Test eof is reached when parsing format strings

[alexcrichton]

Otherwise extra stuff after a lone '}' character is simply ignored, which is
very bad.

Closes #8938

[huonw]

Wouldn't this be best to actually signal an error when an unopened } is encountered?

[alexcrichton]

The way the parser currently works is that it just halts parsing on an } character. That way the parser recursively calls itself when parsing the interiors of methods. I thought it turned out to be pretty nice, but this was the one corner case that it encountered where it got a bit ugly.

I haven't exactly written a lot of hand-written parsers, so this could probably be re-implemented in some other fashion. I was just happy that the only fields of the parser were the source string an an iterator.

[alexcrichton]

The relevant code is:

fn select(&mut self) -> ~Method<'self> {                                   
    // Consume arms one at a time                                          
    loop {                                                                 
        let selector = ...;
        let pieces = self.collect();                                       
        arms.push(SelectArm { selector: selector, result: pieces });   
        ...
    }                                                                      
}                                                                          

Which may just be too clever by a half for this.