Allow optional variadic arguments for methods/functions

[yoramdelangen]

I was implementing the variadic arguments into our extension allow for the following signatures:

// no arguments - impl 1
$client->query('SELECT * FROM Employees');

// one or more arguments
$client->query('SELECT * FROM Employees WHERE Employee_ID = ?', 1);
$client->query('SELECT * FROM Employees WHERE Employee_ID = ? OR Employee_ID = ?', 1, 2);
$client->query('SELECT * FROM Employees WHERE Employee_ID = ? OR Employee_ID = ?', [1, 2]);

// reference arguments - impl 2
$a = 1;
$client->query('SELECT * FROM Employees WHERE Employee_ID = ?', $a);
$b = [1, 2];
$client->query('SELECT * FROM Employees WHERE Employee_ID = ? OR Employee_ID = ?', $b);
$client->query('SELECT * FROM Employees WHERE Employee_ID = ? OR Employee_ID = ?', ...$b);
$client->query('SELECT * FROM Employees WHERE Employee_ID = ? OR Employee_ID = ?', ...[1, 2]);

This raised multiple issues for me:

1. "impl 1": macro #[optional(params)] parameter forces you to set defaults. But only literals are allowed, so vec![], Vec::new(), None etc. do not work.
2. "impl 1": params: Option<&[&Zval]> it worked.. kinda.. but raised 2 problems:
   • only allowed referenced parameters/arguments via variables, dunno why.
   • removed Option<...>, and then this missed the implementation for FromZvalMut for &[&Zval]. So I added implementation, in the PR because its nice allow handle for Option<&[&Zval]>.

Fixes

1. Resolved by checking when requiring defaults for optional arguments if its not variadic.
2. Resolved by adding the FromZvalMut implementation for &[&Zval].

[Xenira]

Thanks for the contribution. Will have a look this evening.

[Xenira]

Sorry, for the delay.
Had a look at this and another alternative to consider would be to allow other tokens and not only literals in the default macro.
Haven't found the time to actually recreate this locally as my week was busier than expected, but expect to have a closer look tomorrow or friday.

Also you seem to need to run cargo fmt.

[yoramdelangen]

@Xenira thanks for reaching out! I have pushed code formatting into the branch, all checks should pass now!