Match expression - report usage of void

conf/config.level2.neon

@@ -11,6 +11,7 @@ rules:
 	- PHPStan\Rules\Cast\InvalidCastRule
 	- PHPStan\Rules\Cast\InvalidPartOfEncapsedStringRule
 	- PHPStan\Rules\Cast\PrintRule
+	- PHPStan\Rules\Comparison\UsageOfVoidMatchExpressionRule
 	- PHPStan\Rules\Functions\IncompatibleDefaultParameterTypeRule
 	- PHPStan\Rules\Generics\ClassAncestorsRule
 	- PHPStan\Rules\Generics\ClassTemplateTypeRule

src/Rules/Comparison/UsageOfVoidMatchExpressionRule.php

@@ -0,0 +1,35 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Comparison;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPStan\Type\VoidType;
+
+/**
+ * @implements Rule<Node\Expr\Match_>
+ */
+class UsageOfVoidMatchExpressionRule implements Rule
+{
+
+	public function getNodeType(): string
+	{
+		return Node\Expr\Match_::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		$matchResultType = $scope->getType($node);
+		if (
+			$matchResultType instanceof VoidType
+			&& !$scope->isInFirstLevelStatement()
+		) {
+			return [RuleErrorBuilder::message('Result of match expression (void) is used.')->build()];
+		}
+
+		return [];
+	}
+
+}

tests/PHPStan/Rules/Comparison/UsageOfVoidMatchExpressionRuleTest.php

@@ -0,0 +1,33 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Comparison;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<UsageOfVoidMatchExpressionRule>
+ */
+class UsageOfVoidMatchExpressionRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new UsageOfVoidMatchExpressionRule();
+	}
+
+	public function testRule(): void
+	{
+		if (PHP_VERSION_ID < 80000 && !self::$useStaticReflectionProvider) {
+			$this->markTestSkipped('Test requires PHP 8.0.');
+		}
+
+		$this->analyse([__DIR__ . '/data/void-match.php'], [
+			[
+				'Result of match expression (void) is used.',
+				21,
+			],
+		]);
+	}
+
+}

tests/PHPStan/Rules/Comparison/data/void-match.php

@@ -0,0 +1,28 @@
+<?php // lint >= 8.0
+
+namespace VoidMatch;
+
+class Foo
+{
+
+	public function doFoo(): void
+	{
+
+	}
+
+	public function doBar(int $i): void
+	{
+		match ($i) {
+			1 => $this->doFoo(),
+			2 => $this->doFoo(),
+			default => $this->doFoo(),
+		};
+
+		$a = match ($i) {
+			1 => $this->doFoo(),
+			2 => $this->doFoo(),
+			default => $this->doFoo(),
+		};
+	}
+
+}