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https://github.com/rust-lang/rust.git
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1dd566a6d0
Adding details, clarifying lots of little things, etc. In particular, the commit adds details of an example. I find this very helpful, because it's taken me a long time to understand how this code works.
474 lines
23 KiB
Rust
474 lines
23 KiB
Rust
use super::{Capturing, FlatToken, ForceCollect, Parser, ReplaceRange, TokenCursor};
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use rustc_ast::token::{Delimiter, Token, TokenKind};
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use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree, AttrsTarget, DelimSpacing};
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use rustc_ast::tokenstream::{DelimSpan, LazyAttrTokenStream, Spacing, ToAttrTokenStream};
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use rustc_ast::{self as ast};
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use rustc_ast::{AttrVec, Attribute, HasAttrs, HasTokens};
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use rustc_errors::PResult;
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use rustc_session::parse::ParseSess;
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use rustc_span::{sym, Span, DUMMY_SP};
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use std::{iter, mem};
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/// A wrapper type to ensure that the parser handles outer attributes correctly.
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/// When we parse outer attributes, we need to ensure that we capture tokens
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/// for the attribute target. This allows us to perform cfg-expansion on
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/// a token stream before we invoke a derive proc-macro.
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///
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/// This wrapper prevents direct access to the underlying `ast::AttrVec`.
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/// Parsing code can only get access to the underlying attributes
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/// by passing an `AttrWrapper` to `collect_tokens_trailing_token`.
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/// This makes it difficult to accidentally construct an AST node
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/// (which stores an `ast::AttrVec`) without first collecting tokens.
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///
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/// This struct has its own module, to ensure that the parser code
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/// cannot directly access the `attrs` field.
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#[derive(Debug, Clone)]
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pub struct AttrWrapper {
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attrs: AttrVec,
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// The start of the outer attributes in the token cursor.
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// This allows us to create a `ReplaceRange` for the entire attribute
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// target, including outer attributes.
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start_pos: u32,
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}
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impl AttrWrapper {
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pub(super) fn new(attrs: AttrVec, start_pos: u32) -> AttrWrapper {
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AttrWrapper { attrs, start_pos }
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}
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pub fn empty() -> AttrWrapper {
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AttrWrapper { attrs: AttrVec::new(), start_pos: u32::MAX }
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}
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pub(crate) fn take_for_recovery(self, psess: &ParseSess) -> AttrVec {
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psess.dcx().span_delayed_bug(
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self.attrs.get(0).map(|attr| attr.span).unwrap_or(DUMMY_SP),
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"AttrVec is taken for recovery but no error is produced",
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);
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self.attrs
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}
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/// Prepend `self.attrs` to `attrs`.
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// FIXME: require passing an NT to prevent misuse of this method
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pub(crate) fn prepend_to_nt_inner(self, attrs: &mut AttrVec) {
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let mut self_attrs = self.attrs;
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mem::swap(attrs, &mut self_attrs);
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attrs.extend(self_attrs);
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}
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pub fn is_empty(&self) -> bool {
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self.attrs.is_empty()
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}
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pub fn is_complete(&self) -> bool {
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crate::parser::attr::is_complete(&self.attrs)
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}
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}
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/// Returns `true` if `attrs` contains a `cfg` or `cfg_attr` attribute
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fn has_cfg_or_cfg_attr(attrs: &[Attribute]) -> bool {
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// NOTE: Builtin attributes like `cfg` and `cfg_attr` cannot be renamed via imports.
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// Therefore, the absence of a literal `cfg` or `cfg_attr` guarantees that
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// we don't need to do any eager expansion.
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attrs.iter().any(|attr| {
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attr.ident().is_some_and(|ident| ident.name == sym::cfg || ident.name == sym::cfg_attr)
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})
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}
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// From a value of this type we can reconstruct the `TokenStream` seen by the
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// `f` callback passed to a call to `Parser::collect_tokens_trailing_token`, by
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// replaying the getting of the tokens. This saves us producing a `TokenStream`
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// if it is never needed, e.g. a captured `macro_rules!` argument that is never
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// passed to a proc macro. In practice, token stream creation happens rarely
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// compared to calls to `collect_tokens` (see some statistics in #78736) so we
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// are doing as little up-front work as possible.
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//
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// This also makes `Parser` very cheap to clone, since
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// there is no intermediate collection buffer to clone.
