Strange error message for incorrect format string

[bstrie]

This program:

fn main() {
    println!("{:f.6}", 100.0);
}

...has this output:

ac.rs:2:13: 2:21 error: unterminated format string
ac.rs:2     println!("{:f.6}", 100.0);
                     ^~~~~~~~
error: aborting due to previous error

"unterminated" makes it sound as though the user hasn't used a closing quotation mark. Even if it's not possible to give a good error message here, a message like "unknown format specifier" would be more insightful.