21 files changed, 418 insertions, 158 deletions

diff --git a/src/libstd/Cargo.toml b/src/libstd/Cargo.toml
index 0de9e6fcca5..1c99b091329 100644
--- a/src/libstd/Cargo.toml
+++ b/src/libstd/Cargo.toml
@@ -23,7 +23,7 @@ libc = { version = "0.2.51", default-features = false, features = ['rustc-dep-of
 compiler_builtins = { version = "0.1.16" }
 profiler_builtins = { path = "../libprofiler_builtins", optional = true }
 unwind = { path = "../libunwind" }
-hashbrown = { version = "0.5.0", features = ['rustc-dep-of-std'] }
+hashbrown = { version = "0.6.1", default-features = false, features = ['rustc-dep-of-std'] }
 
 [dependencies.backtrace_rs]
 package = "backtrace"
diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index ff50051ef50..6b0225a1b44 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -2030,6 +2030,31 @@ impl<'a, K, V> Entry<'a, K, V> {
             Vacant(entry) => Vacant(entry),
         }
     }
+
+    /// Sets the value of the entry, and returns an OccupiedEntry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(entry_insert)]
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, String> = HashMap::new();
+    /// let entry = map.entry("poneyland").insert("hoho".to_string());
+    ///
+    /// assert_eq!(entry.key(), &"poneyland");
+    /// ```
+    #[inline]
+    #[unstable(feature = "entry_insert", issue = "65225")]
+    pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V> {
+        match self {
+            Occupied(mut entry) => {
+                entry.insert(value);
+                entry
+            },
+            Vacant(entry) => entry.insert_entry(value),
+        }
+    }
 }
 
 impl<'a, K, V: Default> Entry<'a, K, V> {
@@ -2347,6 +2372,28 @@ impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
     pub fn insert(self, value: V) -> &'a mut V {
         self.base.insert(value)
     }
+
+    /// Sets the value of the entry with the VacantEntry's key,
+    /// and returns an OccupiedEntry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// if let Entry::Vacant(o) = map.entry("poneyland") {
+    ///     o.insert(37);
+    /// }
+    /// assert_eq!(map["poneyland"], 37);
+    /// ```
+    #[inline]
+    fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V> {
+        let base = self.base.insert_entry(value);
+        OccupiedEntry { base }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -2362,6 +2409,8 @@ where
     }
 }
 
+/// Inserts all new key-values from the iterator and replaces values with existing
+/// keys with new values returned from the iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
 where
diff --git a/src/libstd/error.rs b/src/libstd/error.rs
index 4a1bb75d588..6b9a35fccc4 100644
--- a/src/libstd/error.rs
+++ b/src/libstd/error.rs
@@ -269,8 +269,8 @@ impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
-    /// Converts a type of [`Error`] + [`trait@Send`] + [`trait@Sync`] into a box of
-    /// dyn [`Error`] + [`trait@Send`] + [`trait@Sync`].
+    /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of
+    /// dyn [`Error`] + [`Send`] + [`Sync`].
     ///
     /// [`Error`]: ../error/trait.Error.html
     ///
@@ -313,7 +313,7 @@ impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync +
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl From<String> for Box<dyn Error + Send + Sync> {
-    /// Converts a [`String`] into a box of dyn [`Error`] + [`trait@Send`] + [`trait@Sync`].
+    /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     ///
     /// [`Error`]: ../error/trait.Error.html
     ///
@@ -377,7 +377,7 @@ impl From<String> for Box<dyn Error> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
-    /// Converts a [`str`] into a box of dyn [`Error`] + [`trait@Send`] + [`trait@Sync`].
+    /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     ///
     /// [`Error`]: ../error/trait.Error.html
     ///
@@ -420,7 +420,7 @@ impl From<&str> for Box<dyn Error> {
 
 #[stable(feature = "cow_box_error", since = "1.22.0")]
 impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
-    /// Converts a [`Cow`] into a box of dyn [`Error`] + [`trait@Send`] + [`trait@Sync`].
+    /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     ///
     /// [`Cow`]: ../borrow/enum.Cow.html
     /// [`Error`]: ../error/trait.Error.html
diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index d7f4cc5d1fd..483f2ba52ec 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -919,7 +919,7 @@ impl Error for IntoStringError {
         "C string contained non-utf8 bytes"
     }
 
-    fn cause(&self) -> Option<&dyn Error> {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
         Some(&self.error)
     }
 }
diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index 8933f027a06..6595f54162f 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -1090,13 +1090,14 @@ impl Metadata {
 
     /// Returns the creation time listed in this metadata.
     ///
-    /// The returned value corresponds to the `birthtime` field of `stat` on
-    /// Unix platforms and the `ftCreationTime` field on Windows platforms.
+    /// The returned value corresponds to the `btime` field of `statx` on
+    /// Linux kernel starting from to 4.11, the `birthtime` field of `stat` on other
+    /// Unix platforms, and the `ftCreationTime` field on Windows platforms.
     ///
     /// # Errors
     ///
     /// This field may not be available on all platforms, and will return an
-    /// `Err` on platforms where it is not available.
+    /// `Err` on platforms or filesystems where it is not available.
     ///
     /// # Examples
     ///
@@ -1109,7 +1110,7 @@ impl Metadata {
     ///     if let Ok(time) = metadata.created() {
     ///         println!("{:?}", time);
     ///     } else {
-    ///         println!("Not supported on this platform");
+    ///         println!("Not supported on this platform or filesystem");
     ///     }
     ///     Ok(())
     /// }
@@ -3112,8 +3113,10 @@ mod tests {
 
