Fix phpstan/phpstan#11705: Value of a variable is forgotten in case where it ought to be known with certainty

[phpstan-bot]

Summary

When array_key_exists($tag, $theInput) is called with a non-constant key $tag, PHPStan stores the full iterable value type for the expression $theInput[$tag]. If $tag is later narrowed (e.g., in a switch/case), the stored expression type is not updated, causing PHPStan to report incorrect errors because it uses the broad stored type instead of recomputing based on the narrowed key.

Changes

• Modified src/Analyser/MutatingScope.php in resolveType(): when resolving an ArrayDimFetch expression that has a stored expression type, and the dim has been narrowed to a constant scalar value, recompute the offset value type and use it if it is strictly more specific than the stored type
• Added regression test tests/PHPStan/Analyser/nsrt/bug-11705.php

Root cause

ArrayKeyExistsFunctionTypeSpecifyingExtension stores the full getIterableValueType() (e.g., string|array<int,string>) for $theInput[$tag] when the key is non-constant. This stored type takes precedence in resolveType() over computing the type fresh. When $tag is later narrowed to a constant like 'name' inside a switch case, the stored broad type is returned instead of the specific string that getOffsetValueType(ConstantStringType('name')) would produce.

The fix adds a check in resolveType() that, for ArrayDimFetch nodes with stored expression types, recomputes the offset value type when the dim is a constant scalar. If the recomputed type is strictly more specific (stored type is a supertype but not vice versa), the more specific type is used.

Test

Added tests/PHPStan/Analyser/nsrt/bug-11705.php which reproduces the original issue: a shaped array array{'name':string,'owners':array<int,string>} accessed with $theInput[$tag] inside a case 'name': block. Asserts that:

• $tag is correctly narrowed to 'name'
• $theInput[$tag] resolves to string (not string|array<int,string>)
• The narrowing persists after an always-true if ($tag === 'name') check

Fixes phpstan/phpstan#11705