From 137e4c4753f405480d23e0989446156d71bbfcce Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Fri, 23 Jun 2017 13:11:26 +0800
Subject: [PATCH] fix `unused` on `AST_Destructuring` (#2146)

---
 lib/compress.js                | 45 ++--------------------------------
 lib/scope.js                   |  2 +-
 test/compress/destructuring.js | 20 +++++++++++++++
 3 files changed, 23 insertions(+), 44 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 9d54406e..a41c9fac 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2086,7 +2086,6 @@ merge(Compressor.prototype, {
         var var_defs_by_id = new Dictionary();
         var initializations = new Dictionary();
         var destructuring_value = null;
-        var in_definition = false;
         // pass 1: find out which symbols are directly used in
         // this scope (not in nested scopes).
         var scope = this;
@@ -2125,9 +2124,7 @@ merge(Compressor.prototype, {
                             if (def.name instanceof AST_Destructuring) {
                                 var destructuring_cache = destructuring_value;
                                 destructuring_value = def.value;
-                                in_definition = true;
                                 def.walk(tw);
-                                in_definition = false;
                                 destructuring_value = destructuring_cache;
                             } else {
                                 initializations.add(def.name.name, def.value);
@@ -2163,46 +2160,8 @@ merge(Compressor.prototype, {
                     scope = save_scope;
                     return true;
                 }
-                if (node instanceof AST_Destructuring) {
-                    if (!in_definition) {
-                        return true;
-                    }
-                    for (var i = 0; i < node.names.length; i++) {
-                        if (node.names[i] instanceof AST_Destructuring) {
-                            node.names[i].walk(tw);
-                        }
-                        else if (node.names[i] instanceof AST_Expansion) {
-                            if (node.names[i].expression instanceof AST_Symbol) {
-                                initializations.add(node.names[i].expression.name, destructuring_value);
-                            } else if (node.names[i].expression instanceof AST_Destructuring) {
-                                node.names[i].expression.walk(tw);
-                            } else {
-                                throw new Error(string_template("Can't handle expansion of type: {type}", {
-                                    type: Object.getPrototypeOf(node.names[i].expression).TYPE
-                                }));
-                            }
-                        }
-                        else if (node.names[i] instanceof AST_ObjectKeyVal) {
-                            if (typeof node.names[i].key === "string") {
-                                initializations.add(node.names[i].key, destructuring_value);
-                            }
-                        }
-                        else if (node.names[i] instanceof AST_Symbol) {
-                            initializations.add(node.names[i].name, destructuring_value);
-                        }
-                        else if (node.names[i] instanceof AST_DefaultAssign) {
-                            continue;
-                        }
-                        else if (node.names[i] instanceof AST_Hole) {
-                            continue;
-                        }
-                        else {
-                            throw new Error(string_template("Unknown destructuring element of type: {type}", {
-                                type: Object.getPrototypeOf(node.names[i]).TYPE
-                            }));
-                        }
-                    }
-                    return true;
+                if (node.destructuring && destructuring_value) {
+                    initializations.add(node.name, destructuring_value);
                 }
             }
         });
diff --git a/lib/scope.js b/lib/scope.js
index 59e55bab..33890c66 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -132,7 +132,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
             scope = save_scope;
             return true;
         }
-        if (node instanceof AST_Destructuring && node.is_array === false) {
+        if (node instanceof AST_Destructuring) {
             in_destructuring = node;  // These don't nest
             descend();
             in_destructuring = null;
diff --git a/test/compress/destructuring.js b/test/compress/destructuring.js
index 99b5842b..56adf266 100644
--- a/test/compress/destructuring.js
+++ b/test/compress/destructuring.js
@@ -639,3 +639,23 @@ issue_2044_ecma_6_beautify: {
     }
     expect_exact: "({x: a = 1, y = 2 + b, z = 3 - c} = obj);"
 }
+
+issue_2140: {
+    options = {
+        unused: true,
+    }
+    input: {
+        !function() {
+            var t = {};
+            console.log(([t.a] = [42])[0]);
+        }();
+    }
+    expect: {
+        !function() {
+            var t = {};
+            console.log(([t.a] = [42])[0]);
+        }();
+    }
+    expect_stdout: "42"
+    node_version: ">=6"
+}