enable-experimental-regexp-engine v8 flag doesn't work with promises

[brian6932]

Version

v22.9.0

Platform

Microsoft Windows NT 10.0.19044.0 x64

Subsystem

No response

What steps will reproduce the bug?

❯ node --enable-experimental-regexp-engine
Welcome to Node.js v22.9.0.
Type ".help" for more information.
> /foo/l
/foo/l

> (() => /foo/l)()
/foo/l

> await /foo/l
Uncaught SyntaxError:
await /foo/l
       ^

Invalid regular expression flag

> await (async () => /foo/l)()
Uncaught SyntaxError:
await (async () => /foo/l)()
                    ^

Invalid regular expression flag

> await (function() { return /foo/l })()
Uncaught SyntaxError:
await (function() { return /foo/l })()
                            ^

Invalid regular expression flag

> await new Promise(resolve => resolve(/foo/l))
Uncaught SyntaxError:
await new Promise(resolve => resolve(/foo/l))
                                      ^

Invalid regular expression flag

> await Promise.resolve(/foo/l)
Uncaught SyntaxError:
await Promise.resolve(/foo/l)
                       ^

Invalid regular expression flag

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

The linear regex must be created, and wrapped in a Promise, closures experience no such issues.

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

The linear flag should be parsed and executed as expected.

What do you see instead?

Invalid regular expression flag

Additional information

No response

[RedYetiDev]

This seems to be only reproducible in the REPL, and not via an actual script. It probably has to do with top-level await.

[aduh95]

--enable-experimental-regexp-engine is not documented, therefore it's not a flag we support.

node/doc/api/cli.md

Lines 3472 to 3476 in d6175b3

	V8 has its own set of CLI options. Any V8 CLI option that is provided to `node`
	will be passed on to V8 to handle. V8's options have _no stability guarantee_.
	The V8 team themselves don't consider them to be part of their formal API,
	and reserve the right to change them at any time. Likewise, they are not
	covered by the Node.js stability guarantees. Many of the V8

You would probably get better results by passing --no-experimental-repl-await, and/or using the RegExp constructor instead.
Closing as won't fix.

[brian6932]

You would probably get better results by passing --no-experimental-repl-await

I understand, I've ran into this in more than just Node repl (in some eval sandboxes lacking top-level await), and believe there's an underlying v8 or Node bug somewhere here. I don't have enough info as to why it happens though. It's kinda interesting that it's only occurring with the primitive, and not the constructor.

[F3n67u]

This issue is caused by acorn doesn't support linear regex.

Top-level await is not handled by V8 directly, in order to support top-level await, Node use acorn to parse and preprocess top-level await code(see #15566).
When parsing linear regex expression literal, acorn throw a "SyntaxError: Invalid regular expression flag" because it doesn't understand what flag "l" is. You can use https://astexplorer.net/ to test it.

Why it doesn't happen when using Regex constructor like new RegExp("foo", "l")?
I guess acorn just handle flag param as a string, it doesn't parse it like in regex expression literal.