When completing on "svn add", it puts the filename in argument,
even if the filename contains a @ character. The issue is that
svn regards this character as special, to put a revision behind;
and one gets an error "a peg revision is not allowed here":

% touch foo@bar
% svn add fo<tab>

gives

% svn add foo@bar
svn: E200009: 'foo@bar': a peg revision is not allowed here

The solution is to append the @ character to the filename:

% svn add foo@bar@

This is what the completion system should generate.