rustdoc/
visit_ast.rs

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
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
//! The Rust AST Visitor. Extracts useful information and massages it into a form
//! usable for `clean`.

use std::mem;

use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, LocalDefIdSet};
use rustc_hir::intravisit::{Visitor, walk_body, walk_item};
use rustc_hir::{CRATE_HIR_ID, Node};
use rustc_middle::hir::nested_filter;
use rustc_middle::ty::TyCtxt;
use rustc_span::Span;
use rustc_span::def_id::{CRATE_DEF_ID, LOCAL_CRATE};
use rustc_span::hygiene::MacroKind;
use rustc_span::symbol::{Symbol, kw, sym};
use tracing::debug;

use crate::clean::cfg::Cfg;
use crate::clean::utils::{inherits_doc_hidden, should_ignore_res};
use crate::clean::{AttributesExt, NestedAttributesExt, reexport_chain};
use crate::core;

/// This module is used to store stuff from Rust's AST in a more convenient
/// manner (and with prettier names) before cleaning.
#[derive(Debug)]
pub(crate) struct Module<'hir> {
    pub(crate) name: Symbol,
    pub(crate) where_inner: Span,
    pub(crate) mods: Vec<Module<'hir>>,
    pub(crate) def_id: LocalDefId,
    pub(crate) renamed: Option<Symbol>,
    pub(crate) import_id: Option<LocalDefId>,
    /// The key is the item `ItemId` and the value is: (item, renamed, import_id).
    /// We use `FxIndexMap` to keep the insert order.
    pub(crate) items: FxIndexMap<
        (LocalDefId, Option<Symbol>),
        (&'hir hir::Item<'hir>, Option<Symbol>, Option<LocalDefId>),
    >,
    /// Same as for `items`.
    pub(crate) inlined_foreigns: FxIndexMap<(DefId, Option<Symbol>), (Res, LocalDefId)>,
    pub(crate) foreigns: Vec<(&'hir hir::ForeignItem<'hir>, Option<Symbol>)>,
}

impl Module<'_> {
    pub(crate) fn new(
        name: Symbol,
        def_id: LocalDefId,
        where_inner: Span,
        renamed: Option<Symbol>,
        import_id: Option<LocalDefId>,
    ) -> Self {
        Module {
            name,
            def_id,
            where_inner,
            renamed,
            import_id,
            mods: Vec::new(),
            items: FxIndexMap::default(),
            inlined_foreigns: FxIndexMap::default(),
            foreigns: Vec::new(),
        }
    }

    pub(crate) fn where_outer(&self, tcx: TyCtxt<'_>) -> Span {
        tcx.def_span(self.def_id)
    }
}

// FIXME: Should this be replaced with tcx.def_path_str?
fn def_id_to_path(tcx: TyCtxt<'_>, did: DefId) -> Vec<Symbol> {
    let crate_name = tcx.crate_name(did.krate);
    let relative = tcx.def_path(did).data.into_iter().filter_map(|elem| elem.data.get_opt_name());
    std::iter::once(crate_name).chain(relative).collect()
}

pub(crate) struct RustdocVisitor<'a, 'tcx> {
    cx: &'a mut core::DocContext<'tcx>,
    view_item_stack: LocalDefIdSet,
    inlining: bool,
    /// Are the current module and all of its parents public?
    inside_public_path: bool,
    exact_paths: DefIdMap<Vec<Symbol>>,
    modules: Vec<Module<'tcx>>,
    is_importable_from_parent: bool,
    inside_body: bool,
}

impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
    pub(crate) fn new(cx: &'a mut core::DocContext<'tcx>) -> RustdocVisitor<'a, 'tcx> {
        // If the root is re-exported, terminate all recursion.
        let mut stack = LocalDefIdSet::default();
        stack.insert(CRATE_DEF_ID);
        let om = Module::new(
            cx.tcx.crate_name(LOCAL_CRATE),
            CRATE_DEF_ID,
            cx.tcx.hir().root_module().spans.inner_span,
            None,
            None,
        );

        RustdocVisitor {
            cx,
            view_item_stack: stack,
            inlining: false,
            inside_public_path: true,
            exact_paths: Default::default(),
            modules: vec![om],
            is_importable_from_parent: true,
            inside_body: false,
        }
    }

    fn store_path(&mut self, did: DefId) {
        let tcx = self.cx.tcx;
        self.exact_paths.entry(did).or_insert_with(|| def_id_to_path(tcx, did));
    }

    pub(crate) fn visit(mut self) -> Module<'tcx> {
        let root_module = self.cx.tcx.hir().root_module();
        self.visit_mod_contents(CRATE_DEF_ID, root_module);

        let mut top_level_module = self.modules.pop().unwrap();

