Worker with large inline source map aborts process in V8 HandleDebugMagicComments

Version

v26.4.0

Platform

macOS 15.x arm64

Subsystem

worker_threads

What steps will reproduce the bug?

Create a worker entry file with a small amount of executable JavaScript and a very large inline sourceMappingURL=data:... comment, then load it in a worker with a constrained heap.

Minimal repro:

const fs = require("node:fs");
const os = require("node:os");
const path = require("node:path");
const { Worker } = require("node:worker_threads");

const dir = fs.mkdtempSync(path.join(os.tmpdir(), "node-inline-sourcemap-oom-"));

const workerPath = path.join(dir, "worker.cjs");

const source = [
  'const { parentPort } = require("node:worker_threads");',
  'parentPort.postMessage("loaded");',
  'parentPort.close();',
  "",
  "//# sourceMappingURL=data:application/json;base64,",
  "A".repeat(64 * 1024 * 1024),
  "",
].join("\n");

fs.writeFileSync(workerPath, source);

const worker = new Worker(workerPath, {
  resourceLimits: {
    maxOldGenerationSizeMb: 16,
  },
});

worker.on("message", console.log);

worker.on("error", console.error);

worker.on("exit", (code) => {
  console.log("exit", code);
  fs.rmSync(dir, { recursive: true, force: true });
});

Run: node repro.js

How often does it reproduce? Is there a required condition?

It reproduces consistently when the inline sourcemap comment is large enough relative to the worker heap limit.

For comparison, these do not reproduce the same fatal abort:

1. Keeping the same large payload in an external worker.cjs.map file and using //# sourceMappingURL=worker.cjs.map.
2. Putting a similarly large payload in a normal non-sourceMappingURL comment.

What is the expected behavior? Why is that the expected behavior?

The worker should fail gracefully, for example by emitting an error event or exiting with a worker failure, without aborting the entire Node.js process.

Ideally, parsing sourceMappingURL / debug magic comments should not internalize an arbitrarily large data URL into V8 old space during module compilation.

What do you see instead?

The whole Node process aborts with an out-of-memory fatal error before the worker can load the module.

Example stack from Node v26.4.0:

FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory
...
v8::internal::FactoryBase<v8::internal::Factory>::AllocateRawOneByteInternalizedString
v8::internal::FactoryBase<v8::internal::Factory>::NewOneByteInternalizedString
v8::internal::StringTable::LookupKey
v8::internal::FactoryBase<v8::internal::Factory>::InternalizeString
void v8::internal::Parser::HandleDebugMagicComments
v8::internal::Parser::ParseProgram
v8::internal::parsing::ParseProgram
v8::internal::Compiler::GetWrappedFunction
v8::ScriptCompiler::CompileFunction
node::contextify::CompileFunctionForCJSLoader
node::worker::Worker::Run

Additional information

No response

Inizia con il repro.js fornito e con lo stack che passa attraverso V8's Parser::HandleDebugMagicComments, quindi confronta le source map inline ed esterne sotto il limite dell'heap del worker. Traccia l'ingresso del worker attraverso node::worker::Worker::Run e identifica dove si verifica l'allocazione fatale. Il lavoro è completato quando repro non interrompe più il processo Node.js e il worker segnala l'errore correttamente.