Suppress undefined static property error when property_exists() guard is present

[phpstan-bot]

Summary

When property_exists() is called with a class-string first argument (e.g. property_exists(static::class, 'default')), the subsequent static property access static::$default was reported as "Access to an undefined static property" even though the existence check guarded it. This fix teaches PHPStan to recognize that guard.

Changes

• src/Type/Php/PropertyExistsTypeSpecifyingExtension.php: When the first argument to property_exists() is a string type (class-string or constant class name), mark the property_exists() FuncCall expression itself as ConstantBooleanType(true) in scope. Previously, class-string arguments caused the extension to return empty SpecifiedTypes, providing no narrowing. The approach of intersecting HasPropertyType with class-string was not viable because HasPropertyType uses ObjectTypeTrait, making it incompatible with string types in TypeCombinator::intersect() (producing never). This matches the approach already used for non-constant property names.

• src/Rules/Properties/AccessStaticPropertiesCheck.php: Before reporting "Access to an undefined static property", construct a virtual property_exists(ClassName::class, 'propName') FuncCall and check if the scope evaluates it as true. For Name-based class references (static, self, Foo), constructs ClassConstFetch(Name, 'class') as the first argument. For expression-based references ($className::$prop), uses the expression directly.

• phpstan-baseline.neon: Updated expected count for instanceof ConstantStringType in PropertyExistsTypeSpecifyingExtension.php from 2 to 1 (removed the old $objectType instanceof ConstantStringType check).

Analogous cases probed

• Static property assignment (AccessStaticPropertiesInAssignRule): Uses the same AccessStaticPropertiesCheck, so automatically covered. Added regression test.
• Expression-based class access ($className::$prop after property_exists($className, 'prop')): Works because the expression key matches. Added test case.
• Instance properties ($this->prop after property_exists($this, 'prop')): Already handled by existing code in AccessPropertiesCheck (lines 201-209 for dynamic names, and HasPropertyType narrowing for static names).
• HasMethodType vs HasPropertyType with class-string: Investigated why method_exists() correctly narrows class-string types while property_exists() didn't — HasMethodType::isSuperTypeOf checks hasMethod() which class-strings support (for static method calls), but HasPropertyType::isSuperTypeOf checks hasInstanceProperty()/hasStaticProperty() which class-strings don't support. This is why the FuncCall-marking approach was chosen over type intersection.

Root cause

PropertyExistsTypeSpecifyingExtension did not handle class-string first arguments. When the first argument was a ConstantStringType (which includes class-string types), the extension returned empty SpecifiedTypes, so no type narrowing occurred. Meanwhile, AccessStaticPropertiesCheck had no mechanism to detect that a property_exists() guard was present before reporting undefined static properties — unlike AccessPropertiesCheck which already had a virtual property_exists() check for dynamic instance property names.

Test

• tests/PHPStan/Rules/Properties/data/bug-2861.php — Regression test with trait using property_exists(static::class, 'default') and property_exists(self::class, 'default') guards, plus expression-based $className::$prop access. Expects no errors.
• tests/PHPStan/Rules/Properties/data/bug-2861-assign.php — Assignment context regression test with static::$default = 'value' after property_exists() guard. Expects no errors.

Fixes phpstan/phpstan#2861

[VincentLanglet]

Does the same issue exists for method_exists and/or for non-static property/method ?

[phpstan-bot]

Both make tests (12129 tests, all passing) and make phpstan (no errors) pass.

Summary: The reviewer asked whether the same issue exists for method_exists() and/or non-static property/method access. After investigation, the answer is no — all those cases are already handled:

• method_exists() + static methods: Works because HasMethodType can intersect with class-strings (class-strings support hasMethod() for static method calls), and StaticMethodCallCheck already checks $classStringType->hasMethod() at line 72.
• Non-static property_exists(): HasPropertyType narrowing works on object types, and AccessPropertiesCheck has a dynamic property name guard (lines 205-213).
• Non-static method_exists(): HasMethodType narrowing works on object types, and MethodCallCheck has a dynamic method name guard (lines 125-134).

The bug was unique to property_exists() + static properties because HasPropertyType checks instance properties (which class-strings don't support), unlike HasMethodType which checks hasMethod() (which class-strings do support). No code changes needed.

[staabm]

we should also test non-static property fetches, like in https://phpstan.org/r/20ab67ef-ef8b-4f24-8783-1ff18cfe7168

[phpstan-bot]

Done. Added non-static (instance) property fetch test cases as requested by staabm:

• bug-2861.php: Added InstancePropertyAccess class with $this->default and $obj->default reads guarded by property_exists()
• bug-2861-assign.php: Added testInstance() and testInstanceObj() methods with $this->default = 'value' and $obj->default = 'value' writes guarded by property_exists()
• AccessPropertiesRuleTest: Added testBug2861() to verify instance property reads don't trigger errors
• AccessPropertiesInAssignRuleTest: Added testBug2861() to verify instance property writes don't trigger errors

All 12131 tests pass and make phpstan reports no errors.

[staabm]

this if-statement is not covered by a test

[phpstan-bot]

Pushed successfully. Here's a summary of what was done:

Addressing staabm's review comments:

1. Non-static property fetch tests — The remote already had concurrent changes adding InstancePropertyAccess class tests (with $this and $obj patterns) to both bug-2861.php and bug-2861-assign.php. I resolved the rebase conflicts keeping those additions.

2. Uncovered !$objectType->isObject()->yes() branch — Added tests/PHPStan/Analyser/nsrt/bug-2861.php with assertType tests that exercise the object|string narrowing path in PropertyExistsTypeSpecifyingExtension. This covers the branch where the first argument to property_exists() is neither purely string nor purely object, verifying it narrows to class-string|(object&hasProperty(foo)).

[staabm]

hmm somehow the error

Cannot access property $prop on mixed.

did not got fixed with this PR

https://phpstan.org/r/521529b7-8d98-41ad-8499-105fc5c36795

[VincentLanglet]

hmm somehow the error

Cannot access property $prop on mixed.

did not got fixed with this PR

phpstan.org/r/521529b7-8d98-41ad-8499-105fc5c36795

Do you mind opening an issue.

I think it's because we have a isString check
https://github.com/phpstan/phpstan-src/pull/5544/changes#diff-3aeefa37f58b006f6b8f9482b60728f31b093737e51249fe08dbdab566d110f0R71