POC

Author: VincentLanglet

src/Type/Constant/ConstantArrayTypeBuilder.php

@@ -110,11 +110,16 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $opt
 			if ($offsetType === null) {
 				$newAutoIndexes = $optional ? $this->nextAutoIndexes : [];
 				$hasOptional = false;
+				$existingMaxIndex = -1;
 				foreach ($this->keyTypes as $i => $keyType) {
 					if (!$keyType instanceof ConstantIntegerType) {
 						continue;
 					}
 
+					if ($keyType->getValue() > $existingMaxIndex) {
+						$existingMaxIndex = $keyType->getValue();
+					}
+
 					if (!in_array($keyType->getValue(), $this->nextAutoIndexes, true)) {
 						continue;
 					}
@@ -153,6 +158,10 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $opt
 					$this->optionalKeys[] = count($this->keyTypes) - 1;
 				}
 
+				if ($max < 0 || $max > $existingMaxIndex + 1) {
+					$this->isList = $this->isList->and($optional || $hasOptional ? TrinaryLogic::createMaybe() : TrinaryLogic::createNo());
+				}
+
 				if (
 					!$this->disableArrayDegradation
 					&& count($this->keyTypes) > self::ARRAY_COUNT_LIMIT
@@ -199,12 +208,14 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $opt
 					$offsetValue = $offsetType->getValue();
 					if ($offsetValue >= 0) {
 						if ($offsetValue > $min) {
-							if ($offsetValue <= $max) {
+							if ($offsetValue <= $max || $optional) {
 								$this->isList = $this->isList->and(TrinaryLogic::createMaybe());
 							} else {
 								$this->isList = TrinaryLogic::createNo();
 							}
 						}
+					} elseif ($optional) {
+						$this->isList = $this->isList->and(TrinaryLogic::createMaybe());
 					} else {
 						$this->isList = TrinaryLogic::createNo();
 					}
@@ -221,6 +232,8 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $opt
 							$this->nextAutoIndexes[] = $newAutoIndex;
 						}
 					}
+				} elseif ($optional) {
+					$this->isList = $this->isList->and(TrinaryLogic::createMaybe());
 				} else {
 					$this->isList = TrinaryLogic::createNo();
 				}
@@ -285,11 +298,17 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $opt
 				}
 			}
 
-			$this->isList = TrinaryLogic::createNo();
+			if ($optional) {
+				$this->isList = $this->isList->and(TrinaryLogic::createMaybe());
+			} else {
+				$this->isList = TrinaryLogic::createNo();
+			}
 		}
 
 		if ($offsetType === null) {
 			$offsetType = TypeCombinator::union(...array_map(static fn (int $index) => new ConstantIntegerType($index), $this->nextAutoIndexes));
+		} elseif ($optional) {
+			$this->isList = $this->isList->and(TrinaryLogic::createMaybe());
 		} else {
 			$this->isList = TrinaryLogic::createNo();
 		}

tests/PHPStan/Analyser/nsrt/array-is-list-unset.php

@@ -19,7 +19,7 @@ function () {
 	assertType('true', array_is_list($a));
 	unset($a[2]);
 	assertType('array{1, 2}', $a);
-	assertType('false', array_is_list($a));
+	assertType('true', array_is_list($a));
 	$a[] = 4;
 	assertType('array{0: 1, 1: 2, 3: 4}', $a);
 	assertType('false', array_is_list($a));