summaryrefslogtreecommitdiffstats
path: root/vendor/syn/src/buffer.rs
blob: 564ccc75775c85b74333a5666e96424055fd1828 (plain)
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
//! A stably addressed token buffer supporting efficient traversal based on a
//! cheaply copyable cursor.

// This module is heavily commented as it contains most of the unsafe code in
// Syn, and caution should be used when editing it. The public-facing interface
// is 100% safe but the implementation is fragile internally.

use crate::Lifetime;
use proc_macro2::extra::DelimSpan;
use proc_macro2::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
use std::cmp::Ordering;
use std::marker::PhantomData;

/// Internal type which is used instead of `TokenTree` to represent a token tree
/// within a `TokenBuffer`.
enum Entry {
    // Mimicking types from proc-macro.
    // Group entries contain the offset to the matching End entry.
    Group(Group, usize),
    Ident(Ident),
    Punct(Punct),
    Literal(Literal),
    // End entries contain the offset (negative) to the start of the buffer.
    End(isize),
}

/// A buffer that can be efficiently traversed multiple times, unlike
/// `TokenStream` which requires a deep copy in order to traverse more than
/// once.
pub struct TokenBuffer {
    // NOTE: Do not implement clone on this - while the current design could be
    // cloned, other designs which could be desirable may not be cloneable.
    entries: Box<[Entry]>,
}

impl TokenBuffer {
    fn recursive_new(entries: &mut Vec<Entry>, stream: TokenStream) {
        for tt in stream {
            match tt {
                TokenTree::Ident(ident) => entries.push(Entry::Ident(ident)),
                TokenTree::Punct(punct) => entries.push(Entry::Punct(punct)),
                TokenTree::Literal(literal) => entries.push(Entry::Literal(literal)),
                TokenTree::Group(group) => {
                    let group_start_index = entries.len();
                    entries.push(Entry::End(0)); // we replace this below
                    Self::recursive_new(entries, group.stream());
                    let group_end_index = entries.len();
                    entries.push(Entry::End(-(group_end_index as isize)));
                    let group_end_offset = group_end_index - group_start_index;
                    entries[group_start_index] = Entry::Group(group, group_end_offset);
                }
            }
        }
    }

    /// Creates a `TokenBuffer` containing all the tokens from the input
    /// `proc_macro::TokenStream`.
    #[cfg(feature = "proc-macro")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "proc-macro")))]
    pub fn new(stream: proc_macro::TokenStream) -> Self {
        Self::new2(stream.into())
    }

    /// Creates a `TokenBuffer` containing all the tokens from the input
    /// `proc_macro2::TokenStream`.
    pub fn new2(stream: TokenStream) -> Self {
        let mut entries = Vec::new();
        Self::recursive_new(&mut entries, stream);
        entries.push(Entry::End(-(entries.len() as isize)));
        Self {
            entries: entries.into_boxed_slice(),
        }
    }

    /// Creates a cursor referencing the first token in the buffer and able to
    /// traverse until the end of the buffer.
    pub fn begin(&self) -> Cursor {
        let ptr = self.entries.as_ptr();
        unsafe { Cursor::create(ptr, ptr.add(self.entries.len() - 1)) }
    }
}

/// A cheaply copyable cursor into a `TokenBuffer`.
///
/// This cursor holds a shared reference into the immutable data which is used
/// internally to represent a `TokenStream`, and can be efficiently manipulated
/// and copied around.
///
/// An empty `Cursor` can be created directly, or one may create a `TokenBuffer`
/// object and get a cursor to its first token with `begin()`.
pub struct Cursor<'a> {
    // The current entry which the `Cursor` is pointing at.
    ptr: *const Entry,
    // This is the only `Entry::End` object which this cursor is allowed to
    // point at. All other `End` objects are skipped over in `Cursor::create`.
    scope: *const Entry,
    // Cursor is covariant in 'a. This field ensures that our pointers are still
    // valid.
    marker: PhantomData<&'a Entry>,
}

impl<'a> Cursor<'a> {
    /// Creates a cursor referencing a static empty TokenStream.
    pub fn empty() -> Self {
        // It's safe in this situation for us to put an `Entry` object in global
        // storage, despite it not actually being safe to send across threads
        // (`Ident` is a reference into a thread-local table). This is because
        // this entry never includes a `Ident` object.
        //
        // This wrapper struct allows us to break the rules and put a `Sync`
        // object in global storage.
        struct UnsafeSyncEntry(Entry);
        unsafe impl Sync for UnsafeSyncEntry {}
        static EMPTY_ENTRY: UnsafeSyncEntry = UnsafeSyncEntry(Entry::End(0));

        Cursor {
            ptr: &EMPTY_ENTRY.0,
            scope: &EMPTY_ENTRY.0,
            marker: PhantomData,
        }
    }

