See T85805: Introduce ResourceLoader debug mode v2

Identify the patch in which this change happened

rMWb04ec0dfcac1: resourceloader: Add internal handling for debug=2

Understand the reason behind this change

See T85805: Introduce ResourceLoader debug mode v2 and expect the value in future to be 2, not just 1 or 0.

(it is not backward compliant)

It is for normal code using the usual ! or !! operators. Code trying for strict equivalence on a boolean (in JavaScript?!) would have broken, yes. In general it is sadly very risky to assume stability in that the way variables are mangled by PHP might turn up locally after a network fetch (see for example user options).

Ensure the change was properly communicated (e.g. through User-notice) and if not, do so

New debug mode will no doubt be communicated when it's ready. I'm not sure this is an interesting-enough change to waste tens of thousands of people's time with.

Update the documentation on MediaWiki wiki

Sure, good point; done: https://www.mediawiki.org/w/index.php?diff=4458891&oldid=4449944&title=Manual:Interface/JavaScript&diffmode=source

In T277386#6911415, @Huji wrote:

Thanks for the quick response!

Happy to help. Sorry this bit you.

In T277386#6911173, @Jdforrester-WMF wrote:

(it is not backward compliant)

It is for normal code using the usual ! or !! operators. Code trying for strict equivalence on a boolean (in JavaScript?!) would have broken, yes. In general it is sadly very risky to assume stability in that the way variables are mangled by PHP might turn up locally after a network fetch (see for example user options).

If the only use case was in conditional statements, then yes. But at least in one case, the value of this has been used as the key for an object and this caused the code to stop working. See https://github.com/he7d3r/mw-gadget-DebugModeToggle/commit/7cc3d84f7377cc235e4ae87580e55993f3dd70e5 (specifically, lines 30 and 31).

Oh wow, yes, one should never be programmatically interacting with debug mode on production servers. It's for manual debugging, and these kinds of changes of internal characteristics are subject to change without notice. This kind of user script is a really bad idea.

Update the documentation on MediaWiki wiki

Sure, good point; done: https://www.mediawiki.org/w/index.php?diff=4458891&oldid=4449944&title=Manual:Interface/JavaScript&diffmode=source

Thanks; I further edited that page in https://www.mediawiki.org/w/index.php?diff=next&oldid=4458891&diffmode=source and included a link to the original phab task.

Thank you.

In T277386#6911424, @Jdforrester-WMF wrote:

[…] one should never be programmatically interacting with debug mode on production servers. It's for manual debugging, and these kinds of changes of internal characteristics are subject to change without notice. This kind of user script is a really bad idea.

While this was indeed not a supported way of interacting with debug mode, I think this user script is actually quite a good idea!

User scripts don't have to be stable or limited to using officially supported APIs – that's part of what makes them minimal to make and so accessible. So long as it is understood by editors that it may break, and that we can't always help you fix issues, then having it sometimes not work while you wait for a fellow editor to make a fix, might actually be a very worthwhile trade-off (compared to the cost-benefit of doing it "properly", if and when possible).