Update use of libc::timespec to prepare for future libc version

In a future release of the `libc` crate, `libc::timespec` will contain
private padding fields on `*-linux-musl` targets and so the struct will
no longer be able to be created using the literal initialization syntax.

Update places where `libc::timespec` is created to first zero initialize
the value and then update the `tv_sec` and `tv_nsec` fields manually.
Many of these places are in `const fn`s so a helper function
`zero_init_timespec()` is introduced to help with this as
`std::mem::zeroed()` is not a `const` function.

Some matches on `libc::timespec` are also updated to include a trailing
`..` pattern which works when `libc::timespec` has additional, private
fields as well as when it does not (like for
`x86_64-unknown-linux-gnu`).

src/sys/time.rs

@@ -6,6 +6,13 @@ use std::convert::From;
 use std::time::Duration;
 use std::{cmp, fmt, ops};
 
+const fn zero_init_timespec() -> timespec {
+    // `std::mem::zeroed()` is not yet a const fn (https://github.com/rust-lang/rust/issues/62061)
+    // so we will instead initialize an array of the appropriate size to zero and then
+    // transmute it to a timespec value.
+    unsafe { std::mem::transmute([0u8; std::mem::size_of::<timespec>()]) }
+}
+
 #[cfg(any(
     all(feature = "time", any(target_os = "android", target_os = "linux")),
     all(
@@ -20,7 +27,7 @@ use std::{cmp, fmt, ops};
     )
 ))]
 pub(crate) mod timer {
-    use crate::sys::time::TimeSpec;
+    use crate::sys::time::{zero_init_timespec, TimeSpec};
     use bitflags::bitflags;
 
     #[derive(Debug, Clone, Copy)]
@@ -29,14 +36,8 @@ pub(crate) mod timer {
     impl TimerSpec {
         pub const fn none() -> Self {
             Self(libc::itimerspec {
-                it_interval: libc::timespec {
-                    tv_sec: 0,
-                    tv_nsec: 0,
-                },
-                it_value: libc::timespec {
-                    tv_sec: 0,
-                    tv_nsec: 0,
-                },
+                it_interval: zero_init_timespec(),
+                it_value: zero_init_timespec(),
             })
         }
     }
@@ -57,10 +58,7 @@ pub(crate) mod timer {
         fn from(expiration: Expiration) -> TimerSpec {
             match expiration {
                 Expiration::OneShot(t) => TimerSpec(libc::itimerspec {
-                    it_interval: libc::timespec {
-                        tv_sec: 0,
-                        tv_nsec: 0,
-                    },
+                    it_interval: zero_init_timespec(),
                     it_value: *t.as_ref(),
                 }),
                 Expiration::IntervalDelayed(start, interval) => {
@@ -118,6 +116,7 @@ pub(crate) mod timer {
                         libc::timespec {
                             tv_sec: 0,
                             tv_nsec: 0,
+                            ..
                         },
                     it_value: ts,
                 }) => Expiration::OneShot(ts.into()),
@@ -257,18 +256,17 @@ impl PartialOrd for TimeSpec {
 
 impl TimeValLike for TimeSpec {
     #[inline]
+    #[cfg_attr(target_env = "musl", allow(deprecated))]
+    // https://github.com/rust-lang/libc/issues/1848
     fn seconds(seconds: i64) -> TimeSpec {
         assert!(
             (TS_MIN_SECONDS..=TS_MAX_SECONDS).contains(&seconds),
             "TimeSpec out of bounds; seconds={}",
             seconds
         );
-        #[cfg_attr(target_env = "musl", allow(deprecated))]
-        // https://github.com/rust-lang/libc/issues/1848
-        TimeSpec(timespec {
-            tv_sec: seconds as time_t,
-            tv_nsec: 0,
-        })
+        let mut ts = zero_init_timespec();
+        ts.tv_sec = seconds as time_t;
+        TimeSpec(ts)
     }
 
     #[inline]
@@ -292,18 +290,18 @@ impl TimeValLike for TimeSpec {
 
     /// Makes a new `TimeSpec` with given number of nanoseconds.
     #[inline]
+    #[cfg_attr(target_env = "musl", allow(deprecated))]
+    // https://github.com/rust-lang/libc/issues/1848
     fn nanoseconds(nanoseconds: i64) -> TimeSpec {
         let (secs, nanos) = div_mod_floor_64(nanoseconds, NANOS_PER_SEC);
         assert!(
             (TS_MIN_SECONDS..=TS_MAX_SECONDS).contains(&secs),
             "TimeSpec out of bounds"
         );
-        #[cfg_attr(target_env = "musl", allow(deprecated))]
-        // https://github.com/rust-lang/libc/issues/1848
-        TimeSpec(timespec {
-            tv_sec: secs as time_t,
-            tv_nsec: nanos as timespec_tv_nsec_t,
-        })
+        let mut ts = zero_init_timespec();
+        ts.tv_sec = secs as time_t;
+        ts.tv_nsec = nanos as timespec_tv_nsec_t;
+        TimeSpec(ts)
     }
 
     // The cast is not unnecessary on all platforms.
@@ -337,10 +335,10 @@ impl TimeSpec {
     /// Construct a new `TimeSpec` from its components
     #[cfg_attr(target_env = "musl", allow(deprecated))] // https://github.com/rust-lang/libc/issues/1848
     pub const fn new(seconds: time_t, nanoseconds: timespec_tv_nsec_t) -> Self {
-        Self(timespec {
-            tv_sec: seconds,
-            tv_nsec: nanoseconds,
-        })
+        let mut ts = zero_init_timespec();
+        ts.tv_sec = seconds;
+        ts.tv_nsec = nanoseconds;
+        Self(ts)
     }
 
     fn nanos_mod_sec(&self) -> timespec_tv_nsec_t {
@@ -360,13 +358,13 @@ impl TimeSpec {
         self.0.tv_nsec
     }
 
+    #[cfg_attr(target_env = "musl", allow(deprecated))]
+    // https://github.com/rust-lang/libc/issues/1848
     pub const fn from_duration(duration: Duration) -> Self {
-        #[cfg_attr(target_env = "musl", allow(deprecated))]
-        // https://github.com/rust-lang/libc/issues/1848
-        TimeSpec(timespec {
-            tv_sec: duration.as_secs() as time_t,
-            tv_nsec: duration.subsec_nanos() as timespec_tv_nsec_t,
-        })
+        let mut ts = zero_init_timespec();
+        ts.tv_sec = duration.as_secs() as time_t;
+        ts.tv_nsec = duration.subsec_nanos() as timespec_tv_nsec_t;
+        TimeSpec(ts)
     }
 
     pub const fn from_timespec(timespec: timespec) -> Self {