        // `#[macro_export] macro_rules!` items are reexported at the top level of the
        // crate, regardless of where they're defined. We want to document the
        // top level re-export of the macro, not its original definition, since
        // the re-export defines the path that a user will actually see. Accordingly,
        // we add the re-export as an item here, and then skip over the original
        // definition in `visit_item()` below.
        //
        // We also skip `#[macro_export] macro_rules!` that have already been inserted,
        // it can happen if within the same module a `#[macro_export] macro_rules!`
        // is declared but also a reexport of itself producing two exports of the same
        // macro in the same module.
        let mut inserted = FxHashSet::default();
        for child in self.cx.tcx.module_children_local(CRATE_DEF_ID) {
            if !child.reexport_chain.is_empty()
                && let Res::Def(DefKind::Macro(_), def_id) = child.res
                && let Some(local_def_id) = def_id.as_local()
                && self.cx.tcx.has_attr(def_id, sym::macro_export)
                && inserted.insert(def_id)
            {
                let item = self.cx.tcx.hir().expect_item(local_def_id);
                top_level_module
                    .items
                    .insert((local_def_id, Some(item.ident.name)), (item, None, None));
            }
        }

        self.cx.cache.hidden_cfg = self
            .cx
            .tcx
            .hir()
            .attrs(CRATE_HIR_ID)
            .iter()
            .filter(|attr| attr.has_name(sym::doc))
            .flat_map(|attr| attr.meta_item_list().into_iter().flatten())
            .filter(|attr| attr.has_name(sym::cfg_hide))
            .flat_map(|attr| {
                attr.meta_item_list()
                    .unwrap_or(&[])
                    .iter()
                    .filter_map(|attr| {
                        Cfg::parse(attr)
                            .map_err(|e| self.cx.sess().dcx().span_err(e.span, e.msg))
                            .ok()
                    })
                    .collect::<Vec<_>>()
            })
            .chain([
                Cfg::Cfg(sym::test, None),
                Cfg::Cfg(sym::doc, None),
                Cfg::Cfg(sym::doctest, None),
            ])
            .collect();

        self.cx.cache.exact_paths = self.exact_paths;
        top_level_module
    }

    /// This method will go through the given module items in two passes:
    /// 1. The items which are not glob imports/reexports.
    /// 2. The glob imports/reexports.
    fn visit_mod_contents(&mut self, def_id: LocalDefId, m: &'tcx hir::Mod<'tcx>) {
        debug!("Going through module {m:?}");
        // Keep track of if there were any private modules in the path.
        let orig_inside_public_path = self.inside_public_path;
        self.inside_public_path &= self.cx.tcx.local_visibility(def_id).is_public();

        // Reimplementation of `walk_mod` because we need to do it in two passes (explanations in
        // the second loop):
        for &i in m.item_ids {
            let item = self.cx.tcx.hir().item(i);
            if !matches!(item.kind, hir::ItemKind::Use(_, hir::UseKind::Glob)) {
                self.visit_item(item);
            }
        }
        for &i in m.item_ids {
            let item = self.cx.tcx.hir().item(i);
            // To match the way import precedence works, visit glob imports last.
            // Later passes in rustdoc will de-duplicate by name and kind, so if glob-
            // imported items appear last, then they'll be the ones that get discarded.
            if matches!(item.kind, hir::ItemKind::Use(_, hir::UseKind::Glob)) {
                self.visit_item(item);
            }
        }
        self.inside_public_path = orig_inside_public_path;
        debug!("Leaving module {m:?}");
    }

    /// Tries to resolve the target of a `pub use` statement and inlines the
    /// target if it is defined locally and would not be documented otherwise,
    /// or when it is specifically requested with `please_inline`.
    /// (the latter is the case when the import is marked `doc(inline)`)
    ///
    /// Cross-crate inlining occurs later on during crate cleaning
    /// and follows different rules.
    ///
    /// Returns `true` if the target has been inlined.
    fn maybe_inline_local(
        &mut self,
        def_id: LocalDefId,
        res: Res,
        renamed: Option<Symbol>,
        glob: bool,
        please_inline: bool,
    ) -> bool {
        debug!("maybe_inline_local (renamed: {renamed:?}) res: {res:?}");

        if renamed == Some(kw::Underscore) {
            // We never inline `_` reexports.
            return false;
        }

