fix corner case in `merge_vars` (#4289)

fixes #4288

1 files changed, 16 insertions, 4 deletions

diff --git a/lib/compress.js b/lib/compress.js
index fe2e6242..c86bb5f0 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4739,13 +4739,25 @@ merge(Compressor.prototype, {
                 if (node === self) root = segment;
                 if (node instanceof AST_Lambda) {
                     if (node.name) references[node.name.definition().id] = false;
-                    node.each_argname(node.uses_arguments && !tw.has_directive("use strict") ? function(node) {
-                        references[node.definition().id] = false;
+                    var marker = node.uses_arguments && !tw.has_directive("use strict") ? function(node) {
+                        if (node instanceof AST_SymbolFunarg) references[node.definition().id] = false;
                     } : function(node) {
-                        mark(node, false, true);
+                        if (node instanceof AST_SymbolFunarg) mark(node, false, true);
+                    };
+                    var scanner = new TreeWalker(function(ref) {
+                        if (!(ref instanceof AST_SymbolRef)) return;
+                        var def = ref.definition();
+                        var ldef = node.variables.get(ref.name);
+                        if (ldef && (ldef === def || def.undeclared || node.parent_scope.find_variable(ref) === def)) {
+                            references[ldef.id] = false;
+                        }
+                        return true;
+                    });
+                    node.argnames.forEach(function(argname) {
+                        argname.mark_symbol(marker, scanner);
                     });
                 }
-                descend();
+                walk_body(node, tw);
                 pop();
                 return true;
             }