summaryrefslogtreecommitdiffstats
path: root/compiler/rustc_expand/src/config.rs
blob: 3e1acf4382d5bcd48f7f3ba0664786010ddb15a2 (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
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
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
//! Conditional compilation stripping.

use rustc_ast::ptr::P;
use rustc_ast::token::{Delimiter, Token, TokenKind};
use rustc_ast::tokenstream::{AttrAnnotatedTokenStream, AttrAnnotatedTokenTree};
use rustc_ast::tokenstream::{DelimSpan, Spacing};
use rustc_ast::tokenstream::{LazyTokenStream, TokenTree};
use rustc_ast::NodeId;
use rustc_ast::{self as ast, AttrStyle, Attribute, HasAttrs, HasTokens, MetaItem};
use rustc_attr as attr;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::map_in_place::MapInPlace;
use rustc_errors::{error_code, struct_span_err, Applicability, Handler};
use rustc_feature::{Feature, Features, State as FeatureState};
use rustc_feature::{
    ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
};
use rustc_parse::validate_attr;
use rustc_session::parse::feature_err;
use rustc_session::Session;
use rustc_span::edition::{Edition, ALL_EDITIONS};
use rustc_span::symbol::{sym, Symbol};
use rustc_span::{Span, DUMMY_SP};

/// A folder that strips out items that do not belong in the current configuration.
pub struct StripUnconfigured<'a> {
    pub sess: &'a Session,
    pub features: Option<&'a Features>,
    /// If `true`, perform cfg-stripping on attached tokens.
    /// This is only used for the input to derive macros,
    /// which needs eager expansion of `cfg` and `cfg_attr`
    pub config_tokens: bool,
    pub lint_node_id: NodeId,
}

fn get_features(
    sess: &Session,
    span_handler: &Handler,
    krate_attrs: &[ast::Attribute],
) -> Features {
    fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
        let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
        err.span_label(span, "feature has been removed");
        if let Some(reason) = reason {
            err.note(reason);
        }
        err.emit();
    }

    fn active_features_up_to(edition: Edition) -> impl Iterator<Item = &'static Feature> {
        ACTIVE_FEATURES.iter().filter(move |feature| {
            if let Some(feature_edition) = feature.edition {
                feature_edition <= edition
            } else {
                false
            }
        })
    }

    let mut features = Features::default();
    let mut edition_enabled_features = FxHashMap::default();
    let crate_edition = sess.edition();

    for &edition in ALL_EDITIONS {
        if edition <= crate_edition {
            // The `crate_edition` implies its respective umbrella feature-gate
            // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
            edition_enabled_features.insert(edition.feature_name(), edition);
        }
    }

    for feature in active_features_up_to(crate_edition) {
        feature.set(&mut features, DUMMY_SP);
        edition_enabled_features.insert(feature.name, crate_edition);
    }

    // Process the edition umbrella feature-gates first, to ensure
    // `edition_enabled_features` is completed before it's queried.
    for attr in krate_attrs {
        if !attr.has_name(sym::feature) {
            continue;
        }

        let Some(list) = attr.meta_item_list() else {
            continue;
        };

        for mi in list {
            if !mi.is_word() {
                continue;
            }

            let name = mi.name_or_empty();

            let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
            if let Some(edition) = edition {
                if edition <= crate_edition {
                    continue;
                }

                for feature in active_features_up_to(edition) {
                    // FIXME(Manishearth) there is currently no way to set
                    // lib features by edition
                    feature.set(&mut features, DUMMY_SP);
                    edition_enabled_features.insert(feature.name, edition);
                }
            }
        }
    }

    for attr in krate_attrs {
        if !attr.has_name(sym::feature) {
            continue;
        }

        let Some(list) = attr.meta_item_list() else {
            continue;
        };

        let bad_input = |span| {
            struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
        };

        for mi in list {
            let name = match mi.ident() {
                Some(ident) if mi.is_word() => ident.name,
                Some(ident) => {
                    bad_input(mi.span())
                        .span_suggestion(
                            mi.span(),
                            "expected just one word",
                            ident.name,
                            Applicability::MaybeIncorrect,
                        )
                        .emit();
                    continue;
                }
                None => {
                    bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
                    continue;
                }
            };

            if let Some(edition) = edition_enabled_features.get(&name) {
                let msg =
                    &format!("the feature `{}` is included in the Rust {} edition", name, edition);
                span_handler.struct_span_warn_with_code(mi.span(), msg, error_code!(E0705)).emit();
                continue;
            }

