There are efforts to explore MediaWiki-extensions-CodeMirror as an alternative for CodeEditor across the wikiverse. That effort would not be feature-complete without CodeMirror integration in AbuseFilter.
AbuseFilter has a custom Ace mode that depends on the ext.codeEditor.ace module. While not trivial, things appear to work similarly enough that it should be doable to port this to a CodeMirror 6 StreamParser. Better would be to write a grammar for the Lezer parser system, if the AbuseFilter language allows for it.
After we have a working mode, there's a good bit of backend work to go with it. I propose a configuration similar to what we're doing for all the other CodeEditor integrations, with the feature flags $wgAbuseFilterUseCodeEditor and $wgAbuseFilterUseCodeMirror. A new CodeMirrorEditBoxBuilder class could be created to parity AceEditBoxBuilder, and so on.
