Make `const_eval_select` a real intrinsic

11 files changed, 148 insertions, 97 deletions

diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index d610f0a02f4..12e4dfe74fb 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -54,7 +54,9 @@
 )]
 #![allow(missing_docs)]
 
-use crate::marker::{Destruct, DiscriminantKind};
+#[cfg(bootstrap)]
+use crate::marker::Destruct;
+use crate::marker::DiscriminantKind;
 use crate::mem;
 
 // These imports are used for simplifying intra-doc links
@@ -2085,6 +2087,65 @@ extern "rust-intrinsic" {
     /// `ptr` must point to a vtable.
     /// The intrinsic will return the alignment stored in that vtable.
     pub fn vtable_align(ptr: *const ()) -> usize;
+
+    /// Selects which function to call depending on the context.
+    ///
+    /// If this function is evaluated at compile-time, then a call to this
+    /// intrinsic will be replaced with a call to `called_in_const`. It gets
+    /// replaced with a call to `called_at_rt` otherwise.
+    ///
+    /// # Type Requirements
+    ///
+    /// The two functions must be both function items. They cannot be function
+    /// pointers or closures. The first function must be a `const fn`.
+    ///
+    /// `arg` will be the tupled arguments that will be passed to either one of
+    /// the two functions, therefore, both functions must accept the same type of
+    /// arguments. Both functions must return RET.
+    ///
+    /// # Safety
+    ///
+    /// The two functions must behave observably equivalent. Safe code in other
+    /// crates may assume that calling a `const fn` at compile-time and at run-time
+    /// produces the same result. A function that produces a different result when
+    /// evaluated at run-time, or has any other observable side-effects, is
+    /// *unsound*.
+    ///
+    /// Here is an example of how this could cause a problem:
+    /// ```no_run
+    /// #![feature(const_eval_select)]
+    /// #![feature(core_intrinsics)]
+    /// use std::hint::unreachable_unchecked;
+    /// use std::intrinsics::const_eval_select;
+    ///
+    /// // Crate A
+    /// pub const fn inconsistent() -> i32 {
+    ///     fn runtime() -> i32 { 1 }
+    ///     const fn compiletime() -> i32 { 2 }
+    ///
+    ///     unsafe {
+    //          // ⚠ This code violates the required equivalence of `compiletime`
+    ///         // and `runtime`.
+    ///         const_eval_select((), compiletime, runtime)
+    ///     }
+    /// }
+    ///
+    /// // Crate B
+    /// const X: i32 = inconsistent();
+    /// let x = inconsistent();
+    /// if x != X { unsafe { unreachable_unchecked(); }}
+    /// ```
+    ///
+    /// This code causes Undefined Behavior when being run, since the
+    /// `unreachable_unchecked` is actually being reached. The bug is in *crate A*,
+    /// which violates the principle that a `const fn` must behave the same at
+    /// compile-time and at run-time. The unsafe code in crate B is fine.
+    #[cfg(not(bootstrap))]
+    #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
+    pub fn const_eval_select<ARG, F, G, RET>(arg: ARG, called_in_const: F, called_at_rt: G) -> RET
+    where
+        G: FnOnce<ARG, Output = RET>,
+        F: FnOnce<ARG, Output = RET>;
 }
 
 // Some functions are defined here because they accidentally got made
@@ -2095,6 +2156,11 @@ extern "rust-intrinsic" {
 /// Check that the preconditions of an unsafe function are followed, if debug_assertions are on,
 /// and only at runtime.
 ///
+/// This macro should be called as `assert_unsafe_precondition!([Generics](name: Type) => Expression)`
+/// where the names specified will be moved into the macro as captured variables, and defines an item
+/// to call `const_eval_select` on. The tokens inside the square brackets are used to denote generics
+/// for the function declaractions and can be omitted if there is no generics.
+///
 /// # Safety
 ///
 /// Invoking this macro is only sound if the following code is already UB when the passed
@@ -2109,18 +2175,20 @@ extern "rust-intrinsic" {
 /// the occasional mistake, and this check should help them figure things out.
 #[allow_internal_unstable(const_eval_select)] // permit this to be called in stably-const fn
 macro_rules! assert_unsafe_precondition {
-    ($e:expr) => {
+    ($([$($tt:tt)*])?($($i:ident:$ty:ty),*$(,)?) => $e:expr) => {
         if cfg!(debug_assertions) {
-            // Use a closure so that we can capture arbitrary expressions from the invocation
-            let runtime = || {
+            // allow non_snake_case to allow capturing const generics
+            #[allow(non_snake_case)]
+            fn runtime$(<$($tt)*>)?($($i:$ty),*) {
                 if !$e {
                     // abort instead of panicking to reduce impact on code size
                     ::core::intrinsics::abort();
                 }
-            };
-            const fn comptime() {}
+            }
+            #[allow(non_snake_case)]
+            const fn comptime$(<$($tt)*>)?($(_:$ty),*) {}
 
