1 // This implements the dead-code warning pass. It follows middle::reachable
2 // closely. The idea is that all reachable symbols are live, codes called
3 // from live codes are live, and everything else is dead.
5 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
7 use rustc_hir::def::{CtorOf, DefKind, Res};
8 use rustc_hir::def_id::DefId;
9 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
10 use rustc_hir::itemlikevisit::ItemLikeVisitor;
11 use rustc_hir::{Node, PatKind, TyKind};
12 use rustc_middle::hir::map::Map;
13 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
14 use rustc_middle::middle::privacy;
15 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
16 use rustc_session::lint;
18 use rustc_span::symbol::{sym, Symbol};
20 // Any local node that may call something in its body block should be
21 // explored. For example, if it's a live Node::Item that is a
22 // function, then we should explore its block to check for codes that
23 // may need to be marked as live.
24 fn should_explore(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
26 tcx.hir().find(hir_id),
30 | Node::ForeignItem(..)
39 struct MarkSymbolVisitor<'tcx> {
40 worklist: Vec<hir::HirId>,
42 maybe_typeck_results: Option<&'tcx ty::TypeckResults<'tcx>>,
43 live_symbols: FxHashSet<hir::HirId>,
44 repr_has_repr_c: bool,
46 inherited_pub_visibility: bool,
48 ignore_variant_stack: Vec<DefId>,
49 // maps from tuple struct constructors to tuple struct items
50 struct_constructors: FxHashMap<hir::HirId, hir::HirId>,
53 impl<'tcx> MarkSymbolVisitor<'tcx> {
54 /// Gets the type-checking results for the current body.
55 /// As this will ICE if called outside bodies, only call when working with
56 /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
58 fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
59 self.maybe_typeck_results
60 .expect("`MarkSymbolVisitor::typeck_results` called outside of body")
63 fn check_def_id(&mut self, def_id: DefId) {
64 if let Some(def_id) = def_id.as_local() {
65 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
66 if should_explore(self.tcx, hir_id) || self.struct_constructors.contains_key(&hir_id) {
67 self.worklist.push(hir_id);
69 self.live_symbols.insert(hir_id);
73 fn insert_def_id(&mut self, def_id: DefId) {
74 if let Some(def_id) = def_id.as_local() {
75 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
76 debug_assert!(!should_explore(self.tcx, hir_id));
77 self.live_symbols.insert(hir_id);
81 fn handle_res(&mut self, res: Res) {
83 Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::TyAlias, _) => {
84 self.check_def_id(res.def_id());
86 _ if self.in_pat => {}
87 Res::PrimTy(..) | Res::SelfCtor(..) | Res::Local(..) => {}
88 Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => {
89 let variant_id = self.tcx.parent(ctor_def_id).unwrap();
90 let enum_id = self.tcx.parent(variant_id).unwrap();
91 self.check_def_id(enum_id);
92 if !self.ignore_variant_stack.contains(&ctor_def_id) {
93 self.check_def_id(variant_id);
96 Res::Def(DefKind::Variant, variant_id) => {
97 let enum_id = self.tcx.parent(variant_id).unwrap();
98 self.check_def_id(enum_id);
99 if !self.ignore_variant_stack.contains(&variant_id) {
100 self.check_def_id(variant_id);
103 Res::SelfTy(t, i) => {
105 self.check_def_id(t);
107 if let Some((i, _)) = i {
108 self.check_def_id(i);
111 Res::ToolMod | Res::NonMacroAttr(..) | Res::Err => {}
113 self.check_def_id(res.def_id());
118 fn lookup_and_handle_method(&mut self, id: hir::HirId) {
119 if let Some(def_id) = self.typeck_results().type_dependent_def_id(id) {
120 self.check_def_id(def_id);
122 bug!("no type-dependent def for method");
126 fn handle_field_access(&mut self, lhs: &hir::Expr<'_>, hir_id: hir::HirId) {
127 match self.typeck_results().expr_ty_adjusted(lhs).kind() {
129 let index = self.tcx.field_index(hir_id, self.typeck_results());
130 self.insert_def_id(def.non_enum_variant().fields[index].did);
133 _ => span_bug!(lhs.span, "named field access on non-ADT"),
137 fn handle_assign(&mut self, expr: &'tcx hir::Expr<'tcx>) {
140 .expr_adjustments(expr)
142 .any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(_)))
144 self.visit_expr(expr);
145 } else if let hir::ExprKind::Field(base, ..) = expr.kind {
146 // Ignore write to field
147 self.handle_assign(base);
149 self.visit_expr(expr);
153 fn handle_field_pattern_match(
157 pats: &[hir::PatField<'_>],
