Only walk ribs to collect possibly shadowed params if we are adding params in our new rib

Author: compiler-errors

Diff for: compiler/rustc_resolve/src/late.rs

@@ -2667,119 +2667,128 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
         let mut function_type_rib = Rib::new(kind);
         let mut function_value_rib = Rib::new(kind);
         let mut function_lifetime_rib = LifetimeRib::new(lifetime_kind);
-        let mut seen_bindings = FxHashMap::default();
-        // Store all seen lifetimes names from outer scopes.
-        let mut seen_lifetimes = FxHashSet::default();
-
-        // We also can't shadow bindings from associated parent items.
-        for ns in [ValueNS, TypeNS] {
-            for parent_rib in self.ribs[ns].iter().rev() {
-                seen_bindings.extend(parent_rib.bindings.keys().map(|ident| (*ident, ident.span)));
-
-                // Break at mod level, to account for nested items which are
-                // allowed to shadow generic param names.
-                if matches!(parent_rib.kind, RibKind::Module(..)) {
-                    break;
-                }
-            }
-        }
 
-        // Forbid shadowing lifetime bindings
-        for rib in self.lifetime_ribs.iter().rev() {
-            seen_lifetimes.extend(rib.bindings.iter().map(|(ident, _)| *ident));
-            if let LifetimeRibKind::Item = rib.kind {
-                break;
+        // Only check for shadowed bindings if we're declaring new params.
+        if !params.is_empty() {
+            let mut seen_bindings = FxHashMap::default();
+            // Store all seen lifetimes names from outer scopes.
+            let mut seen_lifetimes = FxHashSet::default();
+
+            // We also can't shadow bindings from associated parent items.
+            for ns in [ValueNS, TypeNS] {
+                for parent_rib in self.ribs[ns].iter().rev() {
+                    seen_bindings
+                        .extend(parent_rib.bindings.keys().map(|ident| (*ident, ident.span)));
+
+                    // Break at mod level, to account for nested items which are
+                    // allowed to shadow generic param names.
+                    if matches!(parent_rib.kind, RibKind::Module(..)) {
+                        break;
+                    }
+                }
             }
-        }
-
-        for param in params {
-            let ident = param.ident.normalize_to_macros_2_0();
-            debug!("with_generic_param_rib: {}", param.id);
 
-            if let GenericParamKind::Lifetime = param.kind
-                && let Some(&original) = seen_lifetimes.get(&ident)
-            {
-                diagnostics::signal_lifetime_shadowing(self.r.tcx.sess, original, param.ident);
-                // Record lifetime res, so lowering knows there is something fishy.
-                self.record_lifetime_param(param.id, LifetimeRes::Error);
-                continue;
+            // Forbid shadowing lifetime bindings
+            for rib in self.lifetime_ribs.iter().rev() {
+                seen_lifetimes.extend(rib.bindings.iter().map(|(ident, _)| *ident));
+                if let LifetimeRibKind::Item = rib.kind {
+                    break;
+                }
             }
 
-            match seen_bindings.entry(ident) {
-                Entry::Occupied(entry) => {
-                    let span = *entry.get();
-                    let err = ResolutionError::NameAlreadyUsedInParameterList(ident.name, span);
-                    self.report_error(param.ident.span, err);
-                    let rib = match param.kind {
-                        GenericParamKind::Lifetime => {
-                            // Record lifetime res, so lowering knows there is something fishy.
-                            self.record_lifetime_param(param.id, LifetimeRes::Error);
-                            continue;
-                        }
-                        GenericParamKind::Type { .. } => &mut function_type_rib,
-                        GenericParamKind::Const { .. } => &mut function_value_rib,
-                    };
+            for param in params {
+                let ident = param.ident.normalize_to_macros_2_0();
+                debug!("with_generic_param_rib: {}", param.id);
 
-                    // Taint the resolution in case of errors to prevent follow up errors in typeck
-                    self.r.record_partial_res(param.id, PartialRes::new(Res::Err));
-                    rib.bindings.insert(ident, Res::Err);
+                if let GenericParamKind::Lifetime = param.kind
+                    && let Some(&original) = seen_lifetimes.get(&ident)
+                {
+                    diagnostics::signal_lifetime_shadowing(self.r.tcx.sess, original, param.ident);
+                    // Record lifetime res, so lowering knows there is something fishy.
+                    self.record_lifetime_param(param.id, LifetimeRes::Error);
                     continue;
                 }
-                Entry::Vacant(entry) => {
-                    entry.insert(param.ident.span);
-                }
-            }
 
