Fix non-existent offset when guarding

src/Analyser/TypeSpecifier.php

@@ -291,6 +291,25 @@
 				if ($specifiedTypes !== null) {
 					$result = $result->unionWith($specifiedTypes);
 				}
+				if (
+					$context->true()
+					&& $expr instanceof Node\Expr\BinaryOp\Smaller
+				    && $argType->isList()->yes()
+					&& IntegerRangeType::fromInterval(0, null)->isSuperTypeOf($leftType)->yes()
+				) {
+					$dimFetch = new ArrayDimFetch(
+						$expr->right->getArgs()[0]->value,
+						$expr->left,
+					);
+					$result = $result->unionWith(
+						$this->create(
+							$dimFetch,
+							$argType->getIterableValueType(),
+							TypeSpecifierContext::createTrue(),
+							$scope,
+						)
+					);
+				}
 
 				if (
 					$context->true() && (IntegerRangeType::createAllGreaterThanOrEqualTo(1 - $offset)->isSuperTypeOf($leftType)->yes())
@@ -500,7 +519,7 @@
 				}
 
 				if (count($expr->getArgs()) > 0) {
 					$specifiedTypes = $this->specifyTypesFromConditionalReturnType($context, $expr, $parametersAcceptor, $scope);
 					if ($specifiedTypes !== null) {
 						return $specifiedTypes;
 					}
@@ -510,7 +529,7 @@
 				if ($assertions->getAll() !== []) {
 					$parametersAcceptor ??= ParametersAcceptorSelector::selectFromArgs($scope, $expr->getArgs(), $functionReflection->getVariants(), $functionReflection->getNamedArgumentsVariants());
 
 					$asserts = $assertions->mapTypes(static fn (Type $type) => TemplateTypeHelper::resolveTemplateTypes(
 						$type,
 						$parametersAcceptor->getResolvedTemplateTypeMap(),
 						$parametersAcceptor instanceof ExtendedParametersAcceptor ? $parametersAcceptor->getCallSiteVarianceMap() : TemplateTypeVarianceMap::createEmpty(),
@@ -553,7 +572,7 @@
 				}
 
 				if (count($expr->getArgs()) > 0) {
 					$specifiedTypes = $this->specifyTypesFromConditionalReturnType($context, $expr, $parametersAcceptor, $scope);
 					if ($specifiedTypes !== null) {
 						return $specifiedTypes;
 					}
@@ -563,7 +582,7 @@
 				if ($assertions->getAll() !== []) {
 					$parametersAcceptor ??= ParametersAcceptorSelector::selectFromArgs($scope, $expr->getArgs(), $methodReflection->getVariants(), $methodReflection->getNamedArgumentsVariants());
 
 					$asserts = $assertions->mapTypes(static fn (Type $type) => TemplateTypeHelper::resolveTemplateTypes(
 						$type,
 						$parametersAcceptor->getResolvedTemplateTypeMap(),
 						$parametersAcceptor instanceof ExtendedParametersAcceptor ? $parametersAcceptor->getCallSiteVarianceMap() : TemplateTypeVarianceMap::createEmpty(),
@@ -611,7 +630,7 @@
 				}
 
 				if (count($expr->getArgs()) > 0) {
 					$specifiedTypes = $this->specifyTypesFromConditionalReturnType($context, $expr, $parametersAcceptor, $scope);
 					if ($specifiedTypes !== null) {
 						return $specifiedTypes;
 					}
@@ -621,7 +640,7 @@
 				if ($assertions->getAll() !== []) {
 					$parametersAcceptor ??= ParametersAcceptorSelector::selectFromArgs($scope, $expr->getArgs(), $staticMethodReflection->getVariants(), $staticMethodReflection->getNamedArgumentsVariants());
 
 					$asserts = $assertions->mapTypes(static fn (Type $type) => TemplateTypeHelper::resolveTemplateTypes(
 						$type,
 						$parametersAcceptor->getResolvedTemplateTypeMap(),
 						$parametersAcceptor instanceof ExtendedParametersAcceptor ? $parametersAcceptor->getCallSiteVarianceMap() : TemplateTypeVarianceMap::createEmpty(),

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -700,6 +700,10 @@ public static function dataReportPossiblyNonexistentArrayOffset(): iterable
 				"Offset 'foo' might not exist on array.",
 				9,
 			],
+			[
+				'Offset int might not exist on list<int>.',
+				77
+			],
 		]];
 		yield [true, true, [
 			[
@@ -710,6 +714,10 @@ public static function dataReportPossiblyNonexistentArrayOffset(): iterable
 				'Offset string might not exist on array{foo: 1}.',
 				20,
 			],
+			[
+				'Offset int might not exist on list<int>.',
+				77
+			],
 		]];
 	}
 

tests/PHPStan/Rules/Arrays/data/report-possibly-nonexistent-array-offset.php

@@ -57,4 +57,25 @@ public function nonEmpty(array $a): void
 		echo $a[0];
 	}
 
+	/**
+	 * @param list<int> $array
+	 * @param positive-int $index
+	 */
+	public function guard(array $array, int $index) {
+		if ($index < count($array)) {
+			return $array[$index];
+		}
+		return null;
+	}
+
+
+	/**
+	 * @param list<int> $array
+	 */
+	public function guardNotSafe(array $array, int $index) {
+		if ($index < count($array)) {
+			return $array[$index];
+		}
+		return null;
+	}
 }