         #[cfg(windows)]
         let invalid_options = 87; // ERROR_INVALID_PARAMETER
-        #[cfg(unix)]
+        #[cfg(all(unix, not(target_os = "vxworks")))]
         let invalid_options = "Invalid argument";
+        #[cfg(target_os = "vxworks")]
+        let invalid_options = "invalid argument";
 
         // Test various combinations of creation modes and access modes.
         //
@@ -3441,5 +3444,18 @@ mod tests {
             check!(a.created());
             check!(b.created());
         }
+
+        if cfg!(target_os = "linux") {
+            // Not always available
+            match (a.created(), b.created()) {
+                (Ok(t1), Ok(t2)) => assert!(t1 <= t2),
+                (Err(e1), Err(e2)) if e1.kind() == ErrorKind::Other &&
+                                      e2.kind() == ErrorKind::Other => {}
+                (a, b) => panic!(
+                    "creation time must be always supported or not supported: {:?} {:?}",
+                    a, b,
+                ),
+            }
+        }
     }
 }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 5ff32d7adaf..af6cb656444 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -277,7 +277,6 @@
 #![feature(log_syntax)]
 #![feature(maybe_uninit_ref)]
 #![feature(maybe_uninit_slice)]
-#![feature(mem_take)]
 #![feature(needs_panic_runtime)]
 #![feature(never_type)]
 #![feature(nll)]
diff --git a/src/libstd/net/udp.rs b/src/libstd/net/udp.rs
index a5e7cd992f2..46bbd8855de 100644
--- a/src/libstd/net/udp.rs
+++ b/src/libstd/net/udp.rs
@@ -185,7 +185,6 @@ impl UdpSocket {
     /// # Examples
     ///
     /// ```no_run
-    /// #![feature(udp_peer_addr)]
     /// use std::net::{Ipv4Addr, SocketAddr, SocketAddrV4, UdpSocket};
     ///
     /// let socket = UdpSocket::bind("127.0.0.1:34254").expect("couldn't bind to address");
@@ -199,14 +198,13 @@ impl UdpSocket {
     /// [`NotConnected`]: ../../std/io/enum.ErrorKind.html#variant.NotConnected
     ///
     /// ```no_run
-    /// #![feature(udp_peer_addr)]
     /// use std::net::UdpSocket;
     ///
     /// let socket = UdpSocket::bind("127.0.0.1:34254").expect("couldn't bind to address");
     /// assert_eq!(socket.peer_addr().unwrap_err().kind(),
     ///            ::std::io::ErrorKind::NotConnected);
     /// ```
-    #[unstable(feature = "udp_peer_addr", issue = "59127")]
+    #[stable(feature = "udp_peer_addr", since = "1.40.0")]
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
         self.0.peer_addr()
     }
diff --git a/src/libstd/panic.rs b/src/libstd/panic.rs
index 1d4fd98dd75..24c693790e8 100644
--- a/src/libstd/panic.rs
+++ b/src/libstd/panic.rs
@@ -12,7 +12,9 @@ use crate::ops::{Deref, DerefMut};
 use crate::panicking;
 use crate::ptr::{Unique, NonNull};
 use crate::rc::Rc;
-use crate::sync::{Arc, Mutex, RwLock, atomic};
+use crate::sync::{Arc, Mutex, RwLock};
+#[cfg(not(bootstrap))]
+use crate::sync::atomic;
 use crate::task::{Context, Poll};
 use crate::thread::Result;
 
@@ -240,49 +242,49 @@ impl<T: ?Sized> RefUnwindSafe for Mutex<T> {}
 #[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")]
 impl<T: ?Sized> RefUnwindSafe for RwLock<T> {}
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(target_has_atomic_load_store = "ptr")]
 #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")]
 impl RefUnwindSafe for atomic::AtomicIsize {}
-#[cfg(target_has_atomic = "8")]
+#[cfg(target_has_atomic_load_store = "8")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicI8 {}
-#[cfg(target_has_atomic = "16")]
+#[cfg(target_has_atomic_load_store = "16")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicI16 {}
-#[cfg(target_has_atomic = "32")]
+#[cfg(target_has_atomic_load_store = "32")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicI32 {}
-#[cfg(target_has_atomic = "64")]
+#[cfg(target_has_atomic_load_store = "64")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicI64 {}
-#[cfg(target_has_atomic = "128")]
+#[cfg(target_has_atomic_load_store = "128")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicI128 {}
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(target_has_atomic_load_store = "ptr")]
 #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")]
 impl RefUnwindSafe for atomic::AtomicUsize {}
-#[cfg(target_has_atomic = "8")]
+#[cfg(target_hastarget_has_atomic_load_store_atomic = "8")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicU8 {}
-#[cfg(target_has_atomic = "16")]
+#[cfg(target_has_atomic_load_store = "16")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicU16 {}
-#[cfg(target_has_atomic = "32")]
+#[cfg(target_has_atomic_load_store = "32")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicU32 {}
-#[cfg(target_has_atomic = "64")]
+#[cfg(target_has_atomic_load_store = "64")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicU64 {}
-#[cfg(target_has_atomic = "128")]
+#[cfg(target_has_atomic_load_store = "128")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicU128 {}
 
