Fix phpstan/phpstan#14353: Falsy "Variable might not be defined"

[phpstan-bot]

Summary

False positive "Variable $report_ids might not be defined" reported inside an isset() block after an unrelated foreach loop over the same array that was used to conditionally define the variable.

Changes

• Modified src/Analyser/MutatingScope.php in specifyExpressionType(): when certainty is set to Yes, remove conditional expressions for that variable where the type holder has No certainty (i.e., "variable doesn't exist" conditions)
• Added regression test in tests/PHPStan/Rules/Variables/data/bug-14353.php
• Added test method testBug14353 in tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

Root cause

After a foreach like foreach ($reports as $v) { $report_ids[$v] = 1; }, the scope merge creates conditional expressions tracking the relationship: "if $reports is empty (the loop didn't execute), then $report_ids doesn't exist."

When isset($report_ids) later confirms the variable exists, specifyExpressionType sets certainty to Yes but does not clean up these stale conditional expressions. A subsequent foreach ($reports as $v) {} triggers filterByTruthyValue for the "array is empty" case, which activates the stale conditional expression and removes $report_ids from the scope. The merge then downgrades $report_ids certainty from Yes to Maybe, causing the false positive.

The fix removes No-certainty conditional expressions for a variable when its certainty is explicitly set to Yes, since confirming a variable exists invalidates any conditional that says it doesn't.

Test

Added a rule test reproducing the exact scenario from the issue: a variable defined inside both branches of an if/else (each containing a foreach), checked with isset(), then accessed after an unrelated foreach loop. The test expects no errors.

Fixes phpstan/phpstan#14353