Correctly consider impossible list

Author: VincentLanglet

src/Type/Constant/ConstantArrayType.php

@@ -748,8 +748,12 @@ public function unsetOffset(Type $offsetType, bool $preserveListCertainty = fals
 					$newOptionalKeys,
 					$this->isList,
 					in_array($i, $this->optionalKeys, true),
-					$preserveListCertainty,
 				);
+				if (!$preserveListCertainty) {
+					$newIsList = $newIsList->and(TrinaryLogic::createMaybe());
+				} elseif ($this->isList->yes() && $newIsList->no()) {
+					return new NeverType();
+				}
 
 				return new self($newKeyTypes, $newValueTypes, $this->nextAutoIndexes, $newOptionalKeys, $newIsList);
 			}
@@ -791,8 +795,12 @@ public function unsetOffset(Type $offsetType, bool $preserveListCertainty = fals
 				$optionalKeys,
 				$this->isList,
 				count($optionalKeys) === count($this->optionalKeys),
-				$preserveListCertainty,
 			);
+			if (!$preserveListCertainty) {
+				$newIsList = $newIsList->and(TrinaryLogic::createMaybe());
+			} elseif ($this->isList->yes() && $newIsList->no()) {
+				return new NeverType();
+			}
 
 			return new self($this->keyTypes, $this->valueTypes, $this->nextAutoIndexes, $optionalKeys, $newIsList);
 		}
@@ -817,8 +825,12 @@ public function unsetOffset(Type $offsetType, bool $preserveListCertainty = fals
 			$optionalKeys,
 			$this->isList,
 			count($optionalKeys) === count($this->optionalKeys),
-			$preserveListCertainty,
 		);
+		if (!$preserveListCertainty) {
+			$newIsList = $newIsList->and(TrinaryLogic::createMaybe());
+		} elseif ($this->isList->yes() && $newIsList->no()) {
+			return new NeverType();
+		}
 
 		return new self($this->keyTypes, $this->valueTypes, $this->nextAutoIndexes, $optionalKeys, $newIsList);
 	}
@@ -830,7 +842,7 @@ public function unsetOffset(Type $offsetType, bool $preserveListCertainty = fals
 	 * @param list<ConstantIntegerType|ConstantStringType> $newKeyTypes
 	 * @param int[] $newOptionalKeys
 	 */
-	private static function isListAfterUnset(array $newKeyTypes, array $newOptionalKeys, TrinaryLogic $arrayIsList, bool $unsetOptionalKey, bool $preserveListCertainty): TrinaryLogic
+	private static function isListAfterUnset(array $newKeyTypes, array $newOptionalKeys, TrinaryLogic $arrayIsList, bool $unsetOptionalKey): TrinaryLogic
 	{
 		if (!$unsetOptionalKey || $arrayIsList->no()) {
 			return TrinaryLogic::createNo();
@@ -854,7 +866,7 @@ private static function isListAfterUnset(array $newKeyTypes, array $newOptionalK
 			}
 		}
 
-		return $preserveListCertainty ? $arrayIsList : TrinaryLogic::createMaybe();
+		return $arrayIsList;
 	}
 
 	public function chunkArray(Type $lengthType, TrinaryLogic $preserveKeys): Type

tests/PHPStan/Analyser/nsrt/bug-14177.php

@@ -200,4 +200,25 @@ public function testUnsetInt(array $a, array $b, array $c, int $int): void
 		assertType('bool', array_is_list($a));
 		assertType('false', array_is_list($b));
 	}
+
+	/**
+	 * @param list{0?: string, 1?: string, 2?: string} $l
+	 */
+	public function testFoo($l): void
+	{
+		if (array_key_exists(2, $l, true)) {
+			assertType('true', array_is_list($l));
+			assertType('list{0?: string, 1?: string, 2: string}', $l);
+			if (array_key_exists(1, $l, true)) {
+				assertType('true', array_is_list($l));
+				assertType('list{0?: string, 1: string, 2: string}', $l);
+			} else {
+				assertType('true', array_is_list($l));
+				assertType('*NEVER*', $l);
+			}
+		} else {
+			assertType('true', array_is_list($l));
+			assertType('list{0?: string, 1?: string}', $l);
+		}
+	}
 }