I was not aware of connect command.

Well, maybe those who have used gdb before will look for attach command and may have misconception that the feature is not implemented. That is exactly my case. I think this command should be implemented as an alias or removed. Which do you prefer, or do you have another idea?

I think that attach should be implemented to be used with PID as gdb.
But to avoid this misconception, we can put a message like:
"Attempts to attach to the given process ID.\n" +
"\n" +
"Currently unimplemented.\nUse connect command."
What do you think?

I think that attach should be implemented to be used with PID as gdb.

This was the original intention, but I never got around to implementing it this way because (at least at the time) that seemed fairly non-trivial and would probably have involved using Mono's general-purpose assembly attach mechanism: https://github.com/mono/mono/blob/master/mono/metadata/attach.c

It's quite possible the VSfM team figured out a better solution in the meantime though. I'm not up to date on the issue.

I have no objection to updating attach's help text to point to the connect command until it's actually implemented.

Anyway, this change for attach command is no longer relevant. I'll close this pull request.