How errors should be treated implementing fmt::Display?

Question

I wonder how to convert properly interim errors of other types than fmt::Error which may arise on the track of fn fmt, to the fmt::Error type?

Let's say:

use std::fmt;
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
struct MyStruct {
    x: i32
}

impl fmt::Display for MyStruct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", serde_json::to_string(&self).map_err(|e| /*???*/)?)
    }
}

As shown in the example above, I wonder how should I convert, for instance, serde_json::Error to fmt::Error to comply with the returned fmt::Result trait.

Answer 1

fmt::Error has no fields. It's simply an indicator value that "does not support transmission of an error other than that an error occurred" (docs). So, if you're fine with just returning an error with no other message, then map the error to fmt::Error:

foo.map_err(|_| fmt::Error)