Fix phpstan/phpstan#12601: Array keys cannot be narrowed to non-empty-string when used in templates#5314
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- Stop generalizing non-constant scalar subtypes (non-empty-string, int<0, max>) when inferring template types bounded by array-key - The previous logic generalized ALL scalars for array-key bounds, but only constant values need generalization - Updated existing test expectations in generics-do-not-generalize.php to reflect correct behavior - New regression test in tests/PHPStan/Analyser/nsrt/bug-12601.php
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Mar 29, 2026
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Add a test for https://phpstan.org/r/c448c867-97fd-4e89-966b-974f59dacf5f
Adds a test case from phpstan.org/r/c448c867 verifying that when a list<string> is passed to new ArrayIterator(), the inferred key type is int<0, max> (not generalized to int). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
When an
array<non-empty-string, non-empty-string>was passed to a generic constructor likenew ArrayIterator(...), the key typenon-empty-stringwas incorrectly widened tostring. Similarly,int<0, max>keys were widened toint. This fix preserves non-constant scalar subtypes during template type inference.Changes
src/Type/Generic/TemplateTypeHelper.php: Removed the overly broad first condition ingeneralizeInferredTemplateType()that generalized all scalar types when the template bound wasarray-key. The remaining condition already handles constant values correctly.tests/PHPStan/Analyser/nsrt/generics-do-not-generalize.php: Changed expected types fromArrayIterator<int, string>toArrayIterator<int<0, max>, string>since list keys (int<0, max>) should no longer be generalized.tests/PHPStan/Analyser/nsrt/bug-12601.php: Regression test covering bothnon-empty-stringandint<0, max>key types withArrayIterator.Root cause
In
TemplateTypeHelper::generalizeInferredTemplateType(), there were two conditions for generalizing inferred template types. The first condition ($type->isScalar()->yes() && $isArrayKey) was too broad — it generalized ALL scalar types when the template bound wasarray-key(int|string). This caused non-constant scalar subtypes likenon-empty-stringandint<0, max>to be generalized tostringandintrespectively. The fix removes this condition, leaving only the second condition that correctly targets constant values for generalization.Test
Added
tests/PHPStan/Analyser/nsrt/bug-12601.phpwith two test classes implementingIteratorAggregate:array<non-empty-string, non-empty-string>keys — verifiesArrayIteratorpreservesnon-empty-stringkey typearray<int<0, max>, non-empty-string>keys — verifiesArrayIteratorpreservesint<0, max>key typeFixes phpstan/phpstan#12601