From c2b430f6c5b5d27d860cd2f50ea9305d48607fba Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:58:53 -0400
Subject: [PATCH 1/7] Revert "link once_cell feature to #74465"

This reverts commit fe639057086fa7bef1e964bf3a211517b04bc328.
---
 src/libcore/lazy.rs | 42 +++++++++++++++++-----------------
 src/libcore/lib.rs  |  2 +-
 src/libstd/lazy.rs  | 56 ++++++++++++++++++++++-----------------------
 src/libstd/lib.rs   |  2 +-
 4 files changed, 51 insertions(+), 51 deletions(-)

diff --git a/src/libcore/lazy.rs b/src/libcore/lazy.rs
index 5cf7217ef11e8..e9af66ff64264 100644
--- a/src/libcore/lazy.rs
+++ b/src/libcore/lazy.rs
@@ -26,20 +26,20 @@ use crate::ops::Deref;
 /// assert_eq!(value, "Hello, World!");
 /// assert!(cell.get().is_some());
 /// ```
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub struct OnceCell<T> {
     // Invariant: written to at most once.
     inner: UnsafeCell<Option<T>>,
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T> Default for OnceCell<T> {
     fn default() -> Self {
         Self::new()
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.get() {
@@ -49,7 +49,7 @@ impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Clone> Clone for OnceCell<T> {
     fn clone(&self) -> OnceCell<T> {
         let res = OnceCell::new();
@@ -63,17 +63,17 @@ impl<T: Clone> Clone for OnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: PartialEq> PartialEq for OnceCell<T> {
     fn eq(&self, other: &Self) -> bool {
         self.get() == other.get()
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Eq> Eq for OnceCell<T> {}
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T> From<T> for OnceCell<T> {
     fn from(value: T) -> Self {
         OnceCell { inner: UnsafeCell::new(Some(value)) }
@@ -82,7 +82,7 @@ impl<T> From<T> for OnceCell<T> {
 
 impl<T> OnceCell<T> {
     /// Creates a new empty cell.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new() -> OnceCell<T> {
         OnceCell { inner: UnsafeCell::new(None) }
     }
@@ -90,7 +90,7 @@ impl<T> OnceCell<T> {
     /// Gets the reference to the underlying value.
     ///
     /// Returns `None` if the cell is empty.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get(&self) -> Option<&T> {
         // Safety: Safe due to `inner`'s invariant
         unsafe { &*self.inner.get() }.as_ref()
@@ -99,7 +99,7 @@ impl<T> OnceCell<T> {
     /// Gets the mutable reference to the underlying value.
     ///
     /// Returns `None` if the cell is empty.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_mut(&mut self) -> Option<&mut T> {
         // Safety: Safe because we have unique access
         unsafe { &mut *self.inner.get() }.as_mut()
@@ -127,7 +127,7 @@ impl<T> OnceCell<T> {
     ///
     /// assert!(cell.get().is_some());
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn set(&self, value: T) -> Result<(), T> {
         // Safety: Safe because we cannot have overlapping mutable borrows
         let slot = unsafe { &*self.inner.get() };
@@ -168,7 +168,7 @@ impl<T> OnceCell<T> {
     /// let value = cell.get_or_init(|| unreachable!());
     /// assert_eq!(value, &92);
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_or_init<F>(&self, f: F) -> &T
     where
         F: FnOnce() -> T,
@@ -206,7 +206,7 @@ impl<T> OnceCell<T> {
     /// assert_eq!(value, Ok(&92));
     /// assert_eq!(cell.get(), Some(&92))
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
     where
         F: FnOnce() -> Result<T, E>,
@@ -241,7 +241,7 @@ impl<T> OnceCell<T> {
     /// cell.set("hello".to_string()).unwrap();
     /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn into_inner(self) -> Option<T> {
         // Because `into_inner` takes `self` by value, the compiler statically verifies
         // that it is not currently borrowed. So it is safe to move out `Option<T>`.
@@ -269,7 +269,7 @@ impl<T> OnceCell<T> {
     /// assert_eq!(cell.take(), Some("hello".to_string()));
     /// assert_eq!(cell.get(), None);
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn take(&mut self) -> Option<T> {
         mem::take(self).into_inner()
     }
@@ -298,13 +298,13 @@ impl<T> OnceCell<T> {
 /// //   92
 /// //   92
 /// ```
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub struct Lazy<T, F = fn() -> T> {
     cell: OnceCell<T>,
     init: Cell<Option<F>>,
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: fmt::Debug, F> fmt::Debug for Lazy<T, F> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
@@ -329,7 +329,7 @@ impl<T, F> Lazy<T, F> {
     /// assert_eq!(&*lazy, "HELLO, WORLD!");
     /// # }
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new(init: F) -> Lazy<T, F> {
         Lazy { cell: OnceCell::new(), init: Cell::new(Some(init)) }
     }
@@ -353,7 +353,7 @@ impl<T, F: FnOnce() -> T> Lazy<T, F> {
     /// assert_eq!(Lazy::force(&lazy), &92);
     /// assert_eq!(&*lazy, &92);
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn force(this: &Lazy<T, F>) -> &T {
         this.cell.get_or_init(|| match this.init.take() {
             Some(f) => f(),
@@ -362,7 +362,7 @@ impl<T, F: FnOnce() -> T> Lazy<T, F> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
     type Target = T;
     fn deref(&self) -> &T {
@@ -370,7 +370,7 @@ impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Default> Default for Lazy<T> {
     /// Creates a new lazy value using `Default` as the initializing function.
     fn default() -> Lazy<T> {
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 2e443064706d2..4701503d4103e 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -240,7 +240,7 @@ pub mod char;
 pub mod ffi;
 #[cfg(not(test))] // See #65860
 pub mod iter;
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub mod lazy;
 pub mod option;
 pub mod panic;
diff --git a/src/libstd/lazy.rs b/src/libstd/lazy.rs
index 86e1cfae582e8..094eff17f8916 100644
--- a/src/libstd/lazy.rs
+++ b/src/libstd/lazy.rs
@@ -10,7 +10,7 @@ use crate::{
 };
 
 #[doc(inline)]
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub use core::lazy::*;
 
 /// A synchronization primitive which can be written to only once.
@@ -38,7 +38,7 @@ pub use core::lazy::*;
 /// assert!(value.is_some());
 /// assert_eq!(value.unwrap().as_str(), "Hello, World!");
 /// ```
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub struct SyncOnceCell<T> {
     once: Once,
     // Whether or not the value is initialized is tracked by `state_and_queue`.
@@ -50,24 +50,24 @@ pub struct SyncOnceCell<T> {
 // scoped thread B, which fills the cell, which is
 // then destroyed by A. That is, destructor observes
 // a sent value.
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 unsafe impl<T: Sync + Send> Sync for SyncOnceCell<T> {}
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 unsafe impl<T: Send> Send for SyncOnceCell<T> {}
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SyncOnceCell<T> {}
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: UnwindSafe> UnwindSafe for SyncOnceCell<T> {}
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T> Default for SyncOnceCell<T> {
     fn default() -> SyncOnceCell<T> {
         SyncOnceCell::new()
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: fmt::Debug> fmt::Debug for SyncOnceCell<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.get() {
@@ -77,7 +77,7 @@ impl<T: fmt::Debug> fmt::Debug for SyncOnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Clone> Clone for SyncOnceCell<T> {
     fn clone(&self) -> SyncOnceCell<T> {
         let cell = Self::new();
@@ -91,7 +91,7 @@ impl<T: Clone> Clone for SyncOnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T> From<T> for SyncOnceCell<T> {
     fn from(value: T) -> Self {
         let cell = Self::new();
@@ -102,19 +102,19 @@ impl<T> From<T> for SyncOnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: PartialEq> PartialEq for SyncOnceCell<T> {
     fn eq(&self, other: &SyncOnceCell<T>) -> bool {
         self.get() == other.get()
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Eq> Eq for SyncOnceCell<T> {}
 
