Remove libc_const_extern_fn

This originally existed for MSRV support, then became a necessary hack
to support the old ctest's inability to parse `const fn`. The new ctest
doesn't have this limitation, so remove the config.

Author: tgross35

build.rs

@@ -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
@@ -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 {

src/macros.rs

@@ -298,95 +298,46 @@ macro_rules! c_enum {
 // 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 {