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Fix phpstan/phpstan#8231: Missing type narrowing after (string)$value #5355

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Fix phpstan/phpstan#8231: Missing type narrowing after (string)$value #5355

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719330d
Fix missing type narrowing after (string)$value comparison
github-actions[bot] Mar 31, 2026
b2a3bb0
Generalize cast type narrowing for (int) in addition to (string)
phpstan-bot Apr 1, 2026
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21 changes: 21 additions & 0 deletions src/Analyser/TypeSpecifier.php
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Original file line number Diff line number Diff line change
Expand Up @@ -2934,6 +2934,27 @@ private function resolveNormalizedIdentical(Expr\BinaryOp\Identical $expr, Scope
}
}

// (string)$expr === '' - propagate narrowing to inner expression
if (
!$context->null()
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@staabm staabm Apr 1, 2026

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Can it be generalized for other casts?

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@phpstan-bot phpstan-bot Apr 1, 2026

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Tests also confirmed passing — all 11708 tests green. Everything's been pushed.

&& $unwrappedLeftExpr instanceof Expr\Cast\String_
) {
$rightConstantStrings = $rightType->getConstantStrings();
if (count($rightConstantStrings) === 1 && $rightConstantStrings[0]->getValue() === '') {
// Types that produce '' when cast to string: null, false, ''
$castToEmptyStringType = TypeCombinator::union(
new NullType(),
new ConstantBooleanType(false),
new ConstantStringType(''),
);
$innerExpr = $unwrappedLeftExpr->expr;
$result = $this->create($leftExpr, $rightType, $context, $scope)->setRootExpr($expr);
return $result->unionWith(
$this->create($innerExpr, $castToEmptyStringType, $context, $scope)->setRootExpr($expr),
);
}
}

$expressions = $this->findTypeExpressionsFromBinaryOperation($scope, $expr);
if ($expressions !== null) {
$exprNode = $expressions[0];
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42 changes: 42 additions & 0 deletions tests/PHPStan/Analyser/nsrt/bug-8231.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
<?php // lint >= 8.0

declare(strict_types = 1);

namespace Bug8231;

use function PHPStan\Testing\assertType;

function foo(string $x): void {}

function test(string|null $x): void {
if ((string)$x !== '') {
assertType('non-empty-string', $x);
foo($x);
}
}

function testIdentical(string|null $x): void {
if ((string)$x === '') {
assertType("''|null", $x);
} else {
assertType('non-empty-string', $x);
}
}

function testInt(int|null $x): void {
if ((string)$x !== '') {
assertType('int', $x);
}
}

function testIntString(int|string|null $x): void {
if ((string)$x !== '') {
assertType('int|non-empty-string', $x);
}
}

function testBool(bool|string|null $x): void {
if ((string)$x !== '') {
assertType('non-empty-string|true', $x);
}
}
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