tweaks to comments

Author: folkertdev

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -63,8 +63,9 @@ enum VarArgCompatible {
     /// `T` and `U` are compatible, e.g.
     ///
     /// - They're the same type.
-    /// - One is `usize`/`isize`, the other same-sized fixed-width integer on that target.
-    /// - They are compatible pointer types.
+    /// - One is `usize`/`isize`, the other an integer type of the same width
+    /// and sign on the current target.
+    /// - They are compatible pointer types (see the exact rules below).
     Compatible,
     /// `T` and `U` are definitely not compatible.
     Incompatible,
@@ -838,11 +839,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// Types `T` and `U` are compatible when:
     ///
     /// - `T` and `U` are the same type.
-    /// - `T` is a signed integer and `U` the corresponding unsigned integer,
-    /// - `T` is an unsigned integer and `U` the corresponding signed integer,
+    /// - `T` and `U` are integer types of the same size. When the sign is different a further check
+    /// is needed on the passed value, but that is not done here.
     /// - `T` and `U` are both pointers, and their target types are compatible.
-    /// - `T` is a pointer to `c_void` and `U` is a pointer to `i8` or `u8` (i.e., any "character type").
-    /// - `T` is a pointer to `i8` or `u8` and `U` is a pointer to `c_void`.
+    /// - `T` is a pointer to [`c_void`] and `U` is a pointer to [`i8]` or [`u8`], or vice versa.
     fn validate_c_variadic_compatible_ty(
         &mut self,
         caller_type: Ty<'tcx>,

library/core/src/ffi/va_list.rs

@@ -399,14 +399,10 @@ impl<'f> VaList<'f> {
     /// Types `T` and `U` are compatible when:
     ///
     /// - `T` and `U` are the same type.
-    /// - `T` is a signed integer and `U` the corresponding unsigned integer,
-    /// - `T` is an unsigned integer and `U` the corresponding signed integer,
+    /// - `T` and `U` are integer types of the same size. The value that the caller passes
+    /// must be representable by `T` and `U`.
     /// - `T` and `U` are both pointers, and their target types are compatible.
-    /// - `T` is a pointer to [`c_void`] and `U` is a pointer to [`i8]` or [`u8`].
-    /// - `T` is a pointer to [`i8]` or [`u8`] and `U` is a pointer to [`c_void`].
-    ///
-    /// When `T` and `U` are both integer types, the value that the caller passes must be
-    /// representable by `T` and `U`.
+    /// - `T` is a pointer to [`c_void`] and `U` is a pointer to [`i8]` or [`u8`], or vice versa.
     ///
     /// [`c_void`]: core::ffi::c_void
     #[inline] // Avoid codegen when not used to help backends that don't support VaList.