This follows-up from the discussion at composer/packagist#1458.

Notable PHP-based communities that use Gerrit for code review, that I'm aware of:

• TYPO3 https://review.typo3.org/
• Wikimedia https://gerrit.wikimedia.org/

Primary motiviation: Submit packagse to Packagist.org directly from a self-hosted Gerrit install, such that packages can be installed from distributed tarballs instead of git clone from source. Today this requires a GitHub mirror, which compromises independence and security/access control. In Gerrit, repos may have fine-grained access control, whereas the GitHub mirror would be writable by a different set of users, including all members with "Owner" permissions. The reason this depends on GitHub is that Packagist delegates responsibility for tarballs to drivers, and Git does not have a built-in HTTP protocol for downloading a tarball (Composer/GitDriver::getDist returns null). Instead, this is a non-standard extension that platforms like Gerrit, GitHub, GitLab, etc implement separately.