        if self.cx.output_format.is_json() {
            return false;
        }

        let tcx = self.cx.tcx;
        let Some(ori_res_did) = res.opt_def_id() else {
            return false;
        };

        let document_hidden = self.cx.render_options.document_hidden;
        let use_attrs = tcx.hir().attrs(tcx.local_def_id_to_hir_id(def_id));
        // Don't inline `doc(hidden)` imports so they can be stripped at a later stage.
        let is_no_inline = use_attrs.lists(sym::doc).has_word(sym::no_inline)
            || (document_hidden && use_attrs.lists(sym::doc).has_word(sym::hidden));

        if is_no_inline {
            return false;
        }

        let is_hidden = !document_hidden && tcx.is_doc_hidden(ori_res_did);
        let Some(res_did) = ori_res_did.as_local() else {
            // For cross-crate impl inlining we need to know whether items are
            // reachable in documentation -- a previously unreachable item can be
            // made reachable by cross-crate inlining which we're checking here.
            // (this is done here because we need to know this upfront).
            crate::visit_lib::lib_embargo_visit_item(self.cx, ori_res_did);
            if is_hidden || glob {
                return false;
            }
            // We store inlined foreign items otherwise, it'd mean that the `use` item would be kept
            // around. It's not a problem unless this `use` imports both a local AND a foreign item.
            // If a local item is inlined, its `use` is not supposed to still be around in `clean`,
            // which would make appear the `use` in the generated documentation like the local item
            // was not inlined even though it actually was.
            self.modules
                .last_mut()
                .unwrap()
                .inlined_foreigns
                .insert((ori_res_did, renamed), (res, def_id));
            return true;
        };

        let is_private = !self.cx.cache.effective_visibilities.is_directly_public(tcx, ori_res_did);
        let item = tcx.hir_node_by_def_id(res_did);

        if !please_inline {
            let inherits_hidden = !document_hidden && inherits_doc_hidden(tcx, res_did, None);
            // Only inline if requested or if the item would otherwise be stripped.
            if (!is_private && !inherits_hidden) || (
                is_hidden &&
                // If it's a doc hidden module, we need to keep it in case some of its inner items
                // are re-exported.
                !matches!(item, Node::Item(&hir::Item { kind: hir::ItemKind::Mod(_), .. }))
            ) ||
                // The imported item is public and not `doc(hidden)` so no need to inline it.
                self.reexport_public_and_not_hidden(def_id, res_did)
            {
                return false;
            }
        }

        let is_bang_macro = matches!(
            item,
            Node::Item(&hir::Item { kind: hir::ItemKind::Macro(_, MacroKind::Bang), .. })
        );

        if !self.view_item_stack.insert(res_did) && !is_bang_macro {
            return false;
        }

        let inlined = match item {
            // Bang macros are handled a bit on their because of how they are handled by the
            // compiler. If they have `#[doc(hidden)]` and the re-export doesn't have
            // `#[doc(inline)]`, then we don't inline it.
            Node::Item(_) if is_bang_macro && !please_inline && renamed.is_some() && is_hidden => {
                return false;
            }
            Node::Item(&hir::Item { kind: hir::ItemKind::Mod(ref m), .. }) if glob => {
                let prev = mem::replace(&mut self.inlining, true);
                for &i in m.item_ids {
                    let i = tcx.hir().item(i);
                    self.visit_item_inner(i, None, Some(def_id));
                }
                self.inlining = prev;
                true
            }
            Node::Item(it) if !glob => {
                let prev = mem::replace(&mut self.inlining, true);
                self.visit_item_inner(it, renamed, Some(def_id));
                self.inlining = prev;
                true
            }
            Node::ForeignItem(it) if !glob => {
                let prev = mem::replace(&mut self.inlining, true);
                self.visit_foreign_item_inner(it, renamed);
                self.inlining = prev;
                true
            }
            _ => false,
        };
        self.view_item_stack.remove(&res_did);
        if inlined {
            self.cx.cache.inlined_items.insert(ori_res_did);
        }
        inlined
    }

    /// Returns `true` if the item is visible, meaning it's not `#[doc(hidden)]` or private.
    ///
    /// This function takes into account the entire re-export `use` chain, so it needs the
    /// ID of the "leaf" `use` and the ID of the "root" item.
    fn reexport_public_and_not_hidden(
        &self,
        import_def_id: LocalDefId,
        target_def_id: LocalDefId,
    ) -> bool {
        if self.cx.render_options.document_hidden {
            return true;
        }
        let tcx = self.cx.tcx;
        let item_def_id = reexport_chain(tcx, import_def_id, target_def_id.to_def_id())
            .iter()
            .flat_map(|reexport| reexport.id())
            .map(|id| id.expect_local())
            .nth(1)
            .unwrap_or(target_def_id);
        item_def_id != import_def_id
            && self.cx.cache.effective_visibilities.is_directly_public(tcx, item_def_id.to_def_id())
            && !tcx.is_doc_hidden(item_def_id)
            && !inherits_doc_hidden(tcx, item_def_id, None)
    }

