bug#11314: 24.1.50; Regression: incorrect Lisp indentation for `if' with `@@@@@@'

[Drew Adams]

> >> (if (alpha beta)
> >>     @@@@@@
> >>     bbbbbb
> >>
> >> Yet @@@@@@ is a perfectly good symbol/variable name etc.
> >> This regression was introduced in Emacs 22.
> >
> > I can reproduce this on current master.
> 
> That's because @ has the prefix syntax flag (for ,@).

That explains the implementation bug, I guess.

But there's no backquote or comma here.
And `@@@@@@' is just a normal symbol.

Just as we don't treat comma the same inside
and outside backquote (we raise an error for
the latter), ideally we shouldn't treat @ the
same inside and outside backquote (symbol
syntax for the latter).

And presumably the only uses of @ inside
backquote that should lead to different
indentation would only be when @ follows
comma.