Keep the declared type of a variadic closure parameter

A variadic parameter collects arguments of different positions into one
list; spread again into positional parameters, the union of all of them
fits none. Variadic parameters keep their declared type.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VpbB99tJfUmeArX74xqvHv

Author: ondrejmirtes

src/Analyser/Generics/ClosureSignatureInference.php

@@ -132,7 +132,9 @@ public function getSignatureParameters(MutatingScope $scope, Closure|ArrowFuncti
 
 		$parameters = [];
 		foreach ($declaredParameters as $parameter) {
-			if (!$parameter->passedByReference()->no()) {
+			// a variadic parameter collects arguments of different positions into
+			// one list - spread again, one element type fits none of them
+			if (!$parameter->passedByReference()->no() || $parameter->isVariadic()) {
 				$parameters[] = $parameter;
 				continue;
 			}
@@ -210,7 +212,11 @@ public function getSignatureReturnType(MutatingScope $scope, Closure|ArrowFuncti
 			return $returnType;
 		}
 		$frame = $this->getFrame($scope);
-		if ($frame === null || (!$frame->isObservingClosures() && !$frame->isSettledClosureSite($expr)) || !self::returnsContextTypedExpression($expr)) {
+		if (
+			$frame === null
+			|| (!$frame->isObservingClosures() && !$frame->isSettledClosureSite($expr))
+			|| !self::returnsContextTypedExpression($expr)
+		) {
 			return $returnType;
 		}
 

tests/PHPStan/Analyser/nsrt/closure-signature-from-usages.php

@@ -408,7 +408,7 @@ public function defaultAndVariadic(): void
 		$c(1);
 
 		$d = function (...$xs) {
-			assertType('array<int<0, max>|string, 1|2>', $xs);
+			assertType('array<int<0, max>|string, mixed>', $xs);
 		};
 		$d(1, 2);
 	}
@@ -505,4 +505,14 @@ public function settledClosureSentToGenericTarget(): void
 		assertType('list<int|string>', takesConvertor($convertor));
 	}
 
+	public function variadicParameterKeepsDeclaredType(): void
+	{
+		$inner = static fn (string $a, float $b): array => [$a, $b];
+		$outer = static function (mixed ...$args) use ($inner): array {
+			assertType('array<int<0, max>|string, mixed>', $args);
+			return $inner(...$args);
+		};
+		$outer('x', 1.0);
+	}
+
 }

tests/PHPStan/Rules/Functions/CallCallablesRuleTest.php

@@ -449,6 +449,12 @@ public function testBug15251(): void
 		$this->analyse([__DIR__ . '/../Methods/data/bug-15251.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0.0')]
+	public function testClosureSignatureFromUsages(): void
+	{
+		$this->analyse([__DIR__ . '/data/closure-signature-from-usages.php'], []);
+	}
+
 	#[RequiresPhp('>= 8.2.0')]
 	public function testBug15285(): void
 	{

tests/PHPStan/Rules/Functions/data/closure-signature-from-usages.php

@@ -52,4 +52,8 @@ function (): void {
 		return 'x' . $value;
 	};
 	takesConvertor($convertor);
+
+	$inner = static fn (string $a, float $b): array => [$a, $b];
+	$outer = static fn (mixed ...$args): array => $inner(...$args);
+	$outer('x', 1.0);
 };

turbo-ext/src/ClosureSignatureInference.cpp

@@ -479,7 +479,13 @@ class ClosureSignatureInference
 			if (UNEXPECTED(passedByReference.isUndef())) return zv::Val();
 			zend_long mode = pt_passed_by_reference_mode(passedByReference.raw());
 			if (UNEXPECTED(mode < 0)) return zv::Val();
-			if (mode != PT_PASSED_BY_REFERENCE_NO) {
+			bool isVariadicParameter = false;
+			if (mode == PT_PASSED_BY_REFERENCE_NO) {
+				zv::Val isVariadic = pt_parameter_reflection_call(parameter, PT_PR_IS_VARIADIC);
+				if (UNEXPECTED(isVariadic.isUndef())) return zv::Val();
+				isVariadicParameter = zend_is_true(isVariadic.raw());
+			}
+			if (mode != PT_PASSED_BY_REFERENCE_NO || isVariadicParameter) {
 				parameters.push(zv::Val::copyOf(zv::Ref(parameter)));
 				continue;
 			}