159 let variant = match self.typeck_results().node_type(lhs.hir_id).kind() {
160 ty::Adt(adt, _) => adt.variant_of_res(res),
161 _ => span_bug!(lhs.span, "non-ADT in struct pattern"),
164 if let PatKind::Wild = pat.pat.kind {
167 let index = self.tcx.field_index(pat.hir_id, self.typeck_results());
168 self.insert_def_id(variant.fields[index].did);
172 fn mark_live_symbols(&mut self) {
173 let mut scanned = FxHashSet::default();
174 while let Some(id) = self.worklist.pop() {
175 if !scanned.insert(id) {
179 // in the case of tuple struct constructors we want to check the item, not the generated
180 // tuple struct constructor function
181 let id = self.struct_constructors.get(&id).cloned().unwrap_or(id);
183 if let Some(node) = self.tcx.hir().find(id) {
184 self.live_symbols.insert(id);
185 self.visit_node(node);
190 fn visit_node(&mut self, node: Node<'tcx>) {
191 let had_repr_c = self.repr_has_repr_c;
192 let had_inherited_pub_visibility = self.inherited_pub_visibility;
193 let had_pub_visibility = self.pub_visibility;
194 self.repr_has_repr_c = false;
195 self.inherited_pub_visibility = false;
196 self.pub_visibility = false;
198 Node::Item(item) => {
199 self.pub_visibility = item.vis.node.is_pub();
202 hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
203 let def = self.tcx.adt_def(item.def_id);
204 self.repr_has_repr_c = def.repr.c();
206 intravisit::walk_item(self, &item);
208 hir::ItemKind::Enum(..) => {
209 self.inherited_pub_visibility = self.pub_visibility;
211 intravisit::walk_item(self, &item);
213 hir::ItemKind::ForeignMod { .. } => {}
215 intravisit::walk_item(self, &item);
219 Node::TraitItem(trait_item) => {
220 intravisit::walk_trait_item(self, trait_item);
222 Node::ImplItem(impl_item) => {
223 intravisit::walk_impl_item(self, impl_item);
225 Node::ForeignItem(foreign_item) => {
226 intravisit::walk_foreign_item(self, &foreign_item);
230 self.pub_visibility = had_pub_visibility;
231 self.inherited_pub_visibility = had_inherited_pub_visibility;
232 self.repr_has_repr_c = had_repr_c;
235 fn mark_as_used_if_union(&mut self, adt: &ty::AdtDef, fields: &[hir::ExprField<'_>]) {
236 if adt.is_union() && adt.non_enum_variant().fields.len() > 1 && adt.did.is_local() {
237 for field in fields {
238 let index = self.tcx.field_index(field.hir_id, self.typeck_results());
239 self.insert_def_id(adt.non_enum_variant().fields[index].did);
245 impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
246 type Map = intravisit::ErasedMap<'tcx>;
248 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
249 NestedVisitorMap::None
252 fn visit_nested_body(&mut self, body: hir::BodyId) {
253 let old_maybe_typeck_results =
254 self.maybe_typeck_results.replace(self.tcx.typeck_body(body));
255 let body = self.tcx.hir().body(body);
256 self.visit_body(body);
257 self.maybe_typeck_results = old_maybe_typeck_results;
260 fn visit_variant_data(
262 def: &'tcx hir::VariantData<'tcx>,
264 _: &hir::Generics<'_>,
268 let has_repr_c = self.repr_has_repr_c;
269 let inherited_pub_visibility = self.inherited_pub_visibility;
270 let pub_visibility = self.pub_visibility;
271 let live_fields = def.fields().iter().filter(|f| {
272 has_repr_c || (pub_visibility && (inherited_pub_visibility || f.vis.node.is_pub()))
274 self.live_symbols.extend(live_fields.map(|f| f.hir_id));
276 intravisit::walk_struct_def(self, def);
279 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
281 hir::ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(..)) => {
282 let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
283 self.handle_res(res);
285 hir::ExprKind::MethodCall(..) => {
286 self.lookup_and_handle_method(expr.hir_id);
288 hir::ExprKind::Assign(ref left, ref right, ..) => {
289 self.handle_assign(left);
290 self.visit_expr(right);
293 hir::ExprKind::Field(ref lhs, ..) => {
294 self.handle_field_access(&lhs, expr.hir_id);
296 hir::ExprKind::Struct(ref qpath, ref fields, _) => {
297 let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
298 self.handle_res(res);
299 if let ty::Adt(ref adt, _) = self.typeck_results().expr_ty(expr).kind() {
300 self.mark_as_used_if_union(adt, fields);
306 intravisit::walk_expr(self, expr);
309 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
310 // Inside the body, ignore constructions of variants
311 // necessary for the pattern to match. Those construction sites
312 // can't be reached unless the variant is constructed elsewhere.
