error[E0283]: type annotations needed
  --> $DIR/issue-16966.rs:2:5
   |
LL |     panic!(std::default::Default::default());
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `M` declared on the function `begin_panic`
   |
   = note: cannot satisfy `_: Any`
note: required by a bound in `begin_panic`
  --> $SRC_DIR/std/src/panicking.rs:LL:COL
   |
LL | pub fn begin_panic<M: Any + Send>(msg: M) -> ! {
   |                       ^^^ required by this bound in `begin_panic`
   = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider specifying the type argument in the function call
   |
LL |         $crate::rt::begin_panic::<M>($msg)
   |                                +++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.