Auto merge of #88435 - cjgillot:no-walk-crate, r=Aaron1011

Avoid invoking the hir_crate query to traverse the HIR

Walking the HIR tree is done using the `hir_crate` query. However, this is unnecessary, since `hir_owner(CRATE_DEF_ID)` provides the same information. Since depending on `hir_crate` forces dependents to always be executed, this leads to unnecessary work.

By splitting HIR and attributes visits, we can avoid an edge to `hir_crate` when trying to visit the HIR tree.

compiler/rustc_hir/src/intravisit.rs

@@ -32,7 +32,6 @@
 //! example generator inference, and possibly also HIR borrowck.
 
 use crate::hir::*;
-use crate::hir_id::CRATE_HIR_ID;
 use crate::itemlikevisit::{ItemLikeVisitor, ParItemLikeVisitor};
 use rustc_ast::walk_list;
 use rustc_ast::{Attribute, Label};
@@ -477,17 +476,6 @@ pub trait Visitor<'v>: Sized {
     }
 }
 
-/// Walks the contents of a crate. See also `Crate::visit_all_items`.
-pub fn walk_crate<'v, V: Visitor<'v>>(visitor: &mut V, krate: &'v Crate<'v>) {
-    let top_mod = krate.module();
-    visitor.visit_mod(top_mod, top_mod.inner, CRATE_HIR_ID);
-    for (&id, attrs) in krate.attrs.iter() {
-        for a in *attrs {
-            visitor.visit_attribute(id, a)
-        }
-    }
-}
-
 pub fn walk_mod<'v, V: Visitor<'v>>(visitor: &mut V, module: &'v Mod<'v>, mod_hir_id: HirId) {
     visitor.visit_id(mod_hir_id);
     for &item_id in module.item_ids {

compiler/rustc_incremental/src/persist/dirty_clean.rs

@@ -142,7 +142,7 @@ pub fn check_dirty_clean_annotations(tcx: TyCtxt<'_>) {
         krate.visit_all_item_likes(&mut dirty_clean_visitor);
 
         let mut all_attrs = FindAllAttrs { tcx, found_attrs: vec![] };
-        intravisit::walk_crate(&mut all_attrs, krate);
+        tcx.hir().walk_attributes(&mut all_attrs);
 
         // Note that we cannot use the existing "unused attribute"-infrastructure
         // here, since that is running before codegen. This is also the reason why

compiler/rustc_interface/src/passes.rs

@@ -464,10 +464,6 @@ pub fn lower_to_hir<'res, 'tcx>(
         arena,
     );
 
-    if sess.opts.debugging_opts.hir_stats {
-        hir_stats::print_hir_stats(&hir_crate);
-    }
-
     sess.time("early_lint_checks", || {
         rustc_lint::check_ast_crate(
             sess,

compiler/rustc_lint/src/late.rs

@@ -451,9 +451,8 @@ fn late_lint_pass_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, pass: T)
         // 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, krate);
-
-        hir_visit::walk_crate(cx, krate);
-
+        tcx.hir().walk_toplevel_module(cx);
+        tcx.hir().walk_attributes(cx);
         lint_callback!(cx, check_crate_post, krate);
     })
 }

compiler/rustc_lint/src/levels.rs

@@ -37,7 +37,7 @@ fn lint_levels(tcx: TyCtxt<'_>, (): ()) -> LintLevelMap {
 
     let push = builder.levels.push(tcx.hir().attrs(hir::CRATE_HIR_ID), &store, true);
     builder.levels.register_id(hir::CRATE_HIR_ID);
-    intravisit::walk_crate(&mut builder, krate);
+    tcx.hir().walk_toplevel_module(&mut builder);
     builder.levels.pop(push);
 
     builder.levels.build_map()

compiler/rustc_middle/src/hir/map/mod.rs

@@ -7,9 +7,9 @@ use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::svh::Svh;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
-use rustc_hir::intravisit;
+use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::*;
 use rustc_index::vec::Idx;
@@ -519,6 +519,22 @@ impl<'hir> Map<'hir> {
         }
     }
 
