Fix generic variance with BenevolentUnionType

src/Type/Generic/TemplateTypeVariance.php

@@ -102,12 +102,16 @@ public function isValidVariance(Type $a, Type $b): TrinaryLogic
 			return TrinaryLogic::createYes();
 		}
 
-		if ($b instanceof BenevolentUnionType && !$a instanceof BenevolentUnionType) {
-			$results = [];
-			foreach ($b->getTypes() as $innerType) {
-				$results[] = $this->isValidVariance($a, $innerType);
+		if ($a instanceof BenevolentUnionType) {
+			if (!$a->isSuperTypeOf($b)->no()) {
+				return TrinaryLogic::createYes();
+			}
+		}
+
+		if ($b instanceof BenevolentUnionType) {
+			if (!$b->isSuperTypeOf($a)->no()) {
+				return TrinaryLogic::createYes();
 			}
-			return TrinaryLogic::maxMin(...$results);
 		}
 
 		if ($b instanceof MixedType && !$b instanceof TemplateType) {

tests/PHPStan/Type/Generic/TemplateTypeVarianceTest.php

@@ -0,0 +1,101 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Generic;
+
+use PHPStan\TrinaryLogic;
+use PHPStan\Type\BenevolentUnionType;
+use PHPStan\Type\IntegerType;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use PHPStan\Type\UnionType;
+use PHPStan\Type\VerbosityLevel;
+use PHPUnit\Framework\TestCase;
+
+class TemplateTypeVarianceTest extends TestCase
+{
+
+	public function dataIsValidVariance(): iterable
+	{
+		foreach ([TemplateTypeVariance::createInvariant(), TemplateTypeVariance::createCovariant()] as $variance) {
+			yield [
+				$variance,
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+
+			yield [
+				$variance,
+				new IntegerType(),
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+
+			yield [
+				$variance,
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				new IntegerType(),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+
+			yield [
+				$variance,
+				new StringType(),
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+
+			yield [
+				$variance,
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				new StringType(),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+
+			yield [
+				$variance,
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				new UnionType([new IntegerType(), new StringType()]),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+
+			yield [
+				$variance,
+				new UnionType([new IntegerType(), new StringType()]),
+				new BenevolentUnionType([new IntegerType(), new StringType()]),
+				TrinaryLogic::createYes(),
+				TrinaryLogic::createYes(),
+			];
+		}
+	}
+
+	/**
+	 * @dataProvider dataIsValidVariance
+	 */
+	public function testIsValidVariance(
+		TemplateTypeVariance $variance,
+		Type $a,
+		Type $b,
+		TrinaryLogic $expected,
+		TrinaryLogic $expectedInversed
+	): void
+	{
+		$this->assertSame(
+			$expected->describe(),
+			$variance->isValidVariance($a, $b)->describe(),
+			sprintf('%s->isValidVariance(%s, %s)', $variance->describe(), $a->describe(VerbosityLevel::precise()), $b->describe(VerbosityLevel::precise()))
+		);
+		$this->assertSame(
+			$expectedInversed->describe(),
+			$variance->isValidVariance($b, $a)->describe(),
+			sprintf('%s->isValidVariance(%s, %s)', $variance->describe(), $b->describe(VerbosityLevel::precise()), $a->describe(VerbosityLevel::precise()))
+		);
+	}
+
+}