preventing infinite loops

Author: al3xnag

packages/jsrepl/src/hooks/useCodeEditorRepl.ts

@@ -290,6 +290,6 @@ export default function useCodeEditorRepl(
 
 function updateToken() {
   replDataRef.current = {
-    token: (replDataRef.current.token + 1) % Number.MAX_VALUE,
+    token: (replDataRef.current.token + 1) % Number.MAX_SAFE_INTEGER,
   }
 }

packages/jsrepl/src/lib/bundler/babel/prevent-infinite-loops-plugin.ts

@@ -0,0 +1,61 @@
+// Based on https://github.com/facebook/react/blob/ff595de29af107255fd957ca809d3074c16bcf12/scripts/babel/transform-prevent-infinite-loops.js
+
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2017, Amjad Masad
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+import type { NodePath, PluginObj, template as templateBuilder, types } from '@babel/core'
+
+// Based on https://repl.it/site/blog/infinite-loops.
+
+const MAX_ITERATIONS = 6000
+
+export function preventInfiniteLoopsPlugin({
+  types: t,
+  template,
+}: {
+  types: typeof types
+  template: typeof templateBuilder
+}): PluginObj {
+  const buildGuard = template.statement(`
+    if (%%iterator%%++ > %%maxIterations%%) {
+      throw new RangeError(
+        'Potential infinite loop: exceeded ' + %%maxIterations%% + ' iterations.'
+      );
+    }
+  `)
+
+  return {
+    visitor: {
+      'WhileStatement|ForStatement|DoWhileStatement'(_path) {
+        const path = _path as NodePath<
+          types.WhileStatement | types.ForStatement | types.DoWhileStatement
+        >
+
+        // An iterator that is incremented with each iteration
+        const iterator = path.scope.parent.generateUidIdentifier('loopIt')
+        const iteratorInit = t.numericLiteral(0)
+        path.scope.parent.push({
+          id: iterator,
+          init: iteratorInit,
+        })
+        // If statement and throw error if it matches our criteria
+        const guard = buildGuard({
+          iterator,
+          maxIterations: t.numericLiteral(MAX_ITERATIONS),
+        })
+        const bodyPath = path.get('body')
+        // No block statement e.g. `while (1) 1;`
+        if (!bodyPath.isBlockStatement()) {
+          const statement = bodyPath.node
+          bodyPath.replaceWith(t.blockStatement([guard, statement]))
+        } else {
+          bodyPath.unshiftContainer('body', guard)
+        }
+      },
+    },
+  }
+}