patch export default within sandbox correctly (#5346)

fixes #5345

test/input/reduce/export_default.js

@@ -0,0 +1,17 @@
+var unused;
+export default class {
+    ____11111() {
+        a, b, c, d, e;
+        f, g, h, i, j;
+        k, l, m, n, o;
+        p, q, r, s, t;
+        u, v, w, x, y, z;
+        A, B, C, D, E;
+        F, G, H, I, J;
+        K, L, M, N, O;
+        P, Q, R, S, T;
+        U, V, W, X, Y, Z;
+        $, _;
+        unused;
+    }
+}

test/mocha/reduce.js

@@ -434,4 +434,18 @@ describe("test/reduce.js", function() {
             "// }",
         ].join("\n"));
     });
+    it("Should transform `export default` correctly", function() {
+        var result = reduce_test(read("test/input/reduce/export_default.js"), {
+            compress: false,
+            toplevel: true,
+        });
+        if (result.error) throw result.error;
+        assert.strictEqual(result.code, [
+            "// Can't reproduce test failure",
+            "// minify options: {",
+            '//   "compress": false,',
+            '//   "toplevel": true',
+            "// }",
+        ].join("\n"));
+    });
 });

test/reduce.js

@@ -50,37 +50,34 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
         test_for_diff = test_minify;
         differs = test_for_diff(testcase, minify_options, result_cache, max_timeout);
     }
-    if (!differs) {
     // same stdout result produced when minified
-        return {
+    if (!differs) return {
         code: [
             "// Can't reproduce test failure",
             "// minify options: " + to_comment(minify_options_json)
         ].join("\n"),
         warnings: warnings,
     };
-    } else if (differs.timed_out) {
-        return {
+    if (differs.timed_out) return {
         code: [
             "// Can't reproduce test failure within " + max_timeout + "ms",
             "// minify options: " + to_comment(minify_options_json)
         ].join("\n"),
         warnings: warnings,
     };
-    } else if (differs.error) {
+    if (differs.error) {
         differs.warnings = warnings;
         return differs;
-    } else if (sandbox.is_error(differs.unminified_result)
+    }
+    if (sandbox.is_error(differs.unminified_result)
         && sandbox.is_error(differs.minified_result)
-        && differs.unminified_result.name == differs.minified_result.name) {
-        return {
+        && differs.unminified_result.name == differs.minified_result.name) return {
         code: [
             "// No differences except in error message",
             "// minify options: " + to_comment(minify_options_json)
         ].join("\n"),
         warnings: warnings,
     };
-    } else {
     max_timeout = Math.min(100 * differs.elapsed, max_timeout);
     // Replace expressions with constants that will be parsed into
     // AST_Nodes as required.  Each AST_Node has its own permutation count,
@@ -513,9 +510,10 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
         }
     });
 
-        var diff_error_message;
-        for (var pass = 1; pass <= 3; ++pass) {
-            var testcase_ast = U.parse(testcase);
+    var before_iterations, diff_error_message, passes = 3, testcase_ast;
+    for (var pass = 1; pass <= passes; pass++) {
+        if (before_iterations !== testcase) {
+            testcase_ast = U.parse(testcase);
             if (diff_error_message === testcase) {
                 // only difference detected is in error message, so expose that and try again
                 testcase_ast.transform(new U.TreeTransformer(function(node, descend) {
@@ -546,8 +544,9 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
                 node.start = JSON.parse(JSON.stringify(node.start));
                 node.start._permute = 0;
             }));
-            var before_iterations = testcase;
-            for (var c = 0; c < max_iterations; ++c) {
+            before_iterations = testcase;
+        }
+        for (var c = 0; c < max_iterations; c++) {
             if (verbose && c % (pass == 1 ? 25 : 100) == 0) {
                 log("// reduce test pass " + pass + ", iteration " + c + ": " + testcase.length + " bytes");
             }
@@ -589,10 +588,9 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
                 }
             }
         }
-            if (before_iterations === testcase) break;
-            if (verbose) {
-                log("// reduce test pass " + pass + ": " + testcase.length + " bytes");
-            }
+        if (before_iterations !== testcase) continue;
+        if (c < max_iterations) break;
+        passes++;
     }
     var beautified = U.minify(testcase, {
         compress: false,
@@ -639,7 +637,6 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
     testcase.code += lines.join("\n");
     testcase.warnings = warnings;
     return testcase;
-    }
 };
 
 function to_comment(value) {

test/sandbox.js

@@ -56,7 +56,10 @@ exports.patch_module_statements = function(code) {
     code = code.replace(/\bexport(?:\s*\{[^{}]*}\s*?(?:$|\n|;)|\s+default\b(?:\s*(\(|\{|class\s*\{|class\s+(?=extends\b)|(?:async\s+)?function\s*(?:\*\s*)?\())?|\b)/g, function(match, header) {
         if (!header) return "";
         if (header.length == 1) return "0, " + header;
-        return header.slice(0, -1) + " _" + ++count + header.slice(-1);
+        do {
+            var name = "_export_default_" + ++count;
+        } while (code.indexOf(name) >= 0);
+        return header.slice(0, -1) + " " + name + header.slice(-1);
     }).replace(/\bimport\.meta\b/g, function() {
         return '({ url: "https://example.com/path/index.html" })';
     }).replace(/\bimport\b(?:\s*([^\s('"][^('"]*)\bfrom\b)?\s*(['"]).*?\2(?:$|\n|;)/g, function(match, symbols) {