-#[cfg(target_has_atomic = "8")]
+#[cfg(target_has_atomic_load_store = "8")]
 #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")]
 impl RefUnwindSafe for atomic::AtomicBool {}
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(target_has_atomic_load_store = "ptr")]
 #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")]
 impl<T> RefUnwindSafe for atomic::AtomicPtr<T> {}
 
diff --git a/src/libstd/panicking.rs b/src/libstd/panicking.rs
index 28fb4024404..638ce1679b8 100644
--- a/src/libstd/panicking.rs
+++ b/src/libstd/panicking.rs
@@ -15,9 +15,11 @@ use crate::intrinsics;
 use crate::mem;
 use crate::ptr;
 use crate::raw;
+use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sys::stdio::panic_output;
 use crate::sys_common::rwlock::RWLock;
-use crate::sys_common::{thread_info, util, backtrace};
+use crate::sys_common::{thread_info, util};
+use crate::sys_common::backtrace::{self, RustBacktrace};
 use crate::thread;
 
 #[cfg(not(test))]
@@ -158,16 +160,10 @@ pub fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
 fn default_hook(info: &PanicInfo<'_>) {
     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
-    let log_backtrace = if cfg!(feature = "backtrace") {
-        let panics = update_panic_count(0);
-
-        if panics >= 2 {
-            Some(backtrace_rs::PrintFmt::Full)
-        } else {
-            backtrace::log_enabled()
-        }
+    let backtrace_env = if update_panic_count(0) >= 2 {
+        RustBacktrace::Print(backtrace_rs::PrintFmt::Full)
     } else {
-        None
+        backtrace::rust_backtrace_env()
     };
 
     // The current implementation always returns `Some`.
@@ -187,16 +183,16 @@ fn default_hook(info: &PanicInfo<'_>) {
         let _ = writeln!(err, "thread '{}' panicked at '{}', {}",
                          name, msg, location);
 
-        if cfg!(feature = "backtrace") {
-            use crate::sync::atomic::{AtomicBool, Ordering};
-
-            static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
+        static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 
-            if let Some(format) = log_backtrace {
-                let _ = backtrace::print(err, format);
-            } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
-                let _ = writeln!(err, "note: run with `RUST_BACKTRACE=1` \
-                                       environment variable to display a backtrace.");
+        match backtrace_env {
+            RustBacktrace::Print(format) => drop(backtrace::print(err, format)),
+            RustBacktrace::Disabled => {}
+            RustBacktrace::RuntimeDisabled => {
+                if FIRST_PANIC.swap(false, Ordering::SeqCst) {
+                    let _ = writeln!(err, "note: run with `RUST_BACKTRACE=1` \
+                                           environment variable to display a backtrace.");
+                }
             }
         }
     };
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index fd6ff1032bb..ca81044ee85 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1627,7 +1627,7 @@ impl<'a> From<Cow<'a, Path>> for PathBuf {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<PathBuf> for Arc<Path> {
-    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
+    /// Converts a `PathBuf` into an `Arc` by moving the `PathBuf` data into a new `Arc` buffer.
     #[inline]
     fn from(s: PathBuf) -> Arc<Path> {
         let arc: Arc<OsStr> = Arc::from(s.into_os_string());
@@ -1637,7 +1637,7 @@ impl From<PathBuf> for Arc<Path> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<&Path> for Arc<Path> {
-    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
+    /// Converts a `Path` into an `Arc` by copying the `Path` data into a new `Arc` buffer.
     #[inline]
     fn from(s: &Path) -> Arc<Path> {
         let arc: Arc<OsStr> = Arc::from(s.as_os_str());
@@ -1647,7 +1647,7 @@ impl From<&Path> for Arc<Path> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<PathBuf> for Rc<Path> {
-    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
+    /// Converts a `PathBuf` into an `Rc` by moving the `PathBuf` data into a new `Rc` buffer.
     #[inline]
     fn from(s: PathBuf) -> Rc<Path> {
         let rc: Rc<OsStr> = Rc::from(s.into_os_string());
@@ -1657,7 +1657,7 @@ impl From<PathBuf> for Rc<Path> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<&Path> for Rc<Path> {
-    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
+    /// Converts a `Path` into an `Rc` by copying the `Path` data into a new `Rc` buffer.
     #[inline]
     fn from(s: &Path) -> Rc<Path> {
         let rc: Rc<OsStr> = Rc::from(s.as_os_str());
@@ -2219,6 +2219,7 @@ impl Path {
     /// assert_eq!(Path::new("/etc").join("passwd"), PathBuf::from("/etc/passwd"));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn join<P: AsRef<Path>>(&self, path: P) -> PathBuf {
         self._join(path.as_ref())
     }
diff --git a/src/libstd/rt.rs b/src/libstd/rt.rs
index cf45eb0daba..63e35d5ed91 100644
--- a/src/libstd/rt.rs
+++ b/src/libstd/rt.rs
@@ -44,12 +44,9 @@ fn lang_start_internal(main: &(dyn Fn() -> i32 + Sync + crate::panic::RefUnwindS
         sys::args::init(argc, argv);
 
         // Let's run some code!
-        #[cfg(feature = "backtrace")]
         let exit_code = panic::catch_unwind(|| {
             sys_common::backtrace::__rust_begin_short_backtrace(move || main())
         });
-        #[cfg(not(feature = "backtrace"))]
-        let exit_code = panic::catch_unwind(move || main());
 
         sys_common::cleanup();
         exit_code.unwrap_or(101) as isize
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index 69ecd201063..c2884a28f3c 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -1581,10 +1581,6 @@ impl<T: Send> error::Error for SendError<T> {
     fn description(&self) -> &str {
         "sending on a closed channel"
     }
-
-    fn cause(&self) -> Option<&dyn error::Error> {
-        None
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1624,10 +1620,6 @@ impl<T: Send> error::Error for TrySendError<T> {
             }
         }
     }
-
-    fn cause(&self) -> Option<&dyn error::Error> {
-        None
-    }
 }
 