 impl<T> SyncOnceCell<T> {
     /// Creates a new empty cell.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new() -> SyncOnceCell<T> {
         SyncOnceCell { once: Once::new(), value: UnsafeCell::new(MaybeUninit::uninit()) }
     }
@@ -123,7 +123,7 @@ impl<T> SyncOnceCell<T> {
     ///
     /// Returns `None` if the cell is empty, or being initialized. This
     /// method never blocks.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get(&self) -> Option<&T> {
         if self.is_initialized() {
             // Safe b/c checked is_initialized
@@ -136,7 +136,7 @@ impl<T> SyncOnceCell<T> {
     /// Gets the mutable reference to the underlying value.
     ///
     /// Returns `None` if the cell is empty. This method never blocks.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_mut(&mut self) -> Option<&mut T> {
         if self.is_initialized() {
             // Safe b/c checked is_initialized and we have a unique access
@@ -170,7 +170,7 @@ impl<T> SyncOnceCell<T> {
     ///     assert_eq!(CELL.get(), Some(&92));
     /// }
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn set(&self, value: T) -> Result<(), T> {
         let mut value = Some(value);
         self.get_or_init(|| value.take().unwrap());
@@ -209,7 +209,7 @@ impl<T> SyncOnceCell<T> {
     /// let value = cell.get_or_init(|| unreachable!());
     /// assert_eq!(value, &92);
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_or_init<F>(&self, f: F) -> &T
     where
         F: FnOnce() -> T,
@@ -248,7 +248,7 @@ impl<T> SyncOnceCell<T> {
     /// assert_eq!(value, Ok(&92));
     /// assert_eq!(cell.get(), Some(&92))
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
     where
         F: FnOnce() -> Result<T, E>,
@@ -286,7 +286,7 @@ impl<T> SyncOnceCell<T> {
     /// cell.set("hello".to_string()).unwrap();
     /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn into_inner(mut self) -> Option<T> {
         // Safety: Safe because we immediately free `self` without dropping
         let inner = unsafe { self.take_inner() };
@@ -318,7 +318,7 @@ impl<T> SyncOnceCell<T> {
     /// assert_eq!(cell.take(), Some("hello".to_string()));
     /// assert_eq!(cell.get(), None);
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn take(&mut self) -> Option<T> {
         mem::take(self).into_inner()
     }
@@ -428,13 +428,13 @@ impl<T> Drop for SyncOnceCell<T> {
 ///     //   Some("Hoyten")
 /// }
 /// ```
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub struct SyncLazy<T, F = fn() -> T> {
     cell: SyncOnceCell<T>,
     init: Cell<Option<F>>,
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: fmt::Debug, F> fmt::Debug for SyncLazy<T, F> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
@@ -446,17 +446,17 @@ impl<T: fmt::Debug, F> fmt::Debug for SyncLazy<T, F> {
 // we do create a `&mut Option<F>` in `force`, but this is
 // properly synchronized, so it only happens once
 // so it also does not contribute to this impl.
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 unsafe impl<T, F: Send> Sync for SyncLazy<T, F> where SyncOnceCell<T>: Sync {}
 // auto-derived `Send` impl is OK.
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T, F: RefUnwindSafe> RefUnwindSafe for SyncLazy<T, F> where SyncOnceCell<T>: RefUnwindSafe {}
 
 impl<T, F> SyncLazy<T, F> {
     /// Creates a new lazy value with the given initializing
     /// function.
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new(f: F) -> SyncLazy<T, F> {
         SyncLazy { cell: SyncOnceCell::new(), init: Cell::new(Some(f)) }
     }
@@ -479,7 +479,7 @@ impl<T, F: FnOnce() -> T> SyncLazy<T, F> {
     /// assert_eq!(SyncLazy::force(&lazy), &92);
     /// assert_eq!(&*lazy, &92);
     /// ```
-    #[unstable(feature = "once_cell", issue = "74465")]
+    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn force(this: &SyncLazy<T, F>) -> &T {
         this.cell.get_or_init(|| match this.init.take() {
             Some(f) => f(),
@@ -488,7 +488,7 @@ impl<T, F: FnOnce() -> T> SyncLazy<T, F> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T, F: FnOnce() -> T> Deref for SyncLazy<T, F> {
     type Target = T;
     fn deref(&self) -> &T {
@@ -496,7 +496,7 @@ impl<T, F: FnOnce() -> T> Deref for SyncLazy<T, F> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Default> Default for SyncLazy<T> {
     /// Creates a new lazy value using `Default` as the initializing function.
     fn default() -> SyncLazy<T> {
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 00f2fff94c9a1..21978f0d936f4 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -477,7 +477,7 @@ pub mod process;
 pub mod sync;
 pub mod time;
 
-#[unstable(feature = "once_cell", issue = "74465")]
+#[unstable(feature = "once_cell", issue = "68198")]
 pub mod lazy;
 
 #[stable(feature = "futures_api", since = "1.36.0")]

From 2d907bb619f6d3a667434cf0e2eaa0283af0458b Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:59:10 -0400
Subject: [PATCH 2/7] Revert "include changes to Cargo.lock"

This reverts commit 48844fed2bdc7c40d213131d5e13ab28e47df083.
---
 Cargo.lock | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Cargo.lock b/Cargo.lock
index 8f110403eb842..9b5b6620f79a7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1372,8 +1372,8 @@ checksum = "7e81a7c05f79578dbc15793d8b619db9ba32b4577003ef3af1a91c416798c58d"
 name = "installer"
 version = "0.0.0"
 dependencies = [
- "anyhow",
  "clap",
+ "failure",
  "flate2",
  "lazy_static",
  "num_cpus",

From fd694bb77b563a1a777897ec46229b018e21aa37 Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:59:11 -0400
Subject: [PATCH 3/7] Revert "appease tidy"

This reverts commit 1f1cda65d9a5c88855d3fbcb3912095474e557de.
---
 src/libstd/lazy.rs      | 5 ++++-
 src/libstd/sync/once.rs | 5 +----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/libstd/lazy.rs b/src/libstd/lazy.rs
index 094eff17f8916..761cc2b439f67 100644
--- a/src/libstd/lazy.rs
+++ b/src/libstd/lazy.rs
@@ -116,7 +116,10 @@ impl<T> SyncOnceCell<T> {
     /// Creates a new empty cell.
     #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new() -> SyncOnceCell<T> {
-        SyncOnceCell { once: Once::new(), value: UnsafeCell::new(MaybeUninit::uninit()) }
+        SyncOnceCell {
+            once: Once::new(),
+            value: UnsafeCell::new(MaybeUninit::uninit()),
+        }
     }
 
     /// Gets the reference to the underlying value.
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 64260990824b8..1fce5dc035224 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -414,10 +414,7 @@ impl Once {
                     };
                     // Run the initialization function, letting it know if we're
                     // poisoned or not.
-                    let init_state = OnceState {
-                        poisoned: state_and_queue == POISONED,
-                        set_state_on_drop_to: Cell::new(COMPLETE),
-                    };
+                    let init_state = OnceState { poisoned: state_and_queue == POISONED, set_state_on_drop_to: Cell::new(COMPLETE) };
                     init(&init_state);
                     waiter_queue.set_state_on_drop_to = init_state.set_state_on_drop_to.get();
                     break;

From f9febd507819be60c365d7f3ccd55809309387b3 Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:59:13 -0400
Subject: [PATCH 4/7] Revert "remove inlined lazy::Waiter in favor of
 sync::Once"

This reverts commit d1017940d77f35f841008c3e108e3da5e48a592f.
---
 src/libstd/lazy.rs      | 140 +++++++++++++++++++++++++++++++++++-----
 src/libstd/sync/once.rs |  18 ++----
 2 files changed, 129 insertions(+), 29 deletions(-)

diff --git a/src/libstd/lazy.rs b/src/libstd/lazy.rs
index 761cc2b439f67..aed91df47449f 100644
--- a/src/libstd/lazy.rs
+++ b/src/libstd/lazy.rs
@@ -3,10 +3,12 @@
 use crate::{
     cell::{Cell, UnsafeCell},
     fmt,
+    marker::PhantomData,
     mem::{self, MaybeUninit},
     ops::{Deref, Drop},
     panic::{RefUnwindSafe, UnwindSafe},
-    sync::Once,
+    sync::atomic::{AtomicBool, AtomicUsize, Ordering},
+    thread::{self, Thread},
 };
 
 #[doc(inline)]
@@ -40,7 +42,10 @@ pub use core::lazy::*;
 /// ```
 #[unstable(feature = "once_cell", issue = "68198")]
 pub struct SyncOnceCell<T> {
-    once: Once,
+    // This `state` word is actually an encoded version of just a pointer to a
+    // `Waiter`, so we add the `PhantomData` appropriately.
+    state_and_queue: AtomicUsize,
+    _marker: PhantomData<*mut Waiter>,
     // Whether or not the value is initialized is tracked by `state_and_queue`.
     value: UnsafeCell<MaybeUninit<T>>,
 }
@@ -117,7 +122,8 @@ impl<T> SyncOnceCell<T> {
     #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new() -> SyncOnceCell<T> {
         SyncOnceCell {
-            once: Once::new(),
+            state_and_queue: AtomicUsize::new(INCOMPLETE),
+            _marker: PhantomData,
             value: UnsafeCell::new(MaybeUninit::uninit()),
         }
     }
@@ -129,7 +135,7 @@ impl<T> SyncOnceCell<T> {
     #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get(&self) -> Option<&T> {
         if self.is_initialized() {
-            // Safe b/c checked is_initialized
+            // Safe b/c checked is_initialize
             Some(unsafe { self.get_unchecked() })
         } else {
             None
@@ -142,7 +148,7 @@ impl<T> SyncOnceCell<T> {
     #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_mut(&mut self) -> Option<&mut T> {
         if self.is_initialized() {
-            // Safe b/c checked is_initialized and we have a unique access
+            // Safe b/c checked is_initialize and we have a unique access
             Some(unsafe { self.get_unchecked_mut() })
         } else {
             None
@@ -344,32 +350,37 @@ impl<T> SyncOnceCell<T> {
         }
     }
 
+    /// Safety: synchronizes with store to value via Release/(Acquire|SeqCst).
     #[inline]
     fn is_initialized(&self) -> bool {
-        self.once.is_completed()
+        // An `Acquire` load is enough because that makes all the initialization
+        // operations visible to us, and, this being a fast path, weaker
+        // ordering helps with performance. This `Acquire` synchronizes with
+        // `SeqCst` operations on the slow path.
+        self.state_and_queue.load(Ordering::Acquire) == COMPLETE
     }
 
