`node --v8-options` says that you can use a space between the flag name and value, but it's not true

[nicolo-ribaudo]

Version

v22.5.1

Platform

Linux nic-desktop 6.9.3-76060903-generic #202405300957~1718348209~22.04~7817b67 SMP PREEMPT_DYNAMIC Mon J x86_64 x86_64 x86_64 GNU/Linux

Subsystem

cli

What steps will reproduce the bug?

node --v8-options prints:

The following syntax for options is accepted (both '-' and '--' are ok):
  --flag        (bool flags only)
  --no-flag     (bool flags only)
  --flag=value  (non-bool flags only, no spaces around '=')
  --flag value  (non-bool flags only)
  --            (captures all remaining args in JavaScript)

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

/

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

The help output should match the implementation

What do you see instead?

It's not true that I can use --flag value. If I try running node --arm-arch armv8 foo.js it parses armv8 as the script name, rather than as if it was node --arm-arch=armv8 foo.js

Additional information

No response

[targos]

The output of --v8-options comes from V8 itself:

node/deps/v8/src/flags/flags.cc

Lines 814 to 821 in 4d1d881

	os << "The following syntax for options is accepted (both '-' and '--' are "
	"ok):\n"
	" --flag (bool flags only)\n"
	" --no-flag (bool flags only)\n"
	" --flag=value (non-bool flags only, no spaces around '=')\n"
	" --flag value (non-bool flags only)\n"
	" -- (captures all remaining args in JavaScript)\n\n";
	os << "Options:\n";

[nicolo-ribaudo]

Well that output is correct when using d8 directly 🙂 However, Node.js' logic to decide what to pass to V8 and what to consider as the filename is different from V8, and when Node.js sees --a-v8-flag value it considers value as the filename and doesn't pass it to V8.

[joyeecheung]

We take spaces for setting Node.js flags, there's probably something wrong with our CLI options parsing logic for the V8 options - IIRC, we just split the options "somehow", then feed them to V8 to see if V8 takes them - if V8 takes them they are V8 flags and we remove them from the list, otherwise keep them for Node.js option parsing later, so something might be lacking in the first step. IMO it looks more like a option parsing bug that should be fixed, rather than incorrect doc.

[joyeecheung]

❯ node --max-old-space-size 100 test.js
Error: Value for flag --max-old-space-size of type size_t is out of bounds [0-18446744073709551615]
Error: illegal value for flag --max-old-space-size of type size_t
Try --help for options
node: bad option: --max-old-space-size
node: bad option: --harmony-import-attributes
node: bad option: --no-harmony-import-assertions

Also the error of this isn't exactly pretty, but this has been the case since Node 4, so it's probably some very old bug 😵‍💫 and there might be some very old issues in the ex-iojs repo.

[nicolo-ribaudo]

@joyeecheung Unfortunately supporting V8 options with the space rather than = requires a list of options that accept a value and that don't, because you need to know whether 100 is the option value or the filename in your example. I implemented very similar logic in the split-args.ts file in https://github.com/babel/babel/pull/16706/files#diff-7f26ee14d79b9d9d2936068fef64b790e937272ef72404f608b250fcc0c58d16

V8 doesn't expose that list, so it should be Node.js itself maintaining it and making sure that it's correct every time V8 is updated. Given that as far as I can tell nobody complained about this in many years, and I only noticed because I was trying to understand how Node.js parses its cli arguments, it might be much easier to just consider this as "well, maybe it was a bug but now it's just how it works" and float a patch on top of V8 to remove that output line.