 #[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
@@ -1652,10 +1644,6 @@ impl error::Error for RecvError {
     fn description(&self) -> &str {
         "receiving on a closed channel"
     }
-
-    fn cause(&self) -> Option<&dyn error::Error> {
-        None
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1685,10 +1673,6 @@ impl error::Error for TryRecvError {
             }
         }
     }
-
-    fn cause(&self) -> Option<&dyn error::Error> {
-        None
-    }
 }
 
 #[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
@@ -1726,10 +1710,6 @@ impl error::Error for RecvTimeoutError {
             }
         }
     }
-
-    fn cause(&self) -> Option<&dyn error::Error> {
-        None
-    }
 }
 
 #[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index e529b8c4227..e28fbca7fa1 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -60,10 +60,9 @@ use crate::thread::{self, Thread};
 
 /// A synchronization primitive which can be used to run a one-time global
 /// initialization. Useful for one-time initialization for FFI or related
-/// functionality. This type can only be constructed with the [`ONCE_INIT`]
-/// value or the equivalent [`Once::new`] constructor.
+/// functionality. This type can only be constructed with the [`Once::new`]
+/// constructor.
 ///
-/// [`ONCE_INIT`]: constant.ONCE_INIT.html
 /// [`Once::new`]: struct.Once.html#method.new
 ///
 /// # Examples
diff --git a/src/libstd/sys/unix/fs.rs b/src/libstd/sys/unix/fs.rs
index c2064fca23e..4054cb1f9c5 100644
--- a/src/libstd/sys/unix/fs.rs
+++ b/src/libstd/sys/unix/fs.rs
@@ -41,11 +41,138 @@ pub use crate::sys_common::fs::remove_dir_all;
 
 pub struct File(FileDesc);
 
-#[derive(Clone)]
-pub struct FileAttr {
-    stat: stat64,
+// FIXME: This should be available on Linux with all `target_arch` and `target_env`.
+// https://github.com/rust-lang/libc/issues/1545
+macro_rules! cfg_has_statx {
+    ({ $($then_tt:tt)* } else { $($else_tt:tt)* }) => {
+        cfg_if::cfg_if! {
+            if #[cfg(all(target_os = "linux", target_env = "gnu", any(
+                target_arch = "x86",
+                target_arch = "arm",
+                // target_arch = "mips",
+                target_arch = "powerpc",
+                target_arch = "x86_64",
+                // target_arch = "aarch64",
+                target_arch = "powerpc64",
+                // target_arch = "mips64",
+                // target_arch = "s390x",
+                target_arch = "sparc64",
+            )))] {
+                $($then_tt)*
+            } else {
+                $($else_tt)*
+            }
+        }
+    };
+    ($($block_inner:tt)*) => {
+        #[cfg(all(target_os = "linux", target_env = "gnu", any(
+            target_arch = "x86",
+            target_arch = "arm",
+            // target_arch = "mips",
+            target_arch = "powerpc",
+            target_arch = "x86_64",
+            // target_arch = "aarch64",
+            target_arch = "powerpc64",
+            // target_arch = "mips64",
+            // target_arch = "s390x",
+            target_arch = "sparc64",
+        )))]
+        {
+            $($block_inner)*
+        }
+    };
 }
 
+cfg_has_statx! {{
+    #[derive(Clone)]
+    pub struct FileAttr {
+        stat: stat64,
+        statx_extra_fields: Option<StatxExtraFields>,
+    }
+
+    #[derive(Clone)]
+    struct StatxExtraFields {
+        // This is needed to check if btime is supported by the filesystem.
+        stx_mask: u32,
+        stx_btime: libc::statx_timestamp,
+    }
+
+    // We prefer `statx` on Linux if available, which contains file creation time.
+    // Default `stat64` contains no creation time.
+    unsafe fn try_statx(
+        fd: c_int,
+        path: *const libc::c_char,
+        flags: i32,
+        mask: u32,
+    ) -> Option<io::Result<FileAttr>> {
+        use crate::sync::atomic::{AtomicBool, Ordering};
+
+        // Linux kernel prior to 4.11 or glibc prior to glibc 2.28 don't support `statx`
+        // We store the availability in a global to avoid unnecessary syscalls
+        static HAS_STATX: AtomicBool = AtomicBool::new(true);
+        syscall! {
+            fn statx(
+                fd: c_int,
+                pathname: *const libc::c_char,
+                flags: c_int,
+                mask: libc::c_uint,
+                statxbuf: *mut libc::statx
+            ) -> c_int
+        }
+
+        if !HAS_STATX.load(Ordering::Relaxed) {
+            return None;
+        }
+
+        let mut buf: libc::statx = mem::zeroed();
+        let ret = cvt(statx(fd, path, flags, mask, &mut buf));
+        match ret {
+            Err(err) => match err.raw_os_error() {
+                Some(libc::ENOSYS) => {
+                    HAS_STATX.store(false, Ordering::Relaxed);
+                    return None;
+                }
+                _ => return Some(Err(err)),
+            }
+            Ok(_) => {
+                // We cannot fill `stat64` exhaustively because of private padding fields.
+                let mut stat: stat64 = mem::zeroed();
+                // `c_ulong` on gnu-mips, `dev_t` otherwise
+                stat.st_dev = libc::makedev(buf.stx_dev_major, buf.stx_dev_minor) as _;
+                stat.st_ino = buf.stx_ino as libc::ino64_t;
+                stat.st_nlink = buf.stx_nlink as libc::nlink_t;
+                stat.st_mode = buf.stx_mode as libc::mode_t;
+                stat.st_uid = buf.stx_uid as libc::uid_t;
+                stat.st_gid = buf.stx_gid as libc::gid_t;
+                stat.st_rdev = libc::makedev(buf.stx_rdev_major, buf.stx_rdev_minor) as _;
+                stat.st_size = buf.stx_size as off64_t;
+                stat.st_blksize = buf.stx_blksize as libc::blksize_t;
+                stat.st_blocks = buf.stx_blocks as libc::blkcnt64_t;
+                stat.st_atime = buf.stx_atime.tv_sec as libc::time_t;
+                // `i64` on gnu-x86_64-x32, `c_ulong` otherwise.
+                stat.st_atime_nsec = buf.stx_atime.tv_nsec as _;
+                stat.st_mtime = buf.stx_mtime.tv_sec as libc::time_t;
+                stat.st_mtime_nsec = buf.stx_mtime.tv_nsec as _;
+                stat.st_ctime = buf.stx_ctime.tv_sec as libc::time_t;
+                stat.st_ctime_nsec = buf.stx_ctime.tv_nsec as _;
+
+                let extra = StatxExtraFields {
+                    stx_mask: buf.stx_mask,
+                    stx_btime: buf.stx_btime,
+                };
+
+                Some(Ok(FileAttr { stat, statx_extra_fields: Some(extra) }))
+            }
+        }
+    }
+
+} else {
+    #[derive(Clone)]
+    pub struct FileAttr {
+        stat: stat64,
+    }
+}}
+
 // all DirEntry's will have a reference to this struct
 struct InnerReadDir {
     dirp: Dir,
@@ -97,6 +224,20 @@ pub struct FileType { mode: mode_t }
 #[derive(Debug)]
 pub struct DirBuilder { mode: mode_t }
 
