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refactor: deprecate *MAX constants fitting #3131 #5122

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8372b50
feat: add macro to declare unstable constants
dybucc Jun 18, 2026
c6d3aaa
refactor: deprecate *MAX constants fitting rust-lang/libc#3131
dybucc May 29, 2026
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4 changes: 3 additions & 1 deletion src/fuchsia/mod.rs
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Expand Up @@ -1592,7 +1592,9 @@ pub const LOCK_UN: c_int = 8;
pub const SS_ONSTACK: c_int = 1;
pub const SS_DISABLE: c_int = 2;

pub const PATH_MAX: c_int = 4096;
ct! {
pub const PATH_MAX: c_int = 4096;
}

pub const FD_SETSIZE: c_int = 1024;

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15 changes: 15 additions & 0 deletions src/macros.rs
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Expand Up @@ -402,6 +402,21 @@ macro_rules! offset_of {
}};
}

/// Defines constants with an accompanying doc comment pointing out their
/// instability, and links to the crate documentation for usage guidelines.
macro_rules! ct {
($($it:item)+) => {
$(
/// This constant, among others often used in C for the purposes of denoting the
/// latest value or limit in a set of constants, is likely to change upstream.
/// For correct usage, see the [crate-level documentation][docs].
///
/// [docs]: index.html#usage-recommendations
$it
)+
};
}

#[cfg(test)]
mod tests {
use core::any::TypeId;
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4 changes: 3 additions & 1 deletion src/new/linux_uapi/linux/can/j1939.rs
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Expand Up @@ -57,4 +57,6 @@ s! {
}
}

pub const J1939_FILTER_MAX: c_int = 512;
ct! {
pub const J1939_FILTER_MAX: c_int = 512;
}
5 changes: 4 additions & 1 deletion src/new/linux_uapi/linux/can/raw.rs
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Expand Up @@ -3,7 +3,10 @@
pub use crate::linux::can::*;

pub const SOL_CAN_RAW: c_int = SOL_CAN_BASE + CAN_RAW;
pub const CAN_RAW_FILTER_MAX: c_int = 512;

ct! {
pub const CAN_RAW_FILTER_MAX: c_int = 512;
}

// FIXME(cleanup): use `c_enum!`, which needs to be adapted to allow omitting a type.
pub const CAN_RAW_FILTER: c_int = 1;
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10 changes: 7 additions & 3 deletions src/new/qurt/limits.rs
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Expand Up @@ -27,12 +27,16 @@ pub const USHRT_MAX: c_ushort = 65535;
// POSIX Limits
pub const ARG_MAX: c_int = 4096;
pub const CHILD_MAX: c_int = 25;
pub const LINK_MAX: c_int = 8;

ct! {
pub const LINK_MAX: c_int = 8;
pub const NAME_MAX: c_int = 255;
pub const PATH_MAX: c_int = 260;
}

pub const MAX_CANON: c_int = 255;
pub const MAX_INPUT: c_int = 255;
pub const NAME_MAX: c_int = 255;
pub const OPEN_MAX: c_int = 20;
pub const PATH_MAX: c_int = 260;
pub const PIPE_BUF: c_int = 512;
pub const STREAM_MAX: c_int = 20;
pub const TZNAME_MAX: c_int = 50;
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5 changes: 4 additions & 1 deletion src/new/qurt/signal.rs
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Expand Up @@ -51,7 +51,10 @@ pub const SIG_SETMASK: c_int = 3;
pub const POSIX_MSG: c_int = 7;
pub const POSIX_NOTIF: c_int = 8;
pub const SIGRTMIN: c_int = 10;
pub const SIGRTMAX: c_int = 32;

ct! {
pub const SIGRTMAX: c_int = 32;
}

// Notification types (from QuRT signal.h)
pub const SIGEV_NONE: c_int = 0;
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50 changes: 37 additions & 13 deletions src/unix/aix/mod.rs
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Expand Up @@ -932,7 +932,11 @@ pub const RTAX_IFP: c_int = 4;
pub const RTAX_IFA: c_int = 5;
pub const RTAX_AUTHOR: c_int = 6;
pub const RTAX_BRD: c_int = 7;
pub const RTAX_MAX: c_int = 8;

ct! {
pub const RTAX_MAX: c_int = 8;
}

pub const RTF_UP: c_int = 0x1;
pub const RTF_GATEWAY: c_int = 0x2;
pub const RTF_HOST: c_int = 0x4;
Expand Down Expand Up @@ -1445,7 +1449,18 @@ pub const L_GETPROCINFO: c_int = 7;
pub const L_GETXINFO: c_int = 8;

