fix corner case in unused (#5867)

fixes #5866

lib/compress.js

@@ -8129,6 +8129,7 @@ Compressor.prototype.compress = function(node) {
         }
 
         function trim_destructured(node, value, process, drop, root) {
+            var unwind = true;
             var trimmer = new TreeTransformer(function(node) {
                 if (node instanceof AST_DefaultValue) {
                     if (!(compressor.option("default_values") && value && value.is_defined(compressor))) {
@@ -8146,21 +8147,27 @@ Compressor.prototype.compress = function(node) {
                 }
                 if (node instanceof AST_DestructuredArray) {
                     var save_drop = drop;
+                    var save_unwind = unwind;
                     var save_value = value;
                     if (value instanceof AST_SymbolRef) {
                         drop = false;
                         value = value.fixed_value();
                     }
-                    var native, values;
+                    var last_side_effects, native, values;
                     if (value instanceof AST_Array) {
                         native = true;
                         values = value.elements;
+                        if (save_unwind) for (last_side_effects = values.length; --last_side_effects >= 0;) {
+                            if (values[last_side_effects].has_side_effects(compressor)) break;
+                        }
                     } else {
                         native = value && value.is_string(compressor);
                         values = false;
+                        last_side_effects = node.elements.length;
                     }
                     var elements = [], newValues = drop && [], pos = 0;
                     node.elements.forEach(function(element, index) {
+                        if (save_unwind) unwind = index >= last_side_effects;
                         value = values && values[index];
                         if (value instanceof AST_Hole) {
                             value = null;
@@ -8203,6 +8210,7 @@ Compressor.prototype.compress = function(node) {
                         }
                     }
                     value = save_value;
+                    unwind = save_unwind;
                     drop = save_drop;
                     if (values && newValues) {
                         fill_holes(value, newValues);
@@ -8218,6 +8226,7 @@ Compressor.prototype.compress = function(node) {
                         return null;
                       case 1:
                         if (!drop) break;
+                        if (!unwind) break;
                         if (node === root) break;
                         var sym = elements[0];
                         if (sym.has_side_effects(compressor)) break;
@@ -8236,16 +8245,19 @@ Compressor.prototype.compress = function(node) {
                 }
                 if (node instanceof AST_DestructuredObject) {
                     var save_drop = drop;
+                    var save_unwind = unwind;
                     var save_value = value;
                     if (value instanceof AST_SymbolRef) {
                         drop = false;
                         value = value.fixed_value();
                     }
-                    var prop_keys, prop_map, values;
+                    var last_side_effects, prop_keys, prop_map, values;
                     if (value instanceof AST_Object) {
+                        last_side_effects = -1;
                         prop_keys = [];
                         prop_map = new Dictionary();
                         values = value.properties.map(function(prop, index) {
+                            if (save_unwind && prop.has_side_effects(compressor)) last_side_effects = index;
                             prop = prop.clone();
                             if (prop instanceof AST_Spread) {
                                 prop_map = false;
@@ -8261,6 +8273,8 @@ Compressor.prototype.compress = function(node) {
                             }
                             return prop;
                         });
+                    } else {
+                        last_side_effects = node.properties.length;
                     }
                     if (node.rest) {
                         value = false;
@@ -8283,6 +8297,7 @@ Compressor.prototype.compress = function(node) {
                         return key;
                     }).forEach(function(key, index) {
                         var prop = node.properties[index], trimmed;
+                        if (save_unwind) unwind = index >= last_side_effects;
                         if (key instanceof AST_Node) {
                             drop = false;
                             value = false;
@@ -8323,6 +8338,7 @@ Compressor.prototype.compress = function(node) {
                         }
                     });
                     value = save_value;
+                    unwind = save_unwind;
                     drop = save_drop;
                     if (drop_keys && prop_keys) {
                         value = value.clone();
@@ -8357,6 +8373,7 @@ Compressor.prototype.compress = function(node) {
                         return null;
                       case 1:
                         if (!drop) break;
+                        if (!unwind) break;
                         if (node === root) break;
                         var prop = properties[0];
                         if (prop.key instanceof AST_Node) break;

test/compress/destructured.js

@@ -4007,3 +4007,237 @@ issue_5854_2: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5866_1: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var a = {};
+        var { p: { q: b } } = {
+            p: a,
+            r: a.q = "PASS",
+        };
+        console.log(b);
+    }
+    expect: {
+        var a = {};
+        var { q: b } = {
+            p: a,
+            r: a.q = "PASS",
+        }.p;
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_2: {
+    options = {
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = {}, b;
+        ({ p: { q: b } } = {
+            p: a,
+            r: a.q = "PASS",
+        });
+        console.log(b);
+    }
+    expect: {
+        var b, a = {};
+        ({ q: b } = {
+            p: a,
+            r: a.q = "PASS",
+        }.p);
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_3: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var a = {};
+        var [ { p: b } ] = [ a, a.p = "PASS" ];
+        console.log(b);
+    }
+    expect: {
+        var a = {};
+        var { p: b } = [ a, a.p = "PASS" ][0];
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_4: {
+    options = {
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = {}, b;
+        [ { p: b } ] = [ a, a.p = "PASS" ];
+        console.log(b);
+    }
+    expect: {
+        var b, a = {};
+        ({ p: b } = [ a, a.p = "PASS" ][0]);
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_5: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var a = [];
+        var [ [ b ] ] = [ a, a[0] = "PASS" ];
+        console.log(b);
+    }
+    expect: {
+        var a = [];
+        var [ b ] = [ a, a[0] = "PASS" ][0];
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_6: {
+    options = {
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = [], b;
+        [ [ b ] ] = [ a, a[0] = "PASS" ];
+        console.log(b);
+    }
+    expect: {
+        var b, a = [];
+        [ b ] = [ a, a[0] = "PASS" ][0];
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_7: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var a = {};
+        var [ { p: b }, c ] = [ a, a.p = {} ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect: {
+        var a = {};
+        var [ { p: b }, c ] = [ a, a.p = {} ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_8: {
+    options = {
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = {}, b, c;
+        [ { p: b }, c ] = [ a, a.p = {} ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect: {
+        var b, c, a = {};
+        [ { p: b }, c ] = [ a, a.p = {} ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_9: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var a = {};
+        var [ b, { p: c } ] = [ a.p = {}, a ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect: {
+        var a = {};
+        var [ b, c ] = [ a.p = {}, a.p ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_10: {
+    options = {
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = {}, b, c;
+        [ b, { p: c } ] = [ a.p = {}, a ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect: {
+        var b, c, a = {};
+        [ b, c ] = [ a.p = {}, a.p ];
+        console.log(b === c ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_11: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var a = {};
+        var { p: { q: b } } = { p: a = { q: {} } };
+        console.log(a.q === b ? "PASS" : "FAIL");
+    }
+    expect: {
+        var a = {};
+        var b = { p: (a = { q: {} }).q }.p;
+        console.log(a.q === b ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5866_12: {
+    options = {
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        var a = {}, b;
+        ({ p: { q: b } } = { p: a = { q: {} } });
+        console.log(a.q === b ? "PASS" : "FAIL");
+    }
+    expect: {
+        var b, a = {};
+        b = { p: (a = { q: {} }).q }.p;
+        console.log(a.q === b ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}