Do not let type narrowing define a certainly-undefined variable - #6130
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Removing a type from a certainly-undefined variable proves nothing about its definedness, so a sureNot specification must not create a holder for it. A sure specification (e.g. is_string($a)) still can - the condition can only hold for a defined variable, so it makes the variable defined inside the branch: one error at the test site, no cascade. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019wqGgaD7iqL44t1KgpJS7b
This was referenced Jul 28, 2026
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Extracted from the
resolve-type-rewrite-2branch (follows #6125 and #6129).filterBySpecifiedTypes()created a type holder for a variable the scope knows is certainly undefined, makingisset()-style narrowing "define" it — the classic false negative where only the first use of an undefined variable in a loop was reported. A sureNot specification now skips certainly-undefined variables; sure specifications still apply, since a condition likeis_string($a)can only hold for a defined variable (one error at the test site, no cascade).Verified test-first: the regression test fails on 2.2.x with the line-9
Undefined variableerror missing and line 15 degraded to "might not be defined"; passes with the fix. Full test suite green (17757 tests), self-analysis clean, no other expectation changes.Closes phpstan/phpstan#2032
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https://claude.ai/code/session_019wqGgaD7iqL44t1KgpJS7b