Introduce new PHP cross-version compatibility functions, `array_key_first()`, `array_key_last()`

[desrosj]

PHP 7.3 will introduce two new functions, array_key_first(), and array_key_last(). The two functions return the first and last key of each array respectively, without affecting the internal state of the array (reset(), end() and key() do). The full RFC can be read here: ​https://wiki.php.net/rfc/array_key_first_last

Including a polyfill would allow developers to take advantage of the new functions and write consistent code regardless of a site's PHP version. While polyfills for these two functions are not required for WordPress to be PHP 7.3 compatible, it could be added in the version after 7.3 compatibility is declared.

[SergeyBiryukov]

Related: #43583, #43619.

[manzoorwani.jk]

For array_key_first, foreach is faster than reset while as for array_key_last, end is faster than other approaches like array_slice or array_keys with end.

[ayeshrajans]

I also think it's a good idea to add the polyfills, but also to search existing current(), reset(), and key() calls to make use of this function. I know PHP 7.3 users will appreciate it too.

Patch from @manzoorwanijk is a good start, but now that PHP 7.3 is released, we can make it more closure to the native function. It looks like this patch was taken from the first example in this function page. Symfony/polyfills has a better one that mimics the original functionality with parameter types. I will attach a patch with more optimized polyfills. To make it complete, this patch also contains the original tests from PHP source, so we can make sure it really gives same results as PHP's own tests.

[SergeyBiryukov]

Related: #49652

[audrasjb]

Refreshed patch

[audrasjb]

Damn I forgot the phpunit tests

[hellofromTonya]

Reassigning this ticket and other PHP polyfill tickets to me to get them into 5.9 release.

added tests

Trac ticket: https://core.trac.wordpress.org/ticket/45055

Well darn. Working in the GH UI to edit the file is not capturing the tabs. Weird. Can be fixed during commit.

Well darn. Working in the GH UI to edit the file is not capturing the tabs. Weird. Can be fixed during commit.

[hellofromTonya]

PR 1809 is thoroughly reviewed and ready for commit.

[hellofromTonya]

In 52038:

General: Introduce polyfills for array_key_first() and array_key_last() added in PHP 7.3.0.

PHP 7.3.0 introduced two new functions: array_key_first() and array_key_last(). These two functions return the first and last key of each array respectively, without affecting the internal state of the array.

The polyfills make these two functions available for use in Core on PHP versions less than 7.3.0.

Ref:

• PHP RFC ​https://wiki.php.net/rfc/array_key_first_last
• PHP manual array_key_first() ​https://www.php.net/manual/en/function.array-key-first.php
• PHP manual array_key_last() ​https://www.php.net/manual/en/function.array-key-last.php

Props desrosj, pbearne, costdev, hellofromTonya, ayeshrajans, manzoorwanijk, audrasjb, sergeybiryukov.
Fixes #45055.

Committed via changeset https://core.trac.wordpress.org/changeset/52038.

[hellofromTonya]

Thank you everyone for your contributions! The polyfills and their tests are now committed and will ship in 5.9.