    /// This create method intelligently exits non-explicitly-entered
    /// `None`-delimited scopes when the cursor reaches the end of them,
    /// allowing for them to be treated transparently.
    unsafe fn create(mut ptr: *const Entry, scope: *const Entry) -> Self {
        // NOTE: If we're looking at a `End`, we want to advance the cursor
        // past it, unless `ptr == scope`, which means that we're at the edge of
        // our cursor's scope. We should only have `ptr != scope` at the exit
        // from None-delimited groups entered with `ignore_none`.
        while let Entry::End(_) = *ptr {
            if ptr == scope {
                break;
            }
            ptr = ptr.add(1);
        }

        Cursor {
            ptr,
            scope,
            marker: PhantomData,
        }
    }

    /// Get the current entry.
    fn entry(self) -> &'a Entry {
        unsafe { &*self.ptr }
    }

    /// Bump the cursor to point at the next token after the current one. This
    /// is undefined behavior if the cursor is currently looking at an
    /// `Entry::End`.
    ///
    /// If the cursor is looking at an `Entry::Group`, the bumped cursor will
    /// point at the first token in the group (with the same scope end).
    unsafe fn bump_ignore_group(self) -> Cursor<'a> {
        Cursor::create(self.ptr.offset(1), self.scope)
    }

    /// While the cursor is looking at a `None`-delimited group, move it to look
    /// at the first token inside instead. If the group is empty, this will move
    /// the cursor past the `None`-delimited group.
    ///
    /// WARNING: This mutates its argument.
    fn ignore_none(&mut self) {
        while let Entry::Group(group, _) = self.entry() {
            if group.delimiter() == Delimiter::None {
                unsafe { *self = self.bump_ignore_group() };
            } else {
                break;
            }
        }
    }

    /// Checks whether the cursor is currently pointing at the end of its valid
    /// scope.
    pub fn eof(self) -> bool {
        // We're at eof if we're at the end of our scope.
        self.ptr == self.scope
    }

    /// If the cursor is pointing at a `Group` with the given delimiter, returns
    /// a cursor into that group and one pointing to the next `TokenTree`.
    pub fn group(mut self, delim: Delimiter) -> Option<(Cursor<'a>, DelimSpan, Cursor<'a>)> {
        // If we're not trying to enter a none-delimited group, we want to
        // ignore them. We have to make sure to _not_ ignore them when we want
        // to enter them, of course. For obvious reasons.
        if delim != Delimiter::None {
            self.ignore_none();
        }

        if let Entry::Group(group, end_offset) = self.entry() {
            if group.delimiter() == delim {
                let span = group.delim_span();
                let end_of_group = unsafe { self.ptr.add(*end_offset) };
                let inside_of_group = unsafe { Cursor::create(self.ptr.add(1), end_of_group) };
                let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
                return Some((inside_of_group, span, after_group));
            }
        }

        None
    }

    pub(crate) fn any_group(self) -> Option<(Cursor<'a>, Delimiter, DelimSpan, Cursor<'a>)> {
        if let Entry::Group(group, end_offset) = self.entry() {
            let delimiter = group.delimiter();
            let span = group.delim_span();
            let end_of_group = unsafe { self.ptr.add(*end_offset) };
            let inside_of_group = unsafe { Cursor::create(self.ptr.add(1), end_of_group) };
            let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
            return Some((inside_of_group, delimiter, span, after_group));
        }

        None
    }

    pub(crate) fn any_group_token(self) -> Option<(Group, Cursor<'a>)> {
        if let Entry::Group(group, end_offset) = self.entry() {
            let end_of_group = unsafe { self.ptr.add(*end_offset) };
            let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
            return Some((group.clone(), after_group));
        }

        None
    }

    /// If the cursor is pointing at a `Ident`, returns it along with a cursor
    /// pointing at the next `TokenTree`.
    pub fn ident(mut self) -> Option<(Ident, Cursor<'a>)> {
        self.ignore_none();
        match self.entry() {
            Entry::Ident(ident) => Some((ident.clone(), unsafe { self.bump_ignore_group() })),
            _ => None,
        }
    }

    /// If the cursor is pointing at a `Punct`, returns it along with a cursor
    /// pointing at the next `TokenTree`.
    pub fn punct(mut self) -> Option<(Punct, Cursor<'a>)> {
        self.ignore_none();
        match self.entry() {
            Entry::Punct(punct) if punct.as_char() != '\'' => {
                Some((punct.clone(), unsafe { self.bump_ignore_group() }))
            }
            _ => None,
        }
    }

    /// If the cursor is pointing at a `Literal`, return it along with a cursor
    /// pointing at the next `TokenTree`.
    pub fn literal(mut self) -> Option<(Literal, Cursor<'a>)> {
        self.ignore_none();
        match self.entry() {
            Entry::Literal(literal) => Some((literal.clone(), unsafe { self.bump_ignore_group() })),
            _ => None,
        }
    }

    /// If the cursor is pointing at a `Lifetime`, returns it along with a
    /// cursor pointing at the next `TokenTree`.
    pub fn lifetime(mut self) -> Option<(Lifetime, Cursor<'a>)> {
        self.ignore_none();
        match self.entry() {
            Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
                let next = unsafe { self.bump_ignore_group() };
                let (ident, rest) = next.ident()?;
                let lifetime = Lifetime {
                    apostrophe: punct.span(),
                    ident,
                };
                Some((lifetime, rest))
            }
            _ => None,
        }
    }

