extra.rs

  1// SPDX-License-Identifier: Apache-2.0 OR MIT
  2
  3//! Items which do not have a correspondence to any API in the proc_macro crate,
  4//! but are necessary to include in proc-macro2.
  5
  6use crate::fallback;
  7use crate::imp;
  8use crate::marker::{ProcMacroAutoTraits, MARKER};
  9use crate::Span;
 10use core::fmt::{self, Debug};
 11
 12/// Invalidate any `proc_macro2::Span` that exist on the current thread.
 13///
 14/// The implementation of `Span` uses thread-local data structures and this
 15/// function clears them. Calling any method on a `Span` on the current thread
 16/// created prior to the invalidation will return incorrect values or crash.
 17///
 18/// This function is useful for programs that process more than 2<sup>32</sup>
 19/// bytes of Rust source code on the same thread. Just like rustc, proc-macro2
 20/// uses 32-bit source locations, and these wrap around when the total source
 21/// code processed by the same thread exceeds 2<sup>32</sup> bytes (4
 22/// gigabytes). After a wraparound, `Span` methods such as `source_text()` can
 23/// return wrong data.
 24///
 25/// # Example
 26///
 27/// As of late 2023, there is 200 GB of Rust code published on crates.io.
 28/// Looking at just the newest version of every crate, it is 16 GB of code. So a
 29/// workload that involves parsing it all would overflow a 32-bit source
 30/// location unless spans are being invalidated.
 31///
 32/// ```
 33/// use flate2::read::GzDecoder;
 34/// use std::ffi::OsStr;
 35/// use std::io::{BufReader, Read};
 36/// use std::str::FromStr;
 37/// use tar::Archive;
 38///
 39/// rayon::scope(|s| {
 40///     for krate in every_version_of_every_crate() {
 41///         s.spawn(move |_| {
 42///             proc_macro2::extra::invalidate_current_thread_spans();
 43///
 44///             let reader = BufReader::new(krate);
 45///             let tar = GzDecoder::new(reader);
 46///             let mut archive = Archive::new(tar);
 47///             for entry in archive.entries().unwrap() {
 48///                 let mut entry = entry.unwrap();
 49///                 let path = entry.path().unwrap();
 50///                 if path.extension() != Some(OsStr::new("rs")) {
 51///                     continue;
 52///                 }
 53///                 let mut content = String::new();
 54///                 entry.read_to_string(&mut content).unwrap();
 55///                 match proc_macro2::TokenStream::from_str(&content) {
 56///                     Ok(tokens) => {/* ... */},
 57///                     Err(_) => continue,
 58///                 }
 59///             }
 60///         });
 61///     }
 62/// });
 63/// #
 64/// # fn every_version_of_every_crate() -> Vec<std::fs::File> {
 65/// #     Vec::new()
 66/// # }
 67/// ```
 68///
 69/// # Panics
 70///
 71/// This function is not applicable to and will panic if called from a
 72/// procedural macro.
 73#[cfg(span_locations)]
 74#[cfg_attr(docsrs, doc(cfg(feature = "span-locations")))]
 75pub fn invalidate_current_thread_spans() {
 76    crate::imp::invalidate_current_thread_spans();
 77}
 78
 79/// An object that holds a [`Group`]'s `span_open()` and `span_close()` together
 80/// in a more compact representation than holding those 2 spans individually.
 81///
 82/// [`Group`]: crate::Group
 83#[derive(Copy, Clone)]
 84pub struct DelimSpan {
 85    inner: DelimSpanEnum,
 86    _marker: ProcMacroAutoTraits,
 87}
 88
 89#[derive(Copy, Clone)]
 90enum DelimSpanEnum {
 91    #[cfg(wrap_proc_macro)]
 92    Compiler {
 93        join: proc_macro::Span,
 94        open: proc_macro::Span,
 95        close: proc_macro::Span,
 96    },
 97    Fallback(fallback::Span),
 98}
 99
100impl DelimSpan {
101    pub(crate) fn new(group: &imp::Group) -> Self {
102        #[cfg(wrap_proc_macro)]
103        let inner = match group {
104            imp::Group::Compiler(group) => DelimSpanEnum::Compiler {
105                join: group.span(),
106                open: group.span_open(),
107                close: group.span_close(),
108            },
109            imp::Group::Fallback(group) => DelimSpanEnum::Fallback(group.span()),
110        };
111
112        #[cfg(not(wrap_proc_macro))]
113        let inner = DelimSpanEnum::Fallback(group.span());
114
115        DelimSpan {
116            inner,
117            _marker: MARKER,
118        }
119    }
120
121    /// Returns a span covering the entire delimited group.
122    pub fn join(&self) -> Span {
123        match &self.inner {
124            #[cfg(wrap_proc_macro)]
125            DelimSpanEnum::Compiler { join, .. } => Span::_new(imp::Span::Compiler(*join)),
126            DelimSpanEnum::Fallback(span) => Span::_new_fallback(*span),
127        }
128    }
129
130    /// Returns a span for the opening punctuation of the group only.
131    pub fn open(&self) -> Span {
132        match &self.inner {
133            #[cfg(wrap_proc_macro)]
134            DelimSpanEnum::Compiler { open, .. } => Span::_new(imp::Span::Compiler(*open)),
135            DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.first_byte()),
136        }
137    }
138
139    /// Returns a span for the closing punctuation of the group only.
140    pub fn close(&self) -> Span {
141        match &self.inner {
142            #[cfg(wrap_proc_macro)]
143            DelimSpanEnum::Compiler { close, .. } => Span::_new(imp::Span::Compiler(*close)),
144            DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.last_byte()),
145        }
146    }
147}
148
149impl Debug for DelimSpan {
150    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
151        Debug::fmt(&self.join(), f)
152    }
153}