1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
use super::{Capturing, FlatToken, ForceCollect, Parser, ReplaceRange, TokenCursor, TrailingToken};
use rustc_ast::token::{self, Delimiter, Token, TokenKind};
use rustc_ast::tokenstream::{AttrTokenStream, AttributesData, ToAttrTokenStream};
use rustc_ast::tokenstream::{AttrTokenTree, DelimSpan, LazyAttrTokenStream, Spacing};
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::ops::Range;

/// 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_tokens`.
/// 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: usize,
}

impl AttrWrapper {
    pub(super) fn new(attrs: AttrVec, start_pos: usize) -> AttrWrapper {
        AttrWrapper { attrs, start_pos }
    }
    pub fn empty() -> AttrWrapper {
        AttrWrapper { attrs: AttrVec::new(), start_pos: usize::MAX }
    }

    pub(crate) fn take_for_recovery(self, sess: &ParseSess) -> AttrVec {
        sess.span_diagnostic.delay_span_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;
        std::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)
    })
}

// Produces a `TokenStream` on-demand. Using `cursor_snapshot`
// and `num_calls`, we can reconstruct the `TokenStream` seen
// by the callback. This allows us to avoid producing a `TokenStream`
// if it is never needed - for example, 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.
#[derive(Clone)]
struct LazyAttrTokenStreamImpl {
    start_token: (Token, Spacing),
    cursor_snapshot: TokenCursor,
    num_calls: usize,
    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 =
            std::iter::once((FlatToken::Token(self.start_token.0.clone()), self.start_token.1))
                .chain(std::iter::repeat_with(|| {
                    let token = cursor_snapshot.next();
                    (FlatToken::Token(token.0), token.1)
                }))
                .take(self.num_calls);

        if !self.replace_ranges.is_empty() {
            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, new_tokens) in replace_ranges.into_iter().rev() {
                assert!(!range.is_empty(), "Cannot replace an empty range: {range:?}");
                // Replace ranges are only allowed to decrease the number of tokens.
                assert!(
                    range.len() >= new_tokens.len(),
                    "Range {range:?} has greater len than {new_tokens:?}"
                );

                // Replace any removed tokens with `FlatToken::Empty`.
                // 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 filler = std::iter::repeat((FlatToken::Empty, Spacing::Alone))
                    .take(range.len() - new_tokens.len());

                tokens.splice(
                    (range.start as usize)..(range.end as usize),
                    new_tokens.into_iter().chain(filler),
                );
            }
            make_token_stream(tokens.into_iter(), self.break_last_token)
        } else {
            make_token_stream(tokens, self.break_last_token)
        }
    }
}

impl<'a> Parser<'a> {
    /// Records all tokens consumed by the provided callback,
    /// including the current token. These tokens are collected
    /// into a `LazyAttrTokenStream`, and returned along with the result
    /// of the callback.
    ///
    /// Note: If your callback consumes an opening delimiter
    /// (including the case where you call `collect_tokens`
    /// when the current token is an opening delimiter),
    /// you must also consume the corresponding closing delimiter.
    ///
    /// That is, you can consume
    /// `something ([{ }])` or `([{}])`, but not `([{}]`
    ///
    /// This restriction shouldn't be an issue in practice,
    /// since this function is used to record the tokens for
    /// a parsed AST item, which always has matching delimiters.
    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, TrailingToken)>,
    ) -> PResult<'a, R> {
        // We only bail out when nothing could possibly observe the collected tokens:
        // 1. We cannot be force collecting tokens (since force-collecting requires tokens
        //    by definition
        if matches!(force_collect, ForceCollect::No)
            // None of our outer attributes can require tokens (e.g. a proc-macro)
            && attrs.is_complete()
            // If our target supports custom inner attributes, then we cannot bail
            // out early, since we may need to capture tokens for a custom inner attribute
            // invocation.
            && !R::SUPPORTS_CUSTOM_INNER_ATTRS
            // Never bail out early in `capture_cfg` mode, since there might be `#[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 prev_capturing = std::mem::replace(&mut self.capture_state.capturing, Capturing::Yes);
        let replace_ranges_start = self.capture_state.replace_ranges.len();

        let ret = f(self, attrs.attrs);

        self.capture_state.capturing = prev_capturing;

        let (mut ret, trailing) = ret?;

