Detect private promoted properties whose only reads are self-writes via new self()

[phpstan-bot]

Summary

Detects when a private promoted property is only ever "read" in order to pass its value to the same constructor parameter of the same class (e.g. return new self($this->test)). In such cases, the property is effectively only writing to itself and should be reported as "never read, only written."

Changes

• Modified src/Rules/DeadCode/UnusedPrivatePropertyRule.php:
  • Added a hasTrueRead tracking field to distinguish genuine reads from self-writes
  • After processing all property usages, promoted properties with no true reads have their read flag cleared
  • Added isPropertySelfWrite() helper that uses Scope::getFunctionCallStackWithParameters() to check if a read occurs inside a constructor call of the same class, targeting the same-named parameter
• Added tests/PHPStan/Rules/DeadCode/data/bug-14573.php with comprehensive test cases
• Added test method testBug14573 to UnusedPrivatePropertyRuleTest
• Added 3 baseline entries for newly detected issues in PHPStan's own code

Root cause

The UnusedPrivatePropertyRule previously treated any PropertyRead as evidence that a property is used. However, when a promoted property's only reads are passing its value to new self(...) / new static(...) / new ClassName(...) at the same parameter position, the property is effectively circular — it's only written from constructor and read to write to another instance's constructor. The fix uses the scope's function call stack to identify these self-write reads and exclude them from the "has been read" determination.

Test

The regression test covers:

• Basic case: single promoted property passed to new self() (reported)
• Multiple properties where one has a true read and one doesn't (only the dead one reported)
• Both properties only self-written (both reported)
• Swapped arguments: new self($this->b, $this->a) (NOT reported - different parameter)
• Property with additional genuine read (NOT reported)
• new static() (reported)
• new ClassName() with explicit class name (reported)
• Named arguments: new self(b: $this->b, a: $this->a) (reported)
• Named arguments swapped: new self(b: $this->a, a: $this->b) (NOT reported)
• Property passed to different class constructor (NOT reported)
• Multiple self-write call sites (reported)
• Mixed self-write and true read (NOT reported)
• Property passed to non-constructor method (NOT reported)

Analogous cases probed and found not applicable:

• Static properties: cannot be promoted, so N/A
• Non-promoted properties: the issue specifically scopes to promoted properties where constructor assignment is guaranteed without inspecting the body

Fixes phpstan/phpstan#14573

[ondrejmirtes]

Instead of baselining the PHPStan errors, please actually fix them by removing the promoted properties.

[phpstan-bot]

Done. I addressed the review by removing the unused promoted properties instead of baselining them:

1. IntersectionTypeUnresolvedPropertyPrototypeReflection::$propertyName and UnionTypeUnresolvedPropertyPrototypeReflection::$propertyName — removed from constructors and updated all call sites in IntersectionType.php, UnionType.php, and ObjectType.php.

2. ImpossibleCheckTypeHelper::$universalObjectCratesClasses — removed from constructor and doNotTreatPhpDocTypesAsCertain(), also removed from TypeSpecifyingFunctionsDynamicReturnTypeExtension which only held it to pass here, and updated all 16 test files.

Both make phpstan and make tests pass cleanly.

[ondrejmirtes]

Make sure there are no edits to the baseline file. You've left an empty newline.

[phpstan-bot]

Done. Removed the stray blank line from phpstan-baseline.neon so the baseline file has zero net changes from this PR. Both make phpstan and the tests pass cleanly.