Paired underscores in a username prevents @-mention linking properly

[pkfrank]

Describe the bug
I tried to @-mention the user _morgan_adams_ (DEV profile) and noticed this issue. Instead of auto-linking to the DEV profile properly, it interprets the underscores as Markdown instructions to italicize. This is an issue both in both comments and posts.

To Reproduce
See GIF below.

Expected behavior
The @-mentioned username should link to the DEV account properly.

Screenshots

[Defman21]

IIRC Redcarpet allows you to disable markdown inside words, e.g. some_cool_stuff will be some_cool_stuff, not some cool stuff

[ilonacodes]

@pkfrank you can use backslash to escape underscore in markdown like @\_morgan_adams_. I just tried on dev.to and it seems to work.

[chase-stevens]

Backslash works for me as well per @ilonacodes comment. Is this a bug or expected behavior?

[maestromac]

We aren't expecting our users to have to manually escape those underscore so I'd say this is a bug.

[mariocsee]

If no one is working on this, I think I can take it.

My hunch is that there has to be a check disabling some markdown rules in markdown_fixer.rb for words that start with @ since it's used for mentioning, but will continue tomorrow.

[claracodes]

@mariocsee Are you still on it? I think I would like to have a look at it!

[mariocsee]

@ClaraMorgen I ended up working on something else then. Go for it!