+    /// Walks the contents of a crate. See also `Crate::visit_all_items`.
+    pub fn walk_toplevel_module(self, visitor: &mut impl Visitor<'hir>) {
+        let (top_mod, span, hir_id) = self.get_module(CRATE_DEF_ID);
+        visitor.visit_mod(top_mod, span, hir_id);
+    }
+
+    /// Walks the attributes in a crate.
+    pub fn walk_attributes(self, visitor: &mut impl Visitor<'hir>) {
+        let krate = self.krate();
+        for (&id, attrs) in krate.attrs.iter() {
+            for a in *attrs {
+                visitor.visit_attribute(id, a)
+            }
+        }
+    }
+
     pub fn visit_item_likes_in_module<V>(&self, module: LocalDefId, visitor: &mut V)
     where
         V: ItemLikeVisitor<'hir>,
@@ -934,7 +950,8 @@ pub(super) fn index_hir<'tcx>(tcx: TyCtxt<'tcx>, (): ()) -> &'tcx IndexedHir<'tc
         &tcx.untracked_resolutions.definitions,
         hcx,
     );
-    intravisit::walk_crate(&mut collector, tcx.untracked_crate);
+    let top_mod = tcx.untracked_crate.module();
+    collector.visit_mod(top_mod, top_mod.inner, CRATE_HIR_ID);
 
     let map = collector.finalize_and_compute_crate_hash();
     tcx.arena.alloc(map)

compiler/rustc_passes/src/dead.rs

@@ -775,5 +775,5 @@ pub fn check_crate(tcx: TyCtxt<'_>) {
     let krate = tcx.hir().krate();
     let live_symbols = find_live(tcx, access_levels, krate);
     let mut visitor = DeadVisitor { tcx, live_symbols };
-    intravisit::walk_crate(&mut visitor, krate);
+    tcx.hir().walk_toplevel_module(&mut visitor);
 }

compiler/rustc_passes/src/hir_id_validator.rs

@@ -11,6 +11,10 @@ use rustc_middle::ty::TyCtxt;
 pub fn check_crate(tcx: TyCtxt<'_>) {
     tcx.dep_graph.assert_ignored();
 
+    if tcx.sess.opts.debugging_opts.hir_stats {
+        crate::hir_stats::print_hir_stats(tcx);
+    }
+
     let errors = Lock::new(Vec::new());
     let hir_map = tcx.hir();
 

compiler/rustc_passes/src/hir_stats.rs

@@ -9,6 +9,7 @@ use rustc_hir as hir;
 use rustc_hir::intravisit as hir_visit;
 use rustc_hir::HirId;
 use rustc_middle::hir::map::Map;
+use rustc_middle::ty::TyCtxt;
 use rustc_middle::util::common::to_readable_str;
 use rustc_span::Span;
 
@@ -25,18 +26,19 @@ struct NodeData {
 }
 
 struct StatCollector<'k> {
-    krate: Option<&'k hir::Crate<'k>>,
+    krate: Option<Map<'k>>,
     data: FxHashMap<&'static str, NodeData>,
     seen: FxHashSet<Id>,
 }
 
-pub fn print_hir_stats(krate: &hir::Crate<'_>) {
+pub fn print_hir_stats(tcx: TyCtxt<'_>) {
     let mut collector = StatCollector {
-        krate: Some(krate),
+        krate: Some(tcx.hir()),
         data: FxHashMap::default(),
         seen: FxHashSet::default(),
     };
-    hir_visit::walk_crate(&mut collector, krate);
+    tcx.hir().walk_toplevel_module(&mut collector);
+    tcx.hir().walk_attributes(&mut collector);
     collector.print("HIR STATS");
 }
 

compiler/rustc_passes/src/lib_features.rs

@@ -6,7 +6,7 @@
 
 use rustc_ast::{Attribute, MetaItem, MetaItemKind};
 use rustc_errors::struct_span_err;
-use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
+use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
 use rustc_middle::hir::map::Map;
 use rustc_middle::middle::lib_features::LibFeatures;
 use rustc_middle::ty::query::Providers;
@@ -126,9 +126,7 @@ impl Visitor<'tcx> for LibFeatureCollector<'tcx> {
 
 fn get_lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
     let mut collector = LibFeatureCollector::new(tcx);
-    let krate = tcx.hir().krate();
-
-    intravisit::walk_crate(&mut collector, krate);
+    tcx.hir().walk_attributes(&mut collector);
     collector.lib_features
 }
 

compiler/rustc_passes/src/stability.rs

@@ -8,6 +8,7 @@ use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::hir_id::CRATE_HIR_ID;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::{FieldDef, Generics, HirId, Item, TraitRef, Ty, TyKind, Variant};
 use rustc_middle::hir::map::Map;
@@ -678,7 +679,6 @@ fn stability_index(tcx: TyCtxt<'tcx>, (): ()) -> Index<'tcx> {
         .collect();
 
