Summary

When a function or method is declared to return by reference (e.g. public function &getString(): string), its return value is a valid lvalue that can be passed to a by-reference parameter. PHPStan was incorrectly reporting "expects variables only" for these cases.

Changes

• Added callReturnsByReference() private method to src/Rules/FunctionCallParametersCheck.php that checks if an argument expression is a call to a function/method that returns by reference
• Handles MethodCall, StaticCall, and FuncCall AST node types
• Injected ReflectionProvider into FunctionCallParametersCheck constructor for resolving function reflections (method reflections are resolved via Scope::getMethodReflection())
• Updated all ~20 test files that manually instantiate FunctionCallParametersCheck to pass the new ReflectionProvider parameter
• Added documentation to CLAUDE.md about FunctionCallParametersCheck patterns

Root cause

FunctionCallParametersCheck only allowed variables, array dim fetches, property fetches, and static property fetches as valid by-reference arguments. It did not consider that function/method calls returning by reference also produce valid lvalues. The fix checks the called function/method's returnsByReference() reflection before reporting the error.

Test

Added tests/PHPStan/Rules/Functions/data/bug-757.php with test cases covering:

• Instance method returning by reference (no error)
• Instance method NOT returning by reference (error expected)
• Static method returning by reference (no error)
• Function returning by reference (no error)
• Function NOT returning by reference (error expected)

Fixes phpstan/phpstan#757