Useless format!/to_string in argument of function accepting fmt::Display

[GoldsteinE]

What it does

Detects the use of format!() and .to_string() in arguments to a function expecting impl fmt::Display.

(Possible duplicate of #3021, #3156)

Lint Name

useless_format

Category

perf, pedantic

Advantage

• Remove useless allocation

Drawbacks

• May be hard to implement?

Example

fn foo(_: impl std::fmt::Display) {}

foo("xyz".to_string());
foo(format!("{} {}", 1, 2));

Could be written as:

fn foo(_: impl std::fmt::Display) {}

foo("xyz");
foo(format_args!("{} {}", 1, 2));

[camsteffen]

For .to_string(), this could be an enhancement of unnecessary_to_owned.

I'm not sure about suggesting format_args! because if it is used multiple times there could be a negative perf impact.

[ghost]

@rustbot claim