Use isSuperTypeOf for condition matching in conditional parameter types

Instead of splitting union condition types into individual
ConditionalExpressionHolder instances, use isSuperTypeOf at the
matching site so that a narrowed type (e.g. 'value1') correctly
matches a broader condition type (e.g. 'value1'|'value2').

A new useSubtypeForConditionMatching flag on ConditionalExpressionHolder
limits this relaxed matching to conditional parameter type holders only.
Other holders (from scope merging, assignments, type specifying) keep
strict equals() matching to avoid cascading side effects.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

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

@@ -1758,24 +1758,15 @@ private function enterFunctionLike(
 					$ifType = $parameterType->isNegated() ? $parameterType->getElse() : $parameterType->getIf();
 					$elseType = $parameterType->isNegated() ? $parameterType->getIf() : $parameterType->getElse();
 
-					$ifConditionType = TypeCombinator::intersect($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;
-					}
+					$holder = new ConditionalExpressionHolder([
+						$parameterType->getParameterName() => ExpressionTypeHolder::createYes(new Variable($targetParameterName), TypeCombinator::intersect($targetParameter->getType(), $parameterType->getTarget())),
+					], ExpressionTypeHolder::createYes(new Variable($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), true);
+					$conditionalTypes['$' . $parameter->getName()][$holder->getKey()] = $holder;
 				}
 			}
 
@@ -3227,9 +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;