4 files changed, 19 insertions, 11 deletions
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index d57dabdd78d..fee42ba87c9 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -896,7 +896,8 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
         self.r.potentially_unused_imports.push(import);
         let imported_binding = self.r.import(binding, import);
         if parent == self.r.graph_root {
-            if let Some(entry) = self.r.extern_prelude.get(&ident.normalize_to_macros_2_0()) {
+            let ident = ident.normalize_to_macros_2_0();
+            if let Some(entry) = self.r.extern_prelude.get(&ident) {
                 if expansion != LocalExpnId::ROOT && orig_name.is_some() && !entry.is_import() {
                     self.r.dcx().emit_err(
                         errors::MacroExpandedExternCrateCannotShadowExternArguments {
@@ -913,14 +914,21 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
             let entry = self
                 .r
                 .extern_prelude
-                .entry(ident.normalize_to_macros_2_0())
+                .entry(ident)
                 .or_insert(ExternPreludeEntry { binding: None, introduced_by_item: true });
-            // Binding from `extern crate` item in source code can replace
-            // a binding from `--extern` on command line here.
-            entry.binding = Some(imported_binding);
             if orig_name.is_some() {
                 entry.introduced_by_item = true;
             }
+            // Binding from `extern crate` item in source code can replace
+            // a binding from `--extern` on command line here.
+            if !entry.is_import() {
+                entry.binding = Some(imported_binding)
+            } else if ident.name != kw::Underscore {
+                self.r.dcx().span_delayed_bug(
+                    item.span,
+                    format!("it had been define the external module '{ident}' multiple times"),
+                );
+            }
         }
         self.r.define(parent, ident, TypeNS, imported_binding);
     }
@@ -1150,7 +1158,7 @@ impl<'a, 'b, 'tcx> BuildReducedGraphVisitor<'a, 'b, 'tcx> {
     fn contains_macro_use(&mut self, attrs: &[ast::Attribute]) -> bool {
         for attr in attrs {
             if attr.has_name(sym::macro_escape) {
-                let inner_attribute = matches!(attr.style, ast::AttrStyle::Inner).then_some(());
+                let inner_attribute = matches!(attr.style, ast::AttrStyle::Inner);
                 self.r
                     .dcx()
                     .emit_warn(errors::MacroExternDeprecated { span: attr.span, inner_attribute });
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 942026ef012..bcbdf627b56 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1456,7 +1456,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             let label_span = ident.span.shrink_to_hi();
             let mut spans = MultiSpan::from_span(label_span);
             spans.push_span_label(label_span, "put a macro name here");
-            err.subdiagnostic(MaybeMissingMacroRulesName { spans: spans });
+            err.subdiagnostic(MaybeMissingMacroRulesName { spans });
             return;
         }
 
diff --git a/compiler/rustc_resolve/src/errors.rs b/compiler/rustc_resolve/src/errors.rs
index ad1841e3e89..662b772413b 100644
--- a/compiler/rustc_resolve/src/errors.rs
+++ b/compiler/rustc_resolve/src/errors.rs
@@ -850,7 +850,7 @@ pub(crate) struct MacroExternDeprecated {
     #[primary_span]
     pub(crate) span: Span,
     #[help]
-    pub inner_attribute: Option<()>,
+    pub inner_attribute: bool,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 4a70fc0f308..40fdb01a72c 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -2677,14 +2677,14 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             // 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;
                     }
+
+                    seen_bindings
+                        .extend(parent_rib.bindings.keys().map(|ident| (*ident, ident.span)));
                 }
             }