skip updating when external binding is existed

1 files changed, 13 insertions, 5 deletions

diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index d57dabdd78d..3a27f96dde8 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);
     }