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
//! Implementation of lint checking.
//!
//! The lint checking is mostly consolidated into one pass which runs
//! after all other analyses. Throughout compilation, lint warnings
//! can be added via the `add_lint` method on the Session structure. This
//! requires a span and an ID of the node that the lint is being added to. The
//! lint isn't actually emitted at that time because it is unknown what the
//! actual lint level at that location is.
//!
//! To actually emit lint warnings/errors, a separate pass is used.
//! A context keeps track of the current state of all lint levels.
//! Upon entering a node of the ast which can modify the lint settings, the
//! previous lint state is pushed onto a stack and the ast is then recursed
//! upon. As the ast is traversed, this keeps track of the current lint level
//! for all lint attributes.

use crate::{passes::LateLintPassObject, LateContext, LateLintPass, LintStore};
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_data_structures::sync::{join, Lrc};
use rustc_hir as hir;
use rustc_hir::def_id::{LocalDefId, LocalModDefId};
use rustc_hir::intravisit as hir_visit;
use rustc_hir::HirId;
use rustc_middle::hir::nested_filter;
use rustc_middle::ty::{self, TyCtxt};
use rustc_session::lint::LintPass;
use rustc_session::Session;
use rustc_span::Span;
use std::any::Any;
use std::cell::Cell;
use tracing::debug;

/// Extract the [`LintStore`] from [`Session`].
///
/// This function exists because [`Session::lint_store`] is type-erased.
pub fn unerased_lint_store(sess: &Session) -> &LintStore {
    let store: &Lrc<_> = sess.lint_store.as_ref().unwrap();
    let store: &dyn Any = &**store;
    store.downcast_ref().unwrap()
}

macro_rules! lint_callback { ($cx:expr, $f:ident, $($args:expr),*) => ({
    $cx.pass.$f(&$cx.context, $($args),*);
}) }

/// Implements the AST traversal for late lint passes. `T` provides the
/// `check_*` methods.
pub struct LateContextAndPass<'tcx, T: LateLintPass<'tcx>> {
    context: LateContext<'tcx>,
    pass: T,
}

impl<'tcx, T: LateLintPass<'tcx>> LateContextAndPass<'tcx, T> {
    /// Merge the lints specified by any lint attributes into the
    /// current lint context, call the provided function, then reset the
    /// lints in effect to their previous state.
    fn with_lint_attrs<F>(&mut self, id: HirId, f: F)
    where
        F: FnOnce(&mut Self),
    {
        let attrs = self.context.tcx.hir().attrs(id);
        let prev = self.context.last_node_with_lint_attrs;
        self.context.last_node_with_lint_attrs = id;
        debug!("late context: enter_attrs({:?})", attrs);
        lint_callback!(self, check_attributes, attrs);
        for attr in attrs {
            lint_callback!(self, check_attribute, attr);
        }
        f(self);
        debug!("late context: exit_attrs({:?})", attrs);
        lint_callback!(self, check_attributes_post, attrs);
        self.context.last_node_with_lint_attrs = prev;
    }

    fn with_param_env<F>(&mut self, id: hir::OwnerId, f: F)
    where
        F: FnOnce(&mut Self),
    {
        let old_param_env = self.context.param_env;
        self.context.param_env = self.context.tcx.param_env(id);
        f(self);
        self.context.param_env = old_param_env;
    }

    fn process_mod(&mut self, m: &'tcx hir::Mod<'tcx>, n: HirId) {
        lint_callback!(self, check_mod, m, n);
        hir_visit::walk_mod(self, m, n);
    }
}

impl<'tcx, T: LateLintPass<'tcx>> hir_visit::Visitor<'tcx> for LateContextAndPass<'tcx, T> {
    type NestedFilter = nested_filter::All;

    /// Because lints are scoped lexically, we want to walk nested
    /// items in the context of the outer item, so enable
    /// deep-walking.
    fn nested_visit_map(&mut self) -> Self::Map {
        self.context.tcx.hir()
    }

    fn visit_nested_body(&mut self, body_id: hir::BodyId) {
        let old_enclosing_body = self.context.enclosing_body.replace(body_id);
        let old_cached_typeck_results = self.context.cached_typeck_results.get();

