worker: enable passing command line flags

This PR adds the ability to provide Workers with their own
execArgv flags in replacement of the main thread's execArgv. Only
per-Isolate/per-Environment options are allowed. Per-Process options
and V8 flags are not allowed. Passing an empty execArgv array will
reset per-Isolate and per-Environment options of the Worker to their
defaults. If execArgv option is not passed, the Worker will get
the same flags as the main thread.

Usage example:
```
const worker = new Worker(__filename, {
    execArgv: ['--trace-warnings'],
});
```

PR-URL: https://github.com/nodejs/node/pull/25467
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

2 files changed, 14 insertions, 2 deletions

diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 12b01ffb9b..b33cd27109 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -992,6 +992,9 @@ E('ERR_VM_MODULE_NOT_LINKED',
 E('ERR_VM_MODULE_NOT_MODULE',
   'Provided module is not an instance of Module', Error);
 E('ERR_VM_MODULE_STATUS', 'Module status %s', Error);
+E('ERR_WORKER_INVALID_EXEC_ARGV', (errors) =>
+  `Initiated Worker with invalid execArgv flags: ${errors.join(', ')}`,
+  Error);
 E('ERR_WORKER_PATH',
   'The worker script filename must be an absolute path or a relative ' +
   'path starting with \'./\' or \'../\'. Received "%s"',
diff --git a/lib/internal/worker.js b/lib/internal/worker.js
index 2e1568a738..e20a37af8a 100644
--- a/lib/internal/worker.js
+++ b/lib/internal/worker.js
@@ -8,6 +8,8 @@ const {
   ERR_WORKER_PATH,
   ERR_WORKER_UNSERIALIZABLE_ERROR,
   ERR_WORKER_UNSUPPORTED_EXTENSION,
+  ERR_WORKER_INVALID_EXEC_ARGV,
+  ERR_INVALID_ARG_TYPE,
 } = require('internal/errors').codes;
 const { validateString } = require('internal/validators');
 
@@ -49,7 +51,11 @@ class Worker extends EventEmitter {
     super();
     debug(`[${threadId}] create new worker`, filename, options);
     validateString(filename, 'filename');
-
+    if (options.execArgv && !Array.isArray(options.execArgv)) {
+      throw new ERR_INVALID_ARG_TYPE('options.execArgv',
+                                     'array',
+                                     options.execArgv);
+    }
     if (!options.eval) {
       if (!path.isAbsolute(filename) &&
           !filename.startsWith('./') &&
@@ -68,7 +74,10 @@ class Worker extends EventEmitter {
 
     const url = options.eval ? null : pathToFileURL(filename);
     // Set up the C++ handle for the worker, as well as some internal wiring.
-    this[kHandle] = new WorkerImpl(url);
+    this[kHandle] = new WorkerImpl(url, options.execArgv);
+    if (this[kHandle].invalidExecArgv) {
+      throw new ERR_WORKER_INVALID_EXEC_ARGV(this[kHandle].invalidExecArgv);
+    }
     this[kHandle].onexit = (code) => this[kOnExit](code);
     this[kPort] = this[kHandle].messagePort;
     this[kPort].on('message', (data) => this[kOnMessage](data));