        // When we're not in `capture-cfg` mode, then bail out early if:
        // 1. Our target doesn't support tokens at all (e.g we're parsing an `NtIdent`)
        //    so there's nothing for us to do.
        // 2. 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`- if we already
        // have tokens, or can't even store them, then there's never a need to
        // force collection of new tokens.
        if !self.capture_cfg && matches!(ret.tokens_mut(), None | Some(Some(_))) {
            return Ok(ret);
        }

        // This is very similar to the bail out check at the start of this function.
        // Now that we've parsed an AST node, we have more information available.
        if matches!(force_collect, ForceCollect::No)
            // We now have inner attributes available, so this check is more precise
            // than `attrs.is_complete()` at the start of the function.
            // As a result, we don't need to check `R::SUPPORTS_CUSTOM_INNER_ATTRS`
            && crate::parser::attr::is_complete(ret.attrs())
            // Subtle: We call `has_cfg_or_cfg_attr` with the attrs from `ret`.
            // This ensures that we consider inner attributes (e.g. `#![cfg]`),
            // which require us to have tokens available
            // We also call `has_cfg_or_cfg_attr` at the beginning of this function,
            // but we only bail out if there's no possibility of inner attributes
            // (!R::SUPPORTS_CUSTOM_INNER_ATTRS)
            // We only capture about `#[cfg]` or `#[cfg_attr]` in `capture_cfg`
            // mode - during normal parsing, we don't need any special capturing
            // for those attributes, since they're builtin.
            && !(self.capture_cfg && has_cfg_or_cfg_attr(ret.attrs()))
        {
            return Ok(ret);
        }

        let mut inner_attr_replace_ranges = Vec::new();
        // Take the captured ranges for any inner attributes that we parsed.
        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);
            } else {
                self.sess
                    .span_diagnostic
                    .delay_span_bug(inner_attr.span, "Missing token range for attribute");
            }
        }

        let replace_ranges_end = self.capture_state.replace_ranges.len();

        let mut end_pos = self.num_bump_calls;

        let mut captured_trailing = false;

        // Capture a trailing token if requested by the callback 'f'
        match trailing {
            TrailingToken::None => {}
            TrailingToken::Gt => {
                assert_eq!(self.token.kind, token::Gt);
            }
            TrailingToken::Semi => {
                assert_eq!(self.token.kind, token::Semi);
                end_pos += 1;
                captured_trailing = true;
            }
            TrailingToken::MaybeComma => {
                if self.token.kind == token::Comma {
                    end_pos += 1;
                    captured_trailing = true;
                }
            }
        }

        // 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.
        if self.break_last_token {
            assert!(!captured_trailing, "Cannot set break_last_token and have trailing token");
            end_pos += 1;
        }

        let num_calls = end_pos - start_pos;

        // If we have no attributes, then we will never need to
        // use any replace ranges.
        let replace_ranges: Box<[ReplaceRange]> = if ret.attrs().is_empty() && !self.capture_cfg {
            Box::new([])
        } else {
            // Grab any replace ranges that occur *inside* the current AST node.
            // We will perform the actual replacement when we convert the `LazyAttrTokenStream`
            // to an `AttrTokenStream`.
            let start_calls: u32 = start_pos.try_into().unwrap();
            self.capture_state.replace_ranges[replace_ranges_start..replace_ranges_end]
                .iter()
                .cloned()
                .chain(inner_attr_replace_ranges.iter().cloned())
                .map(|(range, tokens)| {
                    ((range.start - start_calls)..(range.end - start_calls), tokens)
                })
                .collect()
        };

        let tokens = LazyAttrTokenStream::new(LazyAttrTokenStreamImpl {
            start_token,
            num_calls,
            cursor_snapshot,
            break_last_token: self.break_last_token,
            replace_ranges,
        });

