Auto merge of #92441 - cjgillot:resolve-trait-impl-item, r=matthewjasper

Link impl items to corresponding trait items in late resolver.

Hygienically linking trait impl items to declarations in the trait can be done directly by the late resolver. In fact, it is already done to diagnose unknown items.

This PR uses this resolution work and stores the `DefId` of the trait item in the HIR. This avoids having to do this resolution manually later.

r? `@matthewjasper`
Related to #90639. The added `trait_item_id` field can be moved to `ImplItemRef` to be used directly by your PR.

compiler/rustc_ast_lowering/src/index.rs

@@ -335,7 +335,8 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
     fn visit_impl_item_ref(&mut self, ii: &'hir ImplItemRef) {
         // Do not visit the duplicate information in ImplItemRef. We want to
         // map the actual nodes, not the duplicate ones in the *Ref.
-        let ImplItemRef { id, ident: _, kind: _, span: _, defaultness: _ } = *ii;
+        let ImplItemRef { id, ident: _, kind: _, span: _, defaultness: _, trait_item_def_id: _ } =
+            *ii;
 
         self.visit_nested_impl_item(id);
     }

compiler/rustc_ast_lowering/src/item.rs

@@ -925,6 +925,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 }
                 AssocItemKind::MacCall(..) => unimplemented!(),
             },
+            trait_item_def_id: self.resolver.get_partial_res(i.id).map(|r| r.base_res().def_id()),
         }
     }
 

compiler/rustc_hir/src/hir.rs

@@ -2881,6 +2881,8 @@ pub struct ImplItemRef {
     pub kind: AssocItemKind,
     pub span: Span,
     pub defaultness: Defaultness,
+    /// When we are in a trait impl, link to the trait-item's id.
+    pub trait_item_def_id: Option<DefId>,
 }
 
 #[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]

compiler/rustc_hir/src/intravisit.rs

@@ -1088,7 +1088,8 @@ pub fn walk_foreign_item_ref<'v, V: Visitor<'v>>(
 
 pub fn walk_impl_item_ref<'v, V: Visitor<'v>>(visitor: &mut V, impl_item_ref: &'v ImplItemRef) {
     // N.B., deliberately force a compilation error if/when new fields are added.
-    let ImplItemRef { id, ident, ref kind, span: _, ref defaultness } = *impl_item_ref;
+    let ImplItemRef { id, ident, ref kind, span: _, ref defaultness, trait_item_def_id: _ } =
+        *impl_item_ref;
     visitor.visit_nested_impl_item(id);
     visitor.visit_ident(ident);
     visitor.visit_associated_item_kind(kind);

compiler/rustc_middle/src/ty/assoc.rs

@@ -139,21 +139,6 @@ impl<'tcx> AssocItems<'tcx> {
         self.items.get_by_key(name).copied()
     }
 
-    /// Returns an iterator over all associated items with the given name.
-    ///
-    /// Multiple items may have the same name if they are in different `Namespace`s. For example,
-    /// an associated type can have the same name as a method. Use one of the `find_by_name_and_*`
-    /// methods below if you know which item you are looking for.
-    pub fn filter_by_name<'a>(
-        &'a self,
-        tcx: TyCtxt<'a>,
-        ident: Ident,
-        parent_def_id: DefId,
-    ) -> impl 'a + Iterator<Item = &'a ty::AssocItem> {
-        self.filter_by_name_unhygienic(ident.name)
-            .filter(move |item| tcx.hygienic_eq(ident, item.ident, parent_def_id))
-    }
-
     /// Returns the associated item with the given name and `AssocKind`, if one exists.
     pub fn find_by_name_and_kind(
         &self,

compiler/rustc_resolve/src/diagnostics.rs

@@ -602,6 +602,25 @@ impl<'a> Resolver<'a> {
 
                 err
             }
+            ResolutionError::TraitImplMismatch {
+                name,
+                kind,
+                code,
+                trait_item_span,
+                trait_path,
+            } => {
+                let mut err = self.session.struct_span_err_with_code(
+                    span,
+                    &format!(
+                        "item `{}` is an associated {}, which doesn't match its trait `{}`",
+                        name, kind, trait_path,
+                    ),
+                    code,
+                );
+                err.span_label(span, "does not match trait");
+                err.span_label(trait_item_span, "item in trait");
+                err
+            }
         }
     }
 

