399 lines
14 KiB
Rust
399 lines
14 KiB
Rust
//! A stably addressed token buffer supporting efficient traversal based on a
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//! cheaply copyable cursor.
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//!
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//! *This module is available only if Syn is built with the `"parsing"` feature.*
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// This module is heavily commented as it contains most of the unsafe code in
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// Syn, and caution should be used when editing it. The public-facing interface
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// is 100% safe but the implementation is fragile internally.
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#[cfg(all(
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not(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "wasi"))),
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feature = "proc-macro"
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))]
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use crate::proc_macro as pm;
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use crate::Lifetime;
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use proc_macro2::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
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use std::cmp::Ordering;
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use std::marker::PhantomData;
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/// Internal type which is used instead of `TokenTree` to represent a token tree
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/// within a `TokenBuffer`.
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enum Entry {
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// Mimicking types from proc-macro.
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// Group entries contain the offset to the matching End entry.
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Group(Group, usize),
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Ident(Ident),
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Punct(Punct),
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Literal(Literal),
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// End entries contain the offset (negative) to the start of the buffer.
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End(isize),
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}
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/// A buffer that can be efficiently traversed multiple times, unlike
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/// `TokenStream` which requires a deep copy in order to traverse more than
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/// once.
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///
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/// *This type is available only if Syn is built with the `"parsing"` feature.*
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pub struct TokenBuffer {
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// NOTE: Do not implement clone on this - while the current design could be
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// cloned, other designs which could be desirable may not be cloneable.
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entries: Box<[Entry]>,
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}
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impl TokenBuffer {
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fn recursive_new(entries: &mut Vec<Entry>, stream: TokenStream) {
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for tt in stream {
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match tt {
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TokenTree::Ident(ident) => entries.push(Entry::Ident(ident)),
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TokenTree::Punct(punct) => entries.push(Entry::Punct(punct)),
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TokenTree::Literal(literal) => entries.push(Entry::Literal(literal)),
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TokenTree::Group(group) => {
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let group_start_index = entries.len();
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entries.push(Entry::End(0)); // we replace this below
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Self::recursive_new(entries, group.stream());
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let group_end_index = entries.len();
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entries.push(Entry::End(-(group_end_index as isize)));
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let group_end_offset = group_end_index - group_start_index;
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entries[group_start_index] = Entry::Group(group, group_end_offset);
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}
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}
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}
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}
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/// Creates a `TokenBuffer` containing all the tokens from the input
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/// `proc_macro::TokenStream`.
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///
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/// *This method is available only if Syn is built with both the `"parsing"` and
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/// `"proc-macro"` features.*
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#[cfg(all(
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not(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "wasi"))),
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feature = "proc-macro"
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))]
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pub fn new(stream: pm::TokenStream) -> Self {
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Self::new2(stream.into())
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}
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/// Creates a `TokenBuffer` containing all the tokens from the input
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/// `proc_macro2::TokenStream`.
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pub fn new2(stream: TokenStream) -> Self {
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let mut entries = Vec::new();
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Self::recursive_new(&mut entries, stream);
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entries.push(Entry::End(-(entries.len() as isize)));
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Self {
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entries: entries.into_boxed_slice(),
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}
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}
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/// Creates a cursor referencing the first token in the buffer and able to
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/// traverse until the end of the buffer.
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pub fn begin(&self) -> Cursor {
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let ptr = self.entries.as_ptr();
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unsafe { Cursor::create(ptr, ptr.add(self.entries.len() - 1)) }
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}
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}
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/// A cheaply copyable cursor into a `TokenBuffer`.
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///
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/// This cursor holds a shared reference into the immutable data which is used
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/// internally to represent a `TokenStream`, and can be efficiently manipulated
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/// and copied around.
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///
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/// An empty `Cursor` can be created directly, or one may create a `TokenBuffer`
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/// object and get a cursor to its first token with `begin()`.
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///
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/// Two cursors are equal if they have the same location in the same input
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/// stream, and have the same scope.
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///
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/// *This type is available only if Syn is built with the `"parsing"` feature.*
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pub struct Cursor<'a> {
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// The current entry which the `Cursor` is pointing at.
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ptr: *const Entry,
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// This is the only `Entry::End` object which this cursor is allowed to
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// point at. All other `End` objects are skipped over in `Cursor::create`.
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scope: *const Entry,
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// Cursor is covariant in 'a. This field ensures that our pointers are still
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// valid.
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marker: PhantomData<&'a Entry>,
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}
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impl<'a> Cursor<'a> {
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/// Creates a cursor referencing a static empty TokenStream.
