Fix conditional parameter type narrowing for union types with 3+ members

- Split union condition types into individual ConditionalExpressionHolders
- When TypeCombinator::intersect or ::remove produces a UnionType, each member
  gets its own holder so the equals() check can match individual constant types
- New regression test in tests/PHPStan/Analyser/nsrt/bug-10055.php

Author: VincentLanglet

src/Analyser/MutatingScope.php

@@ -1758,15 +1758,24 @@ private function enterFunctionLike(
 					$ifType = $parameterType->isNegated() ? $parameterType->getElse() : $parameterType->getIf();
 					$elseType = $parameterType->isNegated() ? $parameterType->getIf() : $parameterType->getElse();
 
-					$holder = new ConditionalExpressionHolder([
-						$parameterType->getParameterName() => ExpressionTypeHolder::createYes(new Variable($targetParameterName), TypeCombinator::intersect($targetParameter->getType(), $parameterType->getTarget())),
-					], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $ifType));
-					$conditionalTypes['$' . $parameter->getName()][$holder->getKey()] = $holder;
-
-					$holder = new ConditionalExpressionHolder([
-						$parameterType->getParameterName() => ExpressionTypeHolder::createYes(new Variable($targetParameterName), TypeCombinator::remove($targetParameter->getType(), $parameterType->getTarget())),
-					], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $elseType));
-					$conditionalTypes['$' . $parameter->getName()][$holder->getKey()] = $holder;
+					$ifConditionType = TypeCombinator::intersect($targetParameter->getType(), $parameterType->getTarget());
+					$elseConditionType = TypeCombinator::remove($targetParameter->getType(), $parameterType->getTarget());
+
+					$ifConditionTypes = $ifConditionType instanceof UnionType ? $ifConditionType->getTypes() : [$ifConditionType];
+					foreach ($ifConditionTypes as $conditionType) {
+						$holder = new ConditionalExpressionHolder([
+							$parameterType->getParameterName() => ExpressionTypeHolder::createYes(new Variable($targetParameterName), $conditionType),
+						], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $ifType));
+						$conditionalTypes['$' . $parameter->getName()][$holder->getKey()] = $holder;
+					}
+
+					$elseConditionTypes = $elseConditionType instanceof UnionType ? $elseConditionType->getTypes() : [$elseConditionType];
+					foreach ($elseConditionTypes as $conditionType) {
+						$holder = new ConditionalExpressionHolder([
+							$parameterType->getParameterName() => ExpressionTypeHolder::createYes(new Variable($targetParameterName), $conditionType),
+						], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $elseType));
+						$conditionalTypes['$' . $parameter->getName()][$holder->getKey()] = $holder;
+					}
 				}
 			}
 

tests/PHPStan/Analyser/nsrt/bug-10055.php

@@ -0,0 +1,20 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug10055;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param 'value1'|'value2'|'value3' $param1
+ * @param ($param1 is 'value3' ? bool : int) $param2
+ */
+function test(string $param1, int|bool $param2): void
+{
+	match ($param1) {
+		'value1' => assertType('int', $param2),
+		'value2' => assertType('int', $param2),
+		'value3' => assertType('bool', $param2),
+	};
+}