fix corner case in `loops` & `unused` (#4076)

fixes #4075

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 213cead3..a1f3d50c 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4677,7 +4677,9 @@ merge(Compressor.prototype, {
                     sym = sym.expression.tail_node();
                 }
                 var def = sym.definition();
-                if (!def || def.id in in_use_ids) return;
+                if (!def) return;
+                if (def.scope !== self) return;
+                if (def.id in in_use_ids) return;
                 log(sym, "Dropping unused loop variable {name}");
                 var value = node.object.drop_side_effect_free(compressor);
                 if (!value) return in_list ? List.skip : make_node(AST_EmptyStatement, node);