Successor to PR #3523. There are 494 single-line changes (`public function provider` to `public static function provider`) in this PR. None of these were made manually; they were all created with the following script (adapted from
https://stackoverflow.com/questions/25909820/how-to-recursively-iterate-through-files-in-php):
```php
$dir = 'C:/git/unit10prep2/tests/PhpSpreadsheetTests';
$it = new RecursiveDirectoryIterator($dir);
// Loop through files
foreach(new RecursiveIteratorIterator($it) as $file) {
if ($file->getExtension() === 'php') {
$contents = file_get_contents($file);
$new = preg_replace('/public function (\\w*)([Pp])rovider/', 'public static function $1$2rovider', $contents);
if ($new !== $contents) {
echo "changing $file\n";
file_put_contents($file, $new);
}
}
}
```
After this PR, there will be one more, with a small number of test changes, and enabling PhpUnit 10 for Php 8.1+.
* Handling of #REF! Errors in Subtotal, and More
This PR derives from, and supersedes, PR #2870, submitted by @ndench. The problem reported in the original is that SUBTOTAL does not handle #REF! errors in its arguments properly; however, my investigation has enlarged the scope.
The main problem is in Calculation, and it has a simple fix. When the calculation engine finds a reference to an uninitialized cell, it uses `null` as the value. This is appropriate when the cell belongs to a defined sheet; however, for an undefined sheet, #REF! is more appropriate.
With that fix in place, SUBTOTAL still needs a small fix of its own. It tries to parse its cell reference arguments into an array, but, if the reference does not match the expected format (as #REF! will not), this results in referencing undefined array indexes, with attendant messages. That assignment is changed to be more flexible, eliminating the problem and the messages.
Those 2 fixes are sufficient to ensure that the original problem is resolved. It also resolves a similar problem with some other functions (e.g. SUM). However, it does not resolve it for all functions. Or, to be more particular, many functions will return #VALUE! rather than #REF! if this arises, and the same is true for other errors in the function arguments, e.g. #DIV/0!. This PR does not attempt to address all functions; I need to think of a systematic way to pursue that. However, at least for most MathTrig functions, which validate their arguments using a common method, it is relatively easy to get the function to propagate the proper error result.
* Arrange Array The Way call_user_func_array Wants
Problem with Php8.0+ - array passed to call_user_func_array must have int keys before string keys, otherwise Php thinks we are passing positional parameters after keyword parameters.
7 other functions use flattenArrayIndexed, but Subtotal is the only one which uses that result to subsequently pass arguments to call_user_func_array. So the others should not require a change. A specific test is added for SUM to validate that conclusion.
* Change Needed for Hidden Row Filter
Same as change made to Formula Args filter.
oleibman