-            ::core::intrinsics::const_eval_select((), comptime, runtime);
+            ::core::intrinsics::const_eval_select(($($i,)*), comptime, runtime);
         }
     };
 }
@@ -2243,7 +2311,7 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
     // SAFETY: the safety contract for `copy_nonoverlapping` must be
     // upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](src: *const T, dst: *mut T, count: usize) =>
             is_aligned_and_not_null(src)
                 && is_aligned_and_not_null(dst)
                 && is_nonoverlapping(src, dst, count)
@@ -2329,7 +2397,8 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 
     // SAFETY: the safety contract for `copy` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(src) && is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](src: *const T, dst: *mut T) =>
+            is_aligned_and_not_null(src) && is_aligned_and_not_null(dst));
         copy(src, dst, count)
     }
 }
@@ -2397,63 +2466,12 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
 
     // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
         write_bytes(dst, val, count)
     }
 }
 
-/// Selects which function to call depending on the context.
-///
-/// If this function is evaluated at compile-time, then a call to this
-/// intrinsic will be replaced with a call to `called_in_const`. It gets
-/// replaced with a call to `called_at_rt` otherwise.
-///
-/// # Type Requirements
-///
-/// The two functions must be both function items. They cannot be function
-/// pointers or closures.
-///
-/// `arg` will be the arguments that will be passed to either one of the
-/// two functions, therefore, both functions must accept the same type of
-/// arguments. Both functions must return RET.
-///
-/// # Safety
-///
-/// The two functions must behave observably equivalent. Safe code in other
-/// crates may assume that calling a `const fn` at compile-time and at run-time
-/// produces the same result. A function that produces a different result when
-/// evaluated at run-time, or has any other observable side-effects, is
-/// *unsound*.
-///
-/// Here is an example of how this could cause a problem:
-/// ```no_run
-/// #![feature(const_eval_select)]
-/// #![feature(core_intrinsics)]
-/// use std::hint::unreachable_unchecked;
-/// use std::intrinsics::const_eval_select;
-///
-/// // Crate A
-/// pub const fn inconsistent() -> i32 {
-///     fn runtime() -> i32 { 1 }
-///     const fn compiletime() -> i32 { 2 }
-///
-///     unsafe {
-//          // ⚠ This code violates the required equivalence of `compiletime`
-///         // and `runtime`.
-///         const_eval_select((), compiletime, runtime)
-///     }
-/// }
-///
-/// // Crate B
-/// const X: i32 = inconsistent();
-/// let x = inconsistent();
-/// if x != X { unsafe { unreachable_unchecked(); }}
-/// ```
-///
-/// This code causes Undefined Behavior when being run, since the
-/// `unreachable_unchecked` is actually being reached. The bug is in *crate A*,
-/// which violates the principle that a `const fn` must behave the same at
-/// compile-time and at run-time. The unsafe code in crate B is fine.
+#[cfg(bootstrap)]
 #[unstable(
     feature = "const_eval_select",
     issue = "none",
@@ -2475,6 +2493,7 @@ where
     called_at_rt.call_once(arg)
 }
 
+#[cfg(bootstrap)]
 #[unstable(
     feature = "const_eval_select",
     issue = "none",
diff --git a/library/core/src/mem/valid_align.rs b/library/core/src/mem/valid_align.rs
index b9ccc0b4c79..32b2afb72b0 100644
--- a/library/core/src/mem/valid_align.rs
+++ b/library/core/src/mem/valid_align.rs
@@ -28,7 +28,7 @@ impl ValidAlign {
     #[inline]
     pub(crate) const unsafe fn new_unchecked(align: usize) -> Self {
         // SAFETY: Precondition passed to the caller.
-        unsafe { assert_unsafe_precondition!(align.is_power_of_two()) };
+        unsafe { assert_unsafe_precondition!((align: usize) => align.is_power_of_two()) };
 
