Allow BcMath\Number increment/decrement

[mpesari]

This allows ++/-- on BcMath\Number objects when using strict rules.

See https://phpstan.org/r/f3cd9326-5435-4000-b173-9e143d745acb

Related to phpstan/phpstan#13965

Would be nice to include tests for PHP < 8.4, but the tests don't emit any errors because type BcMath\Number is not found. If there's a way to inject a dummy BcMath\Number class then I think it could be done?

[VincentLanglet]

I prefer @ondrejmirtes opinion on such change since by definition this repository is about opinionated rules.

We might arg that rather than writing ++$number or $number + $number you could call the native method $number->add(...)

[VincentLanglet]

This method is also used by isValidForArithmeticOperation so you have more impact than expected for instance it changes the behavior of the rule with

// Addition or Substraction
$a = BcMath\Number + BcMath\Number
$a = int - BcMath\Number

// Unary
$a = - BcMath\Number

// Division, Exponentiation, Modulo, Multiplication
...

I recommend you to add test for those case, and I'm not sure they should stop reporting error.

[mpesari]

You're right, I added more tests based on the existing operators.php test file. Looks like there were no issues with BcMath\Number before... I'm not sure why

[VincentLanglet]

What I meant is that this is maybe safer to handle the special case directly inside isValidForIncrement and isValidForDecrement rather than inside isSubtypeOfNumber.

As an exemple isValidForIncrement has a special case

if ($type->isString()->yes()) {
			// Because `$a = 'a'; $a++;` is valid
			return true;
		}

[VincentLanglet]

All the next operation should be done in dedicated function to avoid modiying the variabel.

As an example in https://phpstan.org/r/1577da80-3b14-4e29-8019-1fa57b3f155a
As an example the line 148 say
Binary operation "+=" between BcMath\Number and 123.456 results in an error.
and then
line 149 Binary operation "+=" between 123.456 and mixed results in an error.

meaning that all the $number variable are now *ERROR* and test nothing.

[VincentLanglet]

Before supporting an union here, you might want to support an union on PHPStan side, cf
https://phpstan.org/r/3e185620-55d1-470c-ba3a-c7ae8dc603fd

[VincentLanglet]

What I meant is that this is maybe safer to handle the special case directly inside isValidForIncrement and isValidForDecrement rather than inside isSubtypeOfNumber.

As an exemple isValidForIncrement has a special case

if ($type->isString()->yes()) {
			// Because `$a = 'a'; $a++;` is valid
			return true;
		}