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pub fn empty() -> Self {
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// It's safe in this situation for us to put an `Entry` object in global
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// storage, despite it not actually being safe to send across threads
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// (`Ident` is a reference into a thread-local table). This is because
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// this entry never includes a `Ident` object.
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//
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// This wrapper struct allows us to break the rules and put a `Sync`
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// object in global storage.
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struct UnsafeSyncEntry(Entry);
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unsafe impl Sync for UnsafeSyncEntry {}
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static EMPTY_ENTRY: UnsafeSyncEntry = UnsafeSyncEntry(Entry::End(0));
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Cursor {
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ptr: &EMPTY_ENTRY.0,
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scope: &EMPTY_ENTRY.0,
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marker: PhantomData,
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}
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}
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/// This create method intelligently exits non-explicitly-entered
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/// `None`-delimited scopes when the cursor reaches the end of them,
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/// allowing for them to be treated transparently.
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unsafe fn create(mut ptr: *const Entry, scope: *const Entry) -> Self {
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// NOTE: If we're looking at a `End`, we want to advance the cursor
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// past it, unless `ptr == scope`, which means that we're at the edge of
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// our cursor's scope. We should only have `ptr != scope` at the exit
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// from None-delimited groups entered with `ignore_none`.
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while let Entry::End(_) = *ptr {
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if ptr == scope {
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break;
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}
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ptr = ptr.add(1);
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}
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Cursor {
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ptr,
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scope,
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marker: PhantomData,
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}
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}
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/// Get the current entry.
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fn entry(self) -> &'a Entry {
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unsafe { &*self.ptr }
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}
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/// Bump the cursor to point at the next token after the current one. This
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/// is undefined behavior if the cursor is currently looking at an
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/// `Entry::End`.
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///
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/// If the cursor is looking at an `Entry::Group`, the bumped cursor will
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/// point at the first token in the group (with the same scope end).
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unsafe fn bump_ignore_group(self) -> Cursor<'a> {
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Cursor::create(self.ptr.offset(1), self.scope)
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}
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/// While the cursor is looking at a `None`-delimited group, move it to look
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/// at the first token inside instead. If the group is empty, this will move
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/// the cursor past the `None`-delimited group.
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///
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/// WARNING: This mutates its argument.
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fn ignore_none(&mut self) {
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while let Entry::Group(group, _) = self.entry() {
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if group.delimiter() == Delimiter::None {
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unsafe { *self = self.bump_ignore_group() };
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} else {
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break;
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}
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}
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}
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/// Checks whether the cursor is currently pointing at the end of its valid
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/// scope.
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pub fn eof(self) -> bool {
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// We're at eof if we're at the end of our scope.
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self.ptr == self.scope
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}
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/// If the cursor is pointing at a `Group` with the given delimiter, returns
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/// a cursor into that group and one pointing to the next `TokenTree`.
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pub fn group(mut self, delim: Delimiter) -> Option<(Cursor<'a>, Span, Cursor<'a>)> {
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// If we're not trying to enter a none-delimited group, we want to
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// ignore them. We have to make sure to _not_ ignore them when we want
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// to enter them, of course. For obvious reasons.
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if delim != Delimiter::None {
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self.ignore_none();
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}
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if let Entry::Group(group, end_offset) = self.entry() {
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if group.delimiter() == delim {
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let end_of_group = unsafe { self.ptr.add(*end_offset) };
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let inside_of_group = unsafe { Cursor::create(self.ptr.add(1), end_of_group) };
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let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
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return Some((inside_of_group, group.span(), after_group));
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}
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}
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None
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}
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/// If the cursor is pointing at a `Ident`, returns it along with a cursor
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/// pointing at the next `TokenTree`.
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pub fn ident(mut self) -> Option<(Ident, Cursor<'a>)> {
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self.ignore_none();
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match self.entry() {
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Entry::Ident(ident) => Some((ident.clone(), unsafe { self.bump_ignore_group() })),
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_ => None,
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}
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}
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/// If the cursor is pointing at a `Punct`, returns it along with a cursor
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/// pointing at the next `TokenTree`.
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pub fn punct(mut self) -> Option<(Punct, Cursor<'a>)> {
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self.ignore_none();
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match self.entry() {
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Entry::Punct(punct) if punct.as_char() != '\'' => {
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Some((punct.clone(), unsafe { self.bump_ignore_group() }))
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}
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_ => None,
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}
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}
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/// If the cursor is pointing at a `Literal`, return it along with a cursor
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/// pointing at the next `TokenTree`.
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pub fn literal(mut self) -> Option<(Literal, Cursor<'a>)> {
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self.ignore_none();
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match self.entry() {
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Entry::Literal(literal) => Some((literal.clone(), unsafe { self.bump_ignore_group() })),
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_ => None,
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}
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}
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/// If the cursor is pointing at a `Lifetime`, returns it along with a
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/// cursor pointing at the next `TokenTree`.
