fix corner case in merge_vars (#4324)

fixes #4323

lib/compress.js

@@ -4784,6 +4784,7 @@ merge(Compressor.prototype, {
                         if (node instanceof AST_SymbolFunarg) mark(node, false, true);
                     };
                     var scanner = new TreeWalker(function(ref) {
+                        if (ref instanceof AST_SymbolDeclaration) references[ref.definition().id] = false;
                         if (!(ref instanceof AST_SymbolRef)) return;
                         var def = ref.definition();
                         var ldef = node.variables.get(ref.name);

test/compress/destructured.js

@@ -1741,3 +1741,39 @@ issue_4321: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4323: {
+    options = {
+        ie8: true,
+        inline: true,
+        merge_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = 0;
+        (function b({
+            [function a() {
+                console.log(typeof a);
+            }()]: d,
+        }) {})(0);
+        (function c(e) {
+            e.p;
+        })(1, console.log);
+    }
+    expect: {
+        var a = 0;
+        (function({
+            [function a() {
+                console.log(typeof a);
+            }()]: d,
+        }) {})(0);
+        e = 1,
+        console.log,
+        void e.p;
+        var e;
+    }
+    expect_stdout: "function"
+    node_version: ">=6"
+}