fix `unused` on var of the same name within catch (#1716)

fixes #1715

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/compress.js b/lib/compress.js
index c60f8632..64c654dd 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1894,7 +1894,13 @@ merge(Compressor.prototype, {
                     if (drop_vars && node instanceof AST_Definitions && !(tt.parent() instanceof AST_ForIn)) {
                         var def = node.definitions.filter(function(def){
                             if (def.value) def.value = def.value.transform(tt);
-                            if (def.name.definition().id in in_use_ids) return true;
+                            var sym = def.name.definition();
+                            if (sym.id in in_use_ids) return true;
+                            if (sym.orig[0] instanceof AST_SymbolCatch
+                                && sym.scope.parent_scope.find_variable(def.name).orig[0] === def.name) {
+                                def.value = def.value && def.value.drop_side_effect_free(compressor);
+                                return true;
+                            }
                             var w = {
                                 name : def.name.name,
                                 file : def.name.start.file,