Wildcards in mailmap to hide transgender people's deadnames

["Florine W. Dekker" <florine@fwdekker.com>]

Hi! I would like to suggest that the mailmap feature accepts (a limited 
form of) wildcards for matching email addresses, which helps transgender 
users configure the mailmap to map their old name ("deadname") and email 
to their new name and email without revealing the old info in the 
mailmap config itself.

For example, consider a user who changed their name from Jane Doe to 
John Doe, and their email from jane.doe@example.com to 
john.doe@example.com. John wants to prevent others from learning their 
old name, but sometimes it's not feasible to rewrite the entire history 
of the repository (e.g. because there are thousands of commits, or 
because this would mess up references between commits). In this case, 
mailmap seems like a good way to prevent people from finding out the old 
name by accident: Just add the line `John Doe <john.doe@example.com> 
<jane.doe@example.com>` to the mailmap config. However, this has the 
unfortunate effect that readers may now accidentally find John's old 
name if they look at the mailmap config.

I suggest that mailmap config files support wildcards in the email 
address. This helps people who have changed their name to specify a 
mapping without revealing their old name in the definition of this 
mapping. Because the * symbol is valid in an email address, I suggest 
the sequence \* to be the wildcard symbol, meaning "0 or more symbols". 
This cannot be misinterpreted in an RFC5322-valid email address, because 
this sequence is not legal in the domain part, is not legal in an 
unquoted local part, and is not legal in a quoted local part unless 
preceded by an unescaped backslash (that is, "jo\\*hn"@doe.com does not 
contain a wildcard). In short, if mailmap encounters the sequence \* in 
an email address, it should interpret the sequence as a wildcard if and 
only if it is not directly preceded by an odd number of backslashes 
regardless of whether the local part is quoted (so \* is a wildcard, \\* 
is not, \\\* is, \\\\* is not).

Now, John can now add the following line to their mailmap config: `John 
Doe <john.doe@example.com> <\*.doe@example.com>`, which does not reveal 
their old name. Someone could always spend more effort to uncover the 
name using more advanced tools, but the point of this feature is to 
prevent accidental discovery of the name in cases where completely 
hiding the name is not feasible.

If you have feedback or comments on this suggestion, please let me know.

- Florine