#![allow(print_literal)] #![warn(useless_format)] struct Foo(pub String); macro_rules! foo { ($($t:tt)*) => (Foo(format!($($t)*))) } fn main() { format!("foo"); format!("{}", "foo"); format!("{:?}", "foo"); // don't warn about debug format!("{:8}", "foo"); format!("{:+}", "foo"); // warn when the format makes no difference format!("{:<}", "foo"); // warn when the format makes no difference format!("foo {}", "bar"); format!("{} bar", "foo"); let arg: String = "".to_owned(); format!("{}", arg); format!("{:?}", arg); // don't warn about debug format!("{:8}", arg); format!("{:+}", arg); // warn when the format makes no difference format!("{:<}", arg); // warn when the format makes no difference format!("foo {}", arg); format!("{} bar", arg); // we don’t want to warn for non-string args, see #697 format!("{}", 42); format!("{:?}", 42); format!("{:+}", 42); format!("foo {}", 42); format!("{} bar", 42); // we only want to warn about `format!` itself println!("foo"); println!("{}", "foo"); println!("foo {}", "foo"); println!("{}", 42); println!("foo {}", 42); // A format! inside a macro should not trigger a warning foo!("should not warn"); }