        // HACK(eddyb) avoid trashing `cached_typeck_results` when we're
        // nested in `visit_fn`, which may have already resulted in them
        // being queried.
        if old_enclosing_body != Some(body_id) {
            self.context.cached_typeck_results.set(None);
        }

        let body = self.context.tcx.hir().body(body_id);
        self.visit_body(body);
        self.context.enclosing_body = old_enclosing_body;

        // See HACK comment above.
        if old_enclosing_body != Some(body_id) {
            self.context.cached_typeck_results.set(old_cached_typeck_results);
        }
    }

    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
        self.with_lint_attrs(param.hir_id, |cx| {
            hir_visit::walk_param(cx, param);
        });
    }

    fn visit_body(&mut self, body: &hir::Body<'tcx>) {
        lint_callback!(self, check_body, body);
        hir_visit::walk_body(self, body);
        lint_callback!(self, check_body_post, body);
    }

    fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
        let generics = self.context.generics.take();
        self.context.generics = it.kind.generics();
        let old_cached_typeck_results = self.context.cached_typeck_results.take();
        let old_enclosing_body = self.context.enclosing_body.take();
        self.with_lint_attrs(it.hir_id(), |cx| {
            cx.with_param_env(it.owner_id, |cx| {
                lint_callback!(cx, check_item, it);
                hir_visit::walk_item(cx, it);
                lint_callback!(cx, check_item_post, it);
            });
        });
        self.context.enclosing_body = old_enclosing_body;
        self.context.cached_typeck_results.set(old_cached_typeck_results);
        self.context.generics = generics;
    }

    fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
        self.with_lint_attrs(it.hir_id(), |cx| {
            cx.with_param_env(it.owner_id, |cx| {
                lint_callback!(cx, check_foreign_item, it);
                hir_visit::walk_foreign_item(cx, it);
            });
        })
    }

    fn visit_pat(&mut self, p: &'tcx hir::Pat<'tcx>) {
        lint_callback!(self, check_pat, p);
        hir_visit::walk_pat(self, p);
    }

    fn visit_expr_field(&mut self, field: &'tcx hir::ExprField<'tcx>) {
        self.with_lint_attrs(field.hir_id, |cx| hir_visit::walk_expr_field(cx, field))
    }

    fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
        ensure_sufficient_stack(|| {
            self.with_lint_attrs(e.hir_id, |cx| {
                lint_callback!(cx, check_expr, e);
                hir_visit::walk_expr(cx, e);
                lint_callback!(cx, check_expr_post, e);
            })
        })
    }

    fn visit_stmt(&mut self, s: &'tcx hir::Stmt<'tcx>) {
        // See `EarlyContextAndPass::visit_stmt` for an explanation
        // of why we call `walk_stmt` outside of `with_lint_attrs`
        self.with_lint_attrs(s.hir_id, |cx| {
            lint_callback!(cx, check_stmt, s);
        });
        hir_visit::walk_stmt(self, s);
    }

    fn visit_fn(
        &mut self,
        fk: hir_visit::FnKind<'tcx>,
        decl: &'tcx hir::FnDecl<'tcx>,
        body_id: hir::BodyId,
        span: Span,
        id: LocalDefId,
    ) {
        // Wrap in typeck results here, not just in visit_nested_body,
        // in order for `check_fn` to be able to use them.
        let old_enclosing_body = self.context.enclosing_body.replace(body_id);
        let old_cached_typeck_results = self.context.cached_typeck_results.take();
        let body = self.context.tcx.hir().body(body_id);
        lint_callback!(self, check_fn, fk, decl, body, span, id);
        hir_visit::walk_fn(self, fk, decl, body_id, id);
        self.context.enclosing_body = old_enclosing_body;
        self.context.cached_typeck_results.set(old_cached_typeck_results);
    }

    fn visit_variant_data(&mut self, s: &'tcx hir::VariantData<'tcx>) {
        lint_callback!(self, check_struct_def, s);
        hir_visit::walk_struct_def(self, s);
    }

    fn visit_field_def(&mut self, s: &'tcx hir::FieldDef<'tcx>) {
        self.with_lint_attrs(s.hir_id, |cx| {
            lint_callback!(cx, check_field_def, s);
            hir_visit::walk_field_def(cx, s);
        })
    }

