Set offset on list keeps list if there's HasOffsetType for all preceeding offsets

Author: staabm

src/Type/IntersectionType.php

@@ -800,8 +800,30 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $uni
 
 		$result = $this->intersectTypes(static fn (Type $type): Type => $type->setOffsetValueType($offsetType, $valueType, $unionValues));
 
-		if ($offsetType !== null && $this->isList()->yes() && $this->isIterableAtLeastOnce()->yes() && (new ConstantIntegerType(1))->isSuperTypeOf($offsetType)->yes()) {
-			$result = TypeCombinator::intersect($result, new AccessoryArrayListType());
+		if (
+			$offsetType !== null
+			&& $this->isList()->yes()
+			&& !$result->isList()->yes()
+		) {
+			if ($this->isIterableAtLeastOnce()->yes() && (new ConstantIntegerType(1))->isSuperTypeOf($offsetType)->yes()) {
+				$result = TypeCombinator::intersect($result, new AccessoryArrayListType());
+			} else {
+				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, $constantScalarValue + 1)->isSuperTypeOf($offsetType)->yes()) {
+							$result = TypeCombinator::intersect($result, new AccessoryArrayListType());
+							break 2;
+						}
+					}
+				}
+			}
 		}
 
 		return $result;

tests/PHPStan/Analyser/nsrt/list-type.php

@@ -128,4 +128,45 @@ public function testSetOffsetExplicitlyWithGap(array $list): void
 		assertType('non-empty-array<int<0, max>, int>&hasOffsetValue(0, 17)&hasOffsetValue(2, 21)', $list);
 	}
 
+	/** @param list<int> $list */
+	function testAppendImmediatelyAfterLastElement(array $list): void
+	{
+		assertType('list<int>', $list);
+		$list[0] = 17;
+		assertType('non-empty-list<int>&hasOffsetValue(0, 17)', $list);
+		$list[1] = 19;
+		assertType('non-empty-list<int>&hasOffsetValue(0, 17)&hasOffsetValue(1, 19)', $list);
+		$list[2] = 21;
+		assertType('non-empty-list<int>&hasOffsetValue(0, 17)&hasOffsetValue(1, 19)&hasOffsetValue(2, 21)', $list);
+		$list[3] = 21;
+		assertType('non-empty-list<int>&hasOffsetValue(0, 17)&hasOffsetValue(1, 19)&hasOffsetValue(2, 21)&hasOffsetValue(3, 21)', $list);
+
+		// hole in the list -> turns it into a array
+
+		$list[5] = 21;
+		assertType('non-empty-array<int<0, max>, int>&hasOffsetValue(0, 17)&hasOffsetValue(1, 19)&hasOffsetValue(2, 21)&hasOffsetValue(3, 21)&hasOffsetValue(5, 21)', $list);
+	}
+
+
+	/** @param list<int> $list */
+	function testKeepListAfterLast(array $list): void
+	{
+		if (isset($list[5])) {
+			assertType('non-empty-list<int>&hasOffsetValue(5, int)', $list);
+			$list[6] = 21;
+			assertType('non-empty-list<int>&hasOffsetValue(5, int)&hasOffsetValue(6, 21)', $list);
+		}
+		assertType('list<int>', $list);
+	}
+
+	/** @param list<int> $list */
+	function testKeepListAfterLastArrayKey(array $list): void
+	{
+		if (array_key_exists(5, $list) && is_int($list[5])) {
+			assertType('non-empty-list<int>&hasOffsetValue(5, int)', $list);
+			$list[6] = 21;
+			assertType('non-empty-list<int>&hasOffsetValue(5, int)&hasOffsetValue(6, 21)', $list);
+		}
+		assertType('list<int>', $list);
+	}
 }