Narrow offsets for lists with HasOffsetType/HasOffsetValueType

src/Type/IntersectionType.php

@@ -28,6 +28,8 @@
 use PHPStan\Type\Accessory\AccessoryNumericStringType;
 use PHPStan\Type\Accessory\AccessoryType;
 use PHPStan\Type\Accessory\AccessoryUppercaseStringType;
+use PHPStan\Type\Accessory\HasOffsetType;
+use PHPStan\Type\Accessory\HasOffsetValueType;
 use PHPStan\Type\Accessory\NonEmptyArrayType;
 use PHPStan\Type\Constant\ConstantArrayType;
 use PHPStan\Type\Constant\ConstantIntegerType;
@@ -45,6 +47,7 @@
 use function count;
 use function implode;
 use function in_array;
+use function is_int;
 use function ksort;
 use function md5;
 use function sprintf;
@@ -738,6 +741,21 @@ public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 			if ((new ConstantIntegerType(0))->isSuperTypeOf($arrayKeyOffsetType)->yes()) {
 				return TrinaryLogic::createYes();
 			}
+
+			foreach ($this->types as $type) {
+				if (!$type instanceof HasOffsetValueType && !$type instanceof HasOffsetType) {
+					continue;
+				}
+
+				foreach ($type->getOffsetType()->getConstantScalarValues() as $constantScalarValue) {
+					if (!is_int($constantScalarValue)) {
+						continue;
+					}
+					if (IntegerRangeType::fromInterval(0, $constantScalarValue)->isSuperTypeOf($arrayKeyOffsetType)->yes()) {
+						return TrinaryLogic::createYes();
+					}
+				}
+			}
 		}
 
 		return $this->intersectResults(static fn (Type $type): TrinaryLogic => $type->hasOffsetValueType($offsetType));

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -900,6 +900,22 @@ public function testNarrowSuperglobals(): void
 		$this->analyse([__DIR__ . '/data/narrow-superglobal.php'], []);
 	}
 
+	public function testBug12605(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12605.php'], [
+			[
+				'Offset 1 might not exist on list<int>.',
+				19,
+			],
+			[
+				'Offset 10 might not exist on non-empty-list<int>.',
+				26,
+			],
+		]);
+	}
+
 	public function testBug11602(): void
 	{
 		$this->reportPossiblyNonexistentGeneralArrayOffset = true;

tests/PHPStan/Rules/Arrays/data/bug-12605.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace Bug12605;
+
+/**
+ * @return list<int>
+ */
+function test(): array
+{
+	return [];
+}
+
+function doFoo(): void {
+	$test = test();
+
+	if (isset($test[3])) {
+		echo $test[1];
+	}
+	echo $test[1];
+}
+
+function doFooBar(): void {
+	$test = test();
+
+	if (isset($test[4])) {
+		echo $test[10];
+	}
+}
+
+function doBaz(): void {
+	$test = test();
+
+	if (array_key_exists(5, $test) && is_int($test[5])) {
+		echo $test[3];
+	}
+}
+