Resolve method reflection for dynamic static calls ($var::method()) to enable purity and side-effect checking

[phpstan-bot]

Summary

When calling a static method on a class-string or object variable (e.g. $enum::from('foo') where $enum is enum-string<BackedEnum>), PHPStan previously failed to resolve the method reflection, treating the call as "call to unknown method" with a possibly-impure point. This caused false positives inside @phpstan-pure functions/methods.

Changes

• src/Analyser/ExprHandler/StaticCallHandler.php:

  • Added an elseif ($expr->class instanceof Expr) branch in processExpr() that resolves the method reflection using getObjectTypeOrClassStringObjectType() — matching the existing approach in resolveType().
  • Added $expr->class instanceof Name guards to the $this-invalidation block (constructor side effects) and the promoted-property initialization block, preventing incorrect scope mutations when calling constructors on other objects via expressions (e.g. $other::__construct()).

• tests/PHPStan/Rules/Pure/PureMethodRuleTest.php: Added testBug14557 covering enum-string<T>::from(), enum-string<T>::tryFrom(), class-string<T>::from(), class-string<T>::tryFrom(), pure static methods via class-string, and impure static methods via class-string.

• tests/PHPStan/Rules/Pure/PureFunctionRuleTest.php: Added testBug14557 covering the same patterns in pure functions.

• tests/PHPStan/Rules/Methods/CallToStaticMethodStatementWithoutSideEffectsRuleTest.php: Updated testDynamicStaticCall expectations — pure dynamic static calls ($foo::pureMethod()) are now correctly detected as having no side effects, which is a natural improvement from resolving the method reflection.

Analogous cases probed

• class-string<T> (not just enum-string<T>): Both are handled by getObjectTypeOrClassStringObjectType() — tested with class-string<SomeClass> calling pure and impure static methods.
• tryFrom() alongside from(): Both tested.
• Pure functions (not just methods): Covered via PureFunctionRuleTest.
• Impure methods via class-string: Tested to confirm they are still correctly flagged.
• Constructor calls on other objects ($other::__construct()): Verified that the $this-invalidation and property-initialization guards prevent incorrect behavior (the MissingReadOnlyPropertyAssignRuleTest::testRedeclaredReadonlyProperties test).
• Dead code detection (CallToStaticMethodStatementWithoutSideEffectsRule): Now correctly detects pure dynamic static calls as having no effect.

Root cause

StaticCallHandler::processExpr() only resolved method reflection when the class part was a Name node (direct class reference like Foo::method()). When the class part was an Expr node (variable like $enum::method()), $methodReflection stayed null, leading to a fallback "call to unknown method" impure point. The resolveType() method already handled this case correctly via getObjectTypeOrClassStringObjectType(), but the purity/side-effect logic in processExpr() did not.

Test

• tests/PHPStan/Rules/Pure/data/bug-14557.php — method-level test with enum-string, class-string, pure and impure static methods
• tests/PHPStan/Rules/Pure/data/bug-14557-function.php — function-level test with enum-string and class-string
• Updated expectations in CallToStaticMethodStatementWithoutSideEffectsRuleTest::testDynamicStaticCall for the improved detection

Fixes phpstan/phpstan#14557
Fixes phpstan/phpstan#5020

[VincentLanglet]

@staabm You're the one who wrote that no error should be reported on line 32

'Call to static method DynamicStaticCall\Foo::doFoo() on a separate line has no effect.'

with the comment // no error, subclass could override static method with impure impl

But still we consider $foo->pureMethod() to be pure while something like
https://phpstan.org/r/e325d706-4fc2-46bd-89f0-f2c3890c9c44
could be written.

Do you agree that

• We should forbid overriding a pure method in an impure way
• We should report @phpstan-impure method which override pure methods.

[staabm]

Do you agree that

* We should forbid overriding a pure method in an impure way

* We should report `@phpstan-impure`  method which override pure methods.

I am not sure we can/should enforce purity across inheritance.
a less aggressive approach would be taking purity only from final classes.

feels like a topic which needs to be discussed with @ondrejmirtes before we implement somthing

[VincentLanglet]

I am not sure we can/should enforce purity across inheritance.

It's already allowed to add @pure over an interface method

a less aggressive approach would be taking purity only from final classes.

That will change a lot of existing behavior.
Maybe it will require a new config parameter

feels like a topic which needs to be discussed with @ondrejmirtes before we implement somthing

Indeed

[VincentLanglet]

feels like a topic which needs to be discussed with @ondrejmirtes before we implement somthing

Seems decided by this answer phpstan/phpstan#14563 (comment)

So IMHO this PR is ready.

[VincentLanglet]

Add non regression test for phpstan/phpstan#5020

It should be a RuleTest which check that there is no If condition is always false. error anymore with the snippet https://phpstan.org/r/ada88746-fd60-4187-abfc-046ed28bf750

[phpstan-bot]

Done. Added a non-regression test for issue #5020 that verifies PHPStan no longer reports "If condition is always false" when a dynamic static call ($transformer::Transform(...)) modifies a by-reference parameter. The test was verified to fail without the fix (reporting the false positive on line 30) and pass with it. All tests pass and make phpstan reports no errors.

[staabm]

add another test for

/**
 * @phpstan-pure
 */
function fromEnum(MyEnum $enum): MyEnum
{
	return $enum::from('foo');
}

which unexpectedly errors before this PR
https://phpstan.org/r/1dccccac-c269-4df9-9cb1-d7715a501d5b

[phpstan-bot]

Done. Added the test case staabm requested — a pure function/method calling $enum::from('foo') where $enum is typed as MyEnum (an object instance, not a class-string or enum-string). Added to both the function-level and method-level test files, updated the error line expectation, and all tests + make phpstan pass.