deprecate --use_strict

[ljharb]

I'd like to reopen the discussion from nodejs/node-v0.x-archive#7479 if possible about somehow deprecating/removing this flag.

Whether the v8 team is willing to remove or rename it, or not (which we should probably re-investigate), I would like node to find a way to have it be removed or renamed.

[Fishrock123]

cc @nodejs/v8

[Fishrock123]

Arguments are passed verbatim to v8, I'm not sure we're keen on altering that..

[mscdex]

I'm -1 on interfering with (or documenting) command-line options provided by v8.

[vkurchatkin]

-1, this flag is useful

[Fishrock123]

-1, this flag is useful

@vkurchatkin Mind to elaborate on that?

[ljharb]

How is it useful? The flag is not the same as "use strict", and it's dangerous to execute sloppy code in strict mode anyways.

[cjihrig]

As recently as #6377, we rejected documenting V8 flags. This goes even further beyond that. I think it would be simplest for people to just not use it.

[ljharb]

The reasons for rejecting documentation is given as "… those are not under our control to change but as soon as we document it they become our responsibility to maintain". This is different - this is ensuring with certainty that no node users could ever depend on the v8 flag, which reduces the maintenance needed from the node core team (aside from maintaining a blacklist, for example)

[ljharb]

In other words, if --use_strict was removed by the v8 team, it's a breaking change for node anyways, documented or not. Blacklisting it lets you control when the breaking change occurs, and prevents it from ever occurring in the future.

[vkurchatkin]

Don't want to state the obvious, but it's useful when you want to run all javascript in strict mode. I think it's well understood that strict mode is not the default mode only because it's not backwards compatible.

[ljharb]

@vkurchatkin yes but --use_strict is not JavaScript, and at least in past versions of node, even some internal modules failed with this flag. If you want to run all of your JS in strict mode, you'd use ES6 modules (babel-transpiled, or one day, native) or put "use strict" on the top of every file - when would you want to run code you didn't author in a nonstandard mode?

[vkurchatkin]

I agree that most people don't need it, but that doesn't mean that we should remove it.

For example I use v8 on android to run some js in strict mode and use node to test this code on desktop. There are no dependencies, so I use --use_strict

[trevnorris]

@ljharb There are 389 options in node --v8-options, and I'm pretty sure ones like --use_strong, or --strong_this or --fast_math or --expose_wasm or --expose_gc or --allow_natives_syntax (all of these I do use in development), are "not JavaScript". This discussion revolves around an obscure flag, just like many others, that sit outside our direct control. It seems strange we'd consider removing only one of potentially many "not JavaScript" or not "useful" ones without taking into consideration all the other flags that should also be removed.

Also, what evidence is there that this flag is actually problematic or harmful in the ecosystem?

[ChALkeR]

@trevnorris People sometimes report issues like «your module is broken and doesn't work … I used --use_strict» to various repos.

Still, I don't think that blacklisting this would do any good — some people might need it, as @vkurchatkin noted, and there are a lot more flags that affect the behaviour in a unsafe way, and not only the ones that @trevnorris noted. E.g. --harmony-* flags often make the process crash in certain situations, etc.

IMO, we shouldn't blacklist anything, but we could print a warning if certain flags are detected (without modifying the flags, though). But such warning should cover much more than just --use-strict — if we introduce such warnings, it would make sense to warn against --harmony flags (reminding that those should be used only for testing, not in production).

Btw, there is even such a thing as https://github.com/isaacs/use-strict.

[Fishrock123]

I'd be in favor of warning against --use_strict and --harmony and --es_staging.

[ChALkeR]

@Fishrock123 And --harmony-*. 😉

[ljharb]

Note as well that if node truly wants VM neutrality, blindly passing through engine flags isn't going to be sustainable - so node may soon have to maintain an exclusion list/inclusion list of flags anyways.

[jasnell]

@Fishrock123 ... docs warning or runtime warning?

[trevnorris]

@ljharb I don't see maintaining that type of exclusion list as an option. It would be impossible to debug and tune for individual VMs if all options to do so were removed. For example, while the v8 module name is specific to the VM, it should be left there for v8 builds. It provides important information if ever debugging a VM specific issue. Similar to what we've been troubleshooting with GC and Typed Arrays.

[Fishrock123]

Note as well that if node truly wants VM neutrality, blindly passing through engine flags isn't going to be sustainable - so node may soon have to maintain an exclusion list/inclusion list of flags anyways.

Could you elaborate why it wouldn't be? I don't see any problem here. (Also, developing our own vm flags is pretty silly and out of scope for sure.)

[Fishrock123]

@jasnell presumably runtime, might have to be in c++ though I think, since this happens before the VM boots up.

[vkurchatkin]

@ljharb this is one of the reasons why true VM neutrality is very unlikely. Each VM has it's own flags for tuning critical subsystems (e.g. GC), which will be very hard to reconcile

[Fishrock123]

I don't see a reason we have to be VM neutral on flags when we can just keep passing flags to the VM that is being used.

[jasnell]

@Fishrock123 ... yep, I've had it on my todo to see if we can hook into process warning easily from native but a simple message printed to stderr on startup works for me.... Perhaps it would be worthwhile printing the warning when any VM specific flag is used? If --no-warnings flag is used, go ahead and skip the warning tho.

[ChALkeR]

@jasnell I don't think this justifies warnings on debug flags, e.g. --trace-gc.

[bnoordhuis]

FTR, I disagree completely with blacklisting or warning. I'm an adult, I don't need a computer program telling me what I should or shouldn't do. It's paternalistic.

[ChALkeR]

@bnoordhuis, this isn't something like "don't do this" kind of warning, I was thinking of something that is more like a friendly reminder, e.g. "Notice: using flagged harmony features might not work as expected and might even crash the process".

[littledan]

About forwarding flags: Chromium embeds V8 by forwarding flags through a special option, --js-flags=<things-to-forward-to-v8>. There are then some Chromium flags, like --javascript-harmony, which explicitly forwards into --harmony to V8. This strategy seems to work well for us. The V8 team frequently adds and removes flags, especially through the lifecycle of developing a new feature, staging it, shipping it, and then removing the conditionality of the feature as it is cemented into the code, so flags are not guaranteed to be a stable interface.

[bnoordhuis]

I'm closing this issue, it's been idle for some time, but reopen if you disagree. I believe the dominant sentiment is that we won't be adopting this proposal.