         // SAFETY: By precondition, this must be a power of two, and
         // our variants encompass all possible powers of two.
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index da41ea53635..6983d83808d 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -1033,10 +1033,13 @@ impl f32 {
                 }
             }
         }
-        // SAFETY: `u32` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_f32_to_u32 = |rt| unsafe { mem::transmute::<f32, u32>(rt) };
+
+        fn rt_f32_to_u32(x: f32) -> u32 {
+            // SAFETY: `u32` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute(x) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((self,), ct_f32_to_u32, rt_f32_to_u32) }
     }
@@ -1121,10 +1124,13 @@ impl f32 {
                 }
             }
         }
-        // SAFETY: `u32` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_u32_to_f32 = |rt| unsafe { mem::transmute::<u32, f32>(rt) };
+
+        fn rt_u32_to_f32(x: u32) -> f32 {
+            // SAFETY: `u32` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute(x) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((v,), ct_u32_to_f32, rt_u32_to_f32) }
     }
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index 631d559df5f..ce64afc0bd8 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -1026,10 +1026,13 @@ impl f64 {
                 }
             }
         }
-        // SAFETY: `u64` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_f64_to_u64 = |rt| unsafe { mem::transmute::<f64, u64>(rt) };
+
+        fn rt_f64_to_u64(rt: f64) -> u64 {
+            // SAFETY: `u64` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute::<f64, u64>(rt) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
     }
@@ -1119,10 +1122,13 @@ impl f64 {
                 }
             }
         }
-        // SAFETY: `u64` is a plain old datatype so we can always... uh...
-        // ...look, just pretend you forgot what you just read.
-        // Stability concerns.
-        let rt_u64_to_f64 = |rt| unsafe { mem::transmute::<u64, f64>(rt) };
+
+        fn rt_u64_to_f64(rt: u64) -> f64 {
+            // SAFETY: `u64` is a plain old datatype so we can always... uh...
+            // ...look, just pretend you forgot what you just read.
+            // Stability concerns.
+            unsafe { mem::transmute::<u64, f64>(rt) }
+        }
         // SAFETY: We use internal implementations that either always work or fail at compile time.
         unsafe { intrinsics::const_eval_select((v,), ct_u64_to_f64, rt_u64_to_f64) }
     }
diff --git a/library/core/src/num/nonzero.rs b/library/core/src/num/nonzero.rs
index 1cf306f2103..532a09736a7 100644
--- a/library/core/src/num/nonzero.rs
+++ b/library/core/src/num/nonzero.rs
@@ -56,7 +56,7 @@ macro_rules! nonzero_integers {
                 pub const unsafe fn new_unchecked(n: $Int) -> Self {
                     // SAFETY: this is guaranteed to be safe by the caller.
                     unsafe {
-                        core::intrinsics::assert_unsafe_precondition!(n != 0);
+                        core::intrinsics::assert_unsafe_precondition!((n: $Int) => n != 0);
                         Self(n)
                     }
                 }
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index f5c72d79755..80bff74f3e9 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -755,9 +755,12 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        let this = self;
         // SAFETY: The comparison has no side-effects, and the intrinsic
         // does this check internally in the CTFE implementation.
-        unsafe { assert_unsafe_precondition!(self >= origin) };
+        unsafe {
+            assert_unsafe_precondition!([T](this: *const T, origin: *const T) => this >= origin)
+        };
 
         let pointee_size = mem::size_of::<T>();
         assert!(0 < pointee_size && pointee_size <= isize::MAX as usize);
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index 41a2685d361..e976abed774 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -886,7 +886,7 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
     // SAFETY: the caller must guarantee that `x` and `y` are
     // valid for writes and properly aligned.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](x: *mut T, y: *mut T, count: usize) =>
             is_aligned_and_not_null(x)
                 && is_aligned_and_not_null(y)
                 && is_nonoverlapping(x, y, count)
@@ -983,7 +983,7 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
     // and cannot overlap `src` since `dst` must point to a distinct
     // allocated object.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
         mem::swap(&mut *dst, &mut src); // cannot overlap
     }
     src
@@ -1470,7 +1470,7 @@ pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 pub unsafe fn read_volatile<T>(src: *const T) -> T {
     // SAFETY: the caller must uphold the safety contract for `volatile_load`.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(src));
+        assert_unsafe_precondition!([T](src: *const T) => is_aligned_and_not_null(src));
         intrinsics::volatile_load(src)
     }
 }
@@ -1541,7 +1541,7 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
 pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
     // SAFETY: the caller must uphold the safety contract for `volatile_store`.
     unsafe {
-        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
         intrinsics::volatile_store(dst, src);
     }
 }
diff --git a/library/core/src/slice/index.rs b/library/core/src/slice/index.rs
index fd7ecf3daf3..3403a5a86f7 100644
--- a/library/core/src/slice/index.rs
+++ b/library/core/src/slice/index.rs
@@ -48,10 +48,12 @@ const fn slice_start_index_len_fail(index: usize, len: usize) -> ! {
 }
 
 // FIXME const-hack
+#[track_caller]
 fn slice_start_index_len_fail_rt(index: usize, len: usize) -> ! {
     panic!("range start index {index} out of range for slice of length {len}");
 }
 
+#[track_caller]
 const fn slice_start_index_len_fail_ct(_: usize, _: usize) -> ! {
     panic!("slice start index is out of range for slice");
 }
@@ -69,10 +71,12 @@ const fn slice_end_index_len_fail(index: usize, len: usize) -> ! {
 }
 
