clippy::useless_format does not parse escaped braces correctly (as in `format!("{{}}")`)

[zgtm]

When a format string is used to output braces, they need to be escaped by doubling them:format!("{{}}") creates a string containing "{}".

The clippy lint clippy::useless_format seems to not know that:

warning: useless use of `format!`

format!("{{}}")
^^^^^^^^^^^^^^^ help: consider using .to_string(): `"{{}}".to_string()`

Here, the recommendation should read "{}".to_string() instead.

Further information:

cargo clippy -V
clippy 0.0.212 (1b89724 2019-01-15)