Fix phpstan/phpstan#14201: Narrow array type when element from reset/current/end is narrowed

- Added conditional expression holders in AssignHandler for reset(), current(), end()
- When $first = reset($items) and $first is later narrowed via instanceof, $items value type is narrowed too
- New regression test in tests/PHPStan/Analyser/nsrt/bug-14201.php

Author: phpstan-bot

src/Analyser/ExprHandler/AssignHandler.php

@@ -48,6 +48,7 @@
 use PHPStan\Type\Accessory\AccessoryArrayListType;
 use PHPStan\Type\Accessory\HasOffsetValueType;
 use PHPStan\Type\Accessory\NonEmptyArrayType;
+use PHPStan\Type\ArrayType;
 use PHPStan\Type\Constant\ConstantArrayType;
 use PHPStan\Type\Constant\ConstantIntegerType;
 use PHPStan\Type\Constant\ConstantStringType;
@@ -60,6 +61,7 @@
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\TypeUtils;
+use PHPStan\Type\UnionType;
 use TypeError;
 use function array_key_last;
 use function array_merge;
@@ -281,6 +283,13 @@ public function processAssignVar(
 					$conditionalExpressions = $this->processSureNotTypesForConditionalExpressionsAfterAssign($scope, $var->name, $conditionalExpressions, $identicalSpecifiedTypes, $falseyType);
 				}
 
+				$conditionalExpressions = $this->processArrayValueExtractionForConditionalExpressions(
+					$scope,
+					$var->name,
+					$conditionalExpressions,
+					$assignedExpr,
+				);
+
 				$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, $assignedExpr), $scopeBeforeAssignEval, $storage);
 				$scope = $scope->assignVariable($var->name, $type, $scope->getNativeType($assignedExpr), TrinaryLogic::createYes());
 				foreach ($conditionalExpressions as $exprString => $holders) {
@@ -1076,4 +1085,69 @@ private function isSameVariable(Expr $a, Expr $b): bool
 		return false;
 	}
 
+	/**
+	 * @param array<string, ConditionalExpressionHolder[]> $conditionalExpressions
+	 * @return array<string, ConditionalExpressionHolder[]>
+	 */
+	private function processArrayValueExtractionForConditionalExpressions(
+		Scope $scope,
+		string $variableName,
+		array $conditionalExpressions,
+		Expr $assignedExpr,
+	): array
+	{
+		if (
+			!$assignedExpr instanceof Expr\FuncCall
+			|| !$assignedExpr->name instanceof Name
+			|| !in_array($assignedExpr->name->toLowerString(), ['reset', 'current', 'end'], true)
+			|| count($assignedExpr->getArgs()) < 1
+		) {
+			return $conditionalExpressions;
+		}
+
+		$arrayArg = $assignedExpr->getArgs()[0]->value;
+		if (!$arrayArg instanceof Variable || !is_string($arrayArg->name)) {
+			return $conditionalExpressions;
+		}
+
+		$arrayArgType = $scope->getType($arrayArg);
+		if (!$arrayArgType->isArray()->yes()) {
+			return $conditionalExpressions;
+		}
+
+		$valueType = $arrayArgType->getIterableValueType();
+		if (!$valueType instanceof UnionType) {
+			return $conditionalExpressions;
+		}
+
+		$valueTypeMembers = $valueType->getTypes();
+		if (count($valueTypeMembers) < 2) {
+			return $conditionalExpressions;
+		}
+
+		$arrayExprString = '$' . $arrayArg->name;
+		$keyType = $arrayArgType->getIterableKeyType();
+
+		foreach ($valueTypeMembers as $memberType) {
+			$narrowedArrayType = TypeCombinator::intersect(
+				$arrayArgType,
+				new ArrayType($keyType, $memberType),
+			);
+
+			$holder = new ConditionalExpressionHolder(
+				['$' . $variableName => ExpressionTypeHolder::createYes(
+					new Variable($variableName),
+					$memberType,
+				)],
+				ExpressionTypeHolder::createYes(
+					$arrayArg,
+					$narrowedArrayType,
+				),
+			);
+			$conditionalExpressions[$arrayExprString][$holder->getKey()] = $holder;
+		}
+
+		return $conditionalExpressions;
+	}
+
 }

tests/PHPStan/Analyser/nsrt/bug-14201.php

@@ -0,0 +1,57 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug14201;
+
+use function PHPStan\Testing\assertType;
+
+class Foo { public function __construct(public string $fooName) {}}
+class Bar { public function __construct(public string $barName) {}}
+
+class HelloWorld
+{
+	/**
+	 * @param Foo[]|Bar[] $items
+	 */
+	public function doitMatch(array $items): void
+	{
+		if ([] === $items) {return; }
+
+		$first = reset($items);
+		match (true) {
+			$first instanceOf Foo => array_map(function ($i) {
+				assertType('Bug14201\Foo', $i);
+				return $i->fooName;
+			}, $items),
+			$first instanceOf Bar => array_map(function ($i) {
+				assertType('Bug14201\Bar', $i);
+				return $i->barName;
+			}, $items),
+			default => throw new \RuntimeException('None of Foo nor Bar')
+		};
+	}
+
+	/**
+	 * @param Foo[]|Bar[] $items
+	 */
+	public function doitIf(array $items): void
+	{
+		if ([] === $items) {return; }
+
+		$first = reset($items);
+		if ($first instanceof Foo) {
+			assertType('non-empty-array<Bug14201\Foo>', $items);
+			array_map(function ($i) {
+				assertType('Bug14201\Foo', $i);
+				return $i->fooName;
+			}, $items);
+		} elseif ($first instanceof Bar) {
+			assertType('non-empty-array<Bug14201\Bar>', $items);
+			array_map(function ($i) {
+				assertType('Bug14201\Bar', $i);
+				return $i->barName;
+			}, $items);
+		}
+	}
+}