Auto merge of #56490 - faern:add-checked-add-to-instant, r=alexcrichton

Add checked_add method to Instant time type

Appending functionality to the already opened topic of `checked_add` on time types over at #55940.

Doing checked addition between an `Instant` and a `Duration` is important to reliably determine a future instant. We could use this in the `parking_lot` crate to compute an instant when in the future to wake a thread up without risking a panic.

8 files changed, 103 insertions, 162 deletions

diff --git a/src/libstd/sys/cloudabi/condvar.rs b/src/libstd/sys/cloudabi/condvar.rs
index ccf848a9be4..3229d98624e 100644
--- a/src/libstd/sys/cloudabi/condvar.rs
+++ b/src/libstd/sys/cloudabi/condvar.rs
@@ -13,7 +13,7 @@ use mem;
 use sync::atomic::{AtomicU32, Ordering};
 use sys::cloudabi::abi;
 use sys::mutex::{self, Mutex};
-use sys::time::dur2intervals;
+use sys::time::checked_dur2intervals;
 use time::Duration;
 
 extern "C" {
@@ -114,6 +114,8 @@ impl Condvar {
 
         // Call into the kernel to wait on the condition variable.
         let condvar = self.condvar.get();
+        let timeout = checked_dur2intervals(&dur)
+            .expect("overflow converting duration to nanoseconds");
         let subscriptions = [
             abi::subscription {
                 type_: abi::eventtype::CONDVAR,
@@ -132,7 +134,7 @@ impl Condvar {
                 union: abi::subscription_union {
                     clock: abi::subscription_clock {
                         clock_id: abi::clockid::MONOTONIC,
-                        timeout: dur2intervals(&dur),
+                        timeout,
                         ..mem::zeroed()
                     },
                 },
diff --git a/src/libstd/sys/cloudabi/thread.rs b/src/libstd/sys/cloudabi/thread.rs
index a76e1fa3345..177321439d8 100644
--- a/src/libstd/sys/cloudabi/thread.rs
+++ b/src/libstd/sys/cloudabi/thread.rs
@@ -16,7 +16,7 @@ use libc;
 use mem;
 use ptr;
 use sys::cloudabi::abi;
-use sys::time::dur2intervals;
+use sys::time::checked_dur2intervals;
 use sys_common::thread::*;
 use time::Duration;
 
@@ -70,13 +70,15 @@ impl Thread {
     }
 
     pub fn sleep(dur: Duration) {
+        let timeout = checked_dur2intervals(&dur)
+            .expect("overflow converting duration to nanoseconds");
         unsafe {
             let subscription = abi::subscription {
                 type_: abi::eventtype::CLOCK,
                 union: abi::subscription_union {
                     clock: abi::subscription_clock {
                         clock_id: abi::clockid::MONOTONIC,
-                        timeout: dur2intervals(&dur),
+                        timeout,
                         ..mem::zeroed()
                     },
                 },
diff --git a/src/libstd/sys/cloudabi/time.rs b/src/libstd/sys/cloudabi/time.rs
index a442d1e4ad7..c9fea18fda6 100644
--- a/src/libstd/sys/cloudabi/time.rs
+++ b/src/libstd/sys/cloudabi/time.rs
@@ -19,15 +19,10 @@ pub struct Instant {
     t: abi::timestamp,
 }
 
-fn checked_dur2intervals(dur: &Duration) -> Option<abi::timestamp> {
+pub fn checked_dur2intervals(dur: &Duration) -> Option<abi::timestamp> {
     dur.as_secs()
-        .checked_mul(NSEC_PER_SEC)
-        .and_then(|nanos| nanos.checked_add(dur.subsec_nanos() as abi::timestamp))
-}
-
-pub fn dur2intervals(dur: &Duration) -> abi::timestamp {
-    checked_dur2intervals(dur)
-        .expect("overflow converting duration to nanoseconds")
+        .checked_mul(NSEC_PER_SEC)?
+        .checked_add(dur.subsec_nanos() as abi::timestamp)
 }
 
 impl Instant {
@@ -47,20 +42,16 @@ impl Instant {
         Duration::new(diff / NSEC_PER_SEC, (diff % NSEC_PER_SEC) as u32)
     }
 
-    pub fn add_duration(&self, other: &Duration) -> Instant {
-        Instant {
-            t: self.t
-                .checked_add(dur2intervals(other))
-                .expect("overflow when adding duration to instant"),
-        }
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant {
+            t: self.t.checked_add(checked_dur2intervals(other)?)?,
+        })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> Instant {
-        Instant {
-            t: self.t
-                .checked_sub(dur2intervals(other))
-                .expect("overflow when subtracting duration from instant"),
-        }
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant {
+            t: self.t.checked_sub(checked_dur2intervals(other)?)?,
+        })
     }
 }
 