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struct LazyAttrTokenStreamImpl {
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start_token: (Token, Spacing),
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cursor_snapshot: TokenCursor,
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num_calls: u32,
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break_last_token: bool,
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replace_ranges: Box<[ReplaceRange]>,
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}
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impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
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fn to_attr_token_stream(&self) -> AttrTokenStream {
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// The token produced by the final call to `{,inlined_}next` was not
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// actually consumed by the callback. The combination of chaining the
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// initial token and using `take` produces the desired result - we
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// produce an empty `TokenStream` if no calls were made, and omit the
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// final token otherwise.
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let mut cursor_snapshot = self.cursor_snapshot.clone();
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let tokens = iter::once(FlatToken::Token(self.start_token.clone()))
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.chain(iter::repeat_with(|| FlatToken::Token(cursor_snapshot.next())))
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.take(self.num_calls as usize);
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if self.replace_ranges.is_empty() {
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make_attr_token_stream(tokens, self.break_last_token)
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} else {
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let mut tokens: Vec<_> = tokens.collect();
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let mut replace_ranges = self.replace_ranges.to_vec();
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replace_ranges.sort_by_key(|(range, _)| range.start);
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#[cfg(debug_assertions)]
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{
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for [(range, tokens), (next_range, next_tokens)] in replace_ranges.array_windows() {
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assert!(
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range.end <= next_range.start || range.end >= next_range.end,
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"Replace ranges should either be disjoint or nested: ({:?}, {:?}) ({:?}, {:?})",
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range,
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tokens,
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next_range,
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next_tokens,
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);
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}
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}
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// Process the replace ranges, starting from the highest start
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// position and working our way back. If have tokens like:
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//
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// `#[cfg(FALSE)] struct Foo { #[cfg(FALSE)] field: bool }`
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//
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// Then we will generate replace ranges for both
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// the `#[cfg(FALSE)] field: bool` and the entire
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// `#[cfg(FALSE)] struct Foo { #[cfg(FALSE)] field: bool }`
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//
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// By starting processing from the replace range with the greatest
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// start position, we ensure that any replace range which encloses
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// another replace range will capture the *replaced* tokens for the inner
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// range, not the original tokens.
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for (range, target) in replace_ranges.into_iter().rev() {
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assert!(!range.is_empty(), "Cannot replace an empty range: {range:?}");
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// Replace the tokens in range with zero or one `FlatToken::AttrsTarget`s, plus
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// enough `FlatToken::Empty`s to fill up the rest of the range. This keeps the
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// total length of `tokens` constant throughout the replacement process, allowing
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// us to use all of the `ReplaceRanges` entries without adjusting indices.
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let target_len = target.is_some() as usize;
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tokens.splice(
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(range.start as usize)..(range.end as usize),
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target
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.into_iter()
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.map(|target| FlatToken::AttrsTarget(target))
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.chain(iter::repeat(FlatToken::Empty).take(range.len() - target_len)),
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);
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}
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make_attr_token_stream(tokens.into_iter(), self.break_last_token)
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}
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}
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}
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impl<'a> Parser<'a> {
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/// Parses code with `f`. If appropriate, it records the tokens (in
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/// `LazyAttrTokenStream` form) that were parsed in the result, accessible
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/// via the `HasTokens` trait. The second (bool) part of the callback's
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/// result indicates if an extra token should be captured, e.g. a comma or
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/// semicolon.
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///
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/// The `attrs` passed in are in `AttrWrapper` form, which is opaque. The
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/// `AttrVec` within is passed to `f`. See the comment on `AttrWrapper` for
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/// details.
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///
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/// Note: If your callback consumes an opening delimiter (including the
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/// case where `self.token` is an opening delimiter on entry to this
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/// function), you must also consume the corresponding closing delimiter.
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/// E.g. you can consume `something ([{ }])` or `([{}])`, but not `([{}]`.
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/// This restriction isn't a problem in practice, because parsed AST items
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/// always have matching delimiters.
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///
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/// The following example code will be used to explain things in comments
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/// below. It has an outer attribute and an inner attribute. Parsing it
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/// involves two calls to this method, one of which is indirectly
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/// recursive.
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/// ```ignore (fake attributes)
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/// #[cfg_eval] // token pos
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/// mod m { // 0.. 3
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/// #[cfg_attr(cond1, attr1)] // 3..12
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/// fn g() { // 12..17
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/// #![cfg_attr(cond2, attr2)] // 17..27
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/// let _x = 3; // 27..32
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/// } // 32..33
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/// } // 33..34
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/// ```
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pub fn collect_tokens_trailing_token<R: HasAttrs + HasTokens>(
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&mut self,
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attrs: AttrWrapper,
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force_collect: ForceCollect,
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f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, (R, bool)>,
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) -> PResult<'a, R> {
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// Skip collection when nothing could observe the collected tokens, i.e.
