Fix phpstan/phpstan#10055: Conditional argument type not properly narrowing type (for constant string unions?)

src/Analyser/ConditionalExpressionHolder.php

@@ -17,6 +17,7 @@ final class ConditionalExpressionHolder
 	public function __construct(
 		private array $conditionExpressionTypeHolders,
 		private ExpressionTypeHolder $typeHolder,
+		private bool $useSubtypeForConditionMatching = false,
 	)
 	{
 		if (count($conditionExpressionTypeHolders) === 0) {
@@ -37,6 +38,11 @@ public function getTypeHolder(): ExpressionTypeHolder
 		return $this->typeHolder;
 	}
 
+	public function useSubtypeForConditionMatching(): bool
+	{
+		return $this->useSubtypeForConditionMatching;
+	}
+
 	public function getKey(): string
 	{
 		$parts = [];

src/Analyser/MutatingScope.php

@@ -1760,12 +1760,12 @@ private function enterFunctionLike(
 
 					$holder = new ConditionalExpressionHolder([
 						$parameterType->getParameterName() => ExpressionTypeHolder::createYes(new Variable($targetParameterName), TypeCombinator::intersect($targetParameter->getType(), $parameterType->getTarget())),
-					], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $ifType));
+					], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $ifType), true);
 					$conditionalTypes['$' . $parameter->getName()][$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()), $elseType));
+					], ExpressionTypeHolder::createYes(new Variable($parameter->getName()), $elseType), true);
 					$conditionalTypes['$' . $parameter->getName()][$holder->getKey()] = $holder;
 				}
 			}
@@ -3218,9 +3218,22 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 				}
 				foreach ($conditionalExpressions as $conditionalExpression) {
 					foreach ($conditionalExpression->getConditionExpressionTypeHolders() as $holderExprString => $conditionalTypeHolder) {
-						if (!array_key_exists($holderExprString, $specifiedExpressions) || !$specifiedExpressions[$holderExprString]->equals($conditionalTypeHolder)) {
+						if (!array_key_exists($holderExprString, $specifiedExpressions)) {
 							continue 2;
 						}
+						$specifiedHolder = $specifiedExpressions[$holderExprString];
+						if (!$specifiedHolder->getCertainty()->equals($conditionalTypeHolder->getCertainty())) {
+							continue 2;
+						}
+						if ($conditionalExpression->useSubtypeForConditionMatching()) {
+							if (!$conditionalTypeHolder->getType()->isSuperTypeOf($specifiedHolder->getType())->yes()) {
+								continue 2;
+							}
+						} else {
+							if (!$specifiedHolder->equals($conditionalTypeHolder)) {
+								continue 2;
+							}
+						}
 					}
 
 					$conditions[$conditionalExprString][] = $conditionalExpression;

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),
+	};
+}