            if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
                // Handled in the separate loop above.
                continue;
            }

            let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
            let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
            if let Some(Feature { state, .. }) = removed.or(stable_removed) {
                if let FeatureState::Removed { reason } | FeatureState::Stabilized { reason } =
                    state
                {
                    feature_removed(span_handler, mi.span(), *reason);
                    continue;
                }
            }

            if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
                let since = Some(Symbol::intern(since));
                features.declared_lang_features.push((name, mi.span(), since));
                features.active_features.insert(name);
                continue;
            }

            if let Some(allowed) = sess.opts.unstable_opts.allow_features.as_ref() {
                if allowed.iter().all(|f| name.as_str() != f) {
                    struct_span_err!(
                        span_handler,
                        mi.span(),
                        E0725,
                        "the feature `{}` is not in the list of allowed features",
                        name
                    )
                    .emit();
                    continue;
                }
            }

            if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
                f.set(&mut features, mi.span());
                features.declared_lang_features.push((name, mi.span(), None));
                features.active_features.insert(name);
                continue;
            }

            features.declared_lib_features.push((name, mi.span()));
            features.active_features.insert(name);
        }
    }

    features
}

// `cfg_attr`-process the crate's attributes and compute the crate's features.
pub fn features(
    sess: &Session,
    mut krate: ast::Crate,
    lint_node_id: NodeId,
) -> (ast::Crate, Features) {
    let mut strip_unconfigured =
        StripUnconfigured { sess, features: None, config_tokens: false, lint_node_id };

    let unconfigured_attrs = krate.attrs.clone();
    let diag = &sess.parse_sess.span_diagnostic;
    let err_count = diag.err_count();
    let features = match strip_unconfigured.configure_krate_attrs(krate.attrs) {
        None => {
            // The entire crate is unconfigured.
            krate.attrs = Vec::new();
            krate.items = Vec::new();
            Features::default()
        }
        Some(attrs) => {
            krate.attrs = attrs;
            let features = get_features(sess, diag, &krate.attrs);
            if err_count == diag.err_count() {
                // Avoid reconfiguring malformed `cfg_attr`s.
                strip_unconfigured.features = Some(&features);
                // Run configuration again, this time with features available
                // so that we can perform feature-gating.
                strip_unconfigured.configure_krate_attrs(unconfigured_attrs);
            }
            features
        }
    };
    (krate, features)
}

#[macro_export]
macro_rules! configure {
    ($this:ident, $node:ident) => {
        match $this.configure($node) {
            Some(node) => node,
            None => return Default::default(),
        }
    };
}

impl<'a> StripUnconfigured<'a> {
    pub fn configure<T: HasAttrs + HasTokens>(&self, mut node: T) -> Option<T> {
        self.process_cfg_attrs(&mut node);
        if self.in_cfg(node.attrs()) {
            self.try_configure_tokens(&mut node);
            Some(node)
        } else {
            None
        }
    }

    fn try_configure_tokens<T: HasTokens>(&self, node: &mut T) {
        if self.config_tokens {
            if let Some(Some(tokens)) = node.tokens_mut() {
                let attr_annotated_tokens = tokens.create_token_stream();
                *tokens = LazyTokenStream::new(self.configure_tokens(&attr_annotated_tokens));
            }
        }
    }

    fn configure_krate_attrs(&self, mut attrs: Vec<ast::Attribute>) -> Option<Vec<ast::Attribute>> {
        attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
        if self.in_cfg(&attrs) { Some(attrs) } else { None }
    }

    /// Performs cfg-expansion on `stream`, producing a new `AttrAnnotatedTokenStream`.
    /// This is only used during the invocation of `derive` proc-macros,
    /// which require that we cfg-expand their entire input.
    /// Normal cfg-expansion operates on parsed AST nodes via the `configure` method
    fn configure_tokens(&self, stream: &AttrAnnotatedTokenStream) -> AttrAnnotatedTokenStream {
        fn can_skip(stream: &AttrAnnotatedTokenStream) -> bool {
            stream.0.iter().all(|(tree, _spacing)| match tree {
                AttrAnnotatedTokenTree::Attributes(_) => false,
                AttrAnnotatedTokenTree::Token(_) => true,
                AttrAnnotatedTokenTree::Delimited(_, _, inner) => can_skip(inner),
            })
        }

