Update the array_is_list compat function, add tests

[swissspidy]

The function was polyfilled via another ticket.

This adds tests that were originally added and simplifies the polyfill (assuming the tests still pass)

Trac ticket: https://core.trac.wordpress.org/ticket/55105

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[costdev]

Thanks for putting the PR together @swissspidy!

I'm happy to go with the shorter function contents, though I haven't had a chance to compare both approaches on large arrays. It would be good to get some benchmarks on that if possible, but not a blocker.

LGTM 👍

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[swissspidy]

Okay so the shorter version fails for the array(NAN) case on PHP 7.0 and PHP 7.1

Benchmarking with a larger array now. Turns out the array_values() approach is faster for the happy path, see https://3v4l.org/EMpT0/perf (foreach) vs https://3v4l.org/1WsAV/perf (array_values())

For the unhappy path the performance seems equal, see https://3v4l.org/5YMl2/perf (foreach), https://3v4l.org/o1SSY/perf (array_values()) and https://3v4l.org/H721m/perf (both).

So that appears to make a case for using both as Symfony does.

[costdev]

Not sure how both can ever be run though. If array_values( $arr ) === $arr, then when would the foreach() run?

[swissspidy]

@costdev It's specifically that the output for using array( NAN ) as the input is different on PHP 7.0 and PHP 7.1. It doesn't really make sense to me.

See https://3v4l.org/nPN8l

[swissspidy]

Tests committed in https://core.trac.wordpress.org/changeset/57535