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