//! Items which do not have a correspondence to any API in the proc_macro crate,

//! but are necessary to include in proc-macro2.

use crate::fallback;

use crate::imp;

use crate::marker::{ProcMacroAutoTraits, MARKER};

use crate::Span;

use core::fmt::{self, Debug};

/// Invalidate any `proc_macro2::Span` that exist on the current thread.

///

/// The implementation of `Span` uses thread-local data structures and this

/// function clears them. Calling any method on a `Span` on the current thread

/// created prior to the invalidation will return incorrect values or crash.

///

/// This function is useful for programs that process more than 2<sup>32</sup>

/// bytes of Rust source code on the same thread. Just like rustc, proc-macro2

/// uses 32-bit source locations, and these wrap around when the total source

/// code processed by the same thread exceeds 2<sup>32</sup> bytes (4

/// gigabytes). After a wraparound, `Span` methods such as `source_text()` can

/// return wrong data.

///

/// # Example

///

/// As of late 2023, there is 200 GB of Rust code published on crates.io.

/// Looking at just the newest version of every crate, it is 16 GB of code. So a

/// workload that involves parsing it all would overflow a 32-bit source

/// location unless spans are being invalidated.

///

/// ```

/// use flate2::read::GzDecoder;

/// use std::ffi::OsStr;

/// use std::io::{BufReader, Read};

/// use std::str::FromStr;

/// use tar::Archive;

///

/// rayon::scope(|s| {

///     for krate in every_version_of_every_crate() {

///         s.spawn(move |_| {

///             proc_macro2::extra::invalidate_current_thread_spans();

///

///             let reader = BufReader::new(krate);

///             let tar = GzDecoder::new(reader);

///             let mut archive = Archive::new(tar);

///             for entry in archive.entries().unwrap() {

///                 let mut entry = entry.unwrap();

///                 let path = entry.path().unwrap();

///                 if path.extension() != Some(OsStr::new("rs")) {

///                     continue;

///                 }

///                 let mut content = String::new();

///                 entry.read_to_string(&mut content).unwrap();

///                 match proc_macro2::TokenStream::from_str(&content) {

///                     Ok(tokens) => {/* ... */},

///                     Err(_) => continue,

///                 }

///             }

///         });

///     }

/// });

/// #

/// # fn every_version_of_every_crate() -> Vec<std::fs::File> {

/// #     Vec::new()

/// # }

/// ```

///

/// # Panics

///

/// This function is not applicable to and will panic if called from a

/// procedural macro.

#[cfg(span_locations)]

#[cfg_attr(docsrs, doc(cfg(feature = "span-locations")))]

pub fn invalidate_current_thread_spans() {

    crate::imp::invalidate_current_thread_spans();

}

/// An object that holds a [`Group`]'s `span_open()` and `span_close()` together

/// in a more compact representation than holding those 2 spans individually.

///

/// [`Group`]: crate::Group

#[derive(Copy, Clone)]

pub struct DelimSpan {

    inner: DelimSpanEnum,

    _marker: ProcMacroAutoTraits,

}

#[derive(Copy, Clone)]

enum DelimSpanEnum {

    #[cfg(wrap_proc_macro)]

    Compiler {

        join: proc_macro::Span,

        open: proc_macro::Span,

        close: proc_macro::Span,

    },

    Fallback(fallback::Span),

}

impl DelimSpan {

    pub(crate) fn new(group: &imp::Group) -> Self {

        #[cfg(wrap_proc_macro)]

        let inner = match group {

            imp::Group::Compiler(group) => DelimSpanEnum::Compiler {

                join: group.span(),

                open: group.span_open(),

                close: group.span_close(),

            },

            imp::Group::Fallback(group) => DelimSpanEnum::Fallback(group.span()),

        };

        #[cfg(not(wrap_proc_macro))]

        let inner = DelimSpanEnum::Fallback(group.span());

        DelimSpan {

            inner,

            _marker: MARKER,

        }

    }

    /// Returns a span covering the entire delimited group.

    pub fn join(&self) -> Span {

        match &self.inner {

            #[cfg(wrap_proc_macro)]

            DelimSpanEnum::Compiler { join, .. } => Span::_new(imp::Span::Compiler(*join)),

            DelimSpanEnum::Fallback(span) => Span::_new_fallback(*span),

        }

    }

    /// Returns a span for the opening punctuation of the group only.

    pub fn open(&self) -> Span {

        match &self.inner {

            #[cfg(wrap_proc_macro)]

            DelimSpanEnum::Compiler { open, .. } => Span::_new(imp::Span::Compiler(*open)),

            DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.first_byte()),

        }

    }

    /// Returns a span for the closing punctuation of the group only.

    pub fn close(&self) -> Span {

        match &self.inner {

            #[cfg(wrap_proc_macro)]

            DelimSpanEnum::Compiler { close, .. } => Span::_new(imp::Span::Compiler(*close)),

            DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.last_byte()),

        }

    }

}

impl Debug for DelimSpan {

    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

        Debug::fmt(&self.join(), f)

    }

}