    fn visit_variant(&mut self, v: &'tcx hir::Variant<'tcx>) {
        self.with_lint_attrs(v.hir_id, |cx| {
            lint_callback!(cx, check_variant, v);
            hir_visit::walk_variant(cx, v);
        })
    }

    fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
        lint_callback!(self, check_ty, t);
        hir_visit::walk_ty(self, t);
    }

    fn visit_infer(&mut self, inf: &'tcx hir::InferArg) {
        hir_visit::walk_inf(self, inf);
    }

    fn visit_mod(&mut self, m: &'tcx hir::Mod<'tcx>, _: Span, n: HirId) {
        if !self.context.only_module {
            self.process_mod(m, n);
        }
    }

    fn visit_local(&mut self, l: &'tcx hir::LetStmt<'tcx>) {
        self.with_lint_attrs(l.hir_id, |cx| {
            lint_callback!(cx, check_local, l);
            hir_visit::walk_local(cx, l);
        })
    }

    fn visit_block(&mut self, b: &'tcx hir::Block<'tcx>) {
        lint_callback!(self, check_block, b);
        hir_visit::walk_block(self, b);
        lint_callback!(self, check_block_post, b);
    }

    fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
        self.with_lint_attrs(a.hir_id, |cx| {
            lint_callback!(cx, check_arm, a);
            hir_visit::walk_arm(cx, a);
        })
    }

    fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
        lint_callback!(self, check_generic_param, p);
        hir_visit::walk_generic_param(self, p);
    }

    fn visit_generics(&mut self, g: &'tcx hir::Generics<'tcx>) {
        lint_callback!(self, check_generics, g);
        hir_visit::walk_generics(self, g);
    }

    fn visit_where_predicate(&mut self, p: &'tcx hir::WherePredicate<'tcx>) {
        hir_visit::walk_where_predicate(self, p);
    }

    fn visit_poly_trait_ref(&mut self, t: &'tcx hir::PolyTraitRef<'tcx>) {
        lint_callback!(self, check_poly_trait_ref, t);
        hir_visit::walk_poly_trait_ref(self, t);
    }

    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
        let generics = self.context.generics.take();
        self.context.generics = Some(trait_item.generics);
        self.with_lint_attrs(trait_item.hir_id(), |cx| {
            cx.with_param_env(trait_item.owner_id, |cx| {
                lint_callback!(cx, check_trait_item, trait_item);
                hir_visit::walk_trait_item(cx, trait_item);
            });
        });
        self.context.generics = generics;
    }

    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
        let generics = self.context.generics.take();
        self.context.generics = Some(impl_item.generics);
        self.with_lint_attrs(impl_item.hir_id(), |cx| {
            cx.with_param_env(impl_item.owner_id, |cx| {
                lint_callback!(cx, check_impl_item, impl_item);
                hir_visit::walk_impl_item(cx, impl_item);
                lint_callback!(cx, check_impl_item_post, impl_item);
            });
        });
        self.context.generics = generics;
    }

    fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
        hir_visit::walk_lifetime(self, lt);
    }

    fn visit_path(&mut self, p: &hir::Path<'tcx>, id: HirId) {
        lint_callback!(self, check_path, p, id);
        hir_visit::walk_path(self, p);
    }
}

// Combines multiple lint passes into a single pass, at runtime. Each
// `check_foo` method in `$methods` within this pass simply calls `check_foo`
// once per `$pass`. Compare with `declare_combined_late_lint_pass`, which is
// similar, but combines lint passes at compile time.
struct RuntimeCombinedLateLintPass<'a, 'tcx> {
    passes: &'a mut [LateLintPassObject<'tcx>],
}