-            if param.ident.name == kw::UnderscoreLifetime {
-                self.r
-                    .dcx()
-                    .emit_err(errors::UnderscoreLifetimeIsReserved { span: param.ident.span });
-                // Record lifetime res, so lowering knows there is something fishy.
-                self.record_lifetime_param(param.id, LifetimeRes::Error);
-                continue;
-            }
+                match seen_bindings.entry(ident) {
+                    Entry::Occupied(entry) => {
+                        let span = *entry.get();
+                        let err = ResolutionError::NameAlreadyUsedInParameterList(ident.name, span);
+                        self.report_error(param.ident.span, err);
+                        let rib = match param.kind {
+                            GenericParamKind::Lifetime => {
+                                // Record lifetime res, so lowering knows there is something fishy.
+                                self.record_lifetime_param(param.id, LifetimeRes::Error);
+                                continue;
+                            }
+                            GenericParamKind::Type { .. } => &mut function_type_rib,
+                            GenericParamKind::Const { .. } => &mut function_value_rib,
+                        };
 
-            if param.ident.name == kw::StaticLifetime {
-                self.r.dcx().emit_err(errors::StaticLifetimeIsReserved {
-                    span: param.ident.span,
-                    lifetime: param.ident,
-                });
-                // Record lifetime res, so lowering knows there is something fishy.
-                self.record_lifetime_param(param.id, LifetimeRes::Error);
-                continue;
-            }
+                        // Taint the resolution in case of errors to prevent follow up errors in typeck
+                        self.r.record_partial_res(param.id, PartialRes::new(Res::Err));
+                        rib.bindings.insert(ident, Res::Err);
+                        continue;
+                    }
+                    Entry::Vacant(entry) => {
+                        entry.insert(param.ident.span);
+                    }
+                }
 
-            let def_id = self.r.local_def_id(param.id);
+                if param.ident.name == kw::UnderscoreLifetime {
+                    self.r
+                        .dcx()
+                        .emit_err(errors::UnderscoreLifetimeIsReserved { span: param.ident.span });
+                    // Record lifetime res, so lowering knows there is something fishy.
+                    self.record_lifetime_param(param.id, LifetimeRes::Error);
+                    continue;
+                }
 
-            // Plain insert (no renaming).
-            let (rib, def_kind) = match param.kind {
-                GenericParamKind::Type { .. } => (&mut function_type_rib, DefKind::TyParam),
-                GenericParamKind::Const { .. } => (&mut function_value_rib, DefKind::ConstParam),
-                GenericParamKind::Lifetime => {
-                    let res = LifetimeRes::Param { param: def_id, binder };
-                    self.record_lifetime_param(param.id, res);
-                    function_lifetime_rib.bindings.insert(ident, (param.id, res));
+                if param.ident.name == kw::StaticLifetime {
+                    self.r.dcx().emit_err(errors::StaticLifetimeIsReserved {
+                        span: param.ident.span,
+                        lifetime: param.ident,
+                    });
+                    // Record lifetime res, so lowering knows there is something fishy.
+                    self.record_lifetime_param(param.id, LifetimeRes::Error);
                     continue;
                 }
-            };
 
-            let res = match kind {
-                RibKind::Item(..) | RibKind::AssocItem => Res::Def(def_kind, def_id.to_def_id()),
-                RibKind::Normal => {
-                    // FIXME(non_lifetime_binders): Stop special-casing
-                    // const params to error out here.
-                    if self.r.tcx.features().non_lifetime_binders
-                        && matches!(param.kind, GenericParamKind::Type { .. })
-                    {
+                let def_id = self.r.local_def_id(param.id);
+
+                // Plain insert (no renaming).
+                let (rib, def_kind) = match param.kind {
+                    GenericParamKind::Type { .. } => (&mut function_type_rib, DefKind::TyParam),
+                    GenericParamKind::Const { .. } => {
+                        (&mut function_value_rib, DefKind::ConstParam)
+                    }
+                    GenericParamKind::Lifetime => {
+                        let res = LifetimeRes::Param { param: def_id, binder };
+                        self.record_lifetime_param(param.id, res);
+                        function_lifetime_rib.bindings.insert(ident, (param.id, res));
+                        continue;
+                    }
+                };
+
+                let res = match kind {
+                    RibKind::Item(..) | RibKind::AssocItem => {
                         Res::Def(def_kind, def_id.to_def_id())
-                    } else {
-                        Res::Err
                     }
-                }
-                _ => span_bug!(param.ident.span, "Unexpected rib kind {:?}", kind),
-            };
-            self.r.record_partial_res(param.id, PartialRes::new(res));
-            rib.bindings.insert(ident, res);
+                    RibKind::Normal => {
+                        // FIXME(non_lifetime_binders): Stop special-casing
+                        // const params to error out here.
+                        if self.r.tcx.features().non_lifetime_binders
+                            && matches!(param.kind, GenericParamKind::Type { .. })
+                        {
+                            Res::Def(def_kind, def_id.to_def_id())
+                        } else {
+                            Res::Err
+                        }
+                    }
+                    _ => span_bug!(param.ident.span, "Unexpected rib kind {:?}", kind),
+                };
+                self.r.record_partial_res(param.id, PartialRes::new(res));
+                rib.bindings.insert(ident, res);
+            }
         }
 
         self.lifetime_ribs.push(function_lifetime_rib);