+    /// Safety: synchronizes with store to value via SeqCst read from state,
+    /// writes value only once because we never get to INCOMPLETE state after a
+    /// successful write.
     #[cold]
     fn initialize<F, E>(&self, f: F) -> Result<(), E>
     where
         F: FnOnce() -> Result<T, E>,
     {
+        let mut f = Some(f);
         let mut res: Result<(), E> = Ok(());
         let slot = &self.value;
-
-        // Ignore poisoning from other threads
-        // If another thread panics, then we'll be able to run our closure
-        self.once.call_once_force(|p| {
+        initialize_inner(&self.state_and_queue, &mut || {
+            let f = f.take().unwrap();
             match f() {
                 Ok(value) => {
                     unsafe { (&mut *slot.get()).write(value) };
+                    true
                 }
                 Err(e) => {
                     res = Err(e);
-
-                    // Treat the underlying `Once` as poisoned since we
-                    // failed to initialize our value. Calls
-                    p.poison();
+                    false
                 }
             }
         });
@@ -396,6 +407,106 @@ impl<T> Drop for SyncOnceCell<T> {
     }
 }
 
+const INCOMPLETE: usize = 0x0;
+const RUNNING: usize = 0x1;
+const COMPLETE: usize = 0x2;
+
+const STATE_MASK: usize = 0x3;
+
+// The alignment here is so that we can stash the state in the lower
+// bits of the `next` pointer
+#[repr(align(4))]
+struct Waiter {
+    thread: Cell<Option<Thread>>,
+    signaled: AtomicBool,
+    next: *const Waiter,
+}
+
+struct WaiterQueue<'a> {
+    state_and_queue: &'a AtomicUsize,
+    set_state_on_drop_to: usize,
+}
+
+impl Drop for WaiterQueue<'_> {
+    fn drop(&mut self) {
+        let state_and_queue =
+            self.state_and_queue.swap(self.set_state_on_drop_to, Ordering::AcqRel);
+
+        assert_eq!(state_and_queue & STATE_MASK, RUNNING);
+
+        unsafe {
+            let mut queue = (state_and_queue & !STATE_MASK) as *const Waiter;
+            while !queue.is_null() {
+                let next = (*queue).next;
+                let thread = (*queue).thread.replace(None).unwrap();
+                (*queue).signaled.store(true, Ordering::Release);
+                queue = next;
+                thread.unpark();
+            }
+        }
+    }
+}
+
+fn initialize_inner(my_state_and_queue: &AtomicUsize, init: &mut dyn FnMut() -> bool) -> bool {
+    let mut state_and_queue = my_state_and_queue.load(Ordering::Acquire);
+
+    loop {
+        match state_and_queue {
+            COMPLETE => return true,
+            INCOMPLETE => {
+                let old = my_state_and_queue.compare_and_swap(
+                    state_and_queue,
+                    RUNNING,
+                    Ordering::Acquire,
+                );
+                if old != state_and_queue {
+                    state_and_queue = old;
+                    continue;
+                }
+                let mut waiter_queue = WaiterQueue {
+                    state_and_queue: my_state_and_queue,
+                    set_state_on_drop_to: INCOMPLETE,
+                };
+                let success = init();
+
+                waiter_queue.set_state_on_drop_to = if success { COMPLETE } else { INCOMPLETE };
+                return success;
+            }
+            _ => {
+                assert!(state_and_queue & STATE_MASK == RUNNING);
+                wait(&my_state_and_queue, state_and_queue);
+                state_and_queue = my_state_and_queue.load(Ordering::Acquire);
+            }
+        }
+    }
+}
+
+fn wait(state_and_queue: &AtomicUsize, mut current_state: usize) {
+    loop {
+        if current_state & STATE_MASK != RUNNING {
+            return;
+        }
+
+        let node = Waiter {
+            thread: Cell::new(Some(thread::current())),
+            signaled: AtomicBool::new(false),
+            next: (current_state & !STATE_MASK) as *const Waiter,
+        };
+        let me = &node as *const Waiter as usize;
+
+        let old = state_and_queue.compare_and_swap(current_state, me | RUNNING, Ordering::Release);
+        if old != current_state {
+            current_state = old;
+            continue;
+        }
+
+        while !node.signaled.load(Ordering::Acquire) {
+            thread::park();
+        }
+        break;
+    }
+}
+
 /// A value which is initialized on the first access.
 ///
 /// This type is a thread-safe `Lazy`, and can be used in statics.
@@ -652,7 +763,6 @@ mod tests {
 
         let res = panic::catch_unwind(|| cell.get_or_try_init(|| -> Result<_, ()> { panic!() }));
         assert!(res.is_err());
-        assert!(!cell.is_initialized());
         assert!(cell.get().is_none());
 
         assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 1fce5dc035224..7dc822db3d027 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -132,7 +132,6 @@ unsafe impl Send for Once {}
 #[derive(Debug)]
 pub struct OnceState {
     poisoned: bool,
-    set_state_on_drop_to: Cell<usize>,
 }
 
 /// Initialization value for static [`Once`] values.
@@ -322,7 +321,7 @@ impl Once {
         }
 
         let mut f = Some(f);
-        self.call_inner(true, &mut |p| f.take().unwrap()(p));
+        self.call_inner(true, &mut |p| f.take().unwrap()(&OnceState { poisoned: p }));
     }
 
     /// Returns `true` if some `call_once` call has completed
@@ -386,7 +385,7 @@ impl Once {
     // currently no way to take an `FnOnce` and call it via virtual dispatch
     // without some allocation overhead.
     #[cold]
-    fn call_inner(&self, ignore_poisoning: bool, init: &mut dyn FnMut(&OnceState)) {
+    fn call_inner(&self, ignore_poisoning: bool, init: &mut dyn FnMut(bool)) {
         let mut state_and_queue = self.state_and_queue.load(Ordering::Acquire);
         loop {
             match state_and_queue {
@@ -414,9 +413,8 @@ impl Once {
                     };
                     // Run the initialization function, letting it know if we're
                     // poisoned or not.
-                    let init_state = OnceState { poisoned: state_and_queue == POISONED, set_state_on_drop_to: Cell::new(COMPLETE) };
-                    init(&init_state);
-                    waiter_queue.set_state_on_drop_to = init_state.set_state_on_drop_to.get();
+                    init(state_and_queue == POISONED);
+                    waiter_queue.set_state_on_drop_to = COMPLETE;
                     break;
                 }
                 _ => {
@@ -556,14 +554,6 @@ impl OnceState {
     pub fn poisoned(&self) -> bool {
         self.poisoned
     }
-
-    /// Poison the associated [`Once`] without explicitly panicking.
-    ///
-    /// [`Once`]: struct.Once.html
-    // NOTE: This is currently only exposed for the `lazy` module
-    pub(crate) fn poison(&self) {
-        self.set_state_on_drop_to.set(POISONED);
-    }
 }
 
 #[cfg(all(test, not(target_os = "emscripten")))]

From fffb1bdc6b4b1d6ab181dce5024a29e261f61299 Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:59:14 -0400
Subject: [PATCH 5/7] Revert "use set() in SyncOnceCell::from"

This reverts commit d1263f5e66d31ad170c524a70aa5f21e08474326.
---
 src/libstd/lazy.rs | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/src/libstd/lazy.rs b/src/libstd/lazy.rs
index aed91df47449f..c7553caa4c056 100644
--- a/src/libstd/lazy.rs
+++ b/src/libstd/lazy.rs
@@ -85,14 +85,14 @@ impl<T: fmt::Debug> fmt::Debug for SyncOnceCell<T> {
 #[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Clone> Clone for SyncOnceCell<T> {
     fn clone(&self) -> SyncOnceCell<T> {
-        let cell = Self::new();
+        let res = SyncOnceCell::new();
         if let Some(value) = self.get() {
-            match cell.set(value.clone()) {
+            match res.set(value.clone()) {
                 Ok(()) => (),
                 Err(_) => unreachable!(),
             }
         }
-        cell
+        res
     }
 }
 
@@ -100,10 +100,8 @@ impl<T: Clone> Clone for SyncOnceCell<T> {
 impl<T> From<T> for SyncOnceCell<T> {
     fn from(value: T) -> Self {
         let cell = Self::new();
-        match cell.set(value) {
-            Ok(()) => cell,
-            Err(_) => unreachable!(),
-        }
+        cell.get_or_init(|| value);
+        cell
     }
 }
 
@@ -157,7 +155,8 @@ impl<T> SyncOnceCell<T> {
 
     /// Sets the contents of this cell to `value`.
     ///
-    /// Returns `Ok(())` if the cell's value was updated.
+    /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was
+    /// full.
     ///
     /// # Examples
     ///
@@ -263,10 +262,8 @@ impl<T> SyncOnceCell<T> {
         F: FnOnce() -> Result<T, E>,
     {
         // Fast path check
-        // NOTE: We need to perform an acquire on the state in this method
-        // in order to correctly synchronize `SyncLazy::force`. This is
-        // currently done by calling `self.get()`, which in turn calls
-        // `self.is_initialized()`, which in turn performs the acquire.
+        // NOTE: This acquire here is important to ensure
+        // `SyncLazy::force` is correctly synchronized
         if let Some(value) = self.get() {
             return Ok(value);
         }
@@ -413,8 +410,6 @@ const COMPLETE: usize = 0x2;
 
 const STATE_MASK: usize = 0x3;
 
-// The alignment here is so that we can stash the state in the lower
-// bits of the `next` pointer
 #[repr(align(4))]
 struct Waiter {
     thread: Cell<Option<Thread>>,

