Drop php4 support for do action first arg array object type in favor of better support of PHP7+ native types

[kkmuffme]

Drop PHP 4 support for do_action with 1 array argument where the array contains only 1 element, in favor of better support for PHP 7+ native types

Trac ticket: https://core.trac.wordpress.org/ticket/60190

[github-actions]

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[johnbillion]

Can you provide some new unit tests that demonstrate the benefit of this change? What can be done after this change that can't be done currently?

[github-actions]

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[kkmuffme]

Yes, I added a test now (which would result in a fatal error without this PR on standard WP 6.5)

[azaozz]

Probably missing something but this change doesn't seem to be part of the trac ticket?

This changes the behavior for false, null, 0, etc. (all things considered "empty" in PHP). After this patch $arg will not be an empty string in these cases, right? Thinking this is a potentially big back-compat break, and also not part of the proposed fix as in the trac ticket.

If this is intentional please open a new ticket with reasoning why this is needed and tests to confirm the back-compat issues it may introduce.

[johnbillion]

$arg is a variadic parameter which means it'll only ever be an array. This change could have been made as part of r46322.

[azaozz]

https://github.com/WordPress/wordpress-develop/pull/5839/files#r2105010248