// sys/limits.h
pub const PATH_MAX: c_int = 1023;

ct! {
pub const PATH_MAX: c_int = 1023;
pub const BC_BASE_MAX: c_int = 99;
pub const BC_DIM_MAX: c_int = 0x800;
pub const BC_SCALE_MAX: c_int = 99;
pub const BC_STRING_MAX: c_int = 0x800;
pub const CHARCLASS_NAME_MAX: c_int = 14;
pub const COLL_WEIGHTS_MAX: c_int = 4;
pub const EXPR_NEST_MAX: c_int = 32;
}

pub const PAGESIZE: c_int = 4096;
pub const IOV_MAX: c_int = 16;
pub const AIO_LISTIO_MAX: c_int = 4096;
Expand All @@ -1454,14 +1469,7 @@ pub const OPEN_MAX: c_int = 65534;
pub const MAX_INPUT: c_int = 512;
pub const MAX_CANON: c_int = 256;
pub const ARG_MAX: c_int = 1048576;
pub const BC_BASE_MAX: c_int = 99;
pub const BC_DIM_MAX: c_int = 0x800;
pub const BC_SCALE_MAX: c_int = 99;
pub const BC_STRING_MAX: c_int = 0x800;
pub const CHARCLASS_NAME_MAX: c_int = 14;
pub const CHILD_MAX: c_int = 128;
pub const COLL_WEIGHTS_MAX: c_int = 4;
pub const EXPR_NEST_MAX: c_int = 32;
pub const NZERO: c_int = 20;

// sys/lockf.h
Expand Down Expand Up @@ -1541,7 +1549,11 @@ pub const MAXPATHLEN: c_int = PATH_MAX + 1;
pub const MAXSYMLINKS: c_int = 20;
pub const MAXHOSTNAMELEN: c_int = 256;
pub const MAXUPRC: c_int = 128;
pub const NGROUPS_MAX: c_ulong = 2048;

ct! {
pub const NGROUPS_MAX: c_ulong = 2048;
}

pub const NGROUPS: c_ulong = NGROUPS_MAX;
pub const NOFILE: c_int = OPEN_MAX;

Expand Down Expand Up @@ -1739,7 +1751,11 @@ pub const SIGXCPU: c_int = 24;
pub const SIGXFSZ: c_int = 25;
pub const SIGTRAP: c_int = 5;
pub const SIGCLD: c_int = 20;
pub const SIGRTMAX: c_int = 57;

ct! {
pub const SIGRTMAX: c_int = 57;
}

pub const SIGRTMIN: c_int = 50;
pub const SI_USER: c_int = 0;
pub const SI_UNDEFINED: c_int = 8;
Expand Down Expand Up @@ -1817,7 +1833,11 @@ pub const AF_INET6: c_int = 24;
pub const AF_INTF: c_int = 20;
pub const AF_RIF: c_int = 21;
pub const AF_NDD: c_int = 23;
pub const AF_MAX: c_int = 30;

ct! {
pub const AF_MAX: c_int = 30;
}

pub const PF_UNSPEC: c_int = AF_UNSPEC;
pub const PF_UNIX: c_int = AF_UNIX;
pub const PF_INET: c_int = AF_INET;
Expand All @@ -1843,7 +1863,11 @@ pub const PF_RIF: c_int = AF_RIF;
pub const PF_INTF: c_int = AF_INTF;
pub const PF_NDD: c_int = AF_NDD;
pub const PF_INET6: c_int = AF_INET6;
pub const PF_MAX: c_int = AF_MAX;

ct! {
pub const PF_MAX: c_int = AF_MAX;
}

pub const SF_CLOSE: c_int = 1;
pub const SF_REUSE: c_int = 2;
pub const SF_DONT_CACHE: c_int = 4;
Expand Down
33 changes: 19 additions & 14 deletions src/unix/bsd/apple/mod.rs
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Expand Up @@ -2014,7 +2014,10 @@ pub const CPU_STATE_USER: c_int = 0;
pub const CPU_STATE_SYSTEM: c_int = 1;
pub const CPU_STATE_IDLE: c_int = 2;
pub const CPU_STATE_NICE: c_int = 3;
pub const CPU_STATE_MAX: c_int = 4;

