composer/composer · error · \InvalidArgumentException

--strict-psr-autoloader mode only works with optimized…

Error message

--strict-psr-autoloader mode only works with optimized autoloader, use --optimize-autoloader or --classmap-authoritative if you want a strict return value.

What it means

In InstallCommand::execute, `--strict-psr-autoloader` (which makes the command exit with code 6 on PSR-4/PSR-0 mapping errors) is only meaningful when the autoloader is dumped in optimized mode. If neither --optimize-autoloader/-o nor --classmap-authoritative/-a is in effect (and config does not enable them), Composer throws InvalidArgumentException because strict checks would run against a non-optimized autoloader and silently never fire.

Solutions

Add --optimize-autoloader (or -o): `composer install --strict-psr-autoloader --optimize-autoloader`.
Or use --classmap-authoritative (or -a), which implicitly enables optimization.
Or set optimize-autoloader / classmap-authoritative in config so the flag has the prerequisite.

Example fix

// before
composer install --strict-psr-autoloader
// after
composer install --strict-psr-autoloader --optimize-autoloader

Defensive patterns

Strategy: validation

Validate before calling

$opts = ['strict-psr-autoloader','optimize-autoloader','classmap-authoritative'];
if (in_array('strict-psr-autoloader', $argv, true)
    && !in_array('optimize-autoloader', $argv, true)
    && !in_array('classmap-authoritative', $argv, true)
    && !in_array(['-o','-a'], array_slice($argv, -2), true)) {
    throw new \InvalidArgumentException('strict-psr-autoloader needs optimization');
}

Prevention

Always pair --strict-psr-autoloader with -o/-a in CI configs.
Centralize the install flags in a Makefile/script so the combo stays correct.

When it happens

Trigger: Running `composer install --strict-psr-autoloader` (or update/dump-autoload with the flag) without also enabling optimization. The check at InstallCommand.php:124 fails when both $optimize and $authoritative are false.

Common situations: CI pipelines that add `--strict-psr-autoloader` to catch PSR violations but forget the required optimizer flag; copying the flag from docs without -o.

Related errors

AI-assisted analysis of composer/composer@c435d285c9 (2026-08-07). Data as JSON: /api/errors/8dcd5c3a025967b8. Report an issue: GitHub.

Appendix: source

Thrown at src/Composer/Command/InstallCommand.php:125

        if (!$composer->getLocker()->isLocked() && !HttpDownloader::isCurlEnabled()) {
            $io->writeError('<warning>Composer is operating significantly slower than normal because you do not have the PHP curl extension enabled.</warning>');
        }

        $commandEvent = new CommandEvent(PluginEvents::COMMAND, 'install', $input, $output);
        $composer->getEventDispatcher()->dispatch($commandEvent->getName(), $commandEvent);

        $install = Installer::create($io, $composer);

        $config = $composer->getConfig();
        [$preferSource, $preferDist] = $this->getPreferredInstallOptions($config, $input);

        $optimize = $input->getOption('optimize-autoloader') || $config->get('optimize-autoloader');
        $authoritative = $input->getOption('classmap-authoritative') || $config->get('classmap-authoritative');
        $apcuPrefix = $input->getOption('apcu-autoloader-prefix');
        $apcu = $apcuPrefix !== null || $input->getOption('apcu-autoloader') || $config->get('apcu-autoloader');

        if ($input->getOption('strict-psr-autoloader') && !$optimize && !$authoritative) {
            throw new \InvalidArgumentException('--strict-psr-autoloader mode only works with optimized autoloader, use --optimize-autoloader or --classmap-authoritative if you want a strict return value.');
        }

        $composer->getInstallationManager()->setOutputProgress(!$input->getOption('no-progress'));

        $install
            ->setDryRun($input->getOption('dry-run'))
            ->setDownloadOnly($input->getOption('download-only'))
            ->setVerbose($input->getOption('verbose'))
            ->setPreferSource($preferSource)
            ->setPreferDist($preferDist)
            ->setDevMode(!$input->getOption('no-dev'))
            ->setDumpAutoloader(!$input->getOption('no-autoloader'))
            ->setOptimizeAutoloader($optimize)
            ->setClassMapAuthoritative($authoritative)
            ->setStrictPsrAutoloader($input->getOption('strict-psr-autoloader'))
            ->setApcuAutoloader($apcu, $apcuPrefix)
            ->setPlatformRequirementFilter($this->getPlatformRequirementFilter($input))
            ->setPolicyConfig($this->createPolicyConfig($composer->getConfig(), $input))

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