Rollup merge of #144519 - clarfonthey:const-system-time, r=jhpratt

Constify `SystemTime` methods
This is separated out from #143949 due to the fact that it touches nontrivial system code. While the same arithmetic methods on `Instant` could be made const, since that type explicitly cannot be constructed at const-time, we don't bother. However, due to the fact that `SystemTime::UNIX_EPOCH` exists, it can be useful to create other anchors at other points in time, and thus these methods should be possible to use in const context.
> Side comment: I would honestly like to just move every single implementation which is a thin wrapper over `Duration` or some integer clock into their own module which is tested on all targets, so that we don't have to worry about code for lower-tier targets not being tested. However, the comments in `std::sys_common` pointing out the desire to move things to `std::sys::common` confused me, particularly due to the fact that `std::sys::common` is taken from the hellish asterisk-import of `std::sys::pal::common` and others.
>
> I think that, for trivial types like this, we should just have a platform-independent module that can be tested on all platforms, to both ensure that the code is properly tested regardless of whether higher-tier platforms needed, and to avoid the extreme mental gymnastics required to determine where in the code it lies.
>
> However, since I'm not on any of the teams maintaining this code and am not involved, I'll settle for just copy-pasting like everyone else has been doing. I just want to express how I'm not happy about that.
**Reviewer note: please only pay attention to the last commit of this PR, until its blocker is merged.**
Since this depends on the previous PR:
`@rustbot` blocked

Author: Kobzol

library/std/src/lib.rs

@@ -281,9 +281,11 @@
 #![feature(cfg_target_thread_local)]
 #![feature(cfi_encoding)]
 #![feature(char_max_len)]
+#![feature(const_trait_impl)]
 #![feature(core_float_math)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
+#![feature(derive_const)]
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(doc_masked)]
@@ -329,6 +331,10 @@
 #![feature(bstr_internals)]
 #![feature(char_internals)]
 #![feature(clone_to_uninit)]
+#![feature(const_cmp)]
+#![feature(const_ops)]
+#![feature(const_option_ops)]
+#![feature(const_try)]
 #![feature(core_intrinsics)]
 #![feature(core_io_borrowed_buf)]
 #![feature(drop_guard)]

library/std/src/sys/pal/hermit/time.rs

@@ -25,8 +25,15 @@ impl Timespec {
 Timespec{t:timespec{ tv_sec, tv_nsec }}
 }
 
-fnsub_timespec(&self,other:&Timespec) -> Result<Duration,Duration>{
-ifself >= other {
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnsub_timespec(&self,other:&Timespec) -> Result<Duration,Duration>{
+// FIXME: const PartialOrd
+letmut cmp = self.t.tv_sec - other.t.tv_sec;
+if cmp == 0{
+ cmp = self.t.tv_nsecasi64 - other.t.tv_nsecasi64;
+}
+
+if cmp >= 0{
 Ok(ifself.t.tv_nsec >= other.t.tv_nsec{
 Duration::new(
 (self.t.tv_sec - other.t.tv_sec)asu64,
@@ -46,20 +53,22 @@ impl Timespec {
 }
 }
 
-fnchecked_add_duration(&self,other:&Duration) -> Option<Timespec>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnchecked_add_duration(&self,other:&Duration) -> Option<Timespec>{
 letmut secs = self.t.tv_sec.checked_add_unsigned(other.as_secs())?;
 
 // Nano calculations can't overflow because nanos are <1B which fit
 // in a u32.
-letmut nsec = other.subsec_nanos() + u32::try_from(self.t.tv_nsec).unwrap();
-if nsec >= NSEC_PER_SEC.try_into().unwrap(){
- nsec -= u32::try_from(NSEC_PER_SEC).unwrap();
+letmut nsec = other.subsec_nanos() + self.t.tv_nsecasu32;
+if nsec >= NSEC_PER_SECasu32{
+ nsec -= NSEC_PER_SECasu32;
  secs = secs.checked_add(1)?;
 }
 Some(Timespec{t:timespec{tv_sec: secs,tv_nsec: nsec as_}})
 }
 
-fnchecked_sub_duration(&self,other:&Duration) -> Option<Timespec>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnchecked_sub_duration(&self,other:&Duration) -> Option<Timespec>{
 letmut secs = self.t.tv_sec.checked_sub_unsigned(other.as_secs())?;
 
