From d75a946707f6f721b69d046f607426d5a3c6f8db Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Sun, 3 Apr 2022 14:57:37 +0100
Subject: [PATCH] fix corner case in `reduce_vars` (#5406)

fixes #5405
---
 lib/compress.js               | 36 +++++++++++++++++++++------------
 test/compress/destructured.js | 38 +++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 13 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 1998311f..918366e2 100644
--- a/lib/compress.js
+++ b/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() {
-                        var value = save();
+                    if (save) fixed = make_fixed(save, function(value) {
                         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() {
-                            var value = save();
+                        if (save) fixed = compressor.option("rests") && make_fixed(save, function(value) {
                             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(),
-                                property: key
+                                expression: value,
+                                property: key,
                             });
-                        };
+                        });
                         node.value.walk(scanner);
                     });
                     if (node.rest) {
diff --git a/test/compress/destructured.js b/test/compress/destructured.js
index 7850d516..9a06c35b 100644
--- a/test/compress/destructured.js
+++ b/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"
+}