+cfg_has_statx! {{
+    impl FileAttr {
+        fn from_stat64(stat: stat64) -> Self {
+            Self { stat, statx_extra_fields: None }
+        }
+    }
+} else {
+    impl FileAttr {
+        fn from_stat64(stat: stat64) -> Self {
+            Self { stat }
+        }
+    }
+}}
+
 impl FileAttr {
     pub fn size(&self) -> u64 { self.stat.st_size as u64 }
     pub fn perm(&self) -> FilePermissions {
@@ -164,6 +305,22 @@ impl FileAttr {
                   target_os = "macos",
                   target_os = "ios")))]
     pub fn created(&self) -> io::Result<SystemTime> {
+        cfg_has_statx! {
+            if let Some(ext) = &self.statx_extra_fields {
+                return if (ext.stx_mask & libc::STATX_BTIME) != 0 {
+                    Ok(SystemTime::from(libc::timespec {
+                        tv_sec: ext.stx_btime.tv_sec as libc::time_t,
+                        tv_nsec: ext.stx_btime.tv_nsec as _,
+                    }))
+                } else {
+                    Err(io::Error::new(
+                        io::ErrorKind::Other,
+                        "creation time is not available for the filesystem",
+                    ))
+                };
+            }
+        }
+
         Err(io::Error::new(io::ErrorKind::Other,
                            "creation time is not available on this platform \
                             currently"))
@@ -306,12 +463,25 @@ impl DirEntry {
 
     #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
     pub fn metadata(&self) -> io::Result<FileAttr> {
-        let fd = cvt(unsafe {dirfd(self.dir.inner.dirp.0)})?;
+        let fd = cvt(unsafe { dirfd(self.dir.inner.dirp.0) })?;
+        let name = self.entry.d_name.as_ptr();
+
+        cfg_has_statx! {
+            if let Some(ret) = unsafe { try_statx(
+                fd,
+                name,
+                libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
+                libc::STATX_ALL,
+            ) } {
+                return ret;
+            }
+        }
+
         let mut stat: stat64 = unsafe { mem::zeroed() };
         cvt(unsafe {
-            fstatat64(fd, self.entry.d_name.as_ptr(), &mut stat, libc::AT_SYMLINK_NOFOLLOW)
+            fstatat64(fd, name, &mut stat, libc::AT_SYMLINK_NOFOLLOW)
         })?;
-        Ok(FileAttr { stat })
+        Ok(FileAttr::from_stat64(stat))
     }
 
     #[cfg(not(any(target_os = "linux", target_os = "emscripten", target_os = "android")))]
@@ -515,11 +685,24 @@ impl File {
     }
 
     pub fn file_attr(&self) -> io::Result<FileAttr> {
+        let fd = self.0.raw();
+
+        cfg_has_statx! {
+            if let Some(ret) = unsafe { try_statx(
+                fd,
+                b"\0" as *const _ as *const libc::c_char,
+                libc::AT_EMPTY_PATH | libc::AT_STATX_SYNC_AS_STAT,
+                libc::STATX_ALL,
+            ) } {
+                return ret;
+            }
+        }
+
         let mut stat: stat64 = unsafe { mem::zeroed() };
         cvt(unsafe {
-            fstat64(self.0.raw(), &mut stat)
+            fstat64(fd, &mut stat)
         })?;
-        Ok(FileAttr { stat })
+        Ok(FileAttr::from_stat64(stat))
     }
 
     pub fn fsync(&self) -> io::Result<()> {
@@ -796,20 +979,44 @@ pub fn link(src: &Path, dst: &Path) -> io::Result<()> {
 