compiler/rustc_resolve/src/late.rs

@@ -1247,15 +1247,14 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             );
             let res = res.base_res();
             if res != Res::Err {
-                new_id = Some(res.def_id());
-                let span = trait_ref.path.span;
                 if let PathResult::Module(ModuleOrUniformRoot::Module(module)) = self.resolve_path(
                     &path,
                     Some(TypeNS),
-                    false,
-                    span,
+                    true,
+                    trait_ref.path.span,
                     CrateLint::SimplePath(trait_ref.ref_id),
                 ) {
+                    new_id = Some(res.def_id());
                     new_val = Some((module, trait_ref.clone()));
                 }
             }
@@ -1324,6 +1323,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                             // If this is a trait impl, ensure the const
                                             // exists in trait
                                             this.check_trait_item(
+                                                item.id,
                                                 item.ident,
                                                 &item.kind,
                                                 ValueNS,
@@ -1359,6 +1359,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                                     // If this is a trait impl, ensure the method
                                                     // exists in trait
                                                     this.check_trait_item(
+                                                        item.id,
                                                         item.ident,
                                                         &item.kind,
                                                         ValueNS,
@@ -1386,6 +1387,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                                     // If this is a trait impl, ensure the type
                                                     // exists in trait
                                                     this.check_trait_item(
+                                                        item.id,
                                                         item.ident,
                                                         &item.kind,
                                                         TypeNS,
@@ -1416,34 +1418,71 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
 
     fn check_trait_item<F>(
         &mut self,
-        ident: Ident,
+        id: NodeId,
+        mut ident: Ident,
         kind: &AssocItemKind,
         ns: Namespace,
         span: Span,
         err: F,
     ) where
         F: FnOnce(Ident, &str, Option<Symbol>) -> ResolutionError<'_>,
     {
-        // If there is a TraitRef in scope for an impl, then the method must be in the
-        // trait.
-        if let Some((module, _)) = self.current_trait_ref {
-            if self
-                .r
-                .resolve_ident_in_module(
-                    ModuleOrUniformRoot::Module(module),
-                    ident,
-                    ns,
-                    &self.parent_scope,
-                    false,
-                    span,
-                )
-                .is_err()
-            {
-                let candidate = self.find_similarly_named_assoc_item(ident.name, kind);
-                let path = &self.current_trait_ref.as_ref().unwrap().1.path;
-                self.report_error(span, err(ident, &path_names_to_string(path), candidate));
+        // If there is a TraitRef in scope for an impl, then the method must be in the trait.
+        let Some((module, _)) = &self.current_trait_ref else { return; };
+        ident.span.normalize_to_macros_2_0_and_adjust(module.expansion);
+        let key = self.r.new_key(ident, ns);
+        let mut binding = self.r.resolution(module, key).try_borrow().ok().and_then(|r| r.binding);
+        debug!(?binding);
+        if binding.is_none() {
+            // We could not find the trait item in the correct namespace.
+            // Check the other namespace to report an error.
+            let ns = match ns {
+                ValueNS => TypeNS,
+                TypeNS => ValueNS,
+                _ => ns,
+            };
+            let key = self.r.new_key(ident, ns);
+            binding = self.r.resolution(module, key).try_borrow().ok().and_then(|r| r.binding);
+            debug!(?binding);
+        }
+        let Some(binding) = binding else {
+            // We could not find the method: report an error.
+            let candidate = self.find_similarly_named_assoc_item(ident.name, kind);
+            let path = &self.current_trait_ref.as_ref().unwrap().1.path;
+            self.report_error(span, err(ident, &path_names_to_string(path), candidate));
+            return;
+        };
+
+        let res = binding.res();
+        let Res::Def(def_kind, _) = res else { bug!() };
+        match (def_kind, kind) {
+            (DefKind::AssocTy, AssocItemKind::TyAlias(..))
+            | (DefKind::AssocFn, AssocItemKind::Fn(..))
+            | (DefKind::AssocConst, AssocItemKind::Const(..)) => {
+                self.r.record_partial_res(id, PartialRes::new(res));
+                return;
             }
+            _ => {}
         }
+
+        // The method kind does not correspond to what appeared in the trait, report.
+        let path = &self.current_trait_ref.as_ref().unwrap().1.path;
+        let (code, kind) = match kind {
+            AssocItemKind::Const(..) => (rustc_errors::error_code!(E0323), "const"),
+            AssocItemKind::Fn(..) => (rustc_errors::error_code!(E0324), "method"),
+            AssocItemKind::TyAlias(..) => (rustc_errors::error_code!(E0325), "type"),
+            AssocItemKind::MacCall(..) => span_bug!(span, "unexpanded macro"),
+        };
+        self.report_error(
+            span,
+            ResolutionError::TraitImplMismatch {
+                name: ident.name,
+                kind,
+                code,
+                trait_path: path_names_to_string(path),
+                trait_item_span: binding.span,
+            },
+        );
     }
 
