fix corner case in reduce_vars (#5406)

fixes #5405

lib/compress.js

@@ -751,6 +751,18 @@ Compressor.prototype.compress = function(node) {
             });
         }
 
+        function make_fixed(save, fn) {
+            var prev_save, prev_value;
+            return function() {
+                var current = save();
+                if (prev_save !== current) {
+                    prev_save = current;
+                    prev_value = fn(current);
+                }
+                return prev_value;
+            };
+        }
+
         function scan_declaration(tw, compressor, lhs, fixed, visit) {
             var scanner = new TreeWalker(function(node) {
                 if (node instanceof AST_DefaultValue) {
@@ -759,15 +771,14 @@ Compressor.prototype.compress = function(node) {
                     node.value.walk(tw);
                     pop(tw);
                     var save = fixed;
-                    if (save) fixed = function() {
+                    if (save) fixed = make_fixed(save, function(value) {
-                        var value = save();
                         var ev;
                         if (is_undefined(value, compressor)
                             || (ev = fuzzy_eval(compressor, value, true)) === undefined) {
                             return make_sequence(node, [ value, node.value ]);
                         }
                         return ev instanceof AST_Node ? node : value;
-                    };
+                    });
                     node.name.walk(scanner);
                     fixed = save;
                     return true;
@@ -777,18 +788,17 @@ Compressor.prototype.compress = function(node) {
                     var save = fixed;
                     node.elements.forEach(function(node, index) {
                         if (node instanceof AST_Hole) return reset_flags(node);
-                        if (save) fixed = function() {
+                        if (save) fixed = make_fixed(save, function(value) {
                             return make_node(AST_Sub, node, {
-                                expression: save(),
+                                expression: value,
                                 property: make_node(AST_Number, node, { value: index }),
                             });
-                        };
+                        });
                         node.walk(scanner);
                     });
                     if (node.rest) {
                         var fixed_node;
-                        if (save) fixed = compressor.option("rests") && function() {
+                        if (save) fixed = compressor.option("rests") && make_fixed(save, function(value) {
-                            var value = save();
                             if (!(value instanceof AST_Array)) return node;
                             for (var i = 0, len = node.elements.length; i < len; i++) {
                                 if (value.elements[i] instanceof AST_Spread) return node;
@@ -796,7 +806,7 @@ Compressor.prototype.compress = function(node) {
                             if (!fixed_node) fixed_node = make_node(AST_Array, node);
                             fixed_node.elements = value.elements.slice(len);
                             return fixed_node;
-                        };
+                        });
                         node.rest.walk(scanner);
                     }
                     fixed = save;
@@ -812,7 +822,7 @@ Compressor.prototype.compress = function(node) {
                             node.key.walk(tw);
                             pop(tw);
                         }
-                        if (save) fixed = function() {
+                        if (save) fixed = make_fixed(save, function(value) {
                             var key = node.key;
                             var type = AST_Sub;
                             if (typeof key == "string") {
@@ -823,10 +833,10 @@ Compressor.prototype.compress = function(node) {
                                 }
                             }
                             return make_node(type, node, {
-                                expression: save(),
+                                expression: value,
-                                property: key
+                                property: key,
+                            });
                         });
-                        };
                         node.value.walk(scanner);
                     });
                     if (node.rest) {

test/compress/destructured.js

@@ -3497,3 +3497,41 @@ issue_5370: {
     expect_stdout: true
     node_version: ">=6"
 }
+
+issue_5405_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unsafe: true,
+    }
+    input: {
+        var [ a ] = [ {} ];
+        console.log(a === a ? "PASS" : "FAIL");
+    }
+    expect: {
+        var [ a ] = [ {} ];
+        console.log(true ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5405_2: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unsafe: true,
+    }
+    input: {
+        var { p: a } = { p: [] };
+        console.log(a === a ? "PASS" : "FAIL");
+    }
+    expect: {
+        var { p: a } = { p: [] };
+        console.log(true ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}