Address review feedback

library/core/src/hint.rs

@@ -98,13 +98,12 @@ use crate::intrinsics;
 #[rustc_const_stable(feature = "const_unreachable_unchecked", since = "1.57.0")]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub const unsafe fn unreachable_unchecked() -> ! {
-    crate::panic::debug_assert_nounwind!(
-        false,
-        "hint::unreachable_unchecked must never be reached"
-    );
     // SAFETY: the safety contract for `intrinsics::unreachable` must
     // be upheld by the caller.
-    unsafe { intrinsics::unreachable() }
+    unsafe {
+        intrinsics::assert_unsafe_precondition!("hint::unreachable_unchecked must never be reached", () => false);
+        intrinsics::unreachable()
+    }
 }
 
 /// Emits a machine instruction to signal the processor that it is running in

library/core/src/panic.rs

@@ -139,6 +139,11 @@ pub macro unreachable_2021 {
     ),
 }
 
+/// Asserts that a boolean expression is `true`, and perform a non-unwinding panic otherwise.
+///
+/// This macro is similar to `debug_assert!`, but is intended to be used in code that should not
+/// unwind. For example, checks in `_unchecked` functions that are intended for debugging but should
+/// not compromise unwind safety.
 #[doc(hidden)]
 #[unstable(feature = "core_panic", issue = "none")]
 #[allow_internal_unstable(core_panic, const_format_args)]

library/core/src/panicking.rs

@@ -84,6 +84,7 @@ pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
 #[rustc_nounwind]
 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
 pub const fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>, force_no_backtrace: bool) -> ! {
+    #[track_caller]
     fn runtime(fmt: fmt::Arguments<'_>, force_no_backtrace: bool) -> ! {
         if cfg!(feature = "panic_immediate_abort") {
             super::intrinsics::abort()
@@ -109,6 +110,7 @@ pub const fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>, force_no_backtrace: boo
     }
 
     #[inline]
+    #[track_caller]
     const fn comptime(fmt: fmt::Arguments<'_>, _force_no_backtrace: bool) -> ! {
         panic_fmt(fmt);
     }