Fix phpstan/phpstan#11533: Foreach to check the type of array is not taken into account

[phpstan-bot]

Summary

When iterating over a constant array of strings (e.g. ['need', 'field']) in a foreach loop and narrowing an array variable's offsets inside the body (via isset + is_string checks with throw), PHPStan did not propagate the per-element type narrowings to the variable after the loop. This caused false positive argument.type errors when passing the array to functions expecting specific key types.

Changes

• Added post-foreach processing in src/Analyser/NodeScopeResolver.php that detects when a foreach iterates over a constant array of string literals and the body narrowed array dim-fetch expressions using the loop variable
• For each defined array variable that was narrowed (not assigned) in the body, adds HasOffsetValueType accessories for each constant string value in the iterated array
• Includes guards to avoid false positives:
  • Checks that the variable's type was not modified (assigned) in the body
  • Checks that the dim-fetch expression type was specifically tracked in the body scope (not just derived from the generic value type)
  • Checks that the narrowing is new (not already present before the foreach)

Root cause

When PHPStan processes a foreach body, the loop variable (e.g. $field) has a union type of all iterated values (e.g. 'need'|'field'). Type narrowing from conditions like is_string($param[$field]) creates expression types for $param[$field] but does not propagate HasOffsetValueType to $param because the dim type is a union (not a single ConstantStringType). After the loop, this narrowing information was lost.

The fix adds a post-foreach processing step that recognizes when a constant string array was iterated and the loop body narrowed dim-fetch expressions using the loop variable, then applies per-element HasOffsetValueType accessories to restore the narrowing information.

Test

Added regression test in tests/PHPStan/Analyser/nsrt/bug-11533.php covering:

• Basic foreach with isset + is_string narrowing and throw (the reported issue)
• Variant using array_key_exists instead of isset

Fixes phpstan/phpstan#11533