    /// Copies all remaining tokens visible from this cursor into a
    /// `TokenStream`.
    pub fn token_stream(self) -> TokenStream {
        let mut tts = Vec::new();
        let mut cursor = self;
        while let Some((tt, rest)) = cursor.token_tree() {
            tts.push(tt);
            cursor = rest;
        }
        tts.into_iter().collect()
    }

    /// If the cursor is pointing at a `TokenTree`, returns it along with a
    /// cursor pointing at the next `TokenTree`.
    ///
    /// Returns `None` if the cursor has reached the end of its stream.
    ///
    /// This method does not treat `None`-delimited groups as transparent, and
    /// will return a `Group(None, ..)` if the cursor is looking at one.
    pub fn token_tree(self) -> Option<(TokenTree, Cursor<'a>)> {
        let (tree, len) = match self.entry() {
            Entry::Group(group, end_offset) => (group.clone().into(), *end_offset),
            Entry::Literal(literal) => (literal.clone().into(), 1),
            Entry::Ident(ident) => (ident.clone().into(), 1),
            Entry::Punct(punct) => (punct.clone().into(), 1),
            Entry::End(_) => return None,
        };

        let rest = unsafe { Cursor::create(self.ptr.add(len), self.scope) };
        Some((tree, rest))
    }

    /// Returns the `Span` of the current token, or `Span::call_site()` if this
    /// cursor points to eof.
    pub fn span(self) -> Span {
        match self.entry() {
            Entry::Group(group, _) => group.span(),
            Entry::Literal(literal) => literal.span(),
            Entry::Ident(ident) => ident.span(),
            Entry::Punct(punct) => punct.span(),
            Entry::End(_) => Span::call_site(),
        }
    }

    /// Returns the `Span` of the token immediately prior to the position of
    /// this cursor, or of the current token if there is no previous one.
    #[cfg(any(feature = "full", feature = "derive"))]
    pub(crate) fn prev_span(mut self) -> Span {
        if start_of_buffer(self) < self.ptr {
            self.ptr = unsafe { self.ptr.offset(-1) };
            if let Entry::End(_) = self.entry() {
                // Locate the matching Group begin token.
                let mut depth = 1;
                loop {
                    self.ptr = unsafe { self.ptr.offset(-1) };
                    match self.entry() {
                        Entry::Group(group, _) => {
                            depth -= 1;
                            if depth == 0 {
                                return group.span();
                            }
                        }
                        Entry::End(_) => depth += 1,
                        Entry::Literal(_) | Entry::Ident(_) | Entry::Punct(_) => {}
                    }
                }
            }
        }
        self.span()
    }

    /// Skip over the next token without cloning it. Returns `None` if this
    /// cursor points to eof.
    ///
    /// This method treats `'lifetimes` as a single token.
    pub(crate) fn skip(self) -> Option<Cursor<'a>> {
        let len = match self.entry() {
            Entry::End(_) => return None,

            // Treat lifetimes as a single tt for the purposes of 'skip'.
            Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
                match unsafe { &*self.ptr.add(1) } {
                    Entry::Ident(_) => 2,
                    _ => 1,
                }
            }

            Entry::Group(_, end_offset) => *end_offset,
            _ => 1,
        };

        Some(unsafe { Cursor::create(self.ptr.add(len), self.scope) })
    }
}

impl<'a> Copy for Cursor<'a> {}

impl<'a> Clone for Cursor<'a> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<'a> Eq for Cursor<'a> {}

impl<'a> PartialEq for Cursor<'a> {
    fn eq(&self, other: &Self) -> bool {
        self.ptr == other.ptr
    }
}

impl<'a> PartialOrd for Cursor<'a> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        if same_buffer(*self, *other) {
            Some(self.ptr.cmp(&other.ptr))
        } else {
            None
        }
    }
}

pub(crate) fn same_scope(a: Cursor, b: Cursor) -> bool {
    a.scope == b.scope
}

pub(crate) fn same_buffer(a: Cursor, b: Cursor) -> bool {
    start_of_buffer(a) == start_of_buffer(b)
}

fn start_of_buffer(cursor: Cursor) -> *const Entry {
    unsafe {
        match &*cursor.scope {
            Entry::End(offset) => cursor.scope.offset(*offset),
            _ => unreachable!(),
        }
    }
}

#[cfg(any(feature = "full", feature = "derive"))]
pub(crate) fn cmp_assuming_same_buffer(a: Cursor, b: Cursor) -> Ordering {
    a.ptr.cmp(&b.ptr)
}

pub(crate) fn open_span_of_group(cursor: Cursor) -> Span {
    match cursor.entry() {
        Entry::Group(group, _) => group.span_open(),
        _ => cursor.span(),
    }
}

pub(crate) fn close_span_of_group(cursor: Cursor) -> Span {
    match cursor.entry() {
        Entry::Group(group, _) => group.span_close(),
        _ => cursor.span(),
    }
}