fix corner case in unused (#5090)

fixes #5089

lib/compress.js

@@ -7276,6 +7276,7 @@ merge(Compressor.prototype, {
             }
 
             function retain_lhs(node) {
+                if (node instanceof AST_DefaultValue) return retain_lhs(node.name);
                 if (node instanceof AST_Destructured) {
                     if (value === null) {
                         value = make_node(AST_Number, node, { value: 0 });
@@ -7289,7 +7290,6 @@ merge(Compressor.prototype, {
                     }
                     return make_node(AST_DestructuredObject, node, { properties: [] });
                 }
-                if (node instanceof AST_DefaultValue) node = node.name;
                 node.__unused = null;
                 return node;
             }

test/compress/rests.js

@@ -950,3 +950,56 @@ issue_4666: {
     expect_stdout: "1 2"
     node_version: ">=6"
 }
+
+issue_5089_1: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var {
+            p: [] = 42,
+            ...o
+        } = {
+            p: [],
+        };
+        console.log(o.p);
+    }
+    expect: {
+        var {
+            p: {},
+            ...o
+        } = {
+            p: 0,
+        };
+        console.log(o.p);
+    }
+    expect_stdout: "undefined"
+    node_version: ">=8"
+}
+
+issue_5089_2: {
+    options = {
+        pure_getters: "strict",
+        unused: true,
+    }
+    input: {
+        var {
+            p: {} = null,
+            ...o
+        } = {
+            p: {},
+        };
+        console.log(o.p);
+    }
+    expect: {
+        var {
+            p: {},
+            ...o
+        } = {
+            p: 0,
+        };
+        console.log(o.p);
+    }
+    expect_stdout: "undefined"
+    node_version: ">=8"
+}