Skip to content

c-variadic: document Clone and Drop instances and require VaArgSafe: Copy #155821

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
folkertdev wants to merge 3 commits into
base: main
Choose a base branch
from
+16 −1
Open

c-variadic: document Clone and Drop instances and require VaArgSafe: Copy #155821

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
d85d5cc
c-variadic: document `Clone` and `Drop` instances
folkertdev Apr 26, 2026
79178df
c-variadic: add a `Copy` bound to `VaArgSafe`
folkertdev Apr 26, 2026
d143239
c-variadic: test that const and mutable void and char pointers implem…
folkertdev Apr 26, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
17 changes: 16 additions & 1 deletion library/core/src/ffi/va_list.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -251,6 +251,9 @@ impl VaList<'_> {

#[rustc_const_unstable(feature = "const_c_variadic", issue = "151787")]
impl<'f> const Clone for VaList<'f> {
/// Clone the [`VaList`], producing a second independent cursor into the variable argument list.
///
/// Corresponds to `va_copy` in C.
#[inline] // Avoid codegen when not used to help backends that don't support VaList.
fn clone(&self) -> Self {
// We only implement Clone and not Copy because some future target might not be able to
Expand All @@ -263,8 +266,14 @@ impl<'f> const Clone for VaList<'f> {

#[rustc_const_unstable(feature = "const_c_variadic", issue = "151787")]
impl<'f> const Drop for VaList<'f> {
/// Drop the [`VaList`].
///
/// Corresponds to `va_end` in C.
#[inline] // Avoid codegen when not used to help backends that don't support VaList.
fn drop(&mut self) {
// Call the rust `va_end` intrinsic, which is a no-op and does not map to LLVM `va_end`.
// The rust intrinsic exists as a hook for Miri to check for UB.
//
// SAFETY: this variable argument list is being dropped, so won't be read from again.
unsafe { va_end(self) }
}
Expand Down Expand Up @@ -324,7 +333,7 @@ mod sealed {
// types with an alignment larger than 8, or with a non-scalar layout. Inline assembly can be used
// to accept unsupported types in the meantime.
#[lang = "va_arg_safe"]
pub unsafe trait VaArgSafe: sealed::Sealed {}
pub unsafe trait VaArgSafe: Copy + sealed::Sealed {}

crate::cfg_select! {
any(target_arch = "avr", target_arch = "msp430") => {
Expand Down Expand Up @@ -381,6 +390,12 @@ const _: () = {
va_arg_safe_check::<crate::ffi::c_ulonglong>();

va_arg_safe_check::<crate::ffi::c_double>();

va_arg_safe_check::<*const crate::ffi::c_void>();
va_arg_safe_check::<*mut crate::ffi::c_void>();

va_arg_safe_check::<*const crate::ffi::c_char>();
va_arg_safe_check::<*mut crate::ffi::c_char>();
};

impl<'f> VaList<'f> {
Expand Down
Loading