FIXME(eddyb) `Literal` should not expose internal `Debug` impls.
#[derive(Clone, Debug)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub struct Literal {
    lit: token::Lit,
    suffix: Option<Symbol>,
    span: Span,
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Literal {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Literal {}

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 round-trips 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.
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        pub fn $name(n: $kind) -> Literal {
            Literal {
                lit: token::Lit::Integer(Symbol::intern(&n.to_string())),
                suffix: Some(Symbol::intern(stringify!($kind))),
                span: Span::call_site(),
            }
        }
    )*)
}

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.
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        pub fn $name(n: $kind) -> Literal {
            Literal {
                lit: token::Lit::Integer(Symbol::intern(&n.to_string())),
                suffix: None,
                span: Span::call_site(),
            }
        }
    )*)
}

impl Literal {
    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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f32_unsuffixed(n: f32) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {}", n);
        }
        Literal {
            lit: token::Lit::Float(Symbol::intern(&n.to_string())),
            suffix: None,
            span: Span::call_site(),
        }
    }

    /// 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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f32_suffixed(n: f32) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {}", n);
        }
        Literal {
            lit: token::Lit::Float(Symbol::intern(&n.to_string())),
            suffix: Some(Symbol::intern("f32")),
            span: Span::call_site(),
        }
    }

    /// 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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f64_unsuffixed(n: f64) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {}", n);
        }
        Literal {
            lit: token::Lit::Float(Symbol::intern(&n.to_string())),
            suffix: None,
            span: Span::call_site(),
        }
    }

    /// 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.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f64_suffixed(n: f64) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {}", n);
        }
        Literal {
            lit: token::Lit::Float(Symbol::intern(&n.to_string())),
            suffix: Some(Symbol::intern("f64")),
            span: Span::call_site(),
        }
    }

    /// String literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn string(string: &str) -> Literal {
        let mut escaped = String::new();
        for ch in string.chars() {
            escaped.extend(ch.escape_debug());
        }
        Literal {
            lit: token::Lit::Str_(Symbol::intern(&escaped)),
            suffix: None,
            span: Span::call_site(),
        }
    }

    /// Character literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn character(ch: char) -> Literal {
        let mut escaped = String::new();
        escaped.extend(ch.escape_unicode());
        Literal {
            lit: token::Lit::Char(Symbol::intern(&escaped)),
            suffix: None,
            span: Span::call_site(),
        }
    }

    /// Byte string literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn byte_string(bytes: &[u8]) -> Literal {
        let string = bytes.iter().cloned().flat_map(ascii::escape_default)
            .map(Into::<char>::into).collect::<String>();
        Literal {
            lit: token::Lit::ByteStr(Symbol::intern(&string)),
            suffix: None,
            span: Span::call_site(),
        }
    }

    /// Returns the span encompassing this literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        self.span
    }

    /// Configures the span associated for this literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.span = span;
    }

    /// 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`.
    // FIXME(SergioBenitez): check that the byte range starts and ends at a
    // UTF-8 boundary of the source. otherwise, it's likely that a panic will
    // occur elsewhere when the source text is printed.
    // FIXME(SergioBenitez): there is no way for the user to know what
    // `self.span()` actually maps to, so this method can currently only be
    // called blindly. For example, `to_string()` for the character 'c' returns
    // "'\u{63}'"; there is no way for the user to know whether the source text
    // was 'c' or whether it was '\u{63}'.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
        let inner = self.span().0;
        let length = inner.hi().to_usize() - inner.lo().to_usize();

        let start = match range.start_bound() {
            Bound::Included(&lo) => lo,
            Bound::Excluded(&lo) => lo + 1,
            Bound::Unbounded => 0,
        };

        let end = match range.end_bound() {
            Bound::Included(&hi) => hi + 1,
            Bound::Excluded(&hi) => hi,
            Bound::Unbounded => length,
        };

        // Bounds check the values, preventing addition overflow and OOB spans.
        if start > u32::max_value() as usize
            || end > u32::max_value() as usize
            || (u32::max_value() - start as u32) < inner.lo().to_u32()
            || (u32::max_value() - end as u32) < inner.lo().to_u32()
            || start >= end
            || end > length
        {
            return None;
        }

        let new_lo = inner.lo() + BytePos::from_usize(start);
        let new_hi = inner.lo() + BytePos::from_usize(end);
        Some(Span(inner.with_lo(new_lo).with_hi(new_hi)))
    }
}

/// Prints the literal as a string that should be losslessly convertible
/// back into the same literal (except for possible rounding for floating point literals).
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Literal {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        TokenStream::from(TokenTree::from(self.clone())).fmt(f)
    }
}