        // If we support tokens at all
        if let Some(target_tokens) = ret.tokens_mut() {
            if target_tokens.is_none() {
                // Store se our newly captured tokens into the AST node
                *target_tokens = Some(tokens.clone());
            }
        }

        let final_attrs = ret.attrs();

        // 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(final_attrs)
        {
            let attr_data = AttributesData { attrs: final_attrs.iter().cloned().collect(), tokens };

            // Replace the entire AST node that we just parsed, including attributes,
            // with a `FlatToken::AttrTarget`. If this AST node is inside an item
            // that has `#[derive]`, then this will allow us to cfg-expand this
            // AST node.
            let start_pos = if has_outer_attrs { attrs.start_pos } else { start_pos };
            let new_tokens = vec![(FlatToken::AttrTarget(attr_data), Spacing::Alone)];

            assert!(!self.break_last_token, "Should not have unglued last token with cfg attr");
            let range: Range<u32> = (start_pos.try_into().unwrap())..(end_pos.try_into().unwrap());
            self.capture_state.replace_ranges.push((range, new_tokens));
            self.capture_state.replace_ranges.extend(inner_attr_replace_ranges);
        }

        // Only clear our `replace_ranges` when we're finished capturing entirely.
        if matches!(self.capture_state.capturing, Capturing::No) {
            self.capture_state.replace_ranges.clear();
            // We don't clear `inner_attr_ranges`, as doing so repeatedly
            // had a measurable performance impact. Most inner attributes that
            // we insert will get removed - when we drop the parser, we'll free
            // up the memory used by any attributes that we didn't remove from the map.
        }
        Ok(ret)
    }
}

/// Converts a flattened iterator of tokens (including open and close delimiter tokens)
/// into a `TokenStream`, creating a `TokenTree::Delimited` for each matching pair
/// of open and close delims.
fn make_token_stream(
    mut iter: impl Iterator<Item = (FlatToken, Spacing)>,
    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)>,
        inner: Vec<AttrTokenTree>,
    }
    let mut stack = vec![FrameData { open_delim_sp: None, inner: vec![] }];
    let mut token_and_spacing = iter.next();
    while let Some((token, spacing)) = token_and_spacing {
        match token {
            FlatToken::Token(Token { kind: TokenKind::OpenDelim(delim), span }) => {
                stack.push(FrameData { open_delim_sp: Some((delim, span)), inner: vec![] });
            }
            FlatToken::Token(Token { kind: TokenKind::CloseDelim(delim), span }) => {
                let frame_data = stack
                    .pop()
                    .unwrap_or_else(|| panic!("Token stack was empty for token: {token:?}"));

                let (open_delim, open_sp) = 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 stream = AttrTokenStream::new(frame_data.inner);
                let delimited = AttrTokenTree::Delimited(dspan, delim, stream);
                stack
                    .last_mut()
                    .unwrap_or_else(|| panic!("Bottom token frame is missing for token: {token:?}"))
                    .inner
                    .push(delimited);
            }
            FlatToken::Token(token) => stack
                .last_mut()
                .expect("Bottom token frame is missing!")
                .inner
                .push(AttrTokenTree::Token(token, spacing)),
            FlatToken::AttrTarget(data) => stack
                .last_mut()
                .expect("Bottom token frame is missing!")
                .inner
                .push(AttrTokenTree::Attributes(data)),
            FlatToken::Empty => {}
        }
        token_and_spacing = iter.next();
    }
    let mut final_buf = stack.pop().expect("Missing final buf!");
    if break_last_token {
        let last_token = final_buf.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));

            final_buf
                .inner
                .push(AttrTokenTree::Token(Token::new(unglued_first, first_span), spacing));
        } else {
            panic!("Unexpected last token {last_token:?}")
        }
    }
    AttrTokenStream::new(final_buf.inner)
}

// Some types are used a lot. Make sure they don't unintentionally get bigger.
#[cfg(all(target_arch = "x86_64", 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, 104);
    // tidy-alphabetical-end
}