1error: unused return value of `Interface::f` that must be used 2 --> tests/ui/must-use.rs:18:5 3 | 418 | Thing.f(); 5 | ^^^^^^^^^ 6 | 7note: the lint level is defined here 8 --> tests/ui/must-use.rs:1:9 9 | 101 | #![deny(unused_must_use)] 11 | ^^^^^^^^^^^^^^^ 12help: use `let _ = ...` to ignore the resulting value 13 | 1418 | let _ = Thing.f(); 15 | +++++++ 16