/// Permanently unstable internal implementation details of this crate. This
/// should not be used.
///
/// These methods are used by the rest of the compiler to generate instances of
/// `TokenStream` to hand to macro definitions, as well as consume the output.
///
/// Note that this module is also intentionally separate from the rest of the
/// crate. This allows the `#[unstable]` directive below to naturally apply to
/// all of the contents.
#[unstable(feature = "proc_macro_internals", issue = "27812")]
#[doc(hidden)]
pub mod __internal {
    use std::cell::Cell;
    use std::ptr;

    use syntax::ast;
    use syntax::ext::base::ExtCtxt;
    use syntax::ptr::P;
    use syntax::parse::{self, ParseSess};
    use syntax::parse::token::{self, Token};
    use syntax::tokenstream;
    use syntax_pos::{BytePos, Loc, DUMMY_SP};
    use syntax_pos::hygiene::{SyntaxContext, Transparency};

    use super::{TokenStream, LexError, Span};

    pub fn lookup_char_pos(pos: BytePos) -> Loc {
        with_sess(|sess, _| sess.source_map().lookup_char_pos(pos))
    }

    pub fn new_token_stream(item: P<ast::Item>) -> TokenStream {
        let token = Token::interpolated(token::NtItem(item));
        TokenStream(tokenstream::TokenTree::Token(DUMMY_SP, token).into())
    }

    pub fn token_stream_wrap(inner: tokenstream::TokenStream) -> TokenStream {
        TokenStream(inner)
    }

    pub fn token_stream_parse_items(stream: TokenStream) -> Result<Vec<P<ast::Item>>, LexError> {
        with_sess(move |sess, _| {
            let mut parser = parse::stream_to_parser(sess, stream.0);
            let mut items = Vec::new();

            while let Some(item) = try!(parser.parse_item().map_err(super::parse_to_lex_err)) {
                items.push(item)
            }

            Ok(items)
        })
    }

    pub fn token_stream_inner(stream: TokenStream) -> tokenstream::TokenStream {
        stream.0
    }

    pub trait Registry {
        fn register_custom_derive(&mut self,
                                  trait_name: &str,
                                  expand: fn(TokenStream) -> TokenStream,
                                  attributes: &[&'static str]);

        fn register_attr_proc_macro(&mut self,
                                    name: &str,
                                    expand: fn(TokenStream, TokenStream) -> TokenStream);

        fn register_bang_proc_macro(&mut self,
                                    name: &str,
                                    expand: fn(TokenStream) -> TokenStream);
    }

    #[derive(Clone, Copy)]
    pub struct ProcMacroData {
        pub def_site: Span,
        pub call_site: Span,
    }

    #[derive(Clone, Copy)]
    struct ProcMacroSess {
        parse_sess: *const ParseSess,
        data: ProcMacroData,
    }

    // Emulate scoped_thread_local!() here essentially
    thread_local! {
        static CURRENT_SESS: Cell<ProcMacroSess> = Cell::new(ProcMacroSess {
            parse_sess: ptr::null(),
            data: ProcMacroData { def_site: Span(DUMMY_SP), call_site: Span(DUMMY_SP) },
        });
    }

    pub fn set_sess<F, R>(cx: &ExtCtxt, f: F) -> R
        where F: FnOnce() -> R
    {
        struct Reset { prev: ProcMacroSess }

        impl Drop for Reset {
            fn drop(&mut self) {
                CURRENT_SESS.with(|p| p.set(self.prev));
            }
        }

        CURRENT_SESS.with(|p| {
            let _reset = Reset { prev: p.get() };

            // No way to determine def location for a proc macro right now, so use call location.
            let location = cx.current_expansion.mark.expn_info().unwrap().call_site;
            let to_span = |transparency| Span(location.with_ctxt(
                SyntaxContext::empty().apply_mark_with_transparency(cx.current_expansion.mark,
                                                                    transparency))
            );
            p.set(ProcMacroSess {
                parse_sess: cx.parse_sess,
                data: ProcMacroData {
                    def_site: to_span(Transparency::Opaque),
                    call_site: to_span(Transparency::Transparent),
                },
            });
            f()
        })
    }

    pub fn in_sess() -> bool
    {
        !CURRENT_SESS.with(|sess| sess.get()).parse_sess.is_null()
    }

    pub fn with_sess<F, R>(f: F) -> R
        where F: FnOnce(&ParseSess, &ProcMacroData) -> R
    {
        let sess = CURRENT_SESS.with(|sess| sess.get());
        if sess.parse_sess.is_null() {
            panic!("procedural macro API is used outside of a procedural macro");
        }
        f(unsafe { &*sess.parse_sess }, &sess.data)
    }
}

fn parse_to_lex_err(mut err: DiagnosticBuilder) -> LexError {
    err.cancel();
    LexError { _inner: () }
}