Fix #5290: "Cannot use [] for reading." false positives

[phpstan-bot]

Summary

PHPStan incorrectly reported "Cannot use [] for reading." when $array[] was passed as an argument to a function/method parameter declared as by-reference. This is a valid PHP pattern — $array[] in a by-reference context creates a new array element and passes the reference to it, rather than reading.

Changes

• Modified src/Analyser/NodeScopeResolver.php in processArgs(): when processing a by-reference argument that is an ArrayDimFetch with null dim ($array[]), enter expression assign context before processing and exit it afterward. This tells the OffsetAccessWithoutDimForReadingRule that the expression is in a write context.
• Added regression test tests/PHPStan/Rules/Arrays/data/bug-5290.php covering named functions, immediately invoked closures with by-ref params, and method calls.
• Uncommented a previously disabled test case in tests/PHPStan/Rules/Arrays/data/offset-access-without-dim-for-reading.php (line 18: (function (&$ref) {})($array[]) which was marked as "Should work but doesn't").

Root cause

The OffsetAccessWithoutDimForReadingRule checks whether an ArrayDimFetch with null dim is in an expression assign context via $scope->isInExpressionAssign(). However, NodeScopeResolver::processArgs() did not enter expression assign context when processing by-reference arguments, so $array[] passed to a &$param was treated as a read rather than a write.

The fix is targeted to only affect ArrayDimFetch nodes with null dim (the $array[] syntax), avoiding broader side effects on other rules like DefinedVariableRule or UnusedPrivatePropertyRule that also check isInExpressionAssign.

Test

Added tests/PHPStan/Rules/Arrays/data/bug-5290.php with three scenarios that all previously produced false positives:

1. set($array[]) — named function with &$value parameter
2. (function (&$ref) {})($array[]) — immediately invoked closure with by-ref parameter
3. $foo->bar($array[]) — method call with &$value parameter

All three expect no errors.

Fixes phpstan/phpstan#5290