From 57ebee9b7f0205b2639eb5b1c04b2be0a5d244ac Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:59:15 -0400
Subject: [PATCH 6/7] Revert "integrate Lazy into std layout"

This reverts commit 237a97760ad79a21ce0655b9f5adc0cc5b5cbc79.
---
 Cargo.lock                |    2 +-
 src/libcore/lazy.rs       |  379 --------------
 src/libcore/lib.rs        |    2 -
 src/libcore/tests/lazy.rs |  124 -----
 src/libcore/tests/lib.rs  |    2 -
 src/libstd/lazy.rs        | 1032 +++++++++++++++++++------------------
 src/libstd/lib.rs         |    7 +-
 7 files changed, 546 insertions(+), 1002 deletions(-)
 delete mode 100644 src/libcore/lazy.rs
 delete mode 100644 src/libcore/tests/lazy.rs

diff --git a/Cargo.lock b/Cargo.lock
index 9b5b6620f79a7..8f110403eb842 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1372,8 +1372,8 @@ checksum = "7e81a7c05f79578dbc15793d8b619db9ba32b4577003ef3af1a91c416798c58d"
 name = "installer"
 version = "0.0.0"
 dependencies = [
+ "anyhow",
  "clap",
- "failure",
  "flate2",
  "lazy_static",
  "num_cpus",
diff --git a/src/libcore/lazy.rs b/src/libcore/lazy.rs
deleted file mode 100644
index e9af66ff64264..0000000000000
--- a/src/libcore/lazy.rs
+++ /dev/null
@@ -1,379 +0,0 @@
-//! Lazy values and one-time initialization of static data.
-
-use crate::cell::{Cell, UnsafeCell};
-use crate::fmt;
-use crate::mem;
-use crate::ops::Deref;
-
-/// A cell which can be written to only once.
-///
-/// Unlike `RefCell`, a `OnceCell` only provides shared `&T` references to its value.
-/// Unlike `Cell`, a `OnceCell` doesn't require copying or replacing the value to access it.
-///
-/// # Examples
-///
-/// ```
-/// #![feature(once_cell)]
-///
-/// use std::lazy::OnceCell;
-///
-/// let cell = OnceCell::new();
-/// assert!(cell.get().is_none());
-///
-/// let value: &String = cell.get_or_init(|| {
-///     "Hello, World!".to_string()
-/// });
-/// assert_eq!(value, "Hello, World!");
-/// assert!(cell.get().is_some());
-/// ```
-#[unstable(feature = "once_cell", issue = "68198")]
-pub struct OnceCell<T> {
-    // Invariant: written to at most once.
-    inner: UnsafeCell<Option<T>>,
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T> Default for OnceCell<T> {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.get() {
-            Some(v) => f.debug_tuple("OnceCell").field(v).finish(),
-            None => f.write_str("OnceCell(Uninit)"),
-        }
-    }
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: Clone> Clone for OnceCell<T> {
-    fn clone(&self) -> OnceCell<T> {
-        let res = OnceCell::new();
-        if let Some(value) = self.get() {
-            match res.set(value.clone()) {
-                Ok(()) => (),
-                Err(_) => unreachable!(),
-            }
-        }
-        res
-    }
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: PartialEq> PartialEq for OnceCell<T> {
-    fn eq(&self, other: &Self) -> bool {
-        self.get() == other.get()
-    }
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: Eq> Eq for OnceCell<T> {}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T> From<T> for OnceCell<T> {
-    fn from(value: T) -> Self {
-        OnceCell { inner: UnsafeCell::new(Some(value)) }
-    }
-}
-
-impl<T> OnceCell<T> {
-    /// Creates a new empty cell.
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub const fn new() -> OnceCell<T> {
-        OnceCell { inner: UnsafeCell::new(None) }
-    }
-
-    /// Gets the reference to the underlying value.
-    ///
-    /// Returns `None` if the cell is empty.
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn get(&self) -> Option<&T> {
-        // Safety: Safe due to `inner`'s invariant
-        unsafe { &*self.inner.get() }.as_ref()
-    }
-
-    /// Gets the mutable reference to the underlying value.
-    ///
-    /// Returns `None` if the cell is empty.
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn get_mut(&mut self) -> Option<&mut T> {
-        // Safety: Safe because we have unique access
-        unsafe { &mut *self.inner.get() }.as_mut()
-    }
-
-    /// Sets the contents of the cell to `value`.
-    ///
-    /// # Errors
-    ///
-    /// This method returns `Ok(())` if the cell was empty and `Err(value)` if
-    /// it was full.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell = OnceCell::new();
-    /// assert!(cell.get().is_none());
-    ///
-    /// assert_eq!(cell.set(92), Ok(()));
-    /// assert_eq!(cell.set(62), Err(62));
-    ///
-    /// assert!(cell.get().is_some());
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn set(&self, value: T) -> Result<(), T> {
-        // Safety: Safe because we cannot have overlapping mutable borrows
-        let slot = unsafe { &*self.inner.get() };
-        if slot.is_some() {
-            return Err(value);
-        }
-
-        // Safety: This is the only place where we set the slot, no races
-        // due to reentrancy/concurrency are possible, and we've
-        // checked that slot is currently `None`, so this write
-        // maintains the `inner`'s invariant.
-        let slot = unsafe { &mut *self.inner.get() };
-        *slot = Some(value);
-        Ok(())
-    }
-
-    /// Gets the contents of the cell, initializing it with `f`
-    /// if the cell was empty.
-    ///
-    /// # Panics
-    ///
-    /// If `f` panics, the panic is propagated to the caller, and the cell
-    /// remains uninitialized.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`. Doing
-    /// so results in a panic.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell = OnceCell::new();
-    /// let value = cell.get_or_init(|| 92);
-    /// assert_eq!(value, &92);
-    /// let value = cell.get_or_init(|| unreachable!());
-    /// assert_eq!(value, &92);
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn get_or_init<F>(&self, f: F) -> &T
-    where
-        F: FnOnce() -> T,
-    {
-        match self.get_or_try_init(|| Ok::<T, !>(f())) {
-            Ok(val) => val,
-        }
-    }
-
-    /// Gets the contents of the cell, initializing it with `f` if
-    /// the cell was empty. If the cell was empty and `f` failed, an
-    /// error is returned.
-    ///
-    /// # Panics
-    ///
-    /// If `f` panics, the panic is propagated to the caller, and the cell
-    /// remains uninitialized.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`. Doing
-    /// so results in a panic.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell = OnceCell::new();
-    /// assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
-    /// assert!(cell.get().is_none());
-    /// let value = cell.get_or_try_init(|| -> Result<i32, ()> {
-    ///     Ok(92)
-    /// });
-    /// assert_eq!(value, Ok(&92));
-    /// assert_eq!(cell.get(), Some(&92))
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
-    where
-        F: FnOnce() -> Result<T, E>,
-    {
-        if let Some(val) = self.get() {
-            return Ok(val);
-        }
-        let val = f()?;
-        // Note that *some* forms of reentrant initialization might lead to
-        // UB (see `reentrant_init` test). I believe that just removing this
-        // `assert`, while keeping `set/get` would be sound, but it seems
-        // better to panic, rather than to silently use an old value.
-        assert!(self.set(val).is_ok(), "reentrant init");
-        Ok(self.get().unwrap())
-    }
-
-    /// Consumes the cell, returning the wrapped value.
-    ///
-    /// Returns `None` if the cell was empty.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell: OnceCell<String> = OnceCell::new();
-    /// assert_eq!(cell.into_inner(), None);
-    ///
-    /// let cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn into_inner(self) -> Option<T> {
-        // Because `into_inner` takes `self` by value, the compiler statically verifies
-        // that it is not currently borrowed. So it is safe to move out `Option<T>`.
-        self.inner.into_inner()
-    }
-
-    /// Takes the value out of this `OnceCell`, moving it back to an uninitialized state.
-    ///
-    /// Has no effect and returns `None` if the `OnceCell` hasn't been initialized.
-    ///
-    /// Safety is guaranteed by requiring a mutable reference.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::OnceCell;
-    ///
-    /// let mut cell: OnceCell<String> = OnceCell::new();
-    /// assert_eq!(cell.take(), None);
-    ///
-    /// let mut cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.take(), Some("hello".to_string()));
-    /// assert_eq!(cell.get(), None);
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn take(&mut self) -> Option<T> {
-        mem::take(self).into_inner()
-    }
-}
-
-/// A value which is initialized on the first access.
-///
-/// # Examples
-///
-/// ```
-/// #![feature(once_cell)]
-///
-/// use std::lazy::Lazy;
-///
-/// let lazy: Lazy<i32> = Lazy::new(|| {
-///     println!("initializing");
-///     92
-/// });
-/// println!("ready");
-/// println!("{}", *lazy);
-/// println!("{}", *lazy);
-///
-/// // Prints:
-/// //   ready
-/// //   initializing
-/// //   92
-/// //   92
-/// ```
-#[unstable(feature = "once_cell", issue = "68198")]
-pub struct Lazy<T, F = fn() -> T> {
-    cell: OnceCell<T>,
-    init: Cell<Option<F>>,
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: fmt::Debug, F> fmt::Debug for Lazy<T, F> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
-    }
-}
-
-impl<T, F> Lazy<T, F> {
-    /// Creates a new lazy value with the given initializing function.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// # fn main() {
-    /// use std::lazy::Lazy;
-    ///
-    /// let hello = "Hello, World!".to_string();
-    ///
-    /// let lazy = Lazy::new(|| hello.to_uppercase());
-    ///
-    /// assert_eq!(&*lazy, "HELLO, WORLD!");
-    /// # }
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub const fn new(init: F) -> Lazy<T, F> {
-        Lazy { cell: OnceCell::new(), init: Cell::new(Some(init)) }
-    }
-}
-
-impl<T, F: FnOnce() -> T> Lazy<T, F> {
-    /// Forces the evaluation of this lazy value and returns a reference to
-    /// the result.
-    ///
-    /// This is equivalent to the `Deref` impl, but is explicit.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::Lazy;
-    ///
-    /// let lazy = Lazy::new(|| 92);
-    ///
-    /// assert_eq!(Lazy::force(&lazy), &92);
-    /// assert_eq!(&*lazy, &92);
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn force(this: &Lazy<T, F>) -> &T {
-        this.cell.get_or_init(|| match this.init.take() {
-            Some(f) => f(),
-            None => panic!("`Lazy` instance has previously been poisoned"),