@@ -95,23 +86,16 @@ impl SystemTime {
         }
     }
 
-    pub fn add_duration(&self, other: &Duration) -> SystemTime {
-        self.checked_add_duration(other)
-            .expect("overflow when adding duration to instant")
-    }
-
     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-        checked_dur2intervals(other)
-            .and_then(|d| self.t.checked_add(d))
-            .map(|t| SystemTime {t})
+        Some(SystemTime {
+            t: self.t.checked_add(checked_dur2intervals(other)?)?,
+        })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime {
-            t: self.t
-                .checked_sub(dur2intervals(other))
-                .expect("overflow when subtracting duration from instant"),
-        }
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        Some(SystemTime {
+            t: self.t.checked_sub(checked_dur2intervals(other)?)?,
+        })
     }
 }
 
diff --git a/src/libstd/sys/redox/time.rs b/src/libstd/sys/redox/time.rs
index beff8d287e7..cb2eab52211 100644
--- a/src/libstd/sys/redox/time.rs
+++ b/src/libstd/sys/redox/time.rs
@@ -41,10 +41,6 @@ impl Timespec {
         }
     }
 
-    fn add_duration(&self, other: &Duration) -> Timespec {
-        self.checked_add_duration(other).expect("overflow when adding duration to time")
-    }
-
     fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = other
             .as_secs()
@@ -67,27 +63,25 @@ impl Timespec {
         })
     }
 
-    fn sub_duration(&self, other: &Duration) -> Timespec {
+    fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = other
             .as_secs()
             .try_into() // <- target type would be `i64`
             .ok()
-            .and_then(|secs| self.t.tv_sec.checked_sub(secs))
-            .expect("overflow when subtracting duration from time");
+            .and_then(|secs| self.t.tv_sec.checked_sub(secs))?;
 
         // Similar to above, nanos can't overflow.
         let mut nsec = self.t.tv_nsec as i32 - other.subsec_nanos() as i32;
         if nsec < 0 {
             nsec += NSEC_PER_SEC as i32;
-            secs = secs.checked_sub(1).expect("overflow when subtracting \
-                                               duration from time");
+            secs = secs.checked_sub(1)?;
         }
-        Timespec {
+        Some(Timespec {
             t: syscall::TimeSpec {
                 tv_sec: secs,
                 tv_nsec: nsec as i32,
             },
-        }
+        })
     }
 }
 
@@ -150,12 +144,12 @@ impl Instant {
         })
     }
 
-    pub fn add_duration(&self, other: &Duration) -> Instant {
-        Instant { t: self.t.add_duration(other) }
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant { t: self.t.checked_add_duration(other)? })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> Instant {
-        Instant { t: self.t.sub_duration(other) }
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant { t: self.t.checked_sub_duration(other)? })
     }
 }
 
@@ -178,16 +172,12 @@ impl SystemTime {
         self.t.sub_timespec(&other.t)
     }
 
-    pub fn add_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime { t: self.t.add_duration(other) }
-    }
-
     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-        self.t.checked_add_duration(other).map(|t| SystemTime { t })
+        Some(SystemTime { t: self.t.checked_add_duration(other)? })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime { t: self.t.sub_duration(other) }
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        Some(SystemTime { t: self.t.checked_sub_duration(other)? })
     }
 }
 
diff --git a/src/libstd/sys/sgx/time.rs b/src/libstd/sys/sgx/time.rs
index b01c992768e..196e1a97fc4 100644
--- a/src/libstd/sys/sgx/time.rs
+++ b/src/libstd/sys/sgx/time.rs
@@ -28,12 +28,12 @@ impl Instant {
         self.0 - other.0
     }
 
-    pub fn add_duration(&self, other: &Duration) -> Instant {
-        Instant(self.0 + *other)
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant(self.0.checked_add(*other)?))
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> Instant {
-        Instant(self.0 - *other)
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant(self.0.checked_sub(*other)?))
     }
 }
 
@@ -47,15 +47,11 @@ impl SystemTime {
         self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
     }
 
-    pub fn add_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime(self.0 + *other)
-    }
-
     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-        self.0.checked_add(*other).map(|d| SystemTime(d))
+        Some(SystemTime(self.0.checked_add(*other)?))
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime(self.0 - *other)
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        Some(SystemTime(self.0.checked_sub(*other)?))
     }
 }
diff --git a/src/libstd/sys/unix/time.rs b/src/libstd/sys/unix/time.rs
index 1f9539c36e0..8f8aaa88b22 100644
--- a/src/libstd/sys/unix/time.rs
+++ b/src/libstd/sys/unix/time.rs
@@ -42,10 +42,6 @@ impl Timespec {
         }
     }
 