 pub fn stat(p: &Path) -> io::Result<FileAttr> {
     let p = cstr(p)?;
+
+    cfg_has_statx! {
+        if let Some(ret) = unsafe { try_statx(
+            libc::AT_FDCWD,
+            p.as_ptr(),
+            libc::AT_STATX_SYNC_AS_STAT,
+            libc::STATX_ALL,
+        ) } {
+            return ret;
+        }
+    }
+
     let mut stat: stat64 = unsafe { mem::zeroed() };
     cvt(unsafe {
         stat64(p.as_ptr(), &mut stat)
     })?;
-    Ok(FileAttr { stat })
+    Ok(FileAttr::from_stat64(stat))
 }
 
 pub fn lstat(p: &Path) -> io::Result<FileAttr> {
     let p = cstr(p)?;
+
+    cfg_has_statx! {
+        if let Some(ret) = unsafe { try_statx(
+            libc::AT_FDCWD,
+            p.as_ptr(),
+            libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
+            libc::STATX_ALL,
+        ) } {
+            return ret;
+        }
+    }
+
     let mut stat: stat64 = unsafe { mem::zeroed() };
     cvt(unsafe {
         lstat64(p.as_ptr(), &mut stat)
     })?;
-    Ok(FileAttr { stat })
+    Ok(FileAttr::from_stat64(stat))
 }
 
 pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
diff --git a/src/libstd/sys/vxworks/fs.rs b/src/libstd/sys/vxworks/fs.rs
index 51fdb1c0e55..adb08d8005a 100644
--- a/src/libstd/sys/vxworks/fs.rs
+++ b/src/libstd/sys/vxworks/fs.rs
@@ -400,13 +400,27 @@ impl FromInner<c_int> for File {
 
 impl fmt::Debug for File {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fn get_path(_fd: c_int) -> Option<PathBuf> {
-            // FIXME(#:(): implement this for VxWorks
-            None
+        fn get_path(fd: c_int) -> Option<PathBuf> {
+            let mut buf = vec![0;libc::PATH_MAX as usize];
+            let n = unsafe { libc::ioctl(fd, libc::FIOGETNAME, buf.as_ptr()) };
+            if n == -1 {
+                return None;
+            }
+            let l = buf.iter().position(|&c| c == 0).unwrap();
+            buf.truncate(l as usize);
+            Some(PathBuf::from(OsString::from_vec(buf)))
         }
-        fn get_mode(_fd: c_int) -> Option<(bool, bool)> {
-            // FIXME(#:(): implement this for VxWorks
-            None
+        fn get_mode(fd: c_int) -> Option<(bool, bool)> {
+            let mode = unsafe { libc::fcntl(fd, libc::F_GETFL) };
+            if mode == -1 {
+                return None;
+            }
+            match mode & libc::O_ACCMODE {
+                libc::O_RDONLY => Some((true, false)),
+                libc::O_RDWR => Some((true, true)),
+                libc::O_WRONLY => Some((false, true)),
+                _ => None
+            }
         }
 
         let fd = self.0.raw();
diff --git a/src/libstd/sys/vxworks/rwlock.rs b/src/libstd/sys/vxworks/rwlock.rs
index 718f422ed11..19b123f2b61 100644
--- a/src/libstd/sys/vxworks/rwlock.rs
+++ b/src/libstd/sys/vxworks/rwlock.rs
@@ -25,7 +25,7 @@ impl RWLock {
         let r = libc::pthread_rwlock_rdlock(self.inner.get());
         if r == libc::EAGAIN {
             panic!("rwlock maximum reader count exceeded");
-        } else if r == libc::EDEADLK || *self.write_locked.get() {
+        } else if r == libc::EDEADLK || (r == 0 && *self.write_locked.get()) {
             if r == 0 {
                 self.raw_unlock();
             }
diff --git a/src/libstd/sys/windows/fs.rs b/src/libstd/sys/windows/fs.rs
index 204f6af5fc1..4160123c9a2 100644
--- a/src/libstd/sys/windows/fs.rs
+++ b/src/libstd/sys/windows/fs.rs
@@ -412,7 +412,7 @@ impl File {
 
     pub fn duplicate(&self) -> io::Result<File> {
         Ok(File {
-            handle: self.handle.duplicate(0, true, c::DUPLICATE_SAME_ACCESS)?,
+            handle: self.handle.duplicate(0, false, c::DUPLICATE_SAME_ACCESS)?,
         })
     }
 
diff --git a/src/libstd/sys_common/backtrace.rs b/src/libstd/sys_common/backtrace.rs
index 01711d415d8..9c406ec39cc 100644
--- a/src/libstd/sys_common/backtrace.rs
+++ b/src/libstd/sys_common/backtrace.rs
@@ -7,6 +7,7 @@ use crate::io;
 use crate::borrow::Cow;
 use crate::io::prelude::*;
 use crate::path::{self, Path, PathBuf};
+use crate::sync::atomic::{self, Ordering};
 use crate::sys::mutex::Mutex;
 
 use backtrace_rs::{BacktraceFmt, BytesOrWideString, PrintFmt};
@@ -115,8 +116,10 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
     Ok(())
 }
 
-/// Fixed frame used to clean the backtrace with `RUST_BACKTRACE=1`.
-#[inline(never)]
+/// Fixed frame used to clean the backtrace with `RUST_BACKTRACE=1`. Note that
+/// this is only inline(never) when backtraces in libstd are enabled, otherwise
+/// it's fine to optimize away.
+#[cfg_attr(feature = "backtrace", inline(never))]
 pub fn __rust_begin_short_backtrace<F, T>(f: F) -> T
 where
     F: FnOnce() -> T,
@@ -126,42 +129,49 @@ where
     f()
 }
 
