Error because unnecessary default-arm on match-expression with enums

src/Reflection/InitializerExprTypeResolver.php

@@ -1333,6 +1333,23 @@ public function resolveIdenticalType(Type $leftType, Type $rightType): BooleanTy
 			return new ConstantBooleanType($leftType->equals($rightType));
 		}
 
+		if ($leftType instanceof TypeWithClassName && $rightType instanceof EnumCaseObjectType) {
+			$classReflection = $leftType->getClassReflection();
+			if ($classReflection !== null && $classReflection->isEnum() && $classReflection->getName() === $rightType->getClassName()) {
+				if (count($classReflection->getEnumCases()) === 1) {
+					return new ConstantBooleanType(true);
+				}
+			}
+		}
+		if ($rightType instanceof TypeWithClassName && $leftType instanceof EnumCaseObjectType) {
+			$classReflection = $rightType->getClassReflection();
+			if ($classReflection !== null && $classReflection->isEnum() && $classReflection->getName() === $leftType->getClassName()) {
+				if (count($classReflection->getEnumCases()) === 1) {
+					return new ConstantBooleanType(true);
+				}
+			}
+		}
+
 		$isSuperset = $leftType->isSuperTypeOf($rightType);
 		if ($isSuperset->no()) {
 			return new ConstantBooleanType(false);

tests/PHPStan/Rules/Comparison/MatchExpressionRuleTest.php

@@ -246,4 +246,30 @@ public function testBug7746(): void
 		$this->analyse([__DIR__ . '/data/bug-7746.php'], []);
 	}
 
+	public function testBug8240(): void
+	{
+		if (PHP_VERSION_ID < 80100) {
+			$this->markTestSkipped('Test requires PHP 8.1.');
+		}
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-8240.php'], [
+			[
+				'Match arm comparison between Bug8240\Foo and Bug8240\Foo::BAR is always true.',
+				13,
+			],
+			[
+				'Match arm is unreachable because previous comparison is always true.',
+				14,
+			],
+			[
+				'Match arm comparison between Bug8240\Foo2::BAZ and Bug8240\Foo2::BAZ is always true.',
+				28,
+			],
+			[
+				'Match arm is unreachable because previous comparison is always true.',
+				29,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php

@@ -653,7 +653,7 @@ public function testBug8586(): void
 		$this->checkAlwaysTrueStrictComparison = true;
 		$this->analyse([__DIR__ . '/data/bug-8586.php'], []);
 	}
-	
+
 	public function testBug4242(): void
 	{
 		if (PHP_VERSION_ID < 80100) {

tests/PHPStan/Rules/Comparison/data/bug-8240.php

@@ -0,0 +1,31 @@
+<?php // lint >= 8.1
+
+namespace Bug8240;
+
+enum Foo
+{
+	case BAR;
+}
+
+function doFoo(Foo $foo): int
+{
+	return match ($foo) {
+		Foo::BAR => 5,
+		default => throw new \Exception('This will not be executed')
+	};
+}
+
+enum Foo2
+{
+	case BAR;
+	case BAZ;
+}
+
+function doFoo2(Foo2 $foo): int
+{
+	return match ($foo) {
+		Foo2::BAR => 5,
+		Foo2::BAZ => 15,
+		default => throw new \Exception('This will not be executed')
+	};
+}