Fix: Prevent macro-expanded extern crates from shadowing extern arguments

Author: Delta17920

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1036,6 +1036,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 self.r.dcx().emit_err(
                     errors::MacroExpandedExternCrateCannotShadowExternArguments { span: item.span },
                 );
+                return; // Fix: Stop processing this item to avoid inconsistent resolution state.
             }
 
             use indexmap::map::Entry;

tests/ui/resolve/ice-inconsistent-resolution-149821.rs

@@ -0,0 +1,17 @@
+//@ edition: 2024
+
+mod m {
+    use crate::*;
+    use core;
+}
+
+macro_rules! define_other_core {
+    () => {
+        extern crate std as core;
+        //~^ ERROR macro-expanded `extern crate` items cannot shadow names passed with `--extern`
+    };
+}
+
+define_other_core! {}
+
+fn main() {}

tests/ui/resolve/ice-inconsistent-resolution-149821.stderr

@@ -0,0 +1,13 @@
+error: macro-expanded `extern crate` items cannot shadow names passed with `--extern`
+  --> $DIR/ice-inconsistent-resolution-149821.rs:10:9
+   |
+LL |         extern crate std as core;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | define_other_core! {}
+   | --------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `define_other_core` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error
+