+pub enum RustBacktrace {
+    Print(PrintFmt),
+    Disabled,
+    RuntimeDisabled,
+}
+
 // For now logging is turned off by default, and this function checks to see
 // whether the magical environment variable is present to see if it's turned on.
-pub fn log_enabled() -> Option<PrintFmt> {
-    use crate::sync::atomic::{self, Ordering};
+pub fn rust_backtrace_env() -> RustBacktrace {
+    // If the `backtrace` feature of this crate isn't enabled quickly return
+    // `None` so this can be constant propagated all over the place to turn
+    // optimize away callers.
+    if !cfg!(feature = "backtrace") {
+        return RustBacktrace::Disabled;
+    }
 
     // Setting environment variables for Fuchsia components isn't a standard
     // or easily supported workflow. For now, always display backtraces.
     if cfg!(target_os = "fuchsia") {
-        return Some(PrintFmt::Full);
+        return RustBacktrace::Print(PrintFmt::Full);
     }
 
     static ENABLED: atomic::AtomicIsize = atomic::AtomicIsize::new(0);
     match ENABLED.load(Ordering::SeqCst) {
         0 => {}
-        1 => return None,
-        2 => return Some(PrintFmt::Short),
-        _ => return Some(PrintFmt::Full),
+        1 => return RustBacktrace::RuntimeDisabled,
+        2 => return RustBacktrace::Print(PrintFmt::Short),
+        _ => return RustBacktrace::Print(PrintFmt::Full),
     }
 
-    let val = env::var_os("RUST_BACKTRACE").and_then(|x| {
-        if &x == "0" {
-            None
-        } else if &x == "full" {
-            Some(PrintFmt::Full)
-        } else {
-            Some(PrintFmt::Short)
-        }
-    });
-    ENABLED.store(
-        match val {
-            Some(v) => v as isize,
-            None => 1,
-        },
-        Ordering::SeqCst,
-    );
-    val
+    let (format, cache) = env::var_os("RUST_BACKTRACE")
+        .map(|x| {
+            if &x == "0" {
+                (RustBacktrace::RuntimeDisabled, 1)
+            } else if &x == "full" {
+                (RustBacktrace::Print(PrintFmt::Full), 3)
+            } else {
+                (RustBacktrace::Print(PrintFmt::Short), 2)
+            }
+        })
+        .unwrap_or((RustBacktrace::RuntimeDisabled, 1));
+    ENABLED.store(cache, Ordering::SeqCst);
+    format
 }
 
 /// Prints the filename of the backtrace frame.
diff --git a/src/libstd/sys_common/os_str_bytes.rs b/src/libstd/sys_common/os_str_bytes.rs
index d734f412bf8..3753269adfe 100644
--- a/src/libstd/sys_common/os_str_bytes.rs
+++ b/src/libstd/sys_common/os_str_bytes.rs
@@ -193,7 +193,7 @@ impl Slice {
 pub trait OsStringExt {
     /// Creates an [`OsString`] from a byte vector.
     ///
-    /// See the module docmentation for an example.
+    /// See the module documentation for an example.
     ///
     /// [`OsString`]: ../../../ffi/struct.OsString.html
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -201,7 +201,7 @@ pub trait OsStringExt {
 
     /// Yields the underlying byte vector of this [`OsString`].
     ///
-    /// See the module docmentation for an example.
+    /// See the module documentation for an example.
     ///
     /// [`OsString`]: ../../../ffi/struct.OsString.html
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -226,14 +226,14 @@ pub trait OsStrExt {
     #[stable(feature = "rust1", since = "1.0.0")]
     /// Creates an [`OsStr`] from a byte slice.
     ///
-    /// See the module docmentation for an example.
+    /// See the module documentation for an example.
     ///
     /// [`OsStr`]: ../../../ffi/struct.OsStr.html
     fn from_bytes(slice: &[u8]) -> &Self;
 
     /// Gets the underlying byte view of the [`OsStr`] slice.
     ///
-    /// See the module docmentation for an example.
+    /// See the module documentation for an example.
     ///
     /// [`OsStr`]: ../../../ffi/struct.OsStr.html
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 764041d2f42..0ffa6ace2e4 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -465,12 +465,9 @@ impl Builder {
             }
 
             thread_info::set(imp::guard::current(), their_thread);
-            #[cfg(feature = "backtrace")]
             let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
                 crate::sys_common::backtrace::__rust_begin_short_backtrace(f)
             }));
-            #[cfg(not(feature = "backtrace"))]
-            let try_result = panic::catch_unwind(panic::AssertUnwindSafe(f));
             *their_packet.get() = Some(try_result);
         };
 
diff --git a/src/libstd/time.rs b/src/libstd/time.rs
index 3bf2b8be1fe..e1ae01b602a 100644
--- a/src/libstd/time.rs
+++ b/src/libstd/time.rs
@@ -15,10 +15,10 @@
 use crate::cmp;
 use crate::error::Error;
 use crate::fmt;
-use crate::ops::{Add, Sub, AddAssign, SubAssign};
+use crate::ops::{Add, AddAssign, Sub, SubAssign};
 use crate::sys::time;
-use crate::sys_common::FromInner;
 use crate::sys_common::mutex::Mutex;
+use crate::sys_common::FromInner;
 
