fix corner case in `collapse_vars` (#4445)

fixes #4444

1 files changed, 10 insertions, 4 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 4351768d..a611bf4a 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1814,16 +1814,22 @@ merge(Compressor.prototype, {
                     }
                     if (!(fn instanceof AST_Lambda)) return true;
                     if (def && recursive_ref(compressor, def)) return true;
-                    if (!all(fn.argnames, function(argname) {
-                        return !(argname instanceof AST_Destructured);
-                    })) return true;
                     if (fn.collapse_scanning) return false;
                     fn.collapse_scanning = true;
                     var replace = can_replace;
                     can_replace = false;
                     var after = stop_after;
                     var if_hit = stop_if_hit;
-                    if (fn instanceof AST_Arrow && fn.value) {
+                    if (!all(fn.argnames, function(argname) {
+                        if (argname instanceof AST_DefaultValue) {
+                            argname.value.transform(scanner);
+                            if (abort) return false;
+                            argname = argname.name;
+                        }
+                        return !(argname instanceof AST_Destructured);
+                    })) {
+                        abort = true;
+                    } else if (fn instanceof AST_Arrow && fn.value) {
                         fn.value.transform(scanner);
                     } else for (var i = 0; !abort && i < fn.body.length; i++) {
                         var stat = fn.body[i];