     {
-        let krate = tcx.hir().krate();
         let mut annotator = Annotator {
             tcx,
             index: &mut index,
@@ -711,13 +711,13 @@ fn stability_index(tcx: TyCtxt<'tcx>, (): ()) -> Index<'tcx> {
 
         annotator.annotate(
             CRATE_DEF_ID,
-            krate.module().inner,
+            tcx.hir().span(CRATE_HIR_ID),
             None,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
             InheritConstStability::No,
             InheritStability::No,
-            |v| intravisit::walk_crate(v, krate),
+            |v| tcx.hir().walk_toplevel_module(v),
         );
     }
     index
@@ -908,8 +908,8 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
     if tcx.stability().staged_api[&LOCAL_CRATE] {
         let krate = tcx.hir().krate();
         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
-        missing.check_missing_stability(CRATE_DEF_ID, krate.module().inner);
-        intravisit::walk_crate(&mut missing, krate);
+        missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
+        tcx.hir().walk_toplevel_module(&mut missing);
         krate.visit_all_item_likes(&mut missing.as_deep_visitor());
     }
 

compiler/rustc_privacy/src/lib.rs

@@ -2169,7 +2169,7 @@ fn privacy_access_levels(tcx: TyCtxt<'_>, (): ()) -> &AccessLevels {
         changed: false,
     };
     loop {
-        intravisit::walk_crate(&mut visitor, tcx.hir().krate());
+        tcx.hir().walk_toplevel_module(&mut visitor);
         if visitor.changed {
             visitor.changed = false;
         } else {
@@ -2192,11 +2192,11 @@ fn check_private_in_public(tcx: TyCtxt<'_>, (): ()) {
         in_variant: false,
         old_error_set: Default::default(),
     };
-    intravisit::walk_crate(&mut visitor, krate);
+    tcx.hir().walk_toplevel_module(&mut visitor);
 
     let has_pub_restricted = {
         let mut pub_restricted_visitor = PubRestrictedVisitor { tcx, has_pub_restricted: false };
-        intravisit::walk_crate(&mut pub_restricted_visitor, krate);
+        tcx.hir().walk_toplevel_module(&mut pub_restricted_visitor);
         pub_restricted_visitor.has_pub_restricted
     };
 

compiler/rustc_save_analysis/src/dump_visitor.rs

@@ -1122,7 +1122,7 @@ impl<'tcx> DumpVisitor<'tcx> {
                 attributes: lower_attributes(attrs.to_owned(), &self.save_ctxt),
             },
         );
-        intravisit::walk_crate(self, krate);
+        self.tcx.hir().walk_toplevel_module(self);
     }
 
     fn process_bounds(&mut self, bounds: hir::GenericBounds<'tcx>) {

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -6,8 +6,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace, Res};
-use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
-use rustc_hir::intravisit;
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{ExprKind, Node, QPath};
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
@@ -1011,9 +1010,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         candidates: Vec<DefId>,
     ) {
         let module_did = self.tcx.parent_module(self.body_id);
-        let module_id = self.tcx.hir().local_def_id_to_hir_id(module_did);
-        let krate = self.tcx.hir().krate();
-        let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
+        let (span, found_use) = find_use_placement(self.tcx, module_did);
         if let Some(span) = span {
             let path_strings = candidates.iter().map(|did| {
                 // Produce an additional newline to separate the new use statement
@@ -1606,64 +1603,38 @@ pub fn provide(providers: &mut ty::query::Providers) {
     providers.all_traits = compute_all_traits;
 }
 
-struct UsePlacementFinder<'tcx> {
-    target_module: hir::HirId,
-    span: Option<Span>,
-    found_use: bool,
-    tcx: TyCtxt<'tcx>,
-}
+fn find_use_placement<'tcx>(tcx: TyCtxt<'tcx>, target_module: LocalDefId) -> (Option<Span>, bool) {
+    let mut span = None;
+    let mut found_use = false;
+    let (module, _, _) = tcx.hir().get_module(target_module);
 
