further tweaks

Author: folkertdev

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -820,7 +820,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 let scalar = self.read_scalar(arg_mplace)?;
                 if scalar.to_int(size)? < 0 {
                     throw_ub_format!(
-                        "va_arg value mismatch: value `{value}_{caller_ty}` cannot be represented by type {callee_ty}",
+                        "va_arg value mismatch: value `{value}_{caller_ty}` cannot be represented by type `{callee_ty}`",
                         value = if source_is_signed {
                             scalar.to_int(size)?.to_string()
                         } else {

library/core/src/ffi/va_list.rs

@@ -390,8 +390,12 @@ impl<'f> VaList<'f> {
     ///
     /// # Safety
     ///
-    /// This function is only sound to call when there is another argument to read, and that
-    /// argument is a properly initialized value compatible with the type `T`.
+    /// This function is safe to call only if all of the following conditions are satisfied:
+    ///
+    /// - There is another c-variadic argument to read.
+    /// - The actual type of the argument `U` is compatible with `T` (as defined below).
+    /// - If `U` and `T` are both integer types, then the value passed by the caller must be
+    /// representable in both types.
     ///
     /// Types `T` and `U` are compatible when:
     ///
@@ -400,12 +404,6 @@ impl<'f> VaList<'f> {
     /// - `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`], or vice versa.
     ///
-    /// When `T` and `U` are integer types of the same size but different signedness,
-    /// the value that the caller passes must be representable by both `T` and `U`.
-    ///
-    /// Calling this function with an incompatible type, an invalid value, or when there
-    /// are no more variable arguments, is unsound.
-    ///
     /// [`c_void`]: core::ffi::c_void
     #[inline] // Avoid codegen when not used to help backends that don't support VaList.
     #[rustc_const_unstable(feature = "const_c_variadic", issue = "151787")]

tests/ui/consts/const-eval/c-variadic-fail.rs

@@ -70,17 +70,17 @@ unsafe fn read_cast_numeric() {
     const { read_as::<isize>(-1 as ConcreteIsize) };
 
     const { read_as::<u32>(-1i32) };
-    //~^ ERROR va_arg value mismatch: value `-1_i32` cannot be represented by type u32
+    //~^ ERROR va_arg value mismatch: value `-1_i32` cannot be represented by type `u32`
     const { read_as::<u32>(i32::MIN) };
-    //~^ ERROR va_arg value mismatch: value `-2147483648_i32` cannot be represented by type u32
+    //~^ ERROR va_arg value mismatch: value `-2147483648_i32` cannot be represented by type `u32`
     const { read_as::<i32>(u32::MAX) };
-    //~^ ERROR va_arg value mismatch: value `4294967295_u32` cannot be represented by type i32
+    //~^ ERROR va_arg value mismatch: value `4294967295_u32` cannot be represented by type `i32`
     const { read_as::<i32>(i32::MAX as u32 + 1) };
-    //~^ ERROR va_arg value mismatch: value `2147483648_u32` cannot be represented by type i32
+    //~^ ERROR va_arg value mismatch: value `2147483648_u32` cannot be represented by type `i32`
     const { read_as::<i64>(u64::MAX) };
-    //~^ ERROR va_arg value mismatch: value `18446744073709551615_u64` cannot be represented by type i64
+    //~^ ERROR va_arg value mismatch: value `18446744073709551615_u64` cannot be represented by type `i64`
     const { read_as::<i64>(i64::MAX as u64 + 1) };
-    //~^ ERROR va_arg value mismatch: value `9223372036854775808_u64` cannot be represented by type i64
+    //~^ ERROR va_arg value mismatch: value `9223372036854775808_u64` cannot be represented by type `i64`
 
     const { read_as::<i32>(1u64) };
     //~^ ERROR va_arg type mismatch: requested `i32` is incompatible with next argument of type `u64`

tests/ui/consts/const-eval/c-variadic-fail.stderr

@@ -54,7 +54,7 @@ LL |     const { read_n::<2>(1) }
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0080]: va_arg value mismatch: value `-1_i32` cannot be represented by type u32
+error[E0080]: va_arg value mismatch: value `-1_i32` cannot be represented by type `u32`
   --> $DIR/c-variadic-fail.rs:72:13
    |
 LL |     const { read_as::<u32>(-1i32) };
@@ -82,7 +82,7 @@ LL |     const { read_as::<u32>(-1i32) };
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0080]: va_arg value mismatch: value `-2147483648_i32` cannot be represented by type u32
+error[E0080]: va_arg value mismatch: value `-2147483648_i32` cannot be represented by type `u32`
   --> $DIR/c-variadic-fail.rs:74:13
    |
 LL |     const { read_as::<u32>(i32::MIN) };
@@ -110,7 +110,7 @@ LL |     const { read_as::<u32>(i32::MIN) };
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0080]: va_arg value mismatch: value `4294967295_u32` cannot be represented by type i32
+error[E0080]: va_arg value mismatch: value `4294967295_u32` cannot be represented by type `i32`
   --> $DIR/c-variadic-fail.rs:76:13
    |
 LL |     const { read_as::<i32>(u32::MAX) };
@@ -138,7 +138,7 @@ LL |     const { read_as::<i32>(u32::MAX) };
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0080]: va_arg value mismatch: value `2147483648_u32` cannot be represented by type i32
+error[E0080]: va_arg value mismatch: value `2147483648_u32` cannot be represented by type `i32`
   --> $DIR/c-variadic-fail.rs:78:13
    |
 LL |     const { read_as::<i32>(i32::MAX as u32 + 1) };
@@ -166,7 +166,7 @@ LL |     const { read_as::<i32>(i32::MAX as u32 + 1) };
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0080]: va_arg value mismatch: value `18446744073709551615_u64` cannot be represented by type i64
+error[E0080]: va_arg value mismatch: value `18446744073709551615_u64` cannot be represented by type `i64`
   --> $DIR/c-variadic-fail.rs:80:13
    |
 LL |     const { read_as::<i64>(u64::MAX) };
@@ -194,7 +194,7 @@ LL |     const { read_as::<i64>(u64::MAX) };
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0080]: va_arg value mismatch: value `9223372036854775808_u64` cannot be represented by type i64
+error[E0080]: va_arg value mismatch: value `9223372036854775808_u64` cannot be represented by type `i64`
   --> $DIR/c-variadic-fail.rs:82:13
    |
 LL |     const { read_as::<i64>(i64::MAX as u64 + 1) };