-        })
-    }
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
-    type Target = T;
-    fn deref(&self) -> &T {
-        Lazy::force(self)
-    }
-}
-
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: Default> Default for Lazy<T> {
-    /// Creates a new lazy value using `Default` as the initializing function.
-    fn default() -> Lazy<T> {
-        Lazy::new(T::default)
-    }
-}
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 4701503d4103e..8bf98b50acfed 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -240,8 +240,6 @@ pub mod char;
 pub mod ffi;
 #[cfg(not(test))] // See #65860
 pub mod iter;
-#[unstable(feature = "once_cell", issue = "68198")]
-pub mod lazy;
 pub mod option;
 pub mod panic;
 pub mod panicking;
diff --git a/src/libcore/tests/lazy.rs b/src/libcore/tests/lazy.rs
deleted file mode 100644
index 1c0bddb9aef62..0000000000000
--- a/src/libcore/tests/lazy.rs
+++ /dev/null
@@ -1,124 +0,0 @@
-use core::{
-    cell::Cell,
-    lazy::{Lazy, OnceCell},
-    sync::atomic::{AtomicUsize, Ordering::SeqCst},
-};
-
-#[test]
-fn once_cell() {
-    let c = OnceCell::new();
-    assert!(c.get().is_none());
-    c.get_or_init(|| 92);
-    assert_eq!(c.get(), Some(&92));
-
-    c.get_or_init(|| panic!("Kabom!"));
-    assert_eq!(c.get(), Some(&92));
-}
-
-#[test]
-fn once_cell_get_mut() {
-    let mut c = OnceCell::new();
-    assert!(c.get_mut().is_none());
-    c.set(90).unwrap();
-    *c.get_mut().unwrap() += 2;
-    assert_eq!(c.get_mut(), Some(&mut 92));
-}
-
-#[test]
-fn once_cell_drop() {
-    static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
-    struct Dropper;
-    impl Drop for Dropper {
-        fn drop(&mut self) {
-            DROP_CNT.fetch_add(1, SeqCst);
-        }
-    }
-
-    let x = OnceCell::new();
-    x.get_or_init(|| Dropper);
-    assert_eq!(DROP_CNT.load(SeqCst), 0);
-    drop(x);
-    assert_eq!(DROP_CNT.load(SeqCst), 1);
-}
-
-#[test]
-fn unsync_once_cell_drop_empty() {
-    let x = OnceCell::<&'static str>::new();
-    drop(x);
-}
-
-#[test]
-fn clone() {
-    let s = OnceCell::new();
-    let c = s.clone();
-    assert!(c.get().is_none());
-
-    s.set("hello").unwrap();
-    let c = s.clone();
-    assert_eq!(c.get().map(|c| *c), Some("hello"));
-}
-
-#[test]
-fn from_impl() {
-    assert_eq!(OnceCell::from("value").get(), Some(&"value"));
-    assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
-}
-
-#[test]
-fn partialeq_impl() {
-    assert!(OnceCell::from("value") == OnceCell::from("value"));
-    assert!(OnceCell::from("foo") != OnceCell::from("bar"));
-
-    assert!(OnceCell::<&'static str>::new() == OnceCell::new());
-    assert!(OnceCell::<&'static str>::new() != OnceCell::from("value"));
-}
-
-#[test]
-fn into_inner() {
-    let cell: OnceCell<&'static str> = OnceCell::new();
-    assert_eq!(cell.into_inner(), None);
-    let cell = OnceCell::new();
-    cell.set("hello").unwrap();
-    assert_eq!(cell.into_inner(), Some("hello"));
-}
-
-#[test]
-fn lazy_new() {
-    let called = Cell::new(0);
-    let x = Lazy::new(|| {
-        called.set(called.get() + 1);
-        92
-    });
-
-    assert_eq!(called.get(), 0);
-
-    let y = *x - 30;
-    assert_eq!(y, 62);
-    assert_eq!(called.get(), 1);
-
-    let y = *x - 30;
-    assert_eq!(y, 62);
-    assert_eq!(called.get(), 1);
-}
-
-#[test]
-fn aliasing_in_get() {
-    let x = OnceCell::new();
-    x.set(42).unwrap();
-    let at_x = x.get().unwrap(); // --- (shared) borrow of inner `Option<T>` --+
-    let _ = x.set(27); // <-- temporary (unique) borrow of inner `Option<T>`   |
-    println!("{}", at_x); // <------- up until here ---------------------------+
-}
-
-#[test]
-#[should_panic(expected = "reentrant init")]
-fn reentrant_init() {
-    let x: OnceCell<Box<i32>> = OnceCell::new();
-    let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
-    x.get_or_init(|| {
-        let r = x.get_or_init(|| Box::new(92));
-        dangling_ref.set(Some(r));
-        Box::new(62)
-    });
-    eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
-}
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 47ed6db6c677b..090ce47174566 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -43,7 +43,6 @@
 #![feature(option_unwrap_none)]
 #![feature(peekable_next_if)]
 #![feature(partition_point)]
-#![feature(once_cell)]
 #![feature(unsafe_block_in_unsafe_fn)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
@@ -63,7 +62,6 @@ mod fmt;
 mod hash;
 mod intrinsics;
 mod iter;
-mod lazy;
 mod manually_drop;
 mod mem;
 mod nonzero;
diff --git a/src/libstd/lazy.rs b/src/libstd/lazy.rs
index c7553caa4c056..bcac2dc311aff 100644
--- a/src/libstd/lazy.rs
+++ b/src/libstd/lazy.rs
@@ -1,32 +1,508 @@
-//! Lazy values and one-time initialization of static data.
+//! `lazy` modules provides lazy values and one-time initialization of static data.
+//!
+//! `lazy` provides two new cell-like types, `OnceCell` and `SyncOnceCell`. `OnceCell`
+//! might store arbitrary non-`Copy` types, can be assigned to at most once and provide direct access
+//! to the stored contents. In a nutshell, API looks *roughly* like this:
+//!
+//! ```rust,ignore
+//! impl<T> OnceCell<T> {
+//!     fn new() -> OnceCell<T> { ... }
+//!     fn set(&self, value: T) -> Result<(), T> { ... }
+//!     fn get(&self) -> Option<&T> { ... }
+//! }
+//! ```
+//!
+//! Note that, like with `RefCell` and `Mutex`, the `set` method requires only a shared reference.
+//! Because of the single assignment restriction `get` can return an `&T` instead of `Ref<T>`
+//! or `MutexGuard<T>`.
+//!
+//! The `SyncOnceCell` flavor is thread-safe (that is, implements [`Sync`]) trait, while  `OnceCell` one is not.
+//!
+//! [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html
+//!
+//! # Patterns
+//!
+//! `OnceCell` might be useful for a variety of patterns.
+//!
+//! ## Safe Initialization of global data
+//!
+//! ```rust
+//! use std::{env, io};
+//! use std::lazy::SyncOnceCell;
+//!
+//! #[derive(Debug)]
+//! pub struct Logger {
+//!     // ...
+//! }
+//! static INSTANCE: OnceCell<Logger> = OnceCell::new();
+//!
+//! impl Logger {
+//!     pub fn global() -> &'static Logger {
+//!         INSTANCE.get().expect("logger is not initialized")
+//!     }
+//!
+//!     fn from_cli(args: env::Args) -> Result<Logger, std::io::Error> {
+//!        // ...
+//! #      Ok(Logger {})
+//!     }
+//! }
+//!
+//! fn main() {
+//!     let logger = Logger::from_cli(env::args()).unwrap();
+//!     INSTANCE.set(logger).unwrap();
+//!     // use `Logger::global()` from now on
+//! }
+//! ```
+//!
+//! ## Lazy initialized global data
+//!
+//! This is essentially `lazy_static!` macro, but without a macro.
+//!
+//! ```rust
+//! use std::{sync::Mutex, collections::HashMap};
+//! use lazy::SyncOnceCell;
+//!
+//! fn global_data() -> &'static Mutex<HashMap<i32, String>> {
+//!     static INSTANCE: OnceCell<Mutex<HashMap<i32, String>>> = OnceCell::new();
+//!     INSTANCE.get_or_init(|| {
+//!         let mut m = HashMap::new();
+//!         m.insert(13, "Spica".to_string());
+//!         m.insert(74, "Hoyten".to_string());
+//!         Mutex::new(m)
+//!     })
+//! }
+//! ```
+//!
+//! There are also `sync::Lazy` and `unsync::Lazy` convenience types to streamline this pattern:
+//!
+//! ```rust
+//! use std::{sync::Mutex, collections::HashMap};
+//! use lazy::SyncLazy;
+//!
+//! static GLOBAL_DATA: Lazy<Mutex<HashMap<i32, String>>> = Lazy::new(|| {
+//!     let mut m = HashMap::new();
+//!     m.insert(13, "Spica".to_string());
+//!     m.insert(74, "Hoyten".to_string());
+//!     Mutex::new(m)
+//! });
+//!
+//! fn main() {
+//!     println!("{:?}", GLOBAL_DATA.lock().unwrap());
+//! }
+//! ```
+//!
+//! ## General purpose lazy evaluation
+//!
+//! `Lazy` also works with local variables.
+//!
+//! ```rust
+//! use std::lazy::Lazy;
+//!
+//! fn main() {
+//!     let ctx = vec![1, 2, 3];
+//!     let thunk = Lazy::new(|| {
+//!         ctx.iter().sum::<i32>()
+//!     });
+//!     assert_eq!(*thunk, 6);
+//! }
+//! ```
+//!
+//! If you need a lazy field in a struct, you probably should use `OnceCell`
+//! directly, because that will allow you to access `self` during initialization.
+//!
+//! ```rust
+//! use std::{fs, path::PathBuf};
+//!
+//! use std::lazy::OnceCell;
+//!
+//! struct Ctx {
+//!     config_path: PathBuf,
+//!     config: OnceCell<String>,
+//! }
+//!
+//! impl Ctx {
+//!     pub fn get_config(&self) -> Result<&str, std::io::Error> {
+//!         let cfg = self.config.get_or_try_init(|| {
+//!             fs::read_to_string(&self.config_path)
+//!         })?;
+//!         Ok(cfg.as_str())
+//!     }
+//! }
+//! ```
+//!
+//! ## Building block
+//!
+//! Naturally, it is  possible to build other abstractions on top of `OnceCell`.
+//! For example, this is a `regex!` macro which takes a string literal and returns an
+//! *expression* that evaluates to a `&'static Regex`:
+//!
+//! ```
+//! macro_rules! regex {
+//!     ($re:literal $(,)?) => {{
+//!         static RE: std::lazy::SyncOnceCell<regex::Regex> = std::lazy::SyncOnceCell::new();
+//!         RE.get_or_init(|| regex::Regex::new($re).unwrap())
+//!     }};
+//! }
+//! ```
+//!
+//! This macro can be useful to avoid "compile regex on every loop iteration" problem.
+//!
+//! # Comparison with other interior mutatbility types
+//!
+//! |`!Sync` types         | Access Mode            | Drawbacks                                     |
+//! |----------------------|------------------------|-----------------------------------------------|
+//! |`Cell<T>`             | `T`                    | requires `T: Copy` for `get`                  |
+//! |`RefCell<T>`          | `RefMut<T>` / `Ref<T>` | may panic at runtime                          |
+//! |`OnceCell<T>`         | `&T`                   | assignable only once                          |
+//!
+//! |`Sync` types          | Access Mode            | Drawbacks                                     |
+//! |----------------------|------------------------|-----------------------------------------------|
+//! |`AtomicT`             | `T`                    | works only with certain `Copy` types          |
+//! |`Mutex<T>`            | `MutexGuard<T>`        | may deadlock at runtime, may block the thread |
+//! |`SyncOnceCell<T>`     | `&T`                   | assignable only once, may block the thread    |
+//!
+//! Technically, calling `get_or_init` will also cause a panic or a deadlock if it recursively calls
+//! itself. However, because the assignment can happen only once, such cases should be more rare than
+//! equivalents with `RefCell` and `Mutex`.
 
