fix corner case in unused (#4469)

fixes #4468

lib/compress.js

@@ -5460,7 +5460,7 @@ merge(Compressor.prototype, {
         var calls_to_drop_args = [];
         var fns_with_marked_args = [];
         var trimmer = new TreeTransformer(function(node) {
-            if (node instanceof AST_DefaultValue) return trim_default(tt, trimmer, node);
+            if (node instanceof AST_DefaultValue) return trim_default(trimmer, node);
             if (node instanceof AST_DestructuredArray) {
                 var trim = true;
                 for (var i = node.elements.length; --i >= 0;) {
@@ -5482,10 +5482,13 @@ merge(Compressor.prototype, {
                     node.key = node.key.transform(tt);
                     retain = node.key.has_side_effects(compressor);
                 }
-                if (retain && is_decl(node.value)) return node;
-                var value = node.value.transform(trimmer);
-                if (!value) return List.skip;
-                node.value = value;
+                if (retain && is_decl(node.value)) {
+                    node.value = node.value.transform(tt);
+                } else {
+                    var value = node.value.transform(trimmer);
+                    if (!value) return List.skip;
+                    node.value = value;
+                }
                 return node;
             }
             if (node instanceof AST_SymbolDeclaration) return node.definition().id in in_use_ids ? node : null;
@@ -6042,7 +6045,7 @@ merge(Compressor.prototype, {
             return (node instanceof AST_DefaultValue ? node.name : node) instanceof AST_SymbolDeclaration;
         }
 
-        function trim_default(tt, trimmer, node) {
+        function trim_default(trimmer, node) {
             node.value = node.value.transform(tt);
             var name = node.name.transform(trimmer);
             if (!name) {
@@ -6076,7 +6079,7 @@ merge(Compressor.prototype, {
                     if (compressor.option("default_values") && value && value.is_defined(compressor)) {
                         node = node.name;
                     } else {
-                        return trim_default(tt, trimmer, node);
+                        return trim_default(trimmer, node);
                     }
                 }
                 if (node instanceof AST_DestructuredArray) {
@@ -6125,6 +6128,7 @@ merge(Compressor.prototype, {
                             retain = false;
                         }
                         if (retain && is_decl(prop.value)) {
+                            prop.value = prop.value.transform(tt);
                             properties.push(prop);
                         } else {
                             var newValue = prop.value.transform(trimmer);

test/compress/default-values.js

@@ -1160,3 +1160,31 @@ issue_4461_2: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4468: {
+    options = {
+        evaluate: true,
+        keep_fargs: false,
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function(a) {
+            var {
+                [console.log("PASS")]: b = a && (a.p = 0),
+            } = 0;
+            a;
+        })(1234);
+    }
+    expect: {
+        (function() {
+            var {
+                [console.log("PASS")]: b = 0,
+            } = 0;
+        })();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}