`npm list` checks added in #84586 regress wall time of running tidy

[the8472]

#84586 introduced some checks which execute npm list 4 times. They run unconditionally when executing ./x.py test ..., even if it is just to run tidy. On my system the added wall time exceeds that of running tidy itself.

I'll look into whether the checks themselves can be made be less wasteful. But if there are suggestions how to completely eliminate them or defer them while preserving their original purpose that would be great too.

CC @GuillaumeGomez can you explain the purpose of running this in should_run rather than erroring in run?

[GuillaumeGomez]

To know beforehand if the test should unconditionally be run or not. If the test is run and the npm package isn't installed, we panic.

To be noted that we could make it go down to 2 by switching the order of npm list: currently we check both "local" and "global". Switching the two of them will divide the number of calls by two.

cc @Mark-Simulacrum

[the8472]

I don't have browser-ui-test installed, so it'll fail and no short-circuiting will happen regardless of order.

[GuillaumeGomez]

In case you don't have it it'll check 4 times indeed.

[Mark-Simulacrum]

Hm, this does seem annoying. It's possible we could add some lazily-evaluated default condition so that this never runs if we're not considering default-on steps (if defaults are on, then these npm lists are likely quite fast in comparison to the rest of the logic).