    #[inline]
    fn add_to_current_mod(
        &mut self,
        item: &'tcx hir::Item<'_>,
        renamed: Option<Symbol>,
        parent_id: Option<LocalDefId>,
    ) {
        if self.is_importable_from_parent
            // If we're inside an item, only impl blocks and `macro_rules!` with the `macro_export`
            // attribute can still be visible.
            || match item.kind {
                hir::ItemKind::Impl(..) => true,
                hir::ItemKind::Macro(_, MacroKind::Bang) => {
                    self.cx.tcx.has_attr(item.owner_id.def_id, sym::macro_export)
                }
                _ => false,
            }
        {
            self.modules
                .last_mut()
                .unwrap()
                .items
                .insert((item.owner_id.def_id, renamed), (item, renamed, parent_id));
        }
    }

    fn visit_item_inner(
        &mut self,
        item: &'tcx hir::Item<'_>,
        renamed: Option<Symbol>,
        import_id: Option<LocalDefId>,
    ) {
        debug!("visiting item {item:?}");
        if self.inside_body {
            // Only impls can be "seen" outside a body. For example:
            //
            // ```
            // struct Bar;
            //
            // fn foo() {
            //     impl Bar { fn bar() {} }
            // }
            // Bar::bar();
            // ```
            if let hir::ItemKind::Impl(impl_) = item.kind &&
                // Don't duplicate impls when inlining or if it's implementing a trait, we'll pick
                // them up regardless of where they're located.
                impl_.of_trait.is_none()
            {
                self.add_to_current_mod(item, None, None);
            }
            return;
        }
        let name = renamed.unwrap_or(item.ident.name);
        let tcx = self.cx.tcx;

        let def_id = item.owner_id.to_def_id();
        let is_pub = tcx.visibility(def_id).is_public();

        if is_pub {
            self.store_path(item.owner_id.to_def_id());
        }

        match item.kind {
            hir::ItemKind::ForeignMod { items, .. } => {
                for item in items {
                    let item = tcx.hir().foreign_item(item.id);
                    self.visit_foreign_item_inner(item, None);
                }
            }
            // If we're inlining, skip private items.
            _ if self.inlining && !is_pub => {}
            hir::ItemKind::GlobalAsm(..) => {}
            hir::ItemKind::Use(_, hir::UseKind::ListStem) => {}
            hir::ItemKind::Use(path, kind) => {
                for &res in &path.res {
                    // Struct and variant constructors and proc macro stubs always show up alongside
                    // their definitions, we've already processed them so just discard these.
                    if should_ignore_res(res) {
                        continue;
                    }

                    let attrs = tcx.hir().attrs(tcx.local_def_id_to_hir_id(item.owner_id.def_id));

                    // If there was a private module in the current path then don't bother inlining
                    // anything as it will probably be stripped anyway.
                    if is_pub && self.inside_public_path {
                        let please_inline = attrs.iter().any(|item| match item.meta_item_list() {
                            Some(ref list) if item.has_name(sym::doc) => {
                                list.iter().any(|i| i.has_name(sym::inline))
                            }
                            _ => false,
                        });
                        let is_glob = kind == hir::UseKind::Glob;
                        let ident = if is_glob { None } else { Some(name) };
                        if self.maybe_inline_local(
                            item.owner_id.def_id,
                            res,
                            ident,
                            is_glob,
                            please_inline,
                        ) {
                            debug!("Inlining {:?}", item.owner_id.def_id);
                            continue;
                        }
                    }
                    self.add_to_current_mod(item, renamed, import_id);
                }
            }
            hir::ItemKind::Macro(ref macro_def, _) => {
                // `#[macro_export] macro_rules!` items are handled separately in `visit()`,
                // above, since they need to be documented at the module top level. Accordingly,
                // we only want to handle macros if one of three conditions holds:
                //
                // 1. This macro was defined by `macro`, and thus isn't covered by the case
                //    above.
                // 2. This macro isn't marked with `#[macro_export]`, and thus isn't covered
                //    by the case above.
                // 3. We're inlining, since a reexport where inlining has been requested
                //    should be inlined even if it is also documented at the top level.

