error[E0282]: type annotations needed --> $DIR/issue-16966.rs:2:5 | LL | panic!(std::default::Default::default()); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type of the type parameter `M` declared on the function `begin_panic` | = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info) error: aborting due to previous error For more information about this error, try `rustc --explain E0282`.