Poor error when using single quotes with `println!`

[steveklabnik]

fn main() {
    println!('{}', 5);
}

This error leaves much to be desired:

hello.rs:2:14: 2:16 error: unterminated character constant: '{
hello.rs:2     println!('{}', 5);
                        ^~

The issue is that you need double quotes.

originally found in http://joelmccracken.github.io/entries/a-simple-web-app-in-rust-pt-2b/ /cc @joelmccracken

[bstrie]

Consider changing the title, because this isn't println-specific. The following code exhibits the same error message:

fn main() {
    'abc';
}

[joelmccracken]

I was wondering about this -- I assumed this is a string thing. The way it is worded made me think that it was caused by some fancy println macroings.

[birkenfeld]

The current error is error: character literal may only contain one codepoint: '{

[Mark-Simulacrum]

Looking at the code, there doesn't appear to be a current way to add a help message to this diagnostic, though adding one shouldn't be too hard. Could someone familiar with the parser, perhaps @jseyfried or @nrc, type up a quick mentoring summary for adding a help: Maybe use double quotes (") instead of single quotes (')? It looks like ultimately self.sess.span_diagnostic.struct_span_fatal needs to be called with the appropriate parameters.