313 let len = self.ignore_variant_stack.len();
314 self.ignore_variant_stack.extend(arm.pat.necessary_variants());
315 intravisit::walk_arm(self, arm);
316 self.ignore_variant_stack.truncate(len);
319 fn visit_pat(&mut self, pat: &'tcx hir::Pat<'tcx>) {
322 PatKind::Struct(ref path, ref fields, _) => {
323 let res = self.typeck_results().qpath_res(path, pat.hir_id);
324 self.handle_field_pattern_match(pat, res, fields);
326 PatKind::Path(ref qpath) => {
327 let res = self.typeck_results().qpath_res(qpath, pat.hir_id);
328 self.handle_res(res);
333 intravisit::walk_pat(self, pat);
337 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
338 self.handle_res(path.res);
339 intravisit::walk_path(self, path);
342 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
343 if let TyKind::OpaqueDef(item_id, _) = ty.kind {
344 let item = self.tcx.hir().item(item_id);
345 intravisit::walk_item(self, item);
347 intravisit::walk_ty(self, ty);
350 fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
351 self.live_symbols.insert(c.hir_id);
352 intravisit::walk_anon_const(self, c);
356 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
357 let attrs = tcx.hir().attrs(id);
358 if tcx.sess.contains_name(attrs, sym::lang) {
362 // Stable attribute for #[lang = "panic_impl"]
363 if tcx.sess.contains_name(attrs, sym::panic_handler) {
367 // (To be) stable attribute for #[lang = "oom"]
368 if tcx.sess.contains_name(attrs, sym::alloc_error_handler) {
372 let def_id = tcx.hir().local_def_id(id);
373 let cg_attrs = tcx.codegen_fn_attrs(def_id);
375 // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
376 // forcefully, e.g., for placing it in a specific section.
377 if cg_attrs.contains_extern_indicator() || cg_attrs.flags.contains(CodegenFnAttrFlags::USED) {
381 tcx.lint_level_at_node(lint::builtin::DEAD_CODE, id).0 == lint::Allow
384 // This visitor seeds items that
385 // 1) We want to explicitly consider as live:
386 // * Item annotated with #[allow(dead_code)]
387 // - This is done so that if we want to suppress warnings for a
388 // group of dead functions, we only have to annotate the "root".
389 // For example, if both `f` and `g` are dead and `f` calls `g`,
390 // then annotating `f` with `#[allow(dead_code)]` will suppress
391 // warning for both `f` and `g`.
392 // * Item annotated with #[lang=".."]
393 // - This is because lang items are always callable from elsewhere.
395 // 2) We are not sure to be live or not
396 // * Implementations of traits and trait methods
397 struct LifeSeeder<'k, 'tcx> {
398 worklist: Vec<hir::HirId>,
399 krate: &'k hir::Crate<'k>,
401 // see `MarkSymbolVisitor::struct_constructors`
402 struct_constructors: FxHashMap<hir::HirId, hir::HirId>,
405 impl<'v, 'k, 'tcx> ItemLikeVisitor<'v> for LifeSeeder<'k, 'tcx> {
406 fn visit_item(&mut self, item: &hir::Item<'_>) {
407 let allow_dead_code = has_allow_dead_code_or_lang_attr(self.tcx, item.hir_id());
409 self.worklist.push(item.hir_id());
412 hir::ItemKind::Enum(ref enum_def, _) => {
414 self.worklist.extend(enum_def.variants.iter().map(|variant| variant.id));
417 for variant in enum_def.variants {
418 if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
419 self.struct_constructors.insert(ctor_hir_id, variant.id);
423 hir::ItemKind::Impl(hir::Impl { ref of_trait, items, .. }) => {
424 if of_trait.is_some() {
425 self.worklist.push(item.hir_id());
427 for impl_item_ref in items {
428 let impl_item = self.krate.impl_item(impl_item_ref.id);
429 if of_trait.is_some()
430 || has_allow_dead_code_or_lang_attr(self.tcx, impl_item.hir_id())
432 self.worklist.push(impl_item_ref.id.hir_id());
436 hir::ItemKind::Struct(ref variant_data, _) => {
437 if let Some(ctor_hir_id) = variant_data.ctor_hir_id() {
438 self.struct_constructors.insert(ctor_hir_id, item.hir_id());
445 fn visit_trait_item(&mut self, trait_item: &hir::TraitItem<'_>) {
446 use hir::TraitItemKind::{Const, Fn};
447 if matches!(trait_item.kind, Const(_, Some(_)) | Fn(_, hir::TraitFn::Provided(_)))
448 && has_allow_dead_code_or_lang_attr(self.tcx, trait_item.hir_id())
450 self.worklist.push(trait_item.hir_id());
454 fn visit_impl_item(&mut self, _item: &hir::ImplItem<'_>) {
455 // ignore: we are handling this in `visit_item` above
458 fn visit_foreign_item(&mut self, foreign_item: &hir::ForeignItem<'_>) {
459 use hir::ForeignItemKind::{Fn, Static};
460 if matches!(foreign_item.kind, Static(..) | Fn(..))
