Thread:Project talk:WikiProject Extensions/Git submodules, subtree, or symlinks?/reply (2)

There is a .gitignore file in mediawiki/extensions/ that ignores everything in 'extensions' so MyExtension will not "interfere" at all with updating your core checkout.

If your extension is brand new and you aren't hosting the code anywhere (meaning there is no "remote" for your code), just create a git repo in your project folder itself. ie. Later, when your extension is ready to be published, you can add a remote to your $MyExtension and push it there (including gerrit.mediawiki.org if you want to host there and follow guidelines) I believe you would only use a submodule if $MyExtension were to be deployed with a specific release of MediaWiki proper.

If you want to develop $MyExtension against a specific release of MediaWiki, then after cloning core, checkout the branch you desire.