                let def_id = item.owner_id.to_def_id();
                let is_macro_2_0 = !macro_def.macro_rules;
                let nonexported = !tcx.has_attr(def_id, sym::macro_export);

                if is_macro_2_0 || nonexported || self.inlining {
                    self.add_to_current_mod(item, renamed, import_id);
                }
            }
            hir::ItemKind::Mod(ref m) => {
                self.enter_mod(item.owner_id.def_id, m, name, renamed, import_id);
            }
            hir::ItemKind::Fn(..)
            | hir::ItemKind::ExternCrate(..)
            | hir::ItemKind::Enum(..)
            | hir::ItemKind::Struct(..)
            | hir::ItemKind::Union(..)
            | hir::ItemKind::TyAlias(..)
            | hir::ItemKind::Static(..)
            | hir::ItemKind::Trait(..)
            | hir::ItemKind::TraitAlias(..) => {
                self.add_to_current_mod(item, renamed, import_id);
            }
            hir::ItemKind::Const(..) => {
                // Underscore constants do not correspond to a nameable item and
                // so are never useful in documentation.
                if name != kw::Underscore {
                    self.add_to_current_mod(item, renamed, import_id);
                }
            }
            hir::ItemKind::Impl(impl_) => {
                // Don't duplicate impls when inlining or if it's implementing a trait, we'll pick
                // them up regardless of where they're located.
                if !self.inlining && impl_.of_trait.is_none() {
                    self.add_to_current_mod(item, None, None);
                }
            }
        }
    }

    fn visit_foreign_item_inner(
        &mut self,
        item: &'tcx hir::ForeignItem<'_>,
        renamed: Option<Symbol>,
    ) {
        // If inlining we only want to include public functions.
        if !self.inlining || self.cx.tcx.visibility(item.owner_id).is_public() {
            self.modules.last_mut().unwrap().foreigns.push((item, renamed));
        }
    }

    /// This method will create a new module and push it onto the "modules stack" then call
    /// `visit_mod_contents`. Once done, it'll remove it from the "modules stack" and instead
    /// add into the list of modules of the current module.
    fn enter_mod(
        &mut self,
        id: LocalDefId,
        m: &'tcx hir::Mod<'tcx>,
        name: Symbol,
        renamed: Option<Symbol>,
        import_id: Option<LocalDefId>,
    ) {
        self.modules.push(Module::new(name, id, m.spans.inner_span, renamed, import_id));

        self.visit_mod_contents(id, m);

        let last = self.modules.pop().unwrap();
        self.modules.last_mut().unwrap().mods.push(last);
    }
}

// We need to implement this visitor so it'll go everywhere and retrieve items we're interested in
// such as impl blocks in const blocks.
impl<'a, 'tcx> Visitor<'tcx> for RustdocVisitor<'a, 'tcx> {
    type NestedFilter = nested_filter::All;

    fn nested_visit_map(&mut self) -> Self::Map {
        self.cx.tcx.hir()
    }

    fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
        self.visit_item_inner(i, None, None);
        let new_value = self.is_importable_from_parent
            && matches!(
                i.kind,
                hir::ItemKind::Mod(..)
                    | hir::ItemKind::ForeignMod { .. }
                    | hir::ItemKind::Impl(..)
                    | hir::ItemKind::Trait(..)
            );
        let prev = mem::replace(&mut self.is_importable_from_parent, new_value);
        walk_item(self, i);
        self.is_importable_from_parent = prev;
    }

    fn visit_mod(&mut self, _: &hir::Mod<'tcx>, _: Span, _: hir::HirId) {
        // Handled in `visit_item_inner`
    }

    fn visit_use(&mut self, _: &hir::UsePath<'tcx>, _: hir::HirId) {
        // Handled in `visit_item_inner`
    }

    fn visit_path(&mut self, _: &hir::Path<'tcx>, _: hir::HirId) {
        // Handled in `visit_item_inner`
    }

    fn visit_label(&mut self, _: &rustc_ast::Label) {
        // Unneeded.
    }

    fn visit_infer(&mut self, _: &hir::InferArg) {
        // Unneeded.
    }

    fn visit_lifetime(&mut self, _: &hir::Lifetime) {
        // Unneeded.
    }

    fn visit_body(&mut self, b: &hir::Body<'tcx>) {
        let prev = mem::replace(&mut self.inside_body, true);
        walk_body(self, b);
        self.inside_body = prev;
    }
}