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// all of the following conditions hold.
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// - We are not force collecting tokens (because force collection
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// requires tokens by definition).
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if matches!(force_collect, ForceCollect::No)
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// - None of our outer attributes require tokens.
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&& attrs.is_complete()
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// - Our target doesn't support custom inner attributes (custom
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// inner attribute invocation might require token capturing).
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&& !R::SUPPORTS_CUSTOM_INNER_ATTRS
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// - We are not in `capture_cfg` mode (which requires tokens if
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// the parsed node has `#[cfg]` or `#[cfg_attr]` attributes).
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&& !self.capture_cfg
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{
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return Ok(f(self, attrs.attrs)?.0);
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}
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let start_token = (self.token.clone(), self.token_spacing);
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let cursor_snapshot = self.token_cursor.clone();
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let start_pos = self.num_bump_calls;
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let has_outer_attrs = !attrs.attrs.is_empty();
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let replace_ranges_start = self.capture_state.replace_ranges.len();
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// We set and restore `Capturing::Yes` on either side of the call to
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// `f`, so we can distinguish the outermost call to
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// `collect_tokens_trailing_token` (e.g. parsing `m` in the example
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// above) from any inner (indirectly recursive) calls (e.g. parsing `g`
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// in the example above). This distinction is used below and in
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// `Parser::parse_inner_attributes`.
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let (mut ret, capture_trailing) = {
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let prev_capturing = mem::replace(&mut self.capture_state.capturing, Capturing::Yes);
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let ret_and_trailing = f(self, attrs.attrs);
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self.capture_state.capturing = prev_capturing;
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ret_and_trailing?
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};
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// When we're not in `capture_cfg` mode, then skip collecting and
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// return early if either of the following conditions hold.
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// - `None`: Our target doesn't support tokens at all (e.g. `NtIdent`).
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// - `Some(Some(_))`: Our target already has tokens set (e.g. we've
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// parsed something like `#[my_attr] $item`). The actual parsing code
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// takes care of prepending any attributes to the nonterminal, so we
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// don't need to modify the already captured tokens.
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//
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// Note that this check is independent of `force_collect`. There's no
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// need to collect tokens when we don't support tokens or already have
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// tokens.
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if !self.capture_cfg && matches!(ret.tokens_mut(), None | Some(Some(_))) {
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return Ok(ret);
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}
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// This is similar to the "skip collection" check at the start of this
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// function, but now that we've parsed an AST node we have more
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// information available. (If we return early here that means the
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// setup, such as cloning the token cursor, was unnecessary. That's
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// hard to avoid.)
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//
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// Skip collection when nothing could observe the collected tokens, i.e.
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// all of the following conditions hold.
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// - We are not force collecting tokens.
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if matches!(force_collect, ForceCollect::No)
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// - None of our outer *or* inner attributes require tokens.
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// (`attrs` was just outer attributes, but `ret.attrs()` is outer
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// and inner attributes. That makes this check more precise than
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// `attrs.is_complete()` at the start of the function, and we can
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// skip the subsequent check on `R::SUPPORTS_CUSTOM_INNER_ATTRS`.
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&& crate::parser::attr::is_complete(ret.attrs())
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// - We are not in `capture_cfg` mode, or we are but there are no
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// `#[cfg]` or `#[cfg_attr]` attributes. (During normal
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// non-`capture_cfg` parsing, we don't need any special capturing
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// for those attributes, because they're builtin.)
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&& (!self.capture_cfg || !has_cfg_or_cfg_attr(ret.attrs()))
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{
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return Ok(ret);
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}
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let replace_ranges_end = self.capture_state.replace_ranges.len();
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assert!(
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!(self.break_last_token && capture_trailing),
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"Cannot set break_last_token and have trailing token"
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);
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let end_pos = self.num_bump_calls
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+ capture_trailing as u32
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// If we 'broke' the last token (e.g. breaking a '>>' token to two '>' tokens), then
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// extend the range of captured tokens to include it, since the parser was not actually
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// bumped past it. When the `LazyAttrTokenStream` gets converted into an
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// `AttrTokenStream`, we will create the proper token.
