Skip to content

Remove libc_const_extern_fn #4712

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

Merged
merged 1 commit into from
Sep 23, 2025
Merged

Remove libc_const_extern_fn #4712

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
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
5 changes: 0 additions & 5 deletions build.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,8 +17,6 @@ const ALLOWED_CFGS: &[&str] = &[
"gnu_file_offset_bits64",
// Corresponds to `_TIME_BITS=64` in glibc
"gnu_time_bits64",
// FIXME(ctest): this config shouldn't be needed but ctest can't parse `const extern fn`
"libc_const_extern_fn",
"libc_deny_warnings",
"libc_ctest",
// Corresponds to `__USE_TIME_BITS64` in UAPI
Expand Down Expand Up @@ -144,9 +142,6 @@ fn main() {
set_cfg("libc_deny_warnings");
}

// Set unconditionally when ctest is not being invoked.
set_cfg("libc_const_extern_fn");

// Since Rust 1.80, configuration that isn't recognized by default needs to be provided to
// avoid warnings.
if rustc_minor_ver >= 80 {
Expand Down
144 changes: 38 additions & 106 deletions src/macros.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -279,114 +279,46 @@ macro_rules! c_enum {
(@ty) => { $crate::prelude::CEnumRepr };
}

// This is a pretty horrible hack to allow us to conditionally mark some functions as 'const',
// without requiring users of this macro to care "libc_const_extern_fn".
//
// When 'libc_const_extern_fn' is enabled, we emit the captured 'const' keyword in the expanded
// function.
//
// When 'libc_const_extern_fn' is disabled, we always emit a plain 'pub unsafe extern fn'.
// Note that the expression matched by the macro is exactly the same - this allows
// users of this macro to work whether or not 'libc_const_extern_fn' is enabled
//
// Unfortunately, we need to duplicate most of this macro between the 'cfg_if' blocks.
// This is because 'const unsafe extern fn' won't even parse on older compilers,
// so we need to avoid emitting it at all of 'libc_const_extern_fn'.
//
// Specifically, moving the 'cfg_if' into the macro body will *not* work. Doing so would cause the
// '#[cfg(libc_const_extern_fn)]' to be emitted into user code. The 'cfg' gate will not stop Rust
// from trying to parse the 'pub const unsafe extern fn', so users would get a compiler error even
// when the 'libc_const_extern_fn' feature is disabled.

// FIXME(ctest): ctest can't handle `const extern` functions, we should be able to remove this
// cfg completely.
// FIXME(ctest): ctest can't handle `$(,)?` so we use `$(,)*` which isn't quite correct.
cfg_if! {
if #[cfg(libc_const_extern_fn)] {
/// Define an `unsafe` function that is const as long as `libc_const_extern_fn` is enabled.
macro_rules! f {
($(
$(#[$attr:meta])*
pub $({$constness:ident})* fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
pub $($constness)* unsafe extern "C" fn $i($($arg: $argty),*) -> $ret
$body
)*)
}

/// Define a safe function that is const as long as `libc_const_extern_fn` is enabled.
macro_rules! safe_f {
($(
$(#[$attr:meta])*
pub $({$constness:ident})* fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
pub $($constness)* extern "C" fn $i($($arg: $argty),*) -> $ret
$body
)*)
}

/// A nonpublic function that is const as long as `libc_const_extern_fn` is enabled.
macro_rules! const_fn {
($(
$(#[$attr:meta])*
$({$constness:ident})* fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
$($constness)* fn $i($($arg: $argty),*) -> $ret
$body
)*)
}
} else {
/// Define an `unsafe` function that is const as long as `libc_const_extern_fn` is enabled.
macro_rules! f {
($(
$(#[$attr:meta])*
pub $({$constness:ident})* fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
pub unsafe extern "C" fn $i($($arg: $argty),*) -> $ret
$body
)*)
}
/// Define a `unsafe` function.
macro_rules! f {
($(
$(#[$attr:meta])*
pub $({$constness:ident})? fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
pub $($constness)? unsafe extern "C" fn $i($($arg: $argty),*) -> $ret
$body
)*)
}

/// Define a safe function that is const as long as `libc_const_extern_fn` is enabled.
macro_rules! safe_f {
($(
$(#[$attr:meta])*
pub $({$constness:ident})* fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
pub extern "C" fn $i($($arg: $argty),*) -> $ret
$body
)*)
}
/// Define a safe function.
macro_rules! safe_f {
($(
$(#[$attr:meta])*
pub $({$constness:ident})? fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
pub $($constness)? extern "C" fn $i($($arg: $argty),*) -> $ret
$body
)*)
}

/// A nonpublic function that is const as long as `libc_const_extern_fn` is enabled.
macro_rules! const_fn {
($(
$(#[$attr:meta])*
$({$constness:ident})* fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
fn $i($($arg: $argty),*) -> $ret
$body
)*)
}
}
/// Define a nonpublic function.
macro_rules! const_fn {
($(
$(#[$attr:meta])*
$({$constness:ident})? fn $i:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty
$body:block
)*) => ($(
#[inline]
$(#[$attr])*
$($constness)? fn $i($($arg: $argty),*) -> $ret
$body
)*)
}

macro_rules! __item {
Expand Down