 use crate::{
     cell::{Cell, UnsafeCell},
     fmt,
+    hint::unreachable_unchecked,
     marker::PhantomData,
-    mem::{self, MaybeUninit},
-    ops::{Deref, Drop},
+    ops::Deref,
     panic::{RefUnwindSafe, UnwindSafe},
     sync::atomic::{AtomicBool, AtomicUsize, Ordering},
     thread::{self, Thread},
 };
 
-#[doc(inline)]
-#[unstable(feature = "once_cell", issue = "68198")]
-pub use core::lazy::*;
+/// A cell which can be written to only once. Not thread safe.
+///
+/// Unlike `:td::cell::RefCell`, a `OnceCell` provides simple `&`
+/// references to the contents.
+///
+/// # Example
+/// ```
+/// use std::lazy::OnceCell;
+///
+/// let cell = OnceCell::new();
+/// assert!(cell.get().is_none());
+///
+/// let value: &String = cell.get_or_init(|| {
+///     "Hello, World!".to_string()
+/// });
+/// assert_eq!(value, "Hello, World!");
+/// assert!(cell.get().is_some());
+/// ```
+pub struct OnceCell<T> {
+    // Invariant: written to at most once.
+    inner: UnsafeCell<Option<T>>,
+}
+
+// Similarly to a `Sync` bound on `SyncOnceCell`, we can use
+// `&OnceCell` to sneak a `T` through `catch_unwind`,
+// by initializing the cell in closure and extracting the value in the
+// `Drop`.
+#[cfg(feature = "std")]
+impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T> {}
+#[cfg(feature = "std")]
+impl<T: UnwindSafe> UnwindSafe for OnceCell<T> {}
+
+impl<T> Default for OnceCell<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.get() {
+            Some(v) => f.debug_tuple("OnceCell").field(v).finish(),
+            None => f.write_str("OnceCell(Uninit)"),
+        }
+    }
+}
+
+impl<T: Clone> Clone for OnceCell<T> {
+    fn clone(&self) -> OnceCell<T> {
+        let res = OnceCell::new();
+        if let Some(value) = self.get() {
+            match res.set(value.clone()) {
+                Ok(()) => (),
+                Err(_) => unreachable!(),
+            }
+        }
+        res
+    }
+}
+
+impl<T: PartialEq> PartialEq for OnceCell<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.get() == other.get()
+    }
+}
+
+impl<T: Eq> Eq for OnceCell<T> {}
+
+impl<T> From<T> for OnceCell<T> {
+    fn from(value: T) -> Self {
+        OnceCell { inner: UnsafeCell::new(Some(value)) }
+    }
+}
+
+impl<T> OnceCell<T> {
+    /// Creates a new empty cell.
+    pub const fn new() -> OnceCell<T> {
+        OnceCell { inner: UnsafeCell::new(None) }
+    }
+
+    /// Gets the reference to the underlying value.
+    ///
+    /// Returns `None` if the cell is empty.
+    pub fn get(&self) -> Option<&T> {
+        // Safe due to `inner`'s invariant
+        unsafe { &*self.inner.get() }.as_ref()
+    }
+
+    /// Gets the mutable reference to the underlying value.
+    ///
+    /// Returns `None` if the cell is empty.
+    pub fn get_mut(&mut self) -> Option<&mut T> {
+        // Safe because we have unique access
+        unsafe { &mut *self.inner.get() }.as_mut()
+    }
+
+    /// Sets the contents of this cell to `value`.
+    ///
+    /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was
+    /// full.
+    ///
+    /// # Example
+    /// ```
+    /// use std::lazy::OnceCell;
+    ///
+    /// let cell = OnceCell::new();
+    /// assert!(cell.get().is_none());
+    ///
+    /// assert_eq!(cell.set(92), Ok(()));
+    /// assert_eq!(cell.set(62), Err(62));
+    ///
+    /// assert!(cell.get().is_some());
+    /// ```
+    pub fn set(&self, value: T) -> Result<(), T> {
+        let slot = unsafe { &*self.inner.get() };
+        if slot.is_some() {
+            return Err(value);
+        }
+        let slot = unsafe { &mut *self.inner.get() };
+        // This is the only place where we set the slot, no races
+        // due to reentrancy/concurrency are possible, and we've
+        // checked that slot is currently `None`, so this write
+        // maintains the `inner`'s invariant.
+        *slot = Some(value);
+        Ok(())
+    }
 
