@JeroenDeDauw emailed me to ask about problems with local development of extensions related to the use of `classmap-authoratative: true` in the composer.json file of mediawiki/core.git. When an extension [[https://github.com/JeroenDeDauw/SubPageList/blob/dd892412c62d8994feaa17043f676fcd64e4104c/tests/bootstrap.php#L21-L38 | uses a boostrap.php file for testing that adds PSR0/4 autoloaders]], `classmap-authoratative: true` will keep the PSR autoloader from being consulted.
The use of `classmap-authoratative: true` provides a measurable performance improvement for MediaWiki on the WMF production cluster, but that environment really uses the composer.json in the mediawiki/vendor.git repo and not the composer.json in mediawiki/core.git. Since this setting is merely performance enhancing and can be worked around for WMF and other large scale users, it seems reasonable to change the default behavior to be more friendly to development use.