 #[stable(feature = "time", since = "1.3.0")]
 pub use core::time::Duration;
@@ -216,17 +216,17 @@ impl Instant {
         // * https://bugzilla.mozilla.org/show_bug.cgi?id=1487778 - a similar
         //   Firefox bug
         //
-        // It simply seems that this it just happens so that a lot in the wild
-        // we're seeing panics across various platforms where consecutive calls
+        // It seems that this just happens a lot in the wild.
+        // We're seeing panics across various platforms where consecutive calls
         // to `Instant::now`, such as via the `elapsed` function, are panicking
         // as they're going backwards. Placed here is a last-ditch effort to try
         // to fix things up. We keep a global "latest now" instance which is
         // returned instead of what the OS says if the OS goes backwards.
         //
-        // To hopefully mitigate the impact of this though a few platforms are
+        // To hopefully mitigate the impact of this, a few platforms are
         // whitelisted as "these at least haven't gone backwards yet".
         if time::Instant::actually_monotonic() {
-            return Instant(os_now)
+            return Instant(os_now);
         }
 
         static LOCK: Mutex = Mutex::new();
@@ -353,8 +353,7 @@ impl Add<Duration> for Instant {
     ///
     /// [`checked_add`]: ../../std/time/struct.Instant.html#method.checked_add
     fn add(self, other: Duration) -> Instant {
-        self.checked_add(other)
-            .expect("overflow when adding duration to instant")
+        self.checked_add(other).expect("overflow when adding duration to instant")
     }
 }
 
@@ -370,8 +369,7 @@ impl Sub<Duration> for Instant {
     type Output = Instant;
 
     fn sub(self, other: Duration) -> Instant {
-        self.checked_sub(other)
-            .expect("overflow when subtracting duration from instant")
+        self.checked_sub(other).expect("overflow when subtracting duration from instant")
     }
 }
 
@@ -464,8 +462,7 @@ impl SystemTime {
     /// println!("{:?}", difference);
     /// ```
     #[stable(feature = "time2", since = "1.8.0")]
-    pub fn duration_since(&self, earlier: SystemTime)
-                          -> Result<Duration, SystemTimeError> {
+    pub fn duration_since(&self, earlier: SystemTime) -> Result<Duration, SystemTimeError> {
         self.0.sub_time(&earlier.0).map_err(SystemTimeError)
     }
 
@@ -532,8 +529,7 @@ impl Add<Duration> for SystemTime {
     ///
     /// [`checked_add`]: ../../std/time/struct.SystemTime.html#method.checked_add
     fn add(self, dur: Duration) -> SystemTime {
-        self.checked_add(dur)
-            .expect("overflow when adding duration to instant")
+        self.checked_add(dur).expect("overflow when adding duration to instant")
     }
 }
 
@@ -549,8 +545,7 @@ impl Sub<Duration> for SystemTime {
     type Output = SystemTime;
 
     fn sub(self, dur: Duration) -> SystemTime {
-        self.checked_sub(dur)
-            .expect("overflow when subtracting duration from instant")
+        self.checked_sub(dur).expect("overflow when subtracting duration from instant")
     }
 }
 
@@ -626,7 +621,9 @@ impl SystemTimeError {
 
 #[stable(feature = "time2", since = "1.8.0")]
 impl Error for SystemTimeError {
-    fn description(&self) -> &str { "other time was not earlier than self" }
+    fn description(&self) -> &str {
+        "other time was not earlier than self"
+    }
 }
 
 #[stable(feature = "time2", since = "1.8.0")]
@@ -644,17 +641,16 @@ impl FromInner<time::SystemTime> for SystemTime {
 
 #[cfg(test)]
 mod tests {
-    use super::{Instant, SystemTime, Duration, UNIX_EPOCH};
+    use super::{Duration, Instant, SystemTime, UNIX_EPOCH};
 
     macro_rules! assert_almost_eq {
-        ($a:expr, $b:expr) => ({
+        ($a:expr, $b:expr) => {{
             let (a, b) = ($a, $b);
             if a != b {
-                let (a, b) = if a > b {(a, b)} else {(b, a)};
-                assert!(a - Duration::new(0, 1000) <= b,
-                        "{:?} is not almost equal to {:?}", a, b);
+                let (a, b) = if a > b { (a, b) } else { (b, a) };
+                assert!(a - Duration::new(0, 1000) <= b, "{:?} is not almost equal to {:?}", a, b);
             }
-        })
+        }};
     }
 
     #[test]
@@ -729,7 +725,7 @@ mod tests {
     fn instant_saturating_duration_since_nopanic() {
         let a = Instant::now();
         let ret = (a - Duration::new(1, 0)).saturating_duration_since(a);
-        assert_eq!(ret, Duration::new(0,0));
+        assert_eq!(ret, Duration::new(0, 0));
     }
 
     #[test]
@@ -755,15 +751,14 @@ mod tests {
 
         let second = Duration::new(1, 0);
         assert_almost_eq!(a.duration_since(a - second).unwrap(), second);
-        assert_almost_eq!(a.duration_since(a + second).unwrap_err()
-                           .duration(), second);
+        assert_almost_eq!(a.duration_since(a + second).unwrap_err().duration(), second);
 
         assert_almost_eq!(a - second + second, a);
         assert_almost_eq!(a.checked_sub(second).unwrap().checked_add(second).unwrap(), a);
 
         let one_second_from_epoch = UNIX_EPOCH + Duration::new(1, 0);
-        let one_second_from_epoch2 = UNIX_EPOCH + Duration::new(0, 500_000_000)
-            + Duration::new(0, 500_000_000);
+        let one_second_from_epoch2 =
+            UNIX_EPOCH + Duration::new(0, 500_000_000) + Duration::new(0, 500_000_000);
         assert_eq!(one_second_from_epoch, one_second_from_epoch2);
 
         // checked_add_duration will not panic on overflow