-/// A synchronization primitive which can be written to only once.
+    /// Gets the contents of the cell, initializing it with `f`
+    /// if the cell was empty.
+    ///
+    /// # Panics
+    ///
+    /// If `f` panics, the panic is propagated to the caller, and the cell
+    /// remains uninitialized.
+    ///
+    /// It is an error to reentrantly initialize the cell from `f`. Doing
+    /// so results in a panic.
+    ///
+    /// # Example
+    /// ```
+    /// use std::lazy::OnceCell;
+    ///
+    /// let cell = OnceCell::new();
+    /// let value = cell.get_or_init(|| 92);
+    /// assert_eq!(value, &92);
+    /// let value = cell.get_or_init(|| unreachable!());
+    /// assert_eq!(value, &92);
+    /// ```
+    pub fn get_or_init<F>(&self, f: F) -> &T
+    where
+        F: FnOnce() -> T,
+    {
+        match self.get_or_try_init(|| Ok::<T, !>(f())) {
+            Ok(val) => val,
+        }
+    }
+
+    /// Gets the contents of the cell, initializing it with `f` if
+    /// the cell was empty. If the cell was empty and `f` failed, an
+    /// error is returned.
+    ///
+    /// # Panics
+    ///
+    /// If `f` panics, the panic is propagated to the caller, and the cell
+    /// remains uninitialized.
+    ///
+    /// It is an error to reentrantly initialize the cell from `f`. Doing
+    /// so results in a panic.
+    ///
+    /// # Example
+    /// ```
+    /// use std::lazy::OnceCell;
+    ///
+    /// let cell = OnceCell::new();
+    /// assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
+    /// assert!(cell.get().is_none());
+    /// let value = cell.get_or_try_init(|| -> Result<i32, ()> {
+    ///     Ok(92)
+    /// });
+    /// assert_eq!(value, Ok(&92));
+    /// assert_eq!(cell.get(), Some(&92))
+    /// ```
+    pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
+    where
+        F: FnOnce() -> Result<T, E>,
+    {
+        if let Some(val) = self.get() {
+            return Ok(val);
+        }
+        let val = f()?;
+        // Note that *some* forms of reentrant initialization might lead to
+        // UB (see `reentrant_init` test). I believe that just removing this
+        // `assert`, while keeping `set/get` would be sound, but it seems
+        // better to panic, rather than to silently use an old value.
+        assert!(self.set(val).is_ok(), "reentrant init");
+        Ok(self.get().unwrap())
+    }
+
+    /// Consumes the `OnceCell`, returning the wrapped value.
+    ///
+    /// Returns `None` if the cell was empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::lazy::OnceCell;
+    ///
+    /// let cell: OnceCell<String> = OnceCell::new();
+    /// assert_eq!(cell.into_inner(), None);
+    ///
+    /// let cell = OnceCell::new();
+    /// cell.set("hello".to_string()).unwrap();
+    /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
+    /// ```
+    pub fn into_inner(self) -> Option<T> {
+        // Because `into_inner` takes `self` by value, the compiler statically verifies
+        // that it is not currently borrowed. So it is safe to move out `Option<T>`.
+        self.inner.into_inner()
+    }
+}
+
+/// A value which is initialized on the first access.
 ///
-/// This type is a thread-safe `OnceCell`.
+/// # Example
+/// ```
+/// use std::lazy::Lazy;
 ///
-/// # Examples
+/// let lazy: Lazy<i32> = Lazy::new(|| {
+///     println!("initializing");
+///     92
+/// });
+/// println!("ready");
+/// println!("{}", *lazy);
+/// println!("{}", *lazy);
 ///
+/// // Prints:
+/// //   ready
+/// //   initializing
+/// //   92
+/// //   92
 /// ```
-/// #![feature(once_cell)]
+pub struct Lazy<T, F = fn() -> T> {
+    cell: OnceCell<T>,
+    init: Cell<Option<F>>,
+}
+
+#[cfg(feature = "std")]
+impl<T, F: RefUnwindSafe> RefUnwindSafe for Lazy<T, F> where OnceCell<T>: RefUnwindSafe {}
+
+impl<T: fmt::Debug, F: fmt::Debug> fmt::Debug for Lazy<T, F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
+    }
+}
+
+impl<T, F> Lazy<T, F> {
+    /// Creates a new lazy value with the given initializing function.
+    ///
+    /// # Example
+    /// ```
+    /// # fn main() {
+    /// use std::lazy::Lazy;
+    ///
+    /// let hello = "Hello, World!".to_string();
+    ///
+    /// let lazy = Lazy::new(|| hello.to_uppercase());
+    ///
+    /// assert_eq!(&*lazy, "HELLO, WORLD!");
+    /// # }
+    /// ```
+    pub const fn new(init: F) -> Lazy<T, F> {
+        Lazy { cell: OnceCell::new(), init: Cell::new(Some(init)) }
+    }
+}
+
+impl<T, F: FnOnce() -> T> Lazy<T, F> {
+    /// Forces the evaluation of this lazy value and returns a reference to
+    /// the result.
+    ///
+    /// This is equivalent to the `Deref` impl, but is explicit.
+    ///
+    /// # Example
+    /// ```
+    /// use std::lazy::Lazy;
+    ///
+    /// let lazy = Lazy::new(|| 92);
+    ///
+    /// assert_eq!(Lazy::force(&lazy), &92);
+    /// assert_eq!(&*lazy, &92);
+    /// ```
+    pub fn force(this: &Lazy<T, F>) -> &T {
+        this.cell.get_or_init(|| match this.init.take() {
+            Some(f) => f(),
+            None => panic!("Lazy instance has previously been poisoned"),
+        })
+    }
+}
+
+impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        Lazy::force(self)
+    }
+}
+
+impl<T: Default> Default for Lazy<T> {
+    /// Creates a new lazy value using `Default` as the initializing function.
+    fn default() -> Lazy<T> {
+        Lazy::new(T::default)
+    }
+}
+
+/// A thread-safe cell which can be written to only once.
 ///
+/// `OnceCell` provides `&` references to the contents without RAII guards.
+///
+/// Reading a non-`None` value out of `OnceCell` establishes a
+/// happens-before relationship with a corresponding write. For example, if
+/// thread A initializes the cell with `get_or_init(f)`, and thread B
+/// subsequently reads the result of this call, B also observes all the side
+/// effects of `f`.
+///
+/// # Example
+/// ```
 /// use std::lazy::SyncOnceCell;
 ///
-/// static CELL: SyncOnceCell<String> = SyncOnceCell::new();
+/// static CELL: OnceCell<String> = OnceCell::new();
 /// assert!(CELL.get().is_none());
 ///
 /// std::thread::spawn(|| {
@@ -40,49 +516,44 @@ pub use core::lazy::*;
 /// assert!(value.is_some());
 /// assert_eq!(value.unwrap().as_str(), "Hello, World!");
 /// ```
-#[unstable(feature = "once_cell", issue = "68198")]
 pub struct SyncOnceCell<T> {
     // This `state` word is actually an encoded version of just a pointer to a
     // `Waiter`, so we add the `PhantomData` appropriately.
     state_and_queue: AtomicUsize,
     _marker: PhantomData<*mut Waiter>,
-    // Whether or not the value is initialized is tracked by `state_and_queue`.
-    value: UnsafeCell<MaybeUninit<T>>,
+    // FIXME: switch to `std::mem::MaybeUninit` once we are ready to bump MSRV
+    // that far. It was stabilized in 1.36.0, so, if you are reading this and
+    // it's higher than 1.46.0 outside, please send a PR! ;) (and do the same
+    // for `Lazy`, while we are at it).
+    pub(crate) value: UnsafeCell<Option<T>>,
 }
 
 // Why do we need `T: Send`?
-// Thread A creates a `SyncOnceCell` and shares it with
+// Thread A creates a `OnceCell` and shares it with
 // scoped thread B, which fills the cell, which is
 // then destroyed by A. That is, destructor observes
 // a sent value.
-#[unstable(feature = "once_cell", issue = "68198")]
 unsafe impl<T: Sync + Send> Sync for SyncOnceCell<T> {}
-#[unstable(feature = "once_cell", issue = "68198")]
 unsafe impl<T: Send> Send for SyncOnceCell<T> {}
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SyncOnceCell<T> {}
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: UnwindSafe> UnwindSafe for SyncOnceCell<T> {}
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T> Default for SyncOnceCell<T> {
     fn default() -> SyncOnceCell<T> {
         SyncOnceCell::new()
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: fmt::Debug> fmt::Debug for SyncOnceCell<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.get() {
-            Some(v) => f.debug_tuple("Once").field(v).finish(),
-            None => f.write_str("Once(Uninit)"),
+            Some(v) => f.debug_tuple("SyncOnceCell").field(v).finish(),
+            None => f.write_str("SyncOnceCell(Uninit)"),
         }
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Clone> Clone for SyncOnceCell<T> {
     fn clone(&self) -> SyncOnceCell<T> {
         let res = SyncOnceCell::new();
@@ -96,7 +567,6 @@ impl<T: Clone> Clone for SyncOnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T> From<T> for SyncOnceCell<T> {
     fn from(value: T) -> Self {
         let cell = Self::new();
@@ -105,24 +575,21 @@ impl<T> From<T> for SyncOnceCell<T> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: PartialEq> PartialEq for SyncOnceCell<T> {
     fn eq(&self, other: &SyncOnceCell<T>) -> bool {
         self.get() == other.get()
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Eq> Eq for SyncOnceCell<T> {}
 
 impl<T> SyncOnceCell<T> {
     /// Creates a new empty cell.
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new() -> SyncOnceCell<T> {
         SyncOnceCell {
             state_and_queue: AtomicUsize::new(INCOMPLETE),
             _marker: PhantomData,
-            value: UnsafeCell::new(MaybeUninit::uninit()),
+            value: UnsafeCell::new(None),
         }
     }
 
@@ -130,7 +597,6 @@ impl<T> SyncOnceCell<T> {
     ///
     /// Returns `None` if the cell is empty, or being initialized. This
     /// method never blocks.
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get(&self) -> Option<&T> {
         if self.is_initialized() {
             // Safe b/c checked is_initialize
@@ -142,14 +608,29 @@ impl<T> SyncOnceCell<T> {
 