-    fn add_duration(&self, other: &Duration) -> Timespec {
-        self.checked_add_duration(other).expect("overflow when adding duration to time")
-    }
-
     fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = other
             .as_secs()
@@ -68,27 +64,25 @@ impl Timespec {
         })
     }
 
-    fn sub_duration(&self, other: &Duration) -> Timespec {
+    fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = other
             .as_secs()
             .try_into() // <- target type would be `libc::time_t`
             .ok()
-            .and_then(|secs| self.t.tv_sec.checked_sub(secs))
-            .expect("overflow when subtracting duration from time");
+            .and_then(|secs| self.t.tv_sec.checked_sub(secs))?;
 
         // Similar to above, nanos can't overflow.
         let mut nsec = self.t.tv_nsec as i32 - other.subsec_nanos() as i32;
         if nsec < 0 {
             nsec += NSEC_PER_SEC as i32;
-            secs = secs.checked_sub(1).expect("overflow when subtracting \
-                                               duration from time");
+            secs = secs.checked_sub(1)?;
         }
-        Timespec {
+        Some(Timespec {
             t: libc::timespec {
                 tv_sec: secs,
                 tv_nsec: nsec as _,
             },
-        }
+        })
     }
 }
 
@@ -165,18 +159,16 @@ mod inner {
             Duration::new(nanos / NSEC_PER_SEC, (nanos % NSEC_PER_SEC) as u32)
         }
 
-        pub fn add_duration(&self, other: &Duration) -> Instant {
-            Instant {
-                t: self.t.checked_add(dur2intervals(other))
-                       .expect("overflow when adding duration to instant"),
-            }
+        pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+            Some(Instant {
+                t: self.t.checked_add(checked_dur2intervals(other)?)?,
+            })
         }
 
-        pub fn sub_duration(&self, other: &Duration) -> Instant {
-            Instant {
-                t: self.t.checked_sub(dur2intervals(other))
-                       .expect("overflow when subtracting duration from instant"),
-            }
+        pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+            Some(Instant {
+                t: self.t.checked_sub(checked_dur2intervals(other)?)?,
+            })
         }
     }
 
@@ -199,16 +191,12 @@ mod inner {
             self.t.sub_timespec(&other.t)
         }
 
-        pub fn add_duration(&self, other: &Duration) -> SystemTime {
-            SystemTime { t: self.t.add_duration(other) }
-        }
-
         pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-            self.t.checked_add_duration(other).map(|t| SystemTime { t })
+            Some(SystemTime { t: self.t.checked_add_duration(other)? })
         }
 
-        pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-            SystemTime { t: self.t.sub_duration(other) }
+        pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+            Some(SystemTime { t: self.t.checked_sub_duration(other)? })
         }
     }
 
@@ -236,12 +224,12 @@ mod inner {
         }
     }
 
-    fn dur2intervals(dur: &Duration) -> u64 {
+    fn checked_dur2intervals(dur: &Duration) -> Option<u64> {
+        let nanos = dur.as_secs()
+            .checked_mul(NSEC_PER_SEC)?
+            .checked_add(dur.subsec_nanos() as u64)?;
         let info = info();
-        let nanos = dur.as_secs().checked_mul(NSEC_PER_SEC).and_then(|nanos| {
-            nanos.checked_add(dur.subsec_nanos() as u64)
-        }).expect("overflow converting duration to nanoseconds");
-        mul_div_u64(nanos, info.denom as u64, info.numer as u64)
+        Some(mul_div_u64(nanos, info.denom as u64, info.numer as u64))
     }
 
     fn info() -> &'static libc::mach_timebase_info {
@@ -299,12 +287,12 @@ mod inner {
             })
         }
 
-        pub fn add_duration(&self, other: &Duration) -> Instant {
-            Instant { t: self.t.add_duration(other) }
+        pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+            Some(Instant { t: self.t.checked_add_duration(other)? })
         }
 
-        pub fn sub_duration(&self, other: &Duration) -> Instant {
-            Instant { t: self.t.sub_duration(other) }
+        pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+            Some(Instant { t: self.t.checked_sub_duration(other)? })
         }
     }
 
@@ -327,16 +315,12 @@ mod inner {
             self.t.sub_timespec(&other.t)
         }
 
-        pub fn add_duration(&self, other: &Duration) -> SystemTime {
-            SystemTime { t: self.t.add_duration(other) }
-        }
-
         pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-            self.t.checked_add_duration(other).map(|t| SystemTime { t })
+            Some(SystemTime { t: self.t.checked_add_duration(other)? })
         }
 
