Currently trending on the mediawiki-errors dashboard in Logstash at https://logstash.wikimedia.org/#/dashboard/elasticsearch/mediawiki-errors. About 200 hits per 15 minutes.
Rendering failed. Printing error message.
Coming from regular page views for anonymous user cache misses and logged-in users alike.
At least one instance of it was caused by the presence of an EN DASH in the Math formula as part of a free text expression. It seems the parser fails when such a dash (–) is used in free text labels.
_type mediawiki channel Math host mw1240 http_method GET level WARNING message Rendering failed. Printing error message. referrer https://www.google.com/ server en.wikipedia.org url /wiki/Testing_and_performance_of_IC_engines wiki enwiki
Was fixed by making an edit and changing the EN DASH (U+2013) to a HYPHEN (U+002D).
Math should probably be fixed to not crash on seeing an En-dash. Alternatively, if this can't or shouldn't be supported, the message level should change from WARNING to DEBUG or INFO, since it is a user error in that case, not a software error.
- Verify that this error category (lexing error) triggers a tracking category so that editors can fix the problem.