fix(builtin): avoid unnecessary chdir to prevent worker threads from …

…failing

internal/node/node.bzl

@@ -279,7 +279,15 @@ fi
             fail("""nodejs_binary/nodejs_test only support chdir inside the current package
                     but %s is not a subfolder of %s""" % (ctx.attr.chdir, ctx.label.package))
         chdir_script = ctx.actions.declare_file(_join(relative_dir, "__chdir.js__"))
-        ctx.actions.write(chdir_script, "process.chdir(__dirname)")
+        ctx.actions.write(chdir_script, """
+/* This script is preloaded with --require, meaning it will run for the main node process
+   as well as each worker thread that gets spawned. Calling process.chdir() in a worker
+   is an error in node, so ensure it's only called once for the main process.
+*/
+if (process.cwd() !== __dirname) {
+    process.chdir(__dirname);
+}
+""")
         runfiles.append(chdir_script)
 
         # this join is effectively a $(rootdir) expansion

internal/node/test/chdir/BUILD.bazel

@@ -52,3 +52,10 @@ nodejs_test(
     data = ["build/app.js"],
     entry_point = "test.js",
 )
+
+nodejs_test(
+    name = "test_multithread",
+    chdir = package_name(),
+    data = ["worker.js"],
+    entry_point = "multithread.js",
+)

internal/node/test/chdir/multithread.js

@@ -0,0 +1,18 @@
+const { Worker } = require("worker_threads")
+
+function runWorker(message) {
+  return new Promise((resolve, reject) => {
+    const worker = new Worker("./worker.js", {workerData: {message}});
+    worker.on("message", resolve);
+    worker.on("error", reject);
+    worker.on("exit", code => {
+      if (0 !== code) {
+        reject(new Error(`Worker exited with code ${code}`));
+      }
+    });
+  })
+}
+
+(async () => {
+    await runWorker("foobar");
+})();

internal/node/test/chdir/worker.js

@@ -0,0 +1,4 @@
+const {parentPort, workerData} = require("worker_threads");
+
+console.log(workerData.message);
+parentPort.postMessage(true);