Add array_is_list(array $array) function (rebased)

[TysonAndre]

This function tests if an array contains only sequential integer keys (increasing starting from 0). While this isn't an official type, this usage is consistent with the community usage of "list" as an annotation type, cf. https://psalm.dev/docs/annotating_code/type_syntax/array_types/#lists.

This functionality can be polyfilled, but this implementation should be much faster, as it can check for a packed array.

Rebased version of #4886

RFC: https://wiki.php.net/rfc/is_list

An earlier version of this returned false for non-arrays instead of throwing a TypeError - this was updated to prevent confusion with list-like object types

---

This accepts any type, and deliberately returns false (with no notices) for all non-arrays, e.g. see the test output in the files changed. This is similar to is_callable(), is_numeric(), is_iterable(), etc, which also accept any type:

non-array: throw TypeError
string key: false
mixed keys: false
ordered keys: true

[twose]

Could we rebase against the master, and try to use ZEND_HASH_REVERSE_FOREACH_KEY, just like what you said on #4886 (comment), Thanks!

[itsjavi]

I am concerned about the name because lists do not always contain sequential integers as indices https://www.php.net/manual/en/spl.datastructures.php

is_sequential_list would make more sense to me and would be more obvious

[TysonAndre]

I am concerned about the name because lists do not always contain sequential integers as indices https://www.php.net/manual/en/spl.datastructures.php

1. This is based on the definition of list in languages such as java/c - spl has a variety of issues
2. SplDoublyLinkedList maintains elements in order. It allows you to insert into the middle of the list, but that moves existing elements forwards - the traversal order is always 0..count-1 (Ignoring the fact that it implements Iterator instead of IteratorAggregate meaning that code iterating over the SplDoublyLinkedList or calling next() affects other code iterating over that SplDoublyLinkedList, which can't be changed easily for compatibility reasons)

» php -a
Interactive shell

php > $x = new SplDoublyLinkedList();
php > $x->add(1, 'out of range');

Warning: Uncaught OutOfRangeException: Offset invalid or out of range in php shell code:1
Stack trace:
#0 php shell code(1): SplDoublyLinkedList->add(1, 'out of range')
#1 {main}
  thrown in php shell code on line 1
php > $x->add('key', 'out of range');

Warning: Uncaught OutOfRangeException: Offset invalid or out of range in php shell code:1
Stack trace:
#0 php shell code(1): SplDoublyLinkedList->add('key', 'out of range')
#1 {main}
  thrown in php shell code on line 1
php > $x->add(0, 'in range');
php > $x->add(0, 'insert before old value at key 0');
php > var_export(iterator_to_array($x));
array (
  0 => 'insert before old value at key 0',
  1 => 'in range',
)
php > var_export($x[0]);
'insert before old value at key 0'
php > var_export($x[1]);
'in range'

[nikic]

I'd split this into an inlined fast path (num_elements + packed without holes check) and an out of line slow path (that does the full table scan).

[nikic]

Though I guess with just two usages right now making the whole thing inline isn't terrible either.

[staabm]

This new function is not listed on php.net

https://www.php.net/manual-lookup.php?pattern=array_is_list&scope=quickref