461 && has_allow_dead_code_or_lang_attr(self.tcx, foreign_item.hir_id())
463 self.worklist.push(foreign_item.hir_id());
468 fn create_and_seed_worklist<'tcx>(
470 access_levels: &privacy::AccessLevels,
471 krate: &hir::Crate<'_>,
472 ) -> (Vec<hir::HirId>, FxHashMap<hir::HirId, hir::HirId>) {
473 let worklist = access_levels
478 if level >= privacy::AccessLevel::Reachable { Some(id) } else { None }
483 tcx.entry_fn(()).and_then(|(def_id, _)| {
484 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
487 .collect::<Vec<_>>();
489 // Seed implemented trait items
490 let mut life_seeder =
491 LifeSeeder { worklist, krate, tcx, struct_constructors: Default::default() };
492 krate.visit_all_item_likes(&mut life_seeder);
494 (life_seeder.worklist, life_seeder.struct_constructors)
499 access_levels: &privacy::AccessLevels,
500 krate: &hir::Crate<'_>,
501 ) -> FxHashSet<hir::HirId> {
502 let (worklist, struct_constructors) = create_and_seed_worklist(tcx, access_levels, krate);
503 let mut symbol_visitor = MarkSymbolVisitor {
506 maybe_typeck_results: None,
507 live_symbols: Default::default(),
508 repr_has_repr_c: false,
510 inherited_pub_visibility: false,
511 pub_visibility: false,
512 ignore_variant_stack: vec![],
515 symbol_visitor.mark_live_symbols();
516 symbol_visitor.live_symbols
519 struct DeadVisitor<'tcx> {
521 live_symbols: FxHashSet<hir::HirId>,
524 impl DeadVisitor<'tcx> {
525 fn should_warn_about_item(&mut self, item: &hir::Item<'_>) -> bool {
526 let should_warn = matches!(
528 hir::ItemKind::Static(..)
529 | hir::ItemKind::Const(..)
530 | hir::ItemKind::Fn(..)
531 | hir::ItemKind::TyAlias(..)
532 | hir::ItemKind::Enum(..)
533 | hir::ItemKind::Struct(..)
534 | hir::ItemKind::Union(..)
536 should_warn && !self.symbol_is_live(item.hir_id())
539 fn should_warn_about_field(&mut self, field: &hir::FieldDef<'_>) -> bool {
540 let field_type = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
541 !field.is_positional()
542 && !self.symbol_is_live(field.hir_id)
543 && !field_type.is_phantom_data()
544 && !has_allow_dead_code_or_lang_attr(self.tcx, field.hir_id)
547 fn should_warn_about_variant(&mut self, variant: &hir::Variant<'_>) -> bool {
548 !self.symbol_is_live(variant.id) && !has_allow_dead_code_or_lang_attr(self.tcx, variant.id)
551 fn should_warn_about_foreign_item(&mut self, fi: &hir::ForeignItem<'_>) -> bool {
552 !self.symbol_is_live(fi.hir_id())
553 && !has_allow_dead_code_or_lang_attr(self.tcx, fi.hir_id())
556 // id := HIR id of an item's definition.
557 fn symbol_is_live(&mut self, id: hir::HirId) -> bool {
558 if self.live_symbols.contains(&id) {
561 // If it's a type whose items are live, then it's live, too.