-impl UsePlacementFinder<'tcx> {
-    fn check(
-        tcx: TyCtxt<'tcx>,
-        krate: &'tcx hir::Crate<'tcx>,
-        target_module: hir::HirId,
-    ) -> (Option<Span>, bool) {
-        let mut finder = UsePlacementFinder { target_module, span: None, found_use: false, tcx };
-        intravisit::walk_crate(&mut finder, krate);
-        (finder.span, finder.found_use)
-    }
-}
-
-impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
-    fn visit_mod(&mut self, module: &'tcx hir::Mod<'tcx>, _: Span, hir_id: hir::HirId) {
-        if self.span.is_some() {
-            return;
-        }
-        if hir_id != self.target_module {
-            intravisit::walk_mod(self, module, hir_id);
-            return;
-        }
-        // Find a `use` statement.
-        for &item_id in module.item_ids {
-            let item = self.tcx.hir().item(item_id);
-            match item.kind {
-                hir::ItemKind::Use(..) => {
-                    // Don't suggest placing a `use` before the prelude
-                    // import or other generated ones.
-                    if !item.span.from_expansion() {
-                        self.span = Some(item.span.shrink_to_lo());
-                        self.found_use = true;
-                        return;
-                    }
+    // Find a `use` statement.
+    for &item_id in module.item_ids {
+        let item = tcx.hir().item(item_id);
+        match item.kind {
+            hir::ItemKind::Use(..) => {
+                // Don't suggest placing a `use` before the prelude
+                // import or other generated ones.
+                if !item.span.from_expansion() {
+                    span = Some(item.span.shrink_to_lo());
+                    found_use = true;
+                    break;
                 }
-                // Don't place `use` before `extern crate`...
-                hir::ItemKind::ExternCrate(_) => {}
-                // ...but do place them before the first other item.
-                _ => {
-                    if self.span.map_or(true, |span| item.span < span) {
-                        if !item.span.from_expansion() {
-                            self.span = Some(item.span.shrink_to_lo());
-                            // Don't insert between attributes and an item.
-                            let attrs = self.tcx.hir().attrs(item.hir_id());
-                            // Find the first attribute on the item.
-                            // FIXME: This is broken for active attributes.
-                            for attr in attrs {
-                                if !attr.span.is_dummy()
-                                    && self.span.map_or(true, |span| attr.span < span)
-                                {
-                                    self.span = Some(attr.span.shrink_to_lo());
-                                }
+            }
+            // Don't place `use` before `extern crate`...
+            hir::ItemKind::ExternCrate(_) => {}
+            // ...but do place them before the first other item.
+            _ => {
+                if span.map_or(true, |span| item.span < span) {
+                    if !item.span.from_expansion() {
+                        span = Some(item.span.shrink_to_lo());
+                        // Don't insert between attributes and an item.
+                        let attrs = tcx.hir().attrs(item.hir_id());
+                        // Find the first attribute on the item.
+                        // FIXME: This is broken for active attributes.
+                        for attr in attrs {
+                            if !attr.span.is_dummy() && span.map_or(true, |span| attr.span < span) {
+                                span = Some(attr.span.shrink_to_lo());
                             }
                         }
                     }
@@ -1672,11 +1643,7 @@ impl intravisit::Visitor<'tcx> for UsePlacementFinder<'tcx> {
         }
     }
 
-    type Map = intravisit::ErasedMap<'tcx>;
-
-    fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
-        intravisit::NestedVisitorMap::None
-    }
+    (span, found_use)
 }
 
 fn print_disambiguation_help(

compiler/rustc_typeck/src/collect/type_of.rs

@@ -691,7 +691,7 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
     debug!("find_opaque_ty_constraints: scope={:?}", scope);
 
     if scope == hir::CRATE_HIR_ID {
-        intravisit::walk_crate(&mut locator, tcx.hir().krate());
+        tcx.hir().walk_toplevel_module(&mut locator);
     } else {
         debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
         match tcx.hir().get(scope) {

src/librustdoc/doctest.rs

@@ -116,7 +116,6 @@ crate fn run(options: Options) -> Result<(), ErrorReported> {
             let mut global_ctxt = queries.global_ctxt()?.take();
 
             let collector = global_ctxt.enter(|tcx| {
-                let krate = tcx.hir().krate();
                 let crate_attrs = tcx.hir().attrs(CRATE_HIR_ID);
 