#[allow(rustc::lint_pass_impl_without_macro)]
impl LintPass for RuntimeCombinedLateLintPass<'_, '_> {
    fn name(&self) -> &'static str {
        panic!()
    }
}

macro_rules! impl_late_lint_pass {
    ([], [$($(#[$attr:meta])* fn $f:ident($($param:ident: $arg:ty),*);)*]) => {
        impl<'tcx> LateLintPass<'tcx> for RuntimeCombinedLateLintPass<'_, 'tcx> {
            $(fn $f(&mut self, context: &LateContext<'tcx>, $($param: $arg),*) {
                for pass in self.passes.iter_mut() {
                    pass.$f(context, $($param),*);
                }
            })*
        }
    };
}

crate::late_lint_methods!(impl_late_lint_pass, []);

pub fn late_lint_mod<'tcx, T: LateLintPass<'tcx> + 'tcx>(
    tcx: TyCtxt<'tcx>,
    module_def_id: LocalModDefId,
    builtin_lints: T,
) {
    let context = LateContext {
        tcx,
        enclosing_body: None,
        cached_typeck_results: Cell::new(None),
        param_env: ty::ParamEnv::empty(),
        effective_visibilities: tcx.effective_visibilities(()),
        last_node_with_lint_attrs: tcx.local_def_id_to_hir_id(module_def_id),
        generics: None,
        only_module: true,
    };

    // Note: `passes` is often empty. In that case, it's faster to run
    // `builtin_lints` directly rather than bundling it up into the
    // `RuntimeCombinedLateLintPass`.
    let late_module_passes = &unerased_lint_store(tcx.sess).late_module_passes;
    if late_module_passes.is_empty() {
        late_lint_mod_inner(tcx, module_def_id, context, builtin_lints);
    } else {
        let mut passes: Vec<_> = late_module_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
        passes.push(Box::new(builtin_lints));
        let pass = RuntimeCombinedLateLintPass { passes: &mut passes[..] };
        late_lint_mod_inner(tcx, module_def_id, context, pass);
    }
}

fn late_lint_mod_inner<'tcx, T: LateLintPass<'tcx>>(
    tcx: TyCtxt<'tcx>,
    module_def_id: LocalModDefId,
    context: LateContext<'tcx>,
    pass: T,
) {
    let mut cx = LateContextAndPass { context, pass };

    let (module, _span, hir_id) = tcx.hir().get_module(module_def_id);

    cx.with_lint_attrs(hir_id, |cx| {
        // There is no module lint that will have the crate itself as an item, so check it here.
        if hir_id == hir::CRATE_HIR_ID {
            lint_callback!(cx, check_crate,);
        }

        cx.process_mod(module, hir_id);

        if hir_id == hir::CRATE_HIR_ID {
            lint_callback!(cx, check_crate_post,);
        }
    });
}

fn late_lint_crate<'tcx>(tcx: TyCtxt<'tcx>) {
    // Note: `passes` is often empty.
    let mut passes: Vec<_> =
        unerased_lint_store(tcx.sess).late_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();

    if passes.is_empty() {
        return;
    }

    let context = LateContext {
        tcx,
        enclosing_body: None,
        cached_typeck_results: Cell::new(None),
        param_env: ty::ParamEnv::empty(),
        effective_visibilities: tcx.effective_visibilities(()),
        last_node_with_lint_attrs: hir::CRATE_HIR_ID,
        generics: None,
        only_module: false,
    };

    let pass = RuntimeCombinedLateLintPass { passes: &mut passes[..] };
    late_lint_crate_inner(tcx, context, pass);
}

fn late_lint_crate_inner<'tcx, T: LateLintPass<'tcx>>(
    tcx: TyCtxt<'tcx>,
    context: LateContext<'tcx>,
    pass: T,
) {
    let mut cx = LateContextAndPass { context, pass };

    // Visit the whole crate.
    cx.with_lint_attrs(hir::CRATE_HIR_ID, |cx| {
        // Since the root module isn't visited as an item (because it isn't an
        // item), warn for it here.
        lint_callback!(cx, check_crate,);
        tcx.hir().walk_toplevel_module(cx);
        lint_callback!(cx, check_crate_post,);
    })
}

/// Performs lint checking on a crate.
pub fn check_crate<'tcx>(tcx: TyCtxt<'tcx>) {
    join(
        || {
            tcx.sess.time("crate_lints", || {
                // Run whole crate non-incremental lints
                late_lint_crate(tcx);
            });
        },
        || {
            tcx.sess.time("module_lints", || {
                // Run per-module lints
                tcx.hir().par_for_each_module(|module| tcx.ensure().lint_mod(module));
            });
        },
    );
}