Add diagnostic for accessing an extern static

crates/hir-ty/src/diagnostics/unsafe_check.rs

@@ -87,7 +87,8 @@ fn walk_unsafe(
             let g = resolver.update_to_inner_scope(db.upcast(), def, current);
             let value_or_partial = resolver.resolve_path_in_value_ns(db.upcast(), path);
             if let Some(ResolveValueResult::ValueNs(ValueNs::StaticId(id), _)) = value_or_partial {
-                if db.static_data(id).mutable {
+                let static_data = db.static_data(id);
+                if static_data.mutable || static_data.is_extern {
                     unsafe_expr_cb(UnsafeExpr { expr: current, inside_unsafe_block });
                 }
             }

crates/ide-diagnostics/src/handlers/missing_unsafe.rs

@@ -163,6 +163,31 @@ fn main() {
         );
     }
 
+    #[test]
+    fn missing_unsafe_diagnostic_with_extern_static() {
+        check_diagnostics(
+            r#"
+//- minicore: copy
+
+extern "C" {
+    static EXTERN: i32;
+    static mut EXTERN_MUT: i32;
+}
+
+fn main() {
+    let _x = EXTERN;
+           //^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
+    let _x = EXTERN_MUT;
+           //^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
+    unsafe {
+        let _x = EXTERN;
+        let _x = EXTERN_MUT;
+    }
+}
+"#,
+        );
+    }
+
     #[test]
     fn no_missing_unsafe_diagnostic_with_safe_intrinsic() {
         check_diagnostics(