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.

[Copilot]

Copilot review overview

🟡 Changes recommended

Automatic fixes can change assertion behavior for unpacked arguments, nullable object/scalar unions, and Countable objects.

Review effort: Balanced
Findings: 3

Open (3)

• Skip assertEmpty rewrites for unpacked arguments · New
• Require wholly object-based types for null rewrites · New
• Avoid null rewrites for nullable Countable types · New

What changed in this PR

Adds automatic fixes to PHPStan’s discouraged empty-assertion rule, replacing supported cases with more specific PHPUnit assertions.

Changes:

• Selects replacements using native argument types.
• Adds fix fixtures and tests for supported and unchanged cases.

File	Description
tests/​Rules/​PHPUnit/​data/​assert-empty-is-discouraged-native-union.php.fixed	Expected unchanged union and named-argument assertions.
tests/​Rules/​PHPUnit/​data/​assert-empty-is-discouraged-native-union.php	Union and named-argument fixtures.
tests/​Rules/​PHPUnit/​data/​assert-empty-is-discouraged-fixable.php.fixed	Expected assertion replacements.
tests/​Rules/​PHPUnit/​data/​assert-empty-is-discouraged-fixable.php	Supported and unsupported type fixtures.
tests/​Rules/​PHPUnit/​AssertEmptyIsDiscouragedRuleTest.php	Adds automatic-fix tests.
src/​Rules/​PHPUnit/​AssertEmptyIsDiscouragedRule.php	Implements type-based assertion fixes.

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[SanderMuller]

I checked b207aedaf again. The PHPDoc, SimpleXMLElement, named-argument and mutation points from my first review are fixed, and the tests, PHPStan and CI pass.

The nullable-object fix still changes results. assertEmpty() also treats an EmptyIterator and a Countable with a count of 0 as empty. isBuiltin() only looks at the declared class, and a subclass or an implementation can add either. I ran the rule's fix on these parameter types and then ran each original and fixed line with PHPUnit 9.6:

Parameter	Value at runtime	Original	Fixed
?Collection (user class, Countable)	count() is 0	assertEmpty() passes	assertNull() fails
?MyIterator (extends EmptyIterator)	new instance	passes	fails
?MyArrayObject (extends ArrayObject)	new, empty	passes	fails
?OpenParent (non-final class)	a Countable subclass, count 0	passes	fails
?Thing (interface)	a Countable implementation, count 0	passes	fails
?Foo (non-final class)	a Countable subclass, count 0	assertNotEmpty() fails	assertNotNull() passes
?FinalFoo (final user class)	new instance	assertEmpty() fails	assertNull() fails

Only the final class gives the same result. So the null fix could apply only when each class is final, does not implement Countable, and has no builtin parent. That covers EmptyIterator, ArrayObject and SimpleXMLElement subclasses too.

Copilot's UserDefinedObject|int|null case does not reproduce. The rule leaves Foo|int|null as it is, because getObjectClassReflections() returns nothing when a union member is not an object.

I ran the cases with PHPUnit 9.6 only. The IsEmpty constraint has the same EmptyIterator and Countable checks in 10.5, 11.5 and 12.0.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Nullable unions containing objects and scalars can receive automatic fixes that change assertion outcomes.

Review effort: Balanced
Findings: None

Resolved since last review (3)

• Avoid null rewrites for nullable Countable types
• Require wholly object-based types for null rewrites
• Skip assertEmpty rewrites for unpacked arguments

[Copilot]

Copilot review overview

🔵 Needs a closer look

Trusting PHPDoc finality allows nullable-object fixes that change assertion behavior for runtime subclasses.

Review effort: Balanced
Findings: None

Previously missed (1)

In code that hasn't changed since last review

Require native finality to avoid incorrect nullable class assertions

src/​Rules/​PHPUnit/​AssertEmptyIsDiscouragedRule.php:94

isFinal() accepts PHPDoc @final, which does not prevent runtime subclasses. For a nullable class annotated this way, a subclass implementing Countable with count zero passes assertEmpty() but fails the generated assertNull(); the negated rewrite also changes behavior. Use isFinalByKeyword() to require native finality, consistent with this fixer's use of native types.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Nullable unions containing scalar members can receive autofixes that change assertion behavior.

Review effort: Balanced
Findings: None