Auto merge of #128550 - compiler-errors:shadowed-params-perf, r=petrochenkov

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

No need to collect params from parent ribs if we literally have no params to declare in this new rib.

Attempt to win back some of the perf in https://github.com/rust-lang/rust/pull/128357#issuecomment-2262677031.

Please review with whitespace *off*, the diff should be like 2 lines.

r? petrochenkov

1 files changed, 105 insertions, 96 deletions

diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 4d28c0a3ef1..a5bd2fdd8f3 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -2668,119 +2668,128 @@ 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);