AssertEmptyIsDiscouragedRule is auto-fixable

[staabm]

closes #338

support scalar types. we skip all regular strings which are not non-falsey, because fixing these would yield ugly code like $s == '' || $s == '0'.

we only support the easiest cases for now which have a unambiguous fix and lead more readable code.

[staabm]

//cc @SanderMuller

[SanderMuller]

I checked the fixes against what assertEmpty() does at runtime, at head e7037550f. make tests and make phpstan pass. In five cases the fixed assertion behaves differently from the original. I ran each original and fixed line with real PHPUnit 9.6:

Case	Original	Fixed	Original result	Fixed result
@param int $x, null at runtime	assertNotEmpty($x)	assertNotSame(0, $x)	fails	passes
@param non-falsy-string $x, '0' at runtime	assertNotEmpty($x)	assertNotSame('', $x)	fails	passes
?\SimpleXMLElement $x, <a/>	assertEmpty($x)	assertNull($x)	passes	fails
bool $b	assertEmpty(actual: $b)	assertFalse(actual: $b)	passes	Error: Unknown named parameter $actual
int $i, 0	assertEmpty(message: 'm', actual: $i)	assertSame('', message: 'm', actual: $i)	passes	fails

1. The type comes from $scope->getType(), so a PHPDoc type decides the fix. In a test, the assertion is often what checks that the PHPDoc is right. The negated fixes then accept values that the original rejected (the first two rows). $scope->getNativeType() would avoid that. The non-falsy-string case would then not be fixed at all, but assertEmpty() on a non-falsy string can never pass anyway.

2. An empty SimpleXMLElement is empty for empty(), so assertNull() is not the same. ?object has the same problem, because the object can be a SimpleXMLElement at runtime. Fixing only when (new ObjectType(\SimpleXMLElement::class))->isSuperTypeOf(...) is no() for the type without null would keep ?\stdClass and skip both.

3. The rule reads getArgs()[0] as the asserted value and keeps the arguments as they are:

   • With actual: as a named argument, assertFalse(), assertTrue(), assertCount() and assertNotCount() throw an Error, because their parameter is $condition or $haystack. assertSame(), assertNotSame(), assertNull() and assertNotNull() have $actual, so they work.
   • With message: first, the message string is treated as the asserted value, and the fix becomes assertSame('', ...).

   Skipping the fix when any argument is named would cover both.

The other fixes are equivalent for their types, including the extra message argument (assertCount(0, $array, 'message')). float, plain string and unions without null stay unfixed, as the description says.

The three Mutation Testing reds come from this PR. Infection reports 4 escaped mutants, which change ->yes() to !->no() on the isObject(), isBoolean(), isArray() and isInteger() checks. So the tests have no value for which one of these checks is a "maybe" and the fix must not apply. The other CI checks pass.

I only checked the parameter names in PHPUnit 9.6, not in 10 to 12.