Fix phpstan/phpstan#14347: Regression: Setting array-key in loop doesn't persist with other actions in between

[phpstan-bot]

Summary

When initializing an array entry with ??= in a loop, modifying a different array key in between would cause PHPStan to lose track of the initialized key, resulting in a false positive offsetAccess.notFound error.

Changes

• Added getDynamicArrayDimFetchExpressionTypes() method to src/Analyser/MutatingScope.php to collect expression types for array dim fetches with non-scalar (dynamic) dim expressions
• Added restoreExpressionTypes() method to src/Analyser/MutatingScope.php to directly restore expression type holders without triggering parent-type side effects
• Modified src/Analyser/ExprHandler/AssignHandler.php to save and restore dynamic array dim fetch expression types around assignVariable calls during array dim fetch assignments
• New regression test in tests/PHPStan/Rules/Arrays/data/bug-14347.php

Root cause

When processing an array dim fetch assignment like $arr['all']++, PHPStan computes the new array type and calls assignVariable(), which internally calls invalidateExpression() on the variable. This invalidation removes ALL expression types containing that variable, including $arr[$dynamicKey] which was set by a prior ??= operation.

The NonexistentOffsetInArrayDimFetchRule checks $scope->hasExpressionType($node) at line 72 to skip the error when the expression was previously assigned. With the expression type invalidated, this check fails and the rule reports a false positive.

The fix preserves expression types for dynamic (non-scalar) array dim fetches before the assignVariable call and restores them afterward. Only dynamic dim fetches are preserved to avoid interfering with condition-narrowed types on constant keys (like those from array_key_exists checks).

Test

Added tests/PHPStan/Rules/Arrays/data/bug-14347.php with two functions: countCards (working order) and countCardsBroken (broken order where ??= comes before modifying another key). Both should analyze cleanly with reportPossiblyNonexistentConstantArrayOffset = true.

Fixes phpstan/phpstan#14347