Add test for issue-58490

Author: JohnTitor

src/test/ui/macros/issue-58490.rs

@@ -0,0 +1,26 @@
+// Regression test for #58490
+
+macro_rules! a {
+    ( @1 $i:item ) => {
+        a! { @2 $i }
+    };
+    ( @2 $i:item ) => {
+        $i
+    };
+}
+mod b {
+    a! {
+        @1
+        #[macro_export]
+        macro_rules! b { () => () }
+    }
+    #[macro_export]
+    macro_rules! b { () => () }
+    //~^ ERROR: the name `b` is defined multiple times
+}
+mod c {
+    #[allow(unused_imports)]
+    use crate::b;
+}
+
+fn main() {}

src/test/ui/macros/issue-58490.stderr

@@ -0,0 +1,14 @@
+error[E0428]: the name `b` is defined multiple times
+  --> $DIR/issue-58490.rs:18:5
+   |
+LL |         macro_rules! b { () => () }
+   |         -------------- previous definition of the macro `b` here
+...
+LL |     macro_rules! b { () => () }
+   |     ^^^^^^^^^^^^^^ `b` redefined here
+   |
+   = note: `b` must be defined only once in the macro namespace of this module
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0428`.