     fn resolve_params(&mut self, params: &'ast [Param]) {

compiler/rustc_resolve/src/lib.rs

@@ -262,6 +262,14 @@ enum ResolutionError<'a> {
     SelfInGenericParamDefault,
     /// Error E0767: use of unreachable label
     UnreachableLabel { name: Symbol, definition_span: Span, suggestion: Option<LabelSuggestion> },
+    /// Error E0323, E0324, E0325: mismatch between trait item and impl item.
+    TraitImplMismatch {
+        name: Symbol,
+        kind: &'static str,
+        trait_path: String,
+        trait_item_span: Span,
+        code: rustc_errors::DiagnosticId,
+    },
 }
 
 enum VisResolutionError<'a> {

compiler/rustc_ty_utils/src/assoc.rs

@@ -1,8 +1,7 @@
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, TyCtxt};
 
 pub fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers {
@@ -125,115 +124,14 @@ fn associated_item_from_impl_item_ref(
         hir::AssocItemKind::Type => (ty::AssocKind::Type, false),
     };
 
-    let trait_item_def_id = impl_item_base_id(tcx, parent_def_id, impl_item_ref);
-
     ty::AssocItem {
         ident: impl_item_ref.ident,
         kind,
         vis: tcx.visibility(def_id),
         defaultness: impl_item_ref.defaultness,
         def_id: def_id.to_def_id(),
-        trait_item_def_id,
+        trait_item_def_id: impl_item_ref.trait_item_def_id,
         container: ty::ImplContainer(parent_def_id.to_def_id()),
         fn_has_self_parameter: has_self,
     }
 }
-
-fn impl_item_base_id<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    parent_def_id: LocalDefId,
-    impl_item: &hir::ImplItemRef,
-) -> Option<DefId> {
-    let impl_trait_ref = tcx.impl_trait_ref(parent_def_id)?;
-
-    // If the trait reference itself is erroneous (so the compilation is going
-    // to fail), skip checking the items here -- the `impl_item` table in `tcx`
-    // isn't populated for such impls.
-    if impl_trait_ref.references_error() {
-        return None;
-    }
-
-    // Locate trait items
-    let associated_items = tcx.associated_items(impl_trait_ref.def_id);
-
-    // Match item against trait
-    let mut items = associated_items.filter_by_name(tcx, impl_item.ident, impl_trait_ref.def_id);
-
-    let mut trait_item = items.next()?;
-
-    let is_compatible = |ty: &&ty::AssocItem| match (ty.kind, &impl_item.kind) {
-        (ty::AssocKind::Const, hir::AssocItemKind::Const) => true,
-        (ty::AssocKind::Fn, hir::AssocItemKind::Fn { .. }) => true,
-        (ty::AssocKind::Type, hir::AssocItemKind::Type) => true,
-        _ => false,
-    };
-
-    // If we don't have a compatible item, we'll use the first one whose name matches
-    // to report an error.
-    let mut compatible_kind = is_compatible(&trait_item);
-
-    if !compatible_kind {
-        if let Some(ty_trait_item) = items.find(is_compatible) {
-            compatible_kind = true;
-            trait_item = ty_trait_item;
-        }
-    }
-
-    if compatible_kind {
-        Some(trait_item.def_id)
-    } else {
-        report_mismatch_error(tcx, trait_item.def_id, impl_trait_ref, impl_item);
-        None
-    }
-}
-
-#[inline(never)]
-#[cold]
-fn report_mismatch_error<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_item_def_id: DefId,
-    impl_trait_ref: ty::TraitRef<'tcx>,
-    impl_item: &hir::ImplItemRef,
-) {
-    let mut err = match impl_item.kind {
-        hir::AssocItemKind::Const => {
-            // Find associated const definition.
-            struct_span_err!(
-                tcx.sess,
-                impl_item.span,
-                E0323,
-                "item `{}` is an associated const, which doesn't match its trait `{}`",
-                impl_item.ident,
-                impl_trait_ref.print_only_trait_path()
-            )
-        }
-
-        hir::AssocItemKind::Fn { .. } => {
-            struct_span_err!(
-                tcx.sess,
-                impl_item.span,
-                E0324,
-                "item `{}` is an associated method, which doesn't match its trait `{}`",
-                impl_item.ident,
-                impl_trait_ref.print_only_trait_path()
-            )
-        }
-
-        hir::AssocItemKind::Type => {
-            struct_span_err!(
-                tcx.sess,
-                impl_item.span,
-                E0325,
-                "item `{}` is an associated type, which doesn't match its trait `{}`",
-                impl_item.ident,
-                impl_trait_ref.print_only_trait_path()
-            )
-        }
-    };
-
-    err.span_label(impl_item.span, "does not match trait");
-    if let Some(trait_span) = tcx.hir().span_if_local(trait_item_def_id) {
-        err.span_label(trait_span, "item in trait");
-    }
-    err.emit();
-}