                 let mut opts = scrape_test_config(crate_attrs);
@@ -144,10 +143,8 @@ crate fn run(options: Options) -> Result<(), ErrorReported> {
                 hir_collector.visit_testable(
                     "".to_string(),
                     CRATE_HIR_ID,
-                    krate.module().inner,
-                    |this| {
-                        intravisit::walk_crate(this, krate);
-                    },
+                    tcx.hir().span(CRATE_HIR_ID),
+                    |this| tcx.hir().walk_toplevel_module(this),
                 );
 
                 collector

src/librustdoc/html/render/span_map.rs

@@ -45,7 +45,7 @@ crate fn collect_spans_and_sources(
 
     if include_sources {
         if generate_link_to_definition {
-            intravisit::walk_crate(&mut visitor, tcx.hir().krate());
+            tcx.hir().walk_toplevel_module(&mut visitor);
         }
         let (krate, sources) = sources::collect_local_sources(tcx, src_root, krate);
         (krate, sources, visitor.matches)

src/test/ui/coherence/coherence_inherent.stderr

@@ -5,8 +5,10 @@ LL |         s.the_fn();
    |           ^^^^^^ method not found in `&TheStruct`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use Lib::TheTrait;`
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |     use Lib::TheTrait;
+   |
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_inherent_cc.stderr

@@ -5,8 +5,10 @@ LL |         s.the_fn();
    |           ^^^^^^ method not found in `&TheStruct`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use coherence_inherent_cc_lib::TheTrait;`
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |     use coherence_inherent_cc_lib::TheTrait;
+   |
 
 error: aborting due to previous error
 

src/test/ui/hygiene/no_implicit_prelude.stderr

@@ -23,9 +23,11 @@ LL |         ().clone()
    |            ^^^^^ method not found in `()`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use std::clone::Clone;`
    = note: this error originates in the macro `::bar::m` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |     use std::clone::Clone;
+   |
 
 error: aborting due to 2 previous errors
 

src/test/ui/hygiene/trait_items.stderr

@@ -11,9 +11,11 @@ LL |     pub macro m() { ().f() }
    |                        ^ method not found in `()`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use foo::T;`
    = note: this error originates in the macro `::baz::m` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |     use foo::T;
+   |
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-10465.stderr

@@ -5,8 +5,10 @@ LL |             b.foo();
    |               ^^^ method not found in `&B`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use a::A;`
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |         use a::A;
+   |
 
 error: aborting due to previous error
 

src/test/ui/rust-2018/trait-import-suggestions.stderr

@@ -8,8 +8,10 @@ LL |         x.foobar();
    |           ^^^^^^ method not found in `u32`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use crate::foo::foobar::Foobar;`
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |     use crate::foo::foobar::Foobar;
+   |
 
 error[E0599]: no method named `bar` found for type `u32` in the current scope
   --> $DIR/trait-import-suggestions.rs:28:7

src/test/ui/rust-2021/future-prelude-collision-shadow.stderr

@@ -15,9 +15,6 @@ LL |     fn try_into(self) -> Result<T, Self::Error>;
    |        the method is available for `Rc<u8>` here
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following traits are implemented but not in scope; perhaps add a `use` for one of them:
-           candidate #1: `use crate::m::TryIntoU32;`
-           candidate #2: `use std::convert::TryInto;`
 help: consider wrapping the receiver expression with the appropriate type
    |
 LL |         let _: u32 = Box::new(3u8).try_into().unwrap();
@@ -34,6 +31,12 @@ help: consider wrapping the receiver expression with the appropriate type
    |
 LL |         let _: u32 = Rc::new(3u8).try_into().unwrap();
    |                      ++++++++   +
+help: the following traits are implemented but not in scope; perhaps add a `use` for one of them:
+   |
+LL |     use crate::m::TryIntoU32;
+   |
+LL |     use std::convert::TryInto;
+   |
 
 error: aborting due to previous error
 

src/test/ui/underscore-imports/shadow.stderr

@@ -5,8 +5,10 @@ LL |         x.deref();
    |           ^^^^^ method not found in `&()`
    |
    = help: items from traits can only be used if the trait is in scope
-   = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
-           `use std::ops::Deref;`
+help: the following trait is implemented but not in scope; perhaps add a `use` for it:
+   |
+LL |     use std::ops::Deref;
+   |
 
 error: aborting due to previous error