proc_macro2/
extra.rs

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

proc_macro2/
extra.rs