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+ self.break_last_token as u32;
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let num_calls = end_pos - start_pos;
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// Take the captured ranges for any inner attributes that we parsed in
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// `Parser::parse_inner_attributes`, and pair them in a `ReplaceRange`
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// with `None`, which means the relevant tokens will be removed. (More
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// details below.)
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let mut inner_attr_replace_ranges = Vec::new();
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for inner_attr in ret.attrs().iter().filter(|a| a.style == ast::AttrStyle::Inner) {
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if let Some(attr_range) = self.capture_state.inner_attr_ranges.remove(&inner_attr.id) {
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inner_attr_replace_ranges.push((attr_range, None));
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} else {
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self.dcx().span_delayed_bug(inner_attr.span, "Missing token range for attribute");
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}
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}
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// This is hot enough for `deep-vector` that checking the conditions for an empty iterator
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// is measurably faster than actually executing the iterator.
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let replace_ranges: Box<[ReplaceRange]> =
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if replace_ranges_start == replace_ranges_end && inner_attr_replace_ranges.is_empty() {
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Box::new([])
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} else {
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// Grab any replace ranges that occur *inside* the current AST node. We will
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// perform the actual replacement only when we convert the `LazyAttrTokenStream` to
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// an `AttrTokenStream`.
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self.capture_state.replace_ranges[replace_ranges_start..replace_ranges_end]
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.iter()
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.cloned()
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.chain(inner_attr_replace_ranges.iter().cloned())
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.map(|(range, data)| ((range.start - start_pos)..(range.end - start_pos), data))
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.collect()
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};
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// What is the status here when parsing the example code at the top of this method?
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//
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// When parsing `g`:
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// - `start_pos..end_pos` is `12..33` (`fn g { ... }`, excluding the outer attr).
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// - `inner_attr_replace_ranges` has one entry (`5..15`, when counting from `fn`), to
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// delete the inner attr's tokens.
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// - This entry is put into the lazy tokens for `g`, i.e. deleting the inner attr from
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// those tokens (if they get evaluated).
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// - Those lazy tokens are also put into an `AttrsTarget` that is appended to `self`'s
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// replace ranges at the bottom of this function, for processing when parsing `m`.
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// - `replace_ranges_start..replace_ranges_end` is empty.
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//
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// When parsing `m`:
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// - `start_pos..end_pos` is `0..34` (`mod m`, excluding the `#[cfg_eval]` attribute).
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// - `inner_attr_replace_ranges` is empty.
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// - `replace_range_start..replace_ranges_end` has two entries.
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// - One to delete the inner attribute (`17..27`), obtained when parsing `g` (see above).
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// - One `AttrsTarget` (added below when parsing `g`) to replace all of `g` (`3..33`,
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// including its outer attribute), with:
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// - `attrs`: includes the outer and the inner attr.
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// - `tokens`: lazy tokens for `g` (with its inner attr deleted).
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let tokens = LazyAttrTokenStream::new(LazyAttrTokenStreamImpl {
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start_token,
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num_calls,
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cursor_snapshot,
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break_last_token: self.break_last_token,
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replace_ranges,
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});
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// If we support tokens and don't already have them, store the newly captured tokens.
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if let Some(target_tokens @ None) = ret.tokens_mut() {
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*target_tokens = Some(tokens.clone());
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}
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// If `capture_cfg` is set and we're inside a recursive call to
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// `collect_tokens_trailing_token`, then we need to register a replace range
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// if we have `#[cfg]` or `#[cfg_attr]`. This allows us to run eager cfg-expansion
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// on the captured token stream.
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if self.capture_cfg
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&& matches!(self.capture_state.capturing, Capturing::Yes)
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&& has_cfg_or_cfg_attr(ret.attrs())
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{
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assert!(!self.break_last_token, "Should not have unglued last token with cfg attr");
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// What is the status here when parsing the example code at the top of this method?
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//
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// When parsing `g`, we add two entries:
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// - The `start_pos..end_pos` (`3..33`) entry has a new `AttrsTarget` with:
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// - `attrs`: includes the outer and the inner attr.
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// - `tokens`: lazy tokens for `g` (with its inner attr deleted).
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// - `inner_attr_replace_ranges` contains the one entry to delete the inner attr's
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// tokens (`17..27`).
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//
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// When parsing `m`, we do nothing here.
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// Set things up so that the entire AST node that we just parsed, including attributes,
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// will be replaced with `target` in the lazy token stream. This will allow us to
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// cfg-expand this AST node.
