Fix phpstan/phpstan#14281: Regression: type arrowed too much after identical comparison#5221
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Fix phpstan/phpstan#14281: Regression: type arrowed too much after identical comparison#5221phpstan-bot wants to merge 1 commit intophpstan:2.1.xfrom
phpstan-bot wants to merge 1 commit intophpstan:2.1.xfrom
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…parison - Root cause: commit a063119 introduced parent constructor template inference that resolved TElement to *NEVER* from empty default array parameters - When new TestCollection() was called without arguments, TElement was inferred as *NEVER* (from default []), causing get() to return null instead of mixed - This made assert($data[1] === $collection->get(1)) resolve as assert(0 === null), narrowing $data to *NEVER* (dead code) - Fix: skip NeverType when mapping parent constructor template types to child class - New regression test in tests/PHPStan/Analyser/nsrt/bug-14281.php
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Summary
When a generic child class (e.g.,
TestCollection extends Collection) was instantiated without constructor arguments, and the constructor was defined in the parent class with a default empty array parameter (array $elements = []), PHPStan resolved the template type to*NEVER*instead ofmixed. This caused method return types likeTElement|nullto resolve tonull, which then made===comparisons with known non-null values impossible, narrowing the compared array to*NEVER*(dead code).Changes
NeverTypecheck insrc/Analyser/ExprHandler/NewHandler.php(line ~550) when mapping parent constructor resolved template types to the child class. When a resolved template isNeverType(typically from an empty default array), it is now skipped, allowing the template to fall back to its bound (usuallymixed).tests/PHPStan/Analyser/nsrt/bug-14281.phpRoot cause
Commit
a063119ee("Fix inferring type ofnewwith generic type with constructor in parent class") added logic to simulatenew ParentClass(args)and map the resolved parent template types back to the child class. When called with no arguments (e.g.,new TestCollection()), the parent constructor's default[]parameter resolvedTElementto*NEVER*(since an empty array has element typenever). This was then mapped to the child, makingTestCollection<*NEVER*>instead of the pre-fix behavior ofTestCollection<mixed>.The fix skips
NeverTypeentries when building the resolved type map from the parent constructor, so templates resolved from empty defaults correctly fall back to their bounds.Test
The regression test reproduces the exact scenario from the issue: a
Collection<TElement>with aTestCollectionchild class, whereassert($data[X] === $collection->get(X))should not narrow$datato*NEVER*.Fixes phpstan/phpstan#14281