 // Similar to above, nanos can't overflow.
@@ -213,15 +222,18 @@ impl SystemTime {
 SystemTime(time)
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
 self.0.sub_timespec(&other.0)
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_add_duration(other)?))
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_sub_duration(other)?))
 }
 }

library/std/src/sys/pal/sgx/time.rs

@@ -32,15 +32,22 @@ impl SystemTime {
 SystemTime(usercalls::insecure_time())
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
-self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+// FIXME: ok_or_else with const closures
+matchself.0.checked_sub(other.0){
+Some(duration) => Ok(duration),
+None => Err(other.0 - self.0),
+}
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_add(*other)?))
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_sub(*other)?))
 }
 }

library/std/src/sys/pal/solid/time.rs

@@ -39,19 +39,22 @@ impl SystemTime {
 Self(t)
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
 ifself.0 >= other.0{
 Ok(Duration::from_secs((self.0asu64).wrapping_sub(other.0asu64)))
 }else{
 Err(Duration::from_secs((other.0asu64).wrapping_sub(self.0asu64)))
 }
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_add_unsigned(other.as_secs())?))
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_sub_unsigned(other.as_secs())?))
 }
 }

library/std/src/sys/pal/uefi/time.rs

@@ -80,19 +80,32 @@ impl SystemTime {
 .unwrap_or_else(|| panic!("time not implemented on this platform"))
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
-self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+// FIXME: ok_or_else with const closures
+matchself.0.checked_sub(other.0){
+Some(duration) => Ok(duration),
+None => Err(other.0 - self.0),
+}
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
-let temp = Self(self.0.checked_add(*other)?);
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+let temp = self.0.checked_add(*other)?;
 
 // Check if can be represented in UEFI
-if temp <= MAX_UEFI_TIME{Some(temp)}else{None}
+// FIXME: const PartialOrd
+letmut cmp = temp.as_secs() - MAX_UEFI_TIME.0.as_secs();
+if cmp == 0{
+ cmp = temp.subsec_nanos()asu64 - MAX_UEFI_TIME.0.subsec_nanos()asu64;
+}
+
+if cmp <= 0{Some(SystemTime(temp))}else{None}
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
-self.0.checked_sub(*other).map(Self)
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+Some(SystemTime(self.0.checked_sub(*other)?))
 }
 }
 

library/std/src/sys/pal/unix/time.rs

@@ -38,15 +38,18 @@ impl SystemTime {
 SystemTime{t:Timespec::now(libc::CLOCK_REALTIME)}
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
 self.t.sub_timespec(&other.t)
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime{t:self.t.checked_add_duration(other)? })
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime{t:self.t.checked_sub_duration(other)? })
 }
 }
@@ -133,8 +136,15 @@ impl Timespec {
 Timespec::new(t.tv_secasi64, t.tv_nsecasi64).unwrap()
 }
 
-pubfnsub_timespec(&self,other:&Timespec) -> Result<Duration,Duration>{
-ifself >= other {
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_timespec(&self,other:&Timespec) -> Result<Duration,Duration>{
+// FIXME: const PartialOrd
+letmut cmp = self.tv_sec - other.tv_sec;
+if cmp == 0{
+ cmp = self.tv_nsec.as_inner()asi64 - other.tv_nsec.as_inner()asi64;
+}
+
+if cmp >= 0{
 // NOTE(eddyb) two aspects of this `if`-`else` are required for LLVM
 // to optimize it into a branchless form (see also #75545):
 //
@@ -169,7 +179,8 @@ impl Timespec {
 }
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<Timespec>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<Timespec>{
 letmut secs = self.tv_sec.checked_add_unsigned(other.as_secs())?;
 
 // Nano calculations can't overflow because nanos are <1B which fit
@@ -179,10 +190,11 @@ impl Timespec {
  nsec -= NSEC_PER_SECasu32;
  secs = secs.checked_add(1)?;
 }
-Some(unsafe{Timespec::new_unchecked(secs, nsec.into())})
+Some(unsafe{Timespec::new_unchecked(secs, nsecasi64)})
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<Timespec>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<Timespec>{
 letmut secs = self.tv_sec.checked_sub_unsigned(other.as_secs())?;
 
