Regex shouldn't work

[gwelch-contegix]

Can I get an explanation as to why this regex works (?P<project_id>\w+)(-)(?P<jira_id>\d+)?
It's suggested to use https://regex101.com to test but testing with it matches on all sorts of things that I don't want it to, mainly destroying links, https://regex101.com/r/XPUAgu/4
Now on Mattermost it works how I want it to, but how is https://regex101.com or any other website/knowledge I have access to supposed to help me write a regex for this plugin?
If I write a regex that does work on https://regex101.com (?P<pre>\s|^)(?P<number>KEY-\d{1,4}) https://regex101.com/r/axJv7b/1 it then fails to match properly in Mattermost and also has issues displaying the regex.

[DHaussermann]

@m1lt0n or @hanzei would you know who can help with this question? I don't know if there is a more accurate tool to use a a reference for how the plugin evaluates the expressions.

[robonaj]

It is not obvious from the documentation, but when all options DisableNonWordPrefix, DisableNonWordSuffix, and WordMatch are disabled (which is the case if they are not shown in the /autolink list output), autolink modifies the pattern as seen in the Compile function.
Your regex becomes (?P<MattermostNonWordPrefix>(^|\s))(?P<project_id>\w+)(-)(?P<jira_id>\d+)(?P<MattermostNonWordSuffix>$|[\s\.\!\?\,\)]) - see https://regex101.com/r/fC8DaU/1 with your example