Support conditional return types by union-ing their branches

First baby step for phpstan/phpstan#3853

src/PhpDoc/TypeNodeResolver.php

@@ -20,6 +20,8 @@
 use PHPStan\PhpDocParser\Ast\Type\ArrayTypeNode;
 use PHPStan\PhpDocParser\Ast\Type\CallableTypeNode;
 use PHPStan\PhpDocParser\Ast\Type\CallableTypeParameterNode;
+use PHPStan\PhpDocParser\Ast\Type\ConditionalTypeForParameterNode;
+use PHPStan\PhpDocParser\Ast\Type\ConditionalTypeNode;
 use PHPStan\PhpDocParser\Ast\Type\ConstTypeNode;
 use PHPStan\PhpDocParser\Ast\Type\GenericTypeNode;
 use PHPStan\PhpDocParser\Ast\Type\IdentifierTypeNode;
@@ -121,6 +123,9 @@ public function resolve(TypeNode $typeNode, NameScope $nameScope): Type
 		} elseif ($typeNode instanceof IntersectionTypeNode) {
 			return $this->resolveIntersectionTypeNode($typeNode, $nameScope);
 
+		} elseif ($typeNode instanceof ConditionalTypeNode || $typeNode instanceof ConditionalTypeForParameterNode) {
+			return $this->resolveConditionalTypeNode($typeNode, $nameScope);
+
 		} elseif ($typeNode instanceof ArrayTypeNode) {
 			return $this->resolveArrayTypeNode($typeNode, $nameScope);
 
@@ -438,6 +443,12 @@ private function resolveIntersectionTypeNode(IntersectionTypeNode $typeNode, Nam
 		return TypeCombinator::intersect(...$types);
 	}
 
+	private function resolveConditionalTypeNode(ConditionalTypeNode|ConditionalTypeForParameterNode $typeNode, NameScope $nameScope): Type
+	{
+		$types = $this->resolveMultiple([$typeNode->if, $typeNode->else], $nameScope);
+		return TypeCombinator::union(...$types);
+	}
+
 	private function resolveArrayTypeNode(ArrayTypeNode $typeNode, NameScope $nameScope): Type
 	{
 		$itemType = $this->resolve($typeNode->type, $nameScope);

tests/PHPStan/Analyser/data/bug-3853.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Bug3853;
+
+use function PHPStan\Testing\assertType;
+
+abstract class Test
+{
+	/**
+	 * @template TKey as array-key
+	 * @template TArray as array<TKey, mixed>
+	 *
+	 * @param TArray $array
+	 *
+	 * @return (TArray is non-empty-array ? non-empty-list<TKey> : list<TKey>)
+	 */
+	abstract public function arrayKeys(array $array);
+
+	/**
+	 * @param array $array
+	 * @param non-empty-array $nonEmptyArray
+	 *
+	 * @param array<int, int> $intArray
+	 * @param non-empty-array<int, int> $nonEmptyIntArray
+	 */
+	public function testArrayKeys(array $array, array $nonEmptyArray, array $intArray, array $nonEmptyIntArray): void
+	{
+		assertType('array<int, (int|string)>', $this->arrayKeys($array));
+		assertType('array<int, int>', $this->arrayKeys($intArray));
+
+		// TODO resolve correctly
+		//assertType('non-empty-array<int, (int|string)>', $this->arrayKeys($nonEmptyArray));
+		//assertType('non-empty-array<int, int>', $this->arrayKeys($nonEmptyIntArray));
+
+		assertType('array<int, (int|string)>', $this->arrayKeys($nonEmptyArray));
+		assertType('array<int, int>', $this->arrayKeys($nonEmptyIntArray));
+	}
+
+	/**
+	 * @return ($as_float is true ? float : string)
+	 */
+	abstract public function microtime(bool $as_float = false);
+
+	public function testMicrotime(): void
+	{
+		// TODO resolve correctly
+		//assertType('float', $this->microtime(true));
+		//assertType('string', $this->microtime(false));
+
+		assertType('float|string', $this->microtime(true));
+		assertType('float|string', $this->microtime(false));
+	}
+}