fix corner case in `side_effects` (#4326)

fixes #4325

1 files changed, 20 insertions, 13 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 708b9df3..7434a20d 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -5592,20 +5592,10 @@ merge(Compressor.prototype, {
             } else if (node instanceof AST_ForIn) {
                 if (!drop_vars || !compressor.option("loops")) return;
                 if (!is_empty(node.body)) return;
-                var sym = node.init;
-                if (sym instanceof AST_Definitions) {
-                    sym = sym.definitions[0].name;
-                } else while (sym instanceof AST_PropAccess) {
-                    sym = sym.expression.tail_node();
-                }
-                if (sym instanceof AST_Destructured) return;
+                var sym = get_init_symbol(node);
+                if (!sym) return;
                 var def = sym.definition();
-                if (!def) return;
                 if (def.id in in_use_ids) return;
-                if (def.scope !== self) {
-                    var d = self.find_variable(sym);
-                    if ((d && d.redefined() || d) === def) return;
-                }
                 log(sym, "Dropping unused loop variable {name}");
                 if (for_ins[def.id] === node) delete for_ins[def.id];
                 var body = [];
@@ -5705,6 +5695,16 @@ merge(Compressor.prototype, {
             return rhs.right;
         }
 
+        function get_init_symbol(for_in) {
+            var init = for_in.init;
+            if (init instanceof AST_Definitions) {
+                init = init.definitions[0].name;
+                return init instanceof AST_SymbolDeclaration && init;
+            }
+            while (init instanceof AST_PropAccess) init = init.expression.tail_node();
+            if (init instanceof AST_SymbolRef) return init;
+        }
+
         function scan_ref_scoped(node, descend, init) {
             if (node instanceof AST_Assign && node.left instanceof AST_SymbolRef) {
                 var def = node.left.definition();
@@ -5748,8 +5748,14 @@ merge(Compressor.prototype, {
                 }
                 if (!drop_vars || !compressor.option("loops")) return;
                 if (!is_empty(node.body)) return;
-                if (node.init instanceof AST_Destructured) return;
                 if (node.init.has_side_effects(compressor)) return;
+                var sym = get_init_symbol(node);
+                if (!sym) return;
+                var def = sym.definition();
+                if (def.scope !== self) {
+                    var d = self.find_variable(sym);
+                    if ((d && d.redefined() || d) === def) return;
+                }
                 node.object.walk(tw);
                 return true;
             }
@@ -6259,6 +6265,7 @@ merge(Compressor.prototype, {
                 });
                 // always shallow clone to ensure stripping of negated IIFEs
                 self = self.clone();
+                self.expression = exp.clone();
             }
             if (self instanceof AST_New) {
                 var fn = exp;