-        pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-            SystemTime { t: self.t.sub_duration(other) }
+        pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+            Some(SystemTime { t: self.t.checked_sub_duration(other)? })
         }
     }
 
diff --git a/src/libstd/sys/wasm/time.rs b/src/libstd/sys/wasm/time.rs
index 991e8176edf..cc56773e0ea 100644
--- a/src/libstd/sys/wasm/time.rs
+++ b/src/libstd/sys/wasm/time.rs
@@ -28,12 +28,12 @@ impl Instant {
         self.0 - other.0
     }
 
-    pub fn add_duration(&self, other: &Duration) -> Instant {
-        Instant(self.0 + *other)
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant(self.0.checked_add(*other)?))
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> Instant {
-        Instant(self.0 - *other)
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant(self.0.checked_sub(*other)?))
     }
 }
 
@@ -47,15 +47,11 @@ impl SystemTime {
         self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
     }
 
-    pub fn add_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime(self.0 + *other)
-    }
-
     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-        self.0.checked_add(*other).map(|d| SystemTime(d))
+        Some(SystemTime(self.0.checked_add(*other)?))
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime(self.0 - *other)
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        Some(SystemTime(self.0.checked_sub(*other)?))
     }
 }
diff --git a/src/libstd/sys/windows/time.rs b/src/libstd/sys/windows/time.rs
index c809a0b98ac..bb2c97ea149 100644
--- a/src/libstd/sys/windows/time.rs
+++ b/src/libstd/sys/windows/time.rs
@@ -68,30 +68,27 @@ impl Instant {
         Duration::new(nanos / NANOS_PER_SEC, (nanos % NANOS_PER_SEC) as u32)
     }
 
-    pub fn add_duration(&self, other: &Duration) -> Instant {
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
         let freq = frequency() as u64;
-        let t = other.as_secs().checked_mul(freq).and_then(|i| {
-            (self.t as u64).checked_add(i)
-        }).and_then(|i| {
-            i.checked_add(mul_div_u64(other.subsec_nanos() as u64, freq,
-                                      NANOS_PER_SEC))
-        }).expect("overflow when adding duration to time");
-        Instant {
+        let t = other.as_secs()
+            .checked_mul(freq)?
+            .checked_add(mul_div_u64(other.subsec_nanos() as u64, freq, NANOS_PER_SEC))?
+            .checked_add(self.t as u64)?;
+        Some(Instant {
             t: t as c::LARGE_INTEGER,
-        }
+        })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> Instant {
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
         let freq = frequency() as u64;
         let t = other.as_secs().checked_mul(freq).and_then(|i| {
             (self.t as u64).checked_sub(i)
         }).and_then(|i| {
-            i.checked_sub(mul_div_u64(other.subsec_nanos() as u64, freq,
-                                      NANOS_PER_SEC))
-        }).expect("overflow when subtracting duration from time");
-        Instant {
+            i.checked_sub(mul_div_u64(other.subsec_nanos() as u64, freq, NANOS_PER_SEC))
+        })?;
+        Some(Instant {
             t: t as c::LARGE_INTEGER,
-        }
+        })
     }
 }
 
@@ -127,20 +124,14 @@ impl SystemTime {
         }
     }
 
-    pub fn add_duration(&self, other: &Duration) -> SystemTime {
-        self.checked_add_duration(other).expect("overflow when adding duration to time")
-    }
-
     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-        checked_dur2intervals(other)
-            .and_then(|d| self.intervals().checked_add(d))
-            .map(|i| SystemTime::from_intervals(i))
+        let intervals = self.intervals().checked_add(checked_dur2intervals(other)?)?;
+        Some(SystemTime::from_intervals(intervals))
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-        let intervals = self.intervals().checked_sub(dur2intervals(other))
-                            .expect("overflow when subtracting from time");
-        SystemTime::from_intervals(intervals)
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        let intervals = self.intervals().checked_sub(checked_dur2intervals(other)?)?;
+        Some(SystemTime::from_intervals(intervals))
     }
 }
 
@@ -184,16 +175,12 @@ impl Hash for SystemTime {
     }
 }
 
-fn checked_dur2intervals(d: &Duration) -> Option<i64> {
-    d.as_secs()
-        .checked_mul(INTERVALS_PER_SEC)
-        .and_then(|i| i.checked_add(d.subsec_nanos() as u64 / 100))
-        .and_then(|i| i.try_into().ok())
-}
-
-fn dur2intervals(d: &Duration) -> i64 {
-    checked_dur2intervals(d)
-        .expect("overflow when converting duration to intervals")
+fn checked_dur2intervals(dur: &Duration) -> Option<i64> {
+    dur.as_secs()
+        .checked_mul(INTERVALS_PER_SEC)?
+        .checked_add(dur.subsec_nanos() as u64 / 100)?
+        .try_into()
+        .ok()
 }
 
 fn intervals2dur(intervals: u64) -> Duration {