Underscores in usernames break searching and tagging

[twhiston]

Steps to reproduce the problem

1. Sign up somewhere with a username with an _ in it.
2. Try to search for that user or tag them
3. If your username was 't_whiston' Tags will be truncated to @t and searches will return nothing for the user

Expected behaviour

a username with an _ in it should be taggable and searchable

Actual behaviour

user is not tagged, searches return nothing

Detailed description

Any username with a _ in it is essentially undiscoverable and untaggable. See https://musicians.today/@EDVARDS/110074815178754723 for more info for more background on it.

Specifications

v4.1.1 but think it affects all versions

[ClearlyClaire]

I'm unable to reproduce this, searching for the user works just fine, and underscores in mentions have never been an issue.

However, the user has now moved to another account, so t_whiston will not return anything unless an exact match is searched.

[twhiston]

Strange you can't reproduce this, because it's definitely been a problem for me. Here is a post where I was failed to be tagged because of the _ in my old username, https://musicians.today/@nigelharpur/110012463572212308 and here is another where underscores also appear to result in an @ failing to work properly for a different account https://musicians.today/@EDVARDS/110086445439884241

[ClearlyClaire]

The post at https://musicians.today/@nigelharpur/110012463572212308 did not include the @mastodonmusic.social part of the handle, which means the mention could not be resolved, because you were @t_whiston@mastodonmusic.social, not @t_whiston@musicians.today.

Same with @Simi_Mariechen not mentioning the @troet.cafe part.