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//@ run-pass use std::fmt; struct Foo; impl fmt::Debug for Foo { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { println!("<Foo as Debug>::fmt()"); write!(fmt, "") } } fn test1() { let foo_str = format!("{:?}", Foo); println!("{}", foo_str); } fn test2() { println!("{:?}", Foo); } fn main() { // This works fine test1(); // This fails test2(); }