Migration creation allows invalid aggregate functions in constraints

[jollygreenlaser]

• EdgeDB Version: 4.7+45e4acc
• EdgeDB CLI Version: EdgeDB CLI 5.0.0+c9dfeec
• OS Version: Ubuntu 22, OSX 14.4.1

type User {
   name: str;
}

type HasTwoOrFewerUsers {
   users: User;
   constraint expression on (count(.users) <= 2);
}

This will work to create a migration, but then fail to apply:

InternalServerError: aggregate functions are not allowed in check constraints

If users is updated to be correctly multi then it properly fails at migration creation time:

error: cannot use aggregate functions or operators in a non-aggregating constraint

Seems this should always be caught at creation time.

[msullivan]

I thought this was going to have been fixed by #7128, but it looks like we don't catch this at all, and the error comes from postgres.

The funny bit is that if users is actually a multi link, then we correctly reject it at migration create time!