add combination limit

Author: staabm

src/Type/Php/ImplodeFunctionReturnTypeExtension.php

@@ -6,6 +6,7 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\Internal\CombinationsHelper;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Reflection\InitializerExprTypeResolver;
 use PHPStan\Type\Accessory\AccessoryLiteralStringType;
 use PHPStan\Type\Accessory\AccessoryLowercaseStringType;
 use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
@@ -128,6 +129,10 @@ private function inferConstantType(ConstantArrayType $arrayType, ConstantStringT
 			}
 		}
 
+		if (count($strings) > InitializerExprTypeResolver::CALCULATE_SCALARS_LIMIT) {
+			return null;
+		}
+
 		return TypeCombinator::union(...$strings);
 	}
 

tests/PHPStan/Analyser/nsrt/implode.php

@@ -46,4 +46,9 @@ public function constArrays4($constArr) {
 	public function constArrays5($constArr) {
 		assertType("'1a'|'1b'|'1c'|'2a'|'2b'|'2c'|'3a'|'3b'|'3c'", implode('', $constArr));
 	}
+
+	/** @param array{0: 1, 1: 'a'|'b', 3?: 'c'|'d', 4?: 'e'|'f', 5?: 'g'|'h', 6?: 'x'|'y'} $constArr */
+	public function constArrays6($constArr) {
+		assertType("string", implode('', $constArr));
+	}
 }