562 // This is done to handle the case where, for example, the static
563 // method of a private type is used, but the type itself is never
565 let def_id = self.tcx.hir().local_def_id(id);
566 let inherent_impls = self.tcx.inherent_impls(def_id);
567 for &impl_did in inherent_impls.iter() {
568 for item_did in self.tcx.associated_item_def_ids(impl_did) {
569 if let Some(did) = item_did.as_local() {
570 let item_hir_id = self.tcx.hir().local_def_id_to_hir_id(did);
571 if self.live_symbols.contains(&item_hir_id) {
583 span: rustc_span::Span,
587 if !name.as_str().starts_with('_') {
588 self.tcx.struct_span_lint_hir(lint::builtin::DEAD_CODE, id, span, |lint| {
589 let def_id = self.tcx.hir().local_def_id(id);
590 let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
591 lint.build(&format!("{} is never {}: `{}`", descr, participle, name)).emit()
597 impl Visitor<'tcx> for DeadVisitor<'tcx> {
598 type Map = Map<'tcx>;
600 /// Walk nested items in place so that we don't report dead-code
601 /// on inner functions when the outer function is already getting
602 /// an error. We could do this also by checking the parents, but
603 /// this is how the code is setup and it seems harmless enough.
604 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
605 NestedVisitorMap::All(self.tcx.hir())
608 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
609 if self.should_warn_about_item(item) {
610 // For most items, we want to highlight its identifier
611 let span = match item.kind {
612 hir::ItemKind::Fn(..)
613 | hir::ItemKind::Mod(..)
614 | hir::ItemKind::Enum(..)
615 | hir::ItemKind::Struct(..)
616 | hir::ItemKind::Union(..)
617 | hir::ItemKind::Trait(..)
618 | hir::ItemKind::Impl { .. } => {
619 // FIXME(66095): Because item.span is annotated with things
620 // like expansion data, and ident.span isn't, we use the
621 // def_span method if it's part of a macro invocation
622 // (and thus has a source_callee set).
623 // We should probably annotate ident.span with the macro
624 // context, but that's a larger change.
625 if item.span.source_callee().is_some() {
626 self.tcx.sess.source_map().guess_head_span(item.span)
633 let participle = match item.kind {
634 hir::ItemKind::Struct(..) => "constructed", // Issue #52325
637 self.warn_dead_code(item.hir_id(), span, item.ident.name, participle);
639 // Only continue if we didn't warn
640 intravisit::walk_item(self, item);
646 variant: &'tcx hir::Variant<'tcx>,
647 g: &'tcx hir::Generics<'tcx>,
650 if self.should_warn_about_variant(&variant) {
651 self.warn_dead_code(variant.id, variant.span, variant.ident.name, "constructed");
653 intravisit::walk_variant(self, variant, g, id);
657 fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem<'tcx>) {
658 if self.should_warn_about_foreign_item(fi) {
659 self.warn_dead_code(fi.hir_id(), fi.span, fi.ident.name, "used");
661 intravisit::walk_foreign_item(self, fi);
664 fn visit_field_def(&mut self, field: &'tcx hir::FieldDef<'tcx>) {
665 if self.should_warn_about_field(&field) {
666 self.warn_dead_code(field.hir_id, field.span, field.ident.name, "read");
668 intravisit::walk_field_def(self, field);
671 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
672 match impl_item.kind {
673 hir::ImplItemKind::Const(_, body_id) => {
674 if !self.symbol_is_live(impl_item.hir_id()) {
678 impl_item.ident.name,
682 self.visit_nested_body(body_id)
684 hir::ImplItemKind::Fn(_, body_id) => {
685 if !self.symbol_is_live(impl_item.hir_id()) {
686 // FIXME(66095): Because impl_item.span is annotated with things
687 // like expansion data, and ident.span isn't, we use the
688 // def_span method if it's part of a macro invocation
689 // (and thus has a source_callee set).
690 // We should probably annotate ident.span with the macro
691 // context, but that's a larger change.
692 let span = if impl_item.span.source_callee().is_some() {
693 self.tcx.sess.source_map().guess_head_span(impl_item.span)
697 self.warn_dead_code(impl_item.hir_id(), span, impl_item.ident.name, "used");
699 self.visit_nested_body(body_id)
701 hir::ImplItemKind::TyAlias(..) => {}
705 // Overwrite so that we don't warn the trait item itself.
706 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
707 match trait_item.kind {
708 hir::TraitItemKind::Const(_, Some(body_id))
709 | hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)) => {
710 self.visit_nested_body(body_id)
712 hir::TraitItemKind::Const(_, None)
713 | hir::TraitItemKind::Fn(_, hir::TraitFn::Required(_))
714 | hir::TraitItemKind::Type(..) => {}
719 pub fn check_crate(tcx: TyCtxt<'_>) {
720 let access_levels = &tcx.privacy_access_levels(());
721 let krate = tcx.hir().krate();
722 let live_symbols = find_live(tcx, access_levels, krate);
723 let mut visitor = DeadVisitor { tcx, live_symbols };
724 intravisit::walk_crate(&mut visitor, krate);