Report a data provider that provides no data sets

rules.neon

@@ -19,6 +19,9 @@ conditionalTags:
 	PHPStan\Rules\PHPUnit\ClassAttributeRequiresPhpVersionRule:
 		phpstan.rules.rule: %featureToggles.bleedingEdge%
 
+	PHPStan\Rules\PHPUnit\EmptyDataProviderRule:
+		phpstan.rules.rule: %featureToggles.bleedingEdge%
+
 services:
 	-
 		class: PHPStan\Rules\PHPUnit\DataProviderDeclarationRule
@@ -41,3 +44,6 @@ services:
 
 	-
 		class: PHPStan\Rules\PHPUnit\DataProviderDataRule
+
+	-
+		class: PHPStan\Rules\PHPUnit\EmptyDataProviderRule

src/Rules/PHPUnit/EmptyDataProviderRule.php

@@ -0,0 +1,109 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\PHPUnit;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Node\MethodReturnStatementsNode;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+use PHPUnit\Framework\TestCase;
+use function sprintf;
+use function strcasecmp;
+
+/**
+ * @implements Rule<MethodReturnStatementsNode>
+ */
+class EmptyDataProviderRule implements Rule
+{
+
+	private TestMethodsHelper $testMethodsHelper;
+
+	private DataProviderHelper $dataProviderHelper;
+
+	private PHPUnitVersion $PHPUnitVersion;
+
+	public function __construct(
+		TestMethodsHelper $testMethodsHelper,
+		DataProviderHelper $dataProviderHelper,
+		PHPUnitVersion $PHPUnitVersion
+	)
+	{
+		$this->testMethodsHelper = $testMethodsHelper;
+		$this->dataProviderHelper = $dataProviderHelper;
+		$this->PHPUnitVersion = $PHPUnitVersion;
+	}
+
+	public function getNodeType(): string
+	{
+		return MethodReturnStatementsNode::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if ($this->PHPUnitVersion->rejectsEmptyDataProviders()->no()) {
+			return [];
+		}
+
+		if (!$node->getClassReflection()->is(TestCase::class)) {
+			return [];
+		}
+
+		// A generator yields its data sets one at a time, so whether it provides
+		// any depends on control flow this rule cannot decide.
+		if ($node->isGenerator()) {
+			return [];
+		}
+
+		$returnStatements = $node->getReturnStatements();
+		if ($returnStatements === []) {
+			return [];
+		}
+
+		foreach ($returnStatements as $returnStatement) {
+			$returnExpr = $returnStatement->getReturnNode()->expr;
+			if ($returnExpr === null) {
+				return [];
+			}
+
+			$returnType = $returnStatement->getScope()->getType($returnExpr);
+			if (!$returnType->isIterable()->yes() || !$returnType->isIterableAtLeastOnce()->no()) {
+				return [];
+			}
+		}
+
+		if (!$this->isDataProvider($node, $scope)) {
+			return [];
+		}
+
+		return [
+			RuleErrorBuilder::message(sprintf(
+				'Data provider method %s() provides no data sets, which is an error in PHPUnit 10 and newer.',
+				$node->getMethodName(),
+			))
+				->identifier('phpunit.dataProviderEmpty')
+				->build(),
+		];
+	}
+
+	private function isDataProvider(MethodReturnStatementsNode $node, Scope $scope): bool
+	{
+		$classReflection = $node->getClassReflection();
+
+		foreach ($this->testMethodsHelper->getTestMethods($classReflection, $scope) as $testMethod) {
+			foreach ($this->dataProviderHelper->getDataProviderMethods($scope, $testMethod, $classReflection) as [$providerClassReflection, $providerMethodName]) {
+				// A provider declared in another class is checked when that class is analysed.
+				if ($providerClassReflection === null || $providerClassReflection->getName() !== $classReflection->getName()) {
+					continue;
+				}
+
+				if (strcasecmp($providerMethodName, $node->getMethodName()) === 0) {
+					return true;
+				}
+			}
+		}
+
+		return false;
+	}
+
+}

src/Rules/PHPUnit/PHPUnitVersion.php

@@ -58,6 +58,14 @@ public function requiresStaticDataProviders(): TrinaryLogic
 		return TrinaryLogic::createFromBoolean($this->majorVersion >= 10);
 	}
 
+	public function rejectsEmptyDataProviders(): TrinaryLogic
+	{
+		if ($this->majorVersion === null) {
+			return TrinaryLogic::createMaybe();
+		}
+		return TrinaryLogic::createFromBoolean($this->majorVersion >= 10);
+	}
+
 	public function supportsNamedArgumentsInDataProvider(): TrinaryLogic
 	{
 		if ($this->majorVersion === null) {

tests/Rules/PHPUnit/EmptyDataProviderRuleTest.php

@@ -0,0 +1,96 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\PHPUnit;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use PHPStan\Type\FileTypeMapper;
+use PHPUnit\Framework\Attributes\DataProvider;
+use const PHP_VERSION_ID;
+
+/**
+ * @extends RuleTestCase<EmptyDataProviderRule>
+ */
+class EmptyDataProviderRuleTest extends RuleTestCase
+{
+
+	private ?int $phpunitVersion;
+
+	protected function getRule(): Rule
+	{
+		$phpunitVersion = new PHPUnitVersion($this->phpunitVersion, 0);
+
+		return new EmptyDataProviderRule(
+			new TestMethodsHelper(
+				self::getContainer()->getByType(FileTypeMapper::class),
+				$phpunitVersion,
+			),
+			new DataProviderHelper(
+				$this->createReflectionProvider(),
+				self::getContainer()->getByType(FileTypeMapper::class),
+				self::getContainer()->getService('defaultAnalysisParser'),
+				$phpunitVersion,
+			),
+			$phpunitVersion,
+		);
+	}
+
+	/**
+	 * @dataProvider provideVersions
+	 */
+	#[DataProvider('provideVersions')]
+	public function testRule(?int $version): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			self::markTestSkipped('Test requires PHP 8.0 for attributes.');
+		}
+
+		$this->phpunitVersion = $version;
+
+		$errors = [];
+
+		// PHPUnit 9 skips an empty data provider instead of erroring.
+		if ($version === null || $version >= 10) {
+			$errors[] = [
+				'Data provider method provideData() provides no data sets, which is an error in PHPUnit 10 and newer.',
+				21,
+			];
+			$errors[] = [
+				'Data provider method provideData() provides no data sets, which is an error in PHPUnit 10 and newer.',
+				109,
+			];
+			$errors[] = [
+				'Data provider method provideData() provides no data sets, which is an error in PHPUnit 10 and newer.',
+				158,
+			];
+		}
+
+		// DataProviderHelper only reads the attribute when the detected major version supports it.
+		if ($version !== null && $version >= 10) {
+			$errors[] = [
+				'Data provider method provideData() provides no data sets, which is an error in PHPUnit 10 and newer.',
+				173,
+			];
+		}
+
+		$this->analyse([__DIR__ . '/data/empty-data-provider.php'], $errors);
+	}
+
+	/**
+	 * @return iterable<array{?int}>
+	 */
+	public static function provideVersions(): iterable
+	{
+		yield [null];
+		yield [9];
+		yield [10];
+		yield [11];
+		yield [12];
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return [__DIR__ . '/../../../extension.neon'];
+	}
+
+}