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pub fn lifetime(mut self) -> Option<(Lifetime, Cursor<'a>)> {
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self.ignore_none();
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match self.entry() {
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Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
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let next = unsafe { self.bump_ignore_group() };
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let (ident, rest) = next.ident()?;
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let lifetime = Lifetime {
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apostrophe: punct.span(),
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ident,
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};
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Some((lifetime, rest))
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}
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_ => None,
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}
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}
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/// Copies all remaining tokens visible from this cursor into a
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/// `TokenStream`.
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pub fn token_stream(self) -> TokenStream {
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let mut tts = Vec::new();
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let mut cursor = self;
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while let Some((tt, rest)) = cursor.token_tree() {
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tts.push(tt);
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cursor = rest;
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}
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tts.into_iter().collect()
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}
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/// If the cursor is pointing at a `TokenTree`, returns it along with a
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/// cursor pointing at the next `TokenTree`.
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///
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/// Returns `None` if the cursor has reached the end of its stream.
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///
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/// This method does not treat `None`-delimited groups as transparent, and
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/// will return a `Group(None, ..)` if the cursor is looking at one.
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pub fn token_tree(self) -> Option<(TokenTree, Cursor<'a>)> {
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let (tree, len) = match self.entry() {
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Entry::Group(group, end_offset) => (group.clone().into(), *end_offset),
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Entry::Literal(literal) => (literal.clone().into(), 1),
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Entry::Ident(ident) => (ident.clone().into(), 1),
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Entry::Punct(punct) => (punct.clone().into(), 1),
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Entry::End(_) => return None,
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};
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let rest = unsafe { Cursor::create(self.ptr.add(len), self.scope) };
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Some((tree, rest))
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}
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/// Returns the `Span` of the current token, or `Span::call_site()` if this
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/// cursor points to eof.
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pub fn span(self) -> Span {
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match self.entry() {
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Entry::Group(group, _) => group.span(),
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Entry::Literal(literal) => literal.span(),
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Entry::Ident(ident) => ident.span(),
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Entry::Punct(punct) => punct.span(),
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Entry::End(_) => Span::call_site(),
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}
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}
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/// Skip over the next token without cloning it. Returns `None` if this
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/// cursor points to eof.
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///
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/// This method treats `'lifetimes` as a single token.
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pub(crate) fn skip(self) -> Option<Cursor<'a>> {
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let len = match self.entry() {
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Entry::End(_) => return None,
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// Treat lifetimes as a single tt for the purposes of 'skip'.
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Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
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match unsafe { &*self.ptr.add(1) } {
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Entry::Ident(_) => 2,
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_ => 1,
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}
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}
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Entry::Group(_, end_offset) => *end_offset,
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_ => 1,
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};
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Some(unsafe { Cursor::create(self.ptr.add(len), self.scope) })
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}
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}
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impl<'a> Copy for Cursor<'a> {}
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impl<'a> Clone for Cursor<'a> {
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fn clone(&self) -> Self {
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*self
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}
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}
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impl<'a> Eq for Cursor<'a> {}
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impl<'a> PartialEq for Cursor<'a> {
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fn eq(&self, other: &Self) -> bool {
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self.ptr == other.ptr
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}
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}
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impl<'a> PartialOrd for Cursor<'a> {
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fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
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if same_buffer(*self, *other) {
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Some(self.ptr.cmp(&other.ptr))
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} else {
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None
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}
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}
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}
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pub(crate) fn same_scope(a: Cursor, b: Cursor) -> bool {
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a.scope == b.scope
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}
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pub(crate) fn same_buffer(a: Cursor, b: Cursor) -> bool {
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unsafe {
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match (&*a.scope, &*b.scope) {
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(Entry::End(a_offset), Entry::End(b_offset)) => {
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a.scope.offset(*a_offset) == b.scope.offset(*b_offset)
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}
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_ => unreachable!(),
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}
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}
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}
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#[cfg(any(feature = "full", feature = "derive"))]
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pub(crate) fn cmp_assuming_same_buffer(a: Cursor, b: Cursor) -> Ordering {
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a.ptr.cmp(&b.ptr)
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}
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pub(crate) fn open_span_of_group(cursor: Cursor) -> Span {
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match cursor.entry() {
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Entry::Group(group, _) => group.span_open(),
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_ => cursor.span(),
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}
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}
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pub(crate) fn close_span_of_group(cursor: Cursor) -> Span {
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match cursor.entry() {
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Entry::Group(group, _) => group.span_close(),
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_ => cursor.span(),
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}
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}
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