fix: babel-plugin-minify-mangle-names default parameter error

packages/webcrack/src/ast-utils/matcher.ts

@@ -2,7 +2,10 @@ import { Binding, NodePath } from '@babel/traverse';
 import * as t from '@babel/types';
 import * as m from '@codemod/matchers';
 
-export const anyLiteral: m.Matcher<t.Literal> = m.matcher(
+/**
+ * Matches any literal except for template literals with expressions (that could have side effects)
+ */
+export const safeLiteral: m.Matcher<t.Literal> = m.matcher(
   (node) =>
     t.isLiteral(node) &&
     (!t.isTemplateLiteral(node) || node.expressions.length === 0),

packages/webcrack/src/deobfuscate/merge-object-assignments.ts

@@ -1,7 +1,7 @@
 import { Binding } from '@babel/traverse';
 import * as t from '@babel/types';
 import * as m from '@codemod/matchers';
-import { Transform, anyLiteral, constObjectProperty } from '../ast-utils';
+import { Transform, constObjectProperty, safeLiteral } from '../ast-utils';
 
 /**
  * Merges object assignments into the object expression.
@@ -109,7 +109,7 @@ function hasCircularReference(node: t.Node, binding: Binding) {
 const inlineableObject: m.Matcher<t.Expression> = m.matcher((node) =>
   m
     .or(
-      anyLiteral,
+      safeLiteral,
       m.arrayExpression(m.arrayOf(inlineableObject)),
       m.objectExpression(m.arrayOf(constObjectProperty(inlineableObject))),
     )

packages/webcrack/src/transforms/mangle.ts

@@ -1,7 +1,41 @@
-import traverse, { NodePath } from '@babel/traverse';
+import { statement } from '@babel/template';
+import traverse, { NodePath, Visitor, visitors } from '@babel/traverse';
 import * as t from '@babel/types';
 import mangle from 'babel-plugin-minify-mangle-names';
-import { Transform } from '../ast-utils';
+import { Transform, safeLiteral } from '../ast-utils';
+
+// See https://github.com/j4k0xb/webcrack/issues/41 and https://github.com/babel/minify/issues/1023
+const fixDefaultParamError: Visitor = {
+  Function(path) {
+    const { params } = path.node;
+
+    for (let i = params.length - 1; i >= 0; i--) {
+      const param = params[i];
+      if (!t.isAssignmentPattern(param) || safeLiteral.match(param.right))
+        continue;
+
+      if (!t.isBlockStatement(path.node.body)) {
+        path.node.body = t.blockStatement([t.returnStatement(path.node.body)]);
+      }
+
+      const body = path.get('body') as NodePath<t.BlockStatement>;
+      if (t.isIdentifier(param.left)) {
+        body.unshiftContainer(
+          'body',
+          statement`if (${param.left} === undefined) ${param.left} = ${param.right}`(),
+        );
+      } else {
+        const tempId = path.scope.generateUidIdentifier();
+        body.unshiftContainer(
+          'body',
+          statement`var ${param.left} = ${tempId} === undefined ? ${param.right} : ${tempId}`(),
+        );
+        param.left = tempId;
+      }
+      param.right = t.identifier('undefined');
+    }
+  },
+};
 
 export default {
   name: 'mangle',
@@ -12,8 +46,12 @@ export default {
     // eslint-disable-next-line @typescript-eslint/unbound-method
     const { getSource } = NodePath.prototype;
     NodePath.prototype.getSource = () => '';
+    const visitor = visitors.merge([
+      fixDefaultParamError,
+      mangle({ types: t, traverse }).visitor,
+    ]);
 
-    traverse(ast, mangle({ types: t, traverse }).visitor, undefined, {
+    traverse(ast, visitor, undefined, {
       opts: {
         eval: true,
         topLevel: true,

packages/webcrack/test/mangle.test.ts

@@ -0,0 +1,45 @@
+import { test } from 'vitest';
+import { testTransform } from '.';
+import mangle from '../src/transforms/mangle';
+
+const expectJS = testTransform(mangle);
+
+// https://github.com/j4k0xb/webcrack/issues/41
+test('rename default parameters of function', () => {
+  expectJS(`
+    function func(arg1, arg2 = 0, arg3 = arg1, arg4 = arg1) {
+      return arg1;
+    }
+  `).toMatchInlineSnapshot(`
+    function a(a, b = 0, c = undefined, d = undefined) {
+      if (c === undefined) c = a;
+      if (d === undefined) d = a;
+      return a;
+    }
+  `);
+});
+
+test('rename default parameters of arrow function', () => {
+  expectJS(`
+    const func = (arg1, arg2 = 0, arg3 = arg1, arg4 = arg1) => arg1;
+  `).toMatchInlineSnapshot(`
+    const a = (a, b = 0, c = undefined, d = undefined) => {
+      if (c === undefined) c = a;
+      if (d === undefined) d = a;
+      return a;
+    };
+  `);
+});
+
+test('rename default destructuring parameters', () => {
+  expectJS(`
+    function func(arg1, [arg2] = arg1) {
+      return arg2;
+    }
+  `).toMatchInlineSnapshot(`
+    function a(a, b = undefined) {
+      var [c] = b === undefined ? a : b;
+      return c;
+    }
+  `);
+});