Support narrowing a constant array to a list with count

Author: herndlm

src/Analyser/TypeSpecifier.php

@@ -1061,10 +1061,11 @@ private function specifyTypesForCountFuncCall(
 			$isNormalCount = (new ConstantIntegerType(COUNT_NORMAL))->isSuperTypeOf($mode)->result->or($type->getIterableValueType()->isArray()->negate());
 		}
 
+		$isConstantArray = $type->isConstantArray();
 		$isList = $type->isList();
 		if (
 			!$isNormalCount->yes()
-			|| (!$type->isConstantArray()->yes() && !$isList->yes())
+			|| (!$isConstantArray->yes() && !$isList->yes())
 			|| $type->isIterableAtLeastOnce()->no() // array{} cannot be used for further narrowing
 		) {
 			return null;
@@ -1082,9 +1083,12 @@ private function specifyTypesForCountFuncCall(
 			}
 
 			if (
-				$isList->yes()
-				&& $sizeType instanceof ConstantIntegerType
+				$sizeType instanceof ConstantIntegerType
 				&& $sizeType->getValue() < ConstantArrayTypeBuilder::ARRAY_COUNT_LIMIT
+				&& (
+					$isList->yes()
+					|| $isConstantArray->yes() && $arrayType->getKeyType()->isSuperTypeOf(IntegerRangeType::fromInterval(0, $sizeType->getValue() - 1))->yes()
+				)
 			) {
 				// turn optional offsets non-optional
 				$valueTypesBuilder = ConstantArrayTypeBuilder::createEmpty();

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

@@ -87,6 +87,16 @@ public function doBaz(array $arr): void
 		assertType('1|2', count($arr));
 	}
 
+	public function constantArrayWhichCanBecomeList(string $h): void
+	{
+		preg_match('#^([a-z0-9-]+)\..+$#', $h, $matches);
+		if (count($matches) !== 2) {
+			return;
+		}
+
+		assertType('array{string, non-empty-string}', $matches);
+	}
+
 }
 
 /**