Magento 2 missing bin/magento, lib, dev and setup directories

Pull a Magento 2 project, find bin/magento, lib/, dev/ or setup/ missing, and nothing is wrong with the repo: those directories are deployed out of the magento/magento2-base package by Composer rather than committed. When that deploy step does not run, or runs partially, the files never land and the project looks half-installed.

¶The fix

In most cases a reinstall of the base package re-triggers the deploy and the missing directories reappear:

composer reinstall magento/magento2-base

That forces Composer to remove and re-add the package, which runs the magento-composer-installer deploy step again and copies the mapped files back into place. Worth running bin/magento afterwards to confirm the CLI is back.

¶Why it happens

The deploy is handled by magento/magento-composer-installer, and there is a bug in its copy strategy. The Copy::createDelegate() method uses file_exists(), which dereferences symlinks, so when a symlink with a missing target sits at one of the mapped destination paths, the installer reads it as absent, tries to mkdir() over the existing link node and hits a silent File exists error.

The error swallowing is worse. DeployManager::doDeploy() catches the ErrorException but only logs it under -vvv verbosity, so the remaining mappings get skipped with no warning. The install reports success while setup/ and friends are partially or completely empty.

I’ve raised a GitHub issue with the full reproduction. There’s also a longstanding PR against magento-composer-installer that removes the exception suppression so composer install fails loud and early instead of leaving you with a broken but apparently fine install. It has been open for years awaiting review.

If the reinstall doesn’t stick, check for a dangling symlink at the target paths before assuming Composer is at fault.