What causes "Set provider "%s" must implement "%s"" in rectorphp/rector?

Open the class named in the message and make it implement Rector\Set\SetProviderInterface with a sets() method returning Rector\Set\ValueObject\Set[] instances

rectorphp/rector · error · InvalidConfigurationException

Set provider " " must implement

Error message

Set provider "%s" must implement "%s"

What it means

RectorConfigBuilder::withSetProviders(string ...$setProviders) registers classes that supply extra rule sets. Each class-string is verified with is_a($setProvider, SetProviderInterface::class, true); a class that does not implement Rector\Set\SetProviderInterface throws InvalidConfigurationException naming the offending class and the required interface.

Solutions

Open the class named in the message and make it implement Rector\Set\SetProviderInterface with a sets() method returning Rector\Set\ValueObject\Set[] instances
Fix the namespace/typo so the string matches the real provider class
If you meant a built-in set, use withSets([SomeSetList::CONSTANT]) instead of withSetProviders()
Pass class-strings via SomeProvider::class, never literals or objects

Example fix

// before
return $this->withSetProviders('App\Support\ProjectSetList');

// after
final class ProjectSetProvider implements \Rector\Set\SetProviderInterface
{
    /**
     * @return Set[]
     */
    public function sets(): array
    {
        return [new Set('project-conventions', [SomeRule::class])];
    }
}

return $this->withSetProviders(ProjectSetProvider::class);

Defensive patterns

Strategy: type-guard

Type guard

/** @param class-string ...$providers */
function assertSetProviders(string ...$providers): void
{
    foreach ($providers as $provider) {
        if (! is_a($provider, \Rector\Set\SetProviderInterface::class, true)) {
            throw new InvalidArgumentException(sprintf('%s does not implement SetProviderInterface', $provider));
        }
    }
}

Try / catch

try {
    $builder->withSetProviders(ProjectSetProvider::class);
} catch (InvalidConfigurationException $e) {
    // message names the class and the interface; fix the class-string, not the call
    $logger->error($e->getMessage());
}

Prevention

Always pass SomeProvider::class so the IDE resolves and refactors the symbol
Keep one interface-ful provider per package and register it via composer extra or your bootstrap, not ad-hoc strings
Run a static analyzer (PHPStan) with is-a checks so wrong class-strings fail in CI, not at runtime

When it happens

Trigger: Passing a FQCN that is not a SetProviderInterface implementation: a typo'd namespace, a plain value object, or a SetList constant instead of a provider class. Also triggered by passing a class that only extends a base class without implementing the interface.

Common situations: Copy-pasting a SetList:: constant into withSetProviders(); fat-fingered namespaces after renaming vendor packages; passing an instance or ::class of an unrelated helper while wiring custom sets.

Related errors

AI-assisted analysis of rectorphp/rector@408fcb0ff1 (2026-08-21). Data as JSON: /api/errors/3f462b5836c4e926. Report an issue: GitHub.

Appendix: source

Thrown at src/Configuration/RectorConfigBuilder.php:807

        $this->reportUnusedSkips = $report;
        return $this;
    }
    public function withEditorUrl(string $editorUrl): self
    {
        $this->editorUrl = $editorUrl;
        return $this;
    }
    /**
     * @param class-string<SetProviderInterface> ...$setProviders
     */
    public function withSetProviders(string ...$setProviders): self
    {
        foreach ($setProviders as $setProvider) {
            if (\array_key_exists($setProvider, $this->setProviders)) {
                continue;
            }
            if (!is_a($setProvider, SetProviderInterface::class, \true)) {
                throw new InvalidConfigurationException(sprintf('Set provider "%s" must implement "%s"', $setProvider, SetProviderInterface::class));
            }
            $this->setProviders[$setProvider] = \true;
        }
        return $this;
    }
    /**
     * @param PhpVersion::* $phpVersion
     */
    private function addPhpLevelSets(int $phpVersion): self
    {
        $this->isWithPhpSetsUsed = \true;
        $this->sets = array_merge($this->sets, \Rector\Configuration\PhpLevelSetResolver::resolveFromPhpVersion($phpVersion));
        return $this;
    }
    private function reportDeprecatedPhpSetsMethod(string $methodName): self
    {
        SimpleParameterProvider::addParameter(\Rector\Configuration\Option::DEPRECATED_PHP_SETS_METHODS, $methodName);
        return $this;

View on GitHub (pinned to 408fcb0ff1)