 // FIXME const-hack
+#[track_caller]
 fn slice_end_index_len_fail_rt(index: usize, len: usize) -> ! {
     panic!("range end index {index} out of range for slice of length {len}");
 }
 
+#[track_caller]
 const fn slice_end_index_len_fail_ct(_: usize, _: usize) -> ! {
     panic!("slice end index is out of range for slice");
 }
@@ -88,10 +92,12 @@ const fn slice_index_order_fail(index: usize, end: usize) -> ! {
 }
 
 // FIXME const-hack
+#[track_caller]
 fn slice_index_order_fail_rt(index: usize, end: usize) -> ! {
     panic!("slice index starts at {index} but ends at {end}");
 }
 
+#[track_caller]
 const fn slice_index_order_fail_ct(_: usize, _: usize) -> ! {
     panic!("slice index start is larger than end");
 }
@@ -217,21 +223,23 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
 
     #[inline]
     unsafe fn get_unchecked(self, slice: *const [T]) -> *const T {
+        let this = self;
         // SAFETY: the caller guarantees that `slice` is not dangling, so it
         // cannot be longer than `isize::MAX`. They also guarantee that
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
         // so the call to `add` is safe.
         unsafe {
-            assert_unsafe_precondition!(self < slice.len());
+            assert_unsafe_precondition!([T](this: usize, slice: *const [T]) => this < slice.len());
             slice.as_ptr().add(self)
         }
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut T {
+        let this = self;
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!(self < slice.len());
+            assert_unsafe_precondition!([T](this: usize, slice: *mut [T]) => this < slice.len());
             slice.as_mut_ptr().add(self)
         }
     }
@@ -276,22 +284,26 @@ unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
 
     #[inline]
     unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        let this = ops::Range { start: self.start, end: self.end };
         // SAFETY: the caller guarantees that `slice` is not dangling, so it
         // cannot be longer than `isize::MAX`. They also guarantee that
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
         // so the call to `add` is safe.
 
         unsafe {
-            assert_unsafe_precondition!(self.end >= self.start && self.end <= slice.len());
+            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *const [T]) =>
+            this.end >= this.start && this.end <= slice.len());
             ptr::slice_from_raw_parts(slice.as_ptr().add(self.start), self.end - self.start)
         }
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        let this = ops::Range { start: self.start, end: self.end };
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!(self.end >= self.start && self.end <= slice.len());
+            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *mut [T]) =>
+                this.end >= this.start && this.end <= slice.len());
             ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start), self.end - self.start)
         }
     }
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 1958745b586..6a7150d2986 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -656,10 +656,11 @@ impl<T> [T] {
     #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
     #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
     pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
-        let ptr = self.as_mut_ptr();
+        let this = self;
+        let ptr = this.as_mut_ptr();
         // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
         unsafe {
-            assert_unsafe_precondition!(a < self.len() && b < self.len());
+            assert_unsafe_precondition!([T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len());
             ptr::swap(ptr.add(a), ptr.add(b));
         }
     }
@@ -972,9 +973,10 @@ impl<T> [T] {
     #[inline]
     #[must_use]
     pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
+        let this = self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
+            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
             exact_div(self.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
@@ -1111,10 +1113,11 @@ impl<T> [T] {
     #[inline]
     #[must_use]
     pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
+        let this = &*self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
-            exact_div(self.len(), N)
+            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+            exact_div(this.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
         // a slice of `new_len` many `N` elements chunks.
@@ -1687,7 +1690,7 @@ impl<T> [T] {
         // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
         // is fine.
         unsafe {
-            assert_unsafe_precondition!(mid <= len);
+            assert_unsafe_precondition!((mid: usize, len: usize) => mid <= len);
             (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
         }
     }
diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs
index 107e71ab68b..f1e8bc79bf4 100644
--- a/library/core/src/slice/raw.rs
+++ b/library/core/src/slice/raw.rs
@@ -90,7 +90,7 @@ use crate::ptr;
 pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](data: *const T, len: usize) =>
             is_aligned_and_not_null(data)
                 && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
         );
@@ -134,7 +134,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
 pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
     unsafe {
-        assert_unsafe_precondition!(
+        assert_unsafe_precondition!([T](data: *mut T, len: usize) =>
             is_aligned_and_not_null(data)
                 && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
         );
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index 2120bf61d75..f673aa2a44b 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -91,10 +91,12 @@ const fn slice_error_fail(s: &str, begin: usize, end: usize) -> ! {
     }
 }
 
+#[track_caller]
 const fn slice_error_fail_ct(_: &str, _: usize, _: usize) -> ! {
     panic!("failed to slice string");
 }
 
+#[track_caller]
 fn slice_error_fail_rt(s: &str, begin: usize, end: usize) -> ! {
     const MAX_DISPLAY_LENGTH: usize = 256;
     let trunc_len = s.floor_char_boundary(MAX_DISPLAY_LENGTH);