ct! {
pub const CPU_STATE_MAX: c_int = 4;
}

pub const PROCESSOR_BASIC_INFO: c_int = 1;
pub const PROCESSOR_CPU_LOAD_INFO: c_int = 2;
Expand Down Expand Up @@ -3396,14 +3399,18 @@ pub const HW_TARGET: c_int = 26;
pub const HW_PRODUCT: c_int = 27;
pub const HW_MAXID: c_int = 28;
pub const USER_CS_PATH: c_int = 1;
pub const USER_BC_BASE_MAX: c_int = 2;
pub const USER_BC_DIM_MAX: c_int = 3;
pub const USER_BC_SCALE_MAX: c_int = 4;
pub const USER_BC_STRING_MAX: c_int = 5;
pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
pub const USER_EXPR_NEST_MAX: c_int = 7;
pub const USER_LINE_MAX: c_int = 8;
pub const USER_RE_DUP_MAX: c_int = 9;

ct! {
pub const USER_BC_BASE_MAX: c_int = 2;
pub const USER_BC_DIM_MAX: c_int = 3;
pub const USER_BC_SCALE_MAX: c_int = 4;
pub const USER_BC_STRING_MAX: c_int = 5;
pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
pub const USER_EXPR_NEST_MAX: c_int = 7;
pub const USER_LINE_MAX: c_int = 8;
pub const USER_RE_DUP_MAX: c_int = 9;
}

pub const USER_POSIX2_VERSION: c_int = 10;
pub const USER_POSIX2_C_BIND: c_int = 11;
pub const USER_POSIX2_C_DEV: c_int = 12;
Expand Down Expand Up @@ -3447,10 +3454,6 @@ pub const SIGEV_THREAD: c_int = 3;
pub const AIO_CANCELED: c_int = 2;
pub const AIO_NOTCANCELED: c_int = 4;
pub const AIO_ALLDONE: c_int = 1;
#[deprecated(
since = "0.2.64",
note = "Can vary at runtime. Use sysconf(3) instead"
)]
pub const AIO_LISTIO_MAX: c_int = 16;
pub const LIO_NOP: c_int = 0;
pub const LIO_WRITE: c_int = 2;
Expand Down Expand Up @@ -3526,7 +3529,9 @@ pub const RTV_SSTHRESH: c_int = 0x20;
pub const RTV_RTT: c_int = 0x40;
pub const RTV_RTTVAR: c_int = 0x80;

pub const RTAX_MAX: c_int = 8;
ct! {
pub const RTAX_MAX: c_int = 8;
}

pub const KERN_PROCARGS2: c_int = 49;

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25 changes: 16 additions & 9 deletions src/unix/bsd/freebsdlike/dragonfly/mod.rs
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Expand Up @@ -641,14 +641,18 @@ pub const HW_MACHINE_PLATFORM: c_int = 12;
pub const HW_SENSORS: c_int = 13;
pub const HW_MAXID: c_int = 14;
pub const USER_CS_PATH: c_int = 1;
pub const USER_BC_BASE_MAX: c_int = 2;
pub const USER_BC_DIM_MAX: c_int = 3;
pub const USER_BC_SCALE_MAX: c_int = 4;
pub const USER_BC_STRING_MAX: c_int = 5;
pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
pub const USER_EXPR_NEST_MAX: c_int = 7;
pub const USER_LINE_MAX: c_int = 8;
pub const USER_RE_DUP_MAX: c_int = 9;

ct! {
pub const USER_BC_BASE_MAX: c_int = 2;
pub const USER_BC_DIM_MAX: c_int = 3;
pub const USER_BC_SCALE_MAX: c_int = 4;
pub const USER_BC_STRING_MAX: c_int = 5;
pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
pub const USER_EXPR_NEST_MAX: c_int = 7;
pub const USER_LINE_MAX: c_int = 8;
pub const USER_RE_DUP_MAX: c_int = 9;
}

pub const USER_POSIX2_VERSION: c_int = 10;
pub const USER_POSIX2_C_BIND: c_int = 11;
pub const USER_POSIX2_C_DEV: c_int = 12;
Expand Down Expand Up @@ -1168,7 +1172,10 @@ pub const RTM_VERSION: c_int = 7;
pub const RTAX_MPLS1: c_int = 8;
pub const RTAX_MPLS2: c_int = 9;
pub const RTAX_MPLS3: c_int = 10;
pub const RTAX_MAX: c_int = 11;

ct! {
pub const RTAX_MAX: c_int = 11;
}

const fn _CMSG_ALIGN(n: usize) -> usize {
(n + (size_of::<c_long>() - 1)) & !(size_of::<c_long>() - 1)
Expand Down
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