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let start_pos = if has_outer_attrs { attrs.start_pos } else { start_pos };
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let target = AttrsTarget { attrs: ret.attrs().iter().cloned().collect(), tokens };
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self.capture_state.replace_ranges.push((start_pos..end_pos, Some(target)));
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self.capture_state.replace_ranges.extend(inner_attr_replace_ranges);
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} else if matches!(self.capture_state.capturing, Capturing::No) {
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// Only clear the ranges once we've finished capturing entirely, i.e. we've finished
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// the outermost call to this method.
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self.capture_state.replace_ranges.clear();
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self.capture_state.inner_attr_ranges.clear();
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}
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Ok(ret)
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}
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}
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/// Converts a flattened iterator of tokens (including open and close delimiter tokens) into an
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/// `AttrTokenStream`, creating an `AttrTokenTree::Delimited` for each matching pair of open and
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/// close delims.
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fn make_attr_token_stream(
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iter: impl Iterator<Item = FlatToken>,
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break_last_token: bool,
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) -> AttrTokenStream {
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#[derive(Debug)]
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struct FrameData {
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// This is `None` for the first frame, `Some` for all others.
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open_delim_sp: Option<(Delimiter, Span, Spacing)>,
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inner: Vec<AttrTokenTree>,
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}
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// The stack always has at least one element. Storing it separately makes for shorter code.
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let mut stack_top = FrameData { open_delim_sp: None, inner: vec![] };
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let mut stack_rest = vec![];
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for flat_token in iter {
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match flat_token {
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|
FlatToken::Token((Token { kind: TokenKind::OpenDelim(delim), span }, spacing)) => {
|
|
stack_rest.push(mem::replace(
|
|
&mut stack_top,
|
|
FrameData { open_delim_sp: Some((delim, span, spacing)), inner: vec![] },
|
|
));
|
|
}
|
|
FlatToken::Token((Token { kind: TokenKind::CloseDelim(delim), span }, spacing)) => {
|
|
let frame_data = mem::replace(&mut stack_top, stack_rest.pop().unwrap());
|
|
let (open_delim, open_sp, open_spacing) = frame_data.open_delim_sp.unwrap();
|
|
assert_eq!(
|
|
open_delim, delim,
|
|
"Mismatched open/close delims: open={open_delim:?} close={span:?}"
|
|
);
|
|
let dspan = DelimSpan::from_pair(open_sp, span);
|
|
let dspacing = DelimSpacing::new(open_spacing, spacing);
|
|
let stream = AttrTokenStream::new(frame_data.inner);
|
|
let delimited = AttrTokenTree::Delimited(dspan, dspacing, delim, stream);
|
|
stack_top.inner.push(delimited);
|
|
}
|
|
FlatToken::Token((token, spacing)) => {
|
|
stack_top.inner.push(AttrTokenTree::Token(token, spacing))
|
|
}
|
|
FlatToken::AttrsTarget(target) => {
|
|
stack_top.inner.push(AttrTokenTree::AttrsTarget(target))
|
|
}
|
|
FlatToken::Empty => {}
|
|
}
|
|
}
|
|
|
|
if break_last_token {
|
|
let last_token = stack_top.inner.pop().unwrap();
|
|
if let AttrTokenTree::Token(last_token, spacing) = last_token {
|
|
let unglued_first = last_token.kind.break_two_token_op().unwrap().0;
|
|
|
|
// An 'unglued' token is always two ASCII characters
|
|
let mut first_span = last_token.span.shrink_to_lo();
|
|
first_span = first_span.with_hi(first_span.lo() + rustc_span::BytePos(1));
|
|
|
|
stack_top
|
|
.inner
|
|
.push(AttrTokenTree::Token(Token::new(unglued_first, first_span), spacing));
|
|
} else {
|
|
panic!("Unexpected last token {last_token:?}")
|
|
}
|
|
}
|
|
AttrTokenStream::new(stack_top.inner)
|
|
}
|
|
|
|
// Some types are used a lot. Make sure they don't unintentionally get bigger.
|
|
#[cfg(target_pointer_width = "64")]
|
|
mod size_asserts {
|
|
use super::*;
|
|
use rustc_data_structures::static_assert_size;
|
|
// tidy-alphabetical-start
|
|
static_assert_size!(AttrWrapper, 16);
|
|
static_assert_size!(LazyAttrTokenStreamImpl, 96);
|
|
// tidy-alphabetical-end
|
|
}
|