From 761451fddf18634894cc4ebd9e0b827f270a06a8 Mon Sep 17 00:00:00 2001
From: Takuya Aramaki <takaram71@gmail.com>
Date: Mon, 27 Oct 2025 02:11:50 +0900
Subject: [PATCH 1/2] Refactor `FunctionCallParametersCheck`

`$parameterCount` is always >0 when `$isNativelyVariadic` is true
---
 src/Rules/FunctionCallParametersCheck.php | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/src/Rules/FunctionCallParametersCheck.php b/src/Rules/FunctionCallParametersCheck.php
index 5c3821aa4f..886df0d08d 100644
--- a/src/Rules/FunctionCallParametersCheck.php
+++ b/src/Rules/FunctionCallParametersCheck.php
@@ -603,12 +603,7 @@ private function processArguments(
 			} else {
 				$namedArgumentAlreadyOccurred = true;
 
-				$parametersCount = count($parameters);
-				if (
-					!$isNativelyVariadic
-					|| $parametersCount <= 0
-					|| $isBuiltin
-				) {
+				if (!$isNativelyVariadic || $isBuiltin) {
 					$errors[] = RuleErrorBuilder::message(sprintf($unknownParameterMessage, $argumentName))
 						->identifier('argument.unknown')
 						->line($argumentLine)
@@ -617,6 +612,7 @@ private function processArguments(
 					continue;
 				}
 
+				$parametersCount = count($parameters);
 				$parameter = $parameters[$parametersCount - 1];
 				$originalParameter = $originalParameters[$parametersCount - 1];
 			}

From cf2127522a68104bf036caca40fd502bc7cf3f82 Mon Sep 17 00:00:00 2001
From: Takuya Aramaki <takaram71@gmail.com>
Date: Fri, 31 Oct 2025 00:33:36 +0900
Subject: [PATCH 2/2] Detect duplicated args passed to a variadic parameter

Closes phpstan/phpstan#13710
---
 src/Rules/FunctionCallParametersCheck.php                | 9 +++++++++
 .../Rules/Functions/CallToFunctionParametersRuleTest.php | 4 ++++
 tests/PHPStan/Rules/Functions/data/named-arguments.php   | 5 +++++
 3 files changed, 18 insertions(+)

diff --git a/src/Rules/FunctionCallParametersCheck.php b/src/Rules/FunctionCallParametersCheck.php
index 886df0d08d..955dad6383 100644
--- a/src/Rules/FunctionCallParametersCheck.php
+++ b/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) {
diff --git a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php b/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
index b179c1ff0d..87f6d20496 100644
--- a/tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
+++ b/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';
diff --git a/tests/PHPStan/Rules/Functions/data/named-arguments.php b/tests/PHPStan/Rules/Functions/data/named-arguments.php
index 3e349530b4..4cda8071d1 100644
--- a/tests/PHPStan/Rules/Functions/data/named-arguments.php
+++ b/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);
+}