error[E0277]: `Dummy` doesn't implement `Debug` --> $DIR/issue-107649.rs:105:5 | 105 | dbg!(lib::Dummy); | ^^^^^^^^^^^^^^^^ `Dummy` cannot be formatted using `{:?}` | = help: the trait `Debug` is not implemented for `Dummy` = note: add `#[derive(Debug)]` to `Dummy` or manually `impl Debug for Dummy` = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info) help: consider annotating `Dummy` with `#[derive(Debug)]` --> $DIR/auxiliary/dummy_lib.rs:2:1 | 2 + #[derive(Debug)] 3 | #[path = "auxiliary/dummy_lib.rs"] | error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.