#![crate_type = "lib"] pub trait Foo<'a, T> { fn foo(&'a self) -> T; } pub fn foo<'a, T>(x: &'a Foo<'a, T>) -> T { let x: &'a Foo = x; // ^ the lifetime parameter of Foo is left to be inferred. x.foo() // ^ encoding this method call in metadata triggers an ICE. }