fix corner case in `functions` (#5035)

fixes #5034

1 files changed, 18 insertions, 3 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 3f9678a7..22f4736a 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6562,10 +6562,25 @@ merge(Compressor.prototype, {
                         if (def.orig.length > 1) return null;
                         if (def.assignments > 0) return false;
                         if (def.name == name) return def;
-                        if (name == "await" && is_async(fn)) return false;
-                        if (name == "yield" && is_generator(fn)) return false;
+                        var forbidden;
+                        switch (name) {
+                          case "await":
+                            forbidden = is_async;
+                            break;
+                          case "yield":
+                            forbidden = is_generator;
+                            break;
+                        }
                         return all(def.references, function(ref) {
-                            return ref.scope.find_variable(name) === sym;
+                            var scope = ref.scope;
+                            if (scope.find_variable(name) !== sym) return false;
+                            if (forbidden) {
+                                scope = scope.resolve();
+                                do {
+                                    if (forbidden(scope)) return false;
+                                } while ((scope = scope.parent_scope.resolve()) && scope !== fn);
+                            }
+                            return true;
                         }) && def;
                     }