All Chat Filters Break if a Regex Filter cannot be Read

Submitter: Yoshi
If a chat filter configured to be regex has some sort of problem and cannot be read (e.g. unmatched group parentheses), all other chat filters break completely upon relaunching the game.
This would not be a problem if one were told that the regex filter has some sort of regex problem before creation. However, no indication that something is wrong is visually said.
The only way to know is to look in the minecraft log as the incorrect regex string is created. In the log, this is shown: https://pastebin.com/dUYUu5ty
Upon relaunching the game and having a message be sent in chat, this 5zig/WARN is shown, and no chat filtering is applied at all: https://pastebin.com/jWtDRm6r

Therefore, the simplest solution to this problem is to not allow a regex chat filter be saved/created if there is a regex problem. Additionally, it would be helpful to specify the problem upon attempting to create the filter.

Look for chat filter handling code, likely in a class managing filter configuration and regex validation. The issue mentions logs with regex errors; start by finding where filters are loaded and validated on game launch. Test by creating a malformed regex filter and observing the log output to locate the validation point. The fix involves adding pre-save regex validation and user-facing error messages.

Written by the indexing model from the issue text.