Detect duplicated args passed to a variadic parameter

Closes phpstan/phpstan#13710

Author: takaram

src/Rules/FunctionCallParametersCheck.php

@@ -578,6 +578,7 @@ private function processArguments(
 		$newArguments = [];
 
 		$namedArgumentAlreadyOccurred = false;
+		$namedArgumentsForVariadicParameter = [];
 		foreach ($arguments as $i => [$argumentValue, $argumentValueType, $unpack, $argumentName, $argumentLine]) {
 			if ($argumentName === null) {
 				if (!isset($parameters[$i])) {
@@ -615,6 +616,14 @@ private function processArguments(
 				$parametersCount = count($parameters);
 				$parameter = $parameters[$parametersCount - 1];
 				$originalParameter = $originalParameters[$parametersCount - 1];
+
+				if (isset($namedArgumentsForVariadicParameter[$argumentName])) {
+					$errors[] = RuleErrorBuilder::message(sprintf('Named parameter $%s overwrites previous argument.', $argumentName))
+						->identifier('argument.duplicate')
+						->line($argumentLine)
+						->build();
+				}
+				$namedArgumentsForVariadicParameter[$argumentName] = true;
 			}
 
 			if ($namedArgumentAlreadyOccurred && $argumentName === null && !$unpack) {

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -512,6 +512,10 @@ public function testNamedArguments(): void
 				'Unknown parameter $a in call to function array_merge.',
 				14,
 			],
+			[
+				'Named parameter $var overwrites previous argument.',
+				19,
+			],
 		];
 
 		require_once __DIR__ . '/data/named-arguments-define.php';

tests/PHPStan/Rules/Functions/data/named-arguments.php

@@ -13,3 +13,8 @@ function baz(): void
 	variadicFunction(...['a' => ['b', 'c']]); // works - userland
 	array_merge(...['a' => ['b', 'c']]); // doesn't work - internal
 }
+
+function bug13710(): void
+{
+	variadicFunction(var: 1, var: 2);
+}