        if can_skip(stream) {
            return stream.clone();
        }

        let trees: Vec<_> = stream
            .0
            .iter()
            .flat_map(|(tree, spacing)| match tree.clone() {
                AttrAnnotatedTokenTree::Attributes(mut data) => {
                    let mut attrs: Vec<_> = std::mem::take(&mut data.attrs).into();
                    attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
                    data.attrs = attrs.into();

                    if self.in_cfg(&data.attrs) {
                        data.tokens = LazyTokenStream::new(
                            self.configure_tokens(&data.tokens.create_token_stream()),
                        );
                        Some((AttrAnnotatedTokenTree::Attributes(data), *spacing)).into_iter()
                    } else {
                        None.into_iter()
                    }
                }
                AttrAnnotatedTokenTree::Delimited(sp, delim, mut inner) => {
                    inner = self.configure_tokens(&inner);
                    Some((AttrAnnotatedTokenTree::Delimited(sp, delim, inner), *spacing))
                        .into_iter()
                }
                AttrAnnotatedTokenTree::Token(ref token) if let TokenKind::Interpolated(ref nt) = token.kind => {
                    panic!(
                        "Nonterminal should have been flattened at {:?}: {:?}",
                        token.span, nt
                    );
                }
                AttrAnnotatedTokenTree::Token(token) => {
                    Some((AttrAnnotatedTokenTree::Token(token), *spacing)).into_iter()
                }
            })
            .collect();
        AttrAnnotatedTokenStream::new(trees)
    }

    /// Parse and expand all `cfg_attr` attributes into a list of attributes
    /// that are within each `cfg_attr` that has a true configuration predicate.
    ///
    /// Gives compiler warnings if any `cfg_attr` does not contain any
    /// attributes and is in the original source code. Gives compiler errors if
    /// the syntax of any `cfg_attr` is incorrect.
    fn process_cfg_attrs<T: HasAttrs>(&self, node: &mut T) {
        node.visit_attrs(|attrs| {
            attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
        });
    }

    fn process_cfg_attr(&self, attr: Attribute) -> Vec<Attribute> {
        if attr.has_name(sym::cfg_attr) { self.expand_cfg_attr(attr, true) } else { vec![attr] }
    }

    /// Parse and expand a single `cfg_attr` attribute into a list of attributes
    /// when the configuration predicate is true, or otherwise expand into an
    /// empty list of attributes.
    ///
    /// Gives a compiler warning when the `cfg_attr` contains no attributes and
    /// is in the original source file. Gives a compiler error if the syntax of
    /// the attribute is incorrect.
    pub(crate) fn expand_cfg_attr(&self, attr: Attribute, recursive: bool) -> Vec<Attribute> {
        let Some((cfg_predicate, expanded_attrs)) =
            rustc_parse::parse_cfg_attr(&attr, &self.sess.parse_sess) else {
                return vec![];
            };

        // Lint on zero attributes in source.
        if expanded_attrs.is_empty() {
            self.sess.parse_sess.buffer_lint(
                rustc_lint_defs::builtin::UNUSED_ATTRIBUTES,
                attr.span,
                ast::CRATE_NODE_ID,
                "`#[cfg_attr]` does not expand to any attributes",
            );
        }

        if !attr::cfg_matches(
            &cfg_predicate,
            &self.sess.parse_sess,
            self.lint_node_id,
            self.features,
        ) {
            return vec![];
        }

        if recursive {
            // We call `process_cfg_attr` recursively in case there's a
            // `cfg_attr` inside of another `cfg_attr`. E.g.
            //  `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
            expanded_attrs
                .into_iter()
                .flat_map(|item| self.process_cfg_attr(self.expand_cfg_attr_item(&attr, item)))
                .collect()
        } else {
            expanded_attrs.into_iter().map(|item| self.expand_cfg_attr_item(&attr, item)).collect()
        }
    }

    fn expand_cfg_attr_item(
        &self,
        attr: &Attribute,
        (item, item_span): (ast::AttrItem, Span),
    ) -> Attribute {
        let orig_tokens = attr.tokens().to_tokenstream();

        // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
        // and producing an attribute of the form `#[attr]`. We
        // have captured tokens for `attr` itself, but we need to
        // synthesize tokens for the wrapper `#` and `[]`, which
        // we do below.

        // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
        // for `attr` when we expand it to `#[attr]`
        let mut orig_trees = orig_tokens.into_trees();
        let TokenTree::Token(pound_token @ Token { kind: TokenKind::Pound, .. }, _) = orig_trees.next().unwrap() else {
            panic!("Bad tokens for attribute {:?}", attr);
        };
        let pound_span = pound_token.span;

        let mut trees = vec![(AttrAnnotatedTokenTree::Token(pound_token), Spacing::Alone)];
        if attr.style == AttrStyle::Inner {
            // For inner attributes, we do the same thing for the `!` in `#![some_attr]`
            let TokenTree::Token(bang_token @ Token { kind: TokenKind::Not, .. }, _) = orig_trees.next().unwrap() else {
                panic!("Bad tokens for attribute {:?}", attr);
            };
            trees.push((AttrAnnotatedTokenTree::Token(bang_token), Spacing::Alone));
        }
        // We don't really have a good span to use for the synthesized `[]`
        // in `#[attr]`, so just use the span of the `#` token.
        let bracket_group = AttrAnnotatedTokenTree::Delimited(
            DelimSpan::from_single(pound_span),
            Delimiter::Bracket,
            item.tokens
                .as_ref()
                .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
                .create_token_stream(),
        );
        trees.push((bracket_group, Spacing::Alone));
        let tokens = Some(LazyTokenStream::new(AttrAnnotatedTokenStream::new(trees)));
        let attr = attr::mk_attr_from_item(item, tokens, attr.style, item_span);
        if attr.has_name(sym::crate_type) {
            self.sess.parse_sess.buffer_lint(
                rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
                attr.span,
                ast::CRATE_NODE_ID,
                "`crate_type` within an `#![cfg_attr] attribute is deprecated`",
            );
        }
        if attr.has_name(sym::crate_name) {
            self.sess.parse_sess.buffer_lint(
                rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
                attr.span,
                ast::CRATE_NODE_ID,
                "`crate_name` within an `#![cfg_attr] attribute is deprecated`",
            );
        }
        attr
    }

    /// Determines if a node with the given attributes should be included in this configuration.
    fn in_cfg(&self, attrs: &[Attribute]) -> bool {
        attrs.iter().all(|attr| !is_cfg(attr) || self.cfg_true(attr))
    }

    pub(crate) fn cfg_true(&self, attr: &Attribute) -> bool {
        let meta_item = match validate_attr::parse_meta(&self.sess.parse_sess, attr) {
            Ok(meta_item) => meta_item,
            Err(mut err) => {
                err.emit();
                return true;
            }
        };
        parse_cfg(&meta_item, &self.sess).map_or(true, |meta_item| {
            attr::cfg_matches(&meta_item, &self.sess.parse_sess, self.lint_node_id, self.features)
        })
    }

    /// If attributes are not allowed on expressions, emit an error for `attr`
    pub(crate) fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
        if !self.features.map_or(true, |features| features.stmt_expr_attributes) {
            let mut err = feature_err(
                &self.sess.parse_sess,
                sym::stmt_expr_attributes,
                attr.span,
                "attributes on expressions are experimental",
            );

            if attr.is_doc_comment() {
                err.help("`///` is for documentation comments. For a plain comment, use `//`.");
            }

            err.emit();
        }
    }

    pub fn configure_expr(&self, expr: &mut P<ast::Expr>) {
        for attr in expr.attrs.iter() {
            self.maybe_emit_expr_attr_err(attr);
        }

        // If an expr is valid to cfg away it will have been removed by the
        // outer stmt or expression folder before descending in here.
        // Anything else is always required, and thus has to error out
        // in case of a cfg attr.
        //
        // N.B., this is intentionally not part of the visit_expr() function
        //     in order for filter_map_expr() to be able to avoid this check
        if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(*a)) {
            let msg = "removing an expression is not supported in this position";
            self.sess.parse_sess.span_diagnostic.span_err(attr.span, msg);
        }

        self.process_cfg_attrs(expr);
        self.try_configure_tokens(&mut *expr);
    }
}

pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a MetaItem> {
    let error = |span, msg, suggestion: &str| {
        let mut err = sess.parse_sess.span_diagnostic.struct_span_err(span, msg);
        if !suggestion.is_empty() {
            err.span_suggestion(
                span,
                "expected syntax is",
                suggestion,
                Applicability::HasPlaceholders,
            );
        }
        err.emit();
        None
    };
    let span = meta_item.span;
    match meta_item.meta_item_list() {
        None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
        Some([]) => error(span, "`cfg` predicate is not specified", ""),
        Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
        Some([single]) => match single.meta_item() {
            Some(meta_item) => Some(meta_item),
            None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
        },
    }
}

fn is_cfg(attr: &Attribute) -> bool {
    attr.has_name(sym::cfg)
}