 // Similar to above, nanos can't overflow.
@@ -191,7 +203,7 @@ impl Timespec {
  nsec += NSEC_PER_SECasi32;
  secs = secs.checked_sub(1)?;
 }
-Some(unsafe{Timespec::new_unchecked(secs, nsec.into())})
+Some(unsafe{Timespec::new_unchecked(secs, nsecasi64)})
 }
 
 #[allow(dead_code)]

library/std/src/sys/pal/unsupported/time.rs

@@ -31,15 +31,22 @@ impl SystemTime {
 panic!("time not implemented on this platform")
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
-self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+// FIXME: ok_or_else with const closures
+matchself.0.checked_sub(other.0){
+Some(duration) => Ok(duration),
+None => Err(other.0 - self.0),
+}
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_add(*other)?))
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_sub(*other)?))
 }
 }

library/std/src/sys/pal/wasi/time.rs

@@ -43,23 +43,34 @@ impl SystemTime {
 SystemTime(current_time(wasi::CLOCKID_REALTIME))
 }
 
-pubfnfrom_wasi_timestamp(ts: wasi::Timestamp) -> SystemTime{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnfrom_wasi_timestamp(ts: wasi::Timestamp) -> SystemTime{
 SystemTime(Duration::from_nanos(ts))
 }
 
-pubfnto_wasi_timestamp(&self) -> Option<wasi::Timestamp>{
-self.0.as_nanos().try_into().ok()
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnto_wasi_timestamp(&self) -> Option<wasi::Timestamp>{
+// FIXME: const TryInto
+let ns = self.0.as_nanos();
+if ns <= u64::MAXasu128{Some(ns asu64)}else{None}
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
-self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+// FIXME: ok_or_else with const closures
+matchself.0.checked_sub(other.0){
+Some(duration) => Ok(duration),
+None => Err(other.0 - self.0),
+}
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_add(*other)?))
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 Some(SystemTime(self.0.checked_sub(*other)?))
 }
 }

library/std/src/sys/pal/windows/time.rs

@@ -72,7 +72,8 @@ impl SystemTime {
 }
 }
 
-fnfrom_intervals(intervals:i64) -> SystemTime{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnfrom_intervals(intervals:i64) -> SystemTime{
 SystemTime{
 t: c::FILETIME{
 dwLowDateTime: intervals asu32,
@@ -81,11 +82,13 @@ impl SystemTime {
 }
 }
 
-fnintervals(&self) -> i64{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnintervals(&self) -> i64{
 (self.t.dwLowDateTimeasi64) | ((self.t.dwHighDateTimeasi64) << 32)
 }
 
-pubfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnsub_time(&self,other:&SystemTime) -> Result<Duration,Duration>{
 let me = self.intervals();
 let other = other.intervals();
 if me >= other {
@@ -95,12 +98,14 @@ impl SystemTime {
 }
 }
 
-pubfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_add_duration(&self,other:&Duration) -> Option<SystemTime>{
 let intervals = self.intervals().checked_add(checked_dur2intervals(other)?)?;
 Some(SystemTime::from_intervals(intervals))
 }
 
-pubfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+pubconstfnchecked_sub_duration(&self,other:&Duration) -> Option<SystemTime>{
 let intervals = self.intervals().checked_sub(checked_dur2intervals(other)?)?;
 Some(SystemTime::from_intervals(intervals))
 }
@@ -150,15 +155,18 @@ impl Hash for SystemTime {
 }
 }
 
-fnchecked_dur2intervals(dur:&Duration) -> Option<i64>{
- dur.as_secs()
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnchecked_dur2intervals(dur:&Duration) -> Option<i64>{
+// FIXME: const TryInto
+let secs = dur
+.as_secs()
 .checked_mul(INTERVALS_PER_SEC)?
-.checked_add(dur.subsec_nanos()asu64 / 100)?
-.try_into()
-.ok()
+.checked_add(dur.subsec_nanos()asu64 / 100)?;
+if secs <= i64::MAXasu64{Some(secs.cast_signed())}else{None}
 }
 
-fnintervals2dur(intervals:u64) -> Duration{
+#[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
+constfnintervals2dur(intervals:u64) -> Duration{
 Duration::new(intervals / INTERVALS_PER_SEC,((intervals % INTERVALS_PER_SEC)*100)asu32)
 }