     /// Gets the mutable reference to the underlying value.
     ///
-    /// Returns `None` if the cell is empty. This method never blocks.
-    #[unstable(feature = "once_cell", issue = "68198")]
+    /// Returns `None` if the cell is empty.
     pub fn get_mut(&mut self) -> Option<&mut T> {
-        if self.is_initialized() {
-            // Safe b/c checked is_initialize and we have a unique access
-            Some(unsafe { self.get_unchecked_mut() })
-        } else {
-            None
+        // Safe b/c we have a unique access.
+        unsafe { &mut *self.value.get() }.as_mut()
+    }
+
+    /// Get the reference to the underlying value, without checking if the
+    /// cell is initialized.
+    ///
+    /// Safety:
+    ///
+    /// Caller must ensure that the cell is in initialized state, and that
+    /// the contents are acquired by (synchronized to) this thread.
+    pub unsafe fn get_unchecked(&self) -> &T {
+        debug_assert!(self.is_initialized());
+        let slot: &Option<T> = &*self.value.get();
+        match slot {
+            Some(value) => value,
+            // This unsafe does improve performance, see `examples/bench`.
+            None => {
+                debug_assert!(false);
+                unreachable_unchecked()
+            }
         }
     }
 
@@ -158,11 +639,8 @@ impl<T> SyncOnceCell<T> {
     /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was
     /// full.
     ///
-    /// # Examples
-    ///
+    /// # Example
     /// ```
-    /// #![feature(once_cell)]
-    ///
     /// use std::lazy::SyncOnceCell;
     ///
     /// static CELL: SyncOnceCell<i32> = SyncOnceCell::new();
@@ -178,7 +656,6 @@ impl<T> SyncOnceCell<T> {
     ///     assert_eq!(CELL.get(), Some(&92));
     /// }
     /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn set(&self, value: T) -> Result<(), T> {
         let mut value = Some(value);
         self.get_or_init(|| value.take().unwrap());
@@ -204,11 +681,8 @@ impl<T> SyncOnceCell<T> {
     /// exact outcome is unspecified. Current implementation deadlocks, but
     /// this may be changed to a panic in the future.
     ///
-    /// # Examples
-    ///
+    /// # Example
     /// ```
-    /// #![feature(once_cell)]
-    ///
     /// use std::lazy::SyncOnceCell;
     ///
     /// let cell = SyncOnceCell::new();
@@ -217,7 +691,6 @@ impl<T> SyncOnceCell<T> {
     /// let value = cell.get_or_init(|| unreachable!());
     /// assert_eq!(value, &92);
     /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_or_init<F>(&self, f: F) -> &T
     where
         F: FnOnce() -> T,
@@ -240,11 +713,8 @@ impl<T> SyncOnceCell<T> {
     /// The exact outcome is unspecified. Current implementation
     /// deadlocks, but this may be changed to a panic in the future.
     ///
-    /// # Examples
-    ///
+    /// # Example
     /// ```
-    /// #![feature(once_cell)]
-    ///
     /// use std::lazy::SyncOnceCell;
     ///
     /// let cell = SyncOnceCell::new();
@@ -256,22 +726,18 @@ impl<T> SyncOnceCell<T> {
     /// assert_eq!(value, Ok(&92));
     /// assert_eq!(cell.get(), Some(&92))
     /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
     where
         F: FnOnce() -> Result<T, E>,
     {
         // Fast path check
-        // NOTE: This acquire here is important to ensure
-        // `SyncLazy::force` is correctly synchronized
         if let Some(value) = self.get() {
             return Ok(value);
         }
         self.initialize(f)?;
 
+        // Safe b/c called initialize
         debug_assert!(self.is_initialized());
-
-        // Safety: The inner value has been initialized
         Ok(unsafe { self.get_unchecked() })
     }
 
@@ -281,8 +747,6 @@ impl<T> SyncOnceCell<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(once_cell)]
-    ///
     /// use std::lazy::SyncOnceCell;
     ///
     /// let cell: SyncOnceCell<String> = SyncOnceCell::new();
@@ -292,59 +756,10 @@ impl<T> SyncOnceCell<T> {
     /// cell.set("hello".to_string()).unwrap();
     /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
     /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn into_inner(mut self) -> Option<T> {
-        // Safety: Safe because we immediately free `self` without dropping
-        let inner = unsafe { self.take_inner() };
-
-        // Don't drop this `SyncOnceCell`. We just moved out one of the fields, but didn't set
-        // the state to uninitialized.
-        mem::ManuallyDrop::new(self);
-        inner
-    }
-
-    /// Takes the value out of this `SyncOnceCell`, moving it back to an uninitialized state.
-    ///
-    /// Has no effect and returns `None` if the `SyncOnceCell` hasn't been initialized.
-    ///
-    /// Safety is guaranteed by requiring a mutable reference.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_cell)]
-    ///
-    /// use std::lazy::SyncOnceCell;
-    ///
-    /// let mut cell: SyncOnceCell<String> = SyncOnceCell::new();
-    /// assert_eq!(cell.take(), None);
-    ///
-    /// let mut cell = SyncOnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.take(), Some("hello".to_string()));
-    /// assert_eq!(cell.get(), None);
-    /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
-    pub fn take(&mut self) -> Option<T> {
-        mem::take(self).into_inner()
-    }
-
-    /// Takes the wrapped value out of a `SyncOnceCell`.
-    /// Afterwards the cell is no longer initialized.
-    ///
-    /// Safety: The cell must now be free'd WITHOUT dropping. No other usages of the cell
-    /// are valid. Only used by `into_inner` and `drop`.
-    unsafe fn take_inner(&mut self) -> Option<T> {
-        // The mutable reference guarantees there are no other threads that can observe us
-        // taking out the wrapped value.
-        // Right after this function `self` is supposed to be freed, so it makes little sense
-        // to atomically set the state to uninitialized.
-        if self.is_initialized() {
-            let value = mem::replace(&mut self.value, UnsafeCell::new(MaybeUninit::uninit()));
-            Some(value.into_inner().assume_init())
-        } else {
-            None
-        }
+    pub fn into_inner(self) -> Option<T> {
+        // Because `into_inner` takes `self` by value, the compiler statically verifies
+        // that it is not currently borrowed. So it is safe to move out `Option<T>`.
+        self.value.into_inner()
     }
 
     /// Safety: synchronizes with store to value via Release/(Acquire|SeqCst).
@@ -372,7 +787,7 @@ impl<T> SyncOnceCell<T> {
             let f = f.take().unwrap();
             match f() {
                 Ok(value) => {
-                    unsafe { (&mut *slot.get()).write(value) };
+                    unsafe { *slot.get() = Some(value) };
                     true
                 }
                 Err(e) => {
@@ -383,33 +798,18 @@ impl<T> SyncOnceCell<T> {
         });
         res
     }
-
-    /// Safety: The value must be initialized
-    unsafe fn get_unchecked(&self) -> &T {
-        debug_assert!(self.is_initialized());
-        (&*self.value.get()).get_ref()
-    }
-
-    /// Safety: The value must be initialized
-    unsafe fn get_unchecked_mut(&mut self) -> &mut T {
-        debug_assert!(self.is_initialized());
-        (&mut *self.value.get()).get_mut()
-    }
-}
-
-impl<T> Drop for SyncOnceCell<T> {
-    fn drop(&mut self) {
-        // Safety: The cell is being dropped, so it can't be accessed again
-        unsafe { self.take_inner() };
-    }
 }
 
+// region: copy-paste
+// The following code is copied from `sync::Once`.
+// This should be uncopypasted once we decide the right way to handle panics.
 const INCOMPLETE: usize = 0x0;
 const RUNNING: usize = 0x1;
 const COMPLETE: usize = 0x2;
 
 const STATE_MASK: usize = 0x3;
 
+
 #[repr(align(4))]
 struct Waiter {
     thread: Cell<Option<Thread>>,
@@ -501,21 +901,19 @@ fn wait(state_and_queue: &AtomicUsize, mut current_state: usize) {
         break;
     }
 }
+// endregion: copy-paste
 
 /// A value which is initialized on the first access.
 ///
-/// This type is a thread-safe `Lazy`, and can be used in statics.
-///
-/// # Examples
+/// This type is thread-safe and can be used in statics:
 ///
+/// # Example
 /// ```
-/// #![feature(once_cell)]
-///
 /// use std::collections::HashMap;
 ///
-/// use std::lazy::SyncLazy;
+/// use std::lazy::Lazy;
 ///
-/// static HASHMAP: SyncLazy<HashMap<i32, String>> = SyncLazy::new(|| {
+/// static HASHMAP: Lazy<HashMap<i32, String>> = Lazy::new(|| {
 ///     println!("initializing");
 ///     let mut m = HashMap::new();
 ///     m.insert(13, "Spica".to_string());
@@ -537,16 +935,14 @@ fn wait(state_and_queue: &AtomicUsize, mut current_state: usize) {
 ///     //   Some("Hoyten")
 /// }
 /// ```
-#[unstable(feature = "once_cell", issue = "68198")]
 pub struct SyncLazy<T, F = fn() -> T> {
     cell: SyncOnceCell<T>,
     init: Cell<Option<F>>,
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
-impl<T: fmt::Debug, F> fmt::Debug for SyncLazy<T, F> {
+impl<T: fmt::Debug, F: fmt::Debug> fmt::Debug for SyncLazy<T, F> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
+        f.debug_struct("SyncLazy").field("cell", &self.cell).field("init", &"..").finish()
     }
 }
 
@@ -555,17 +951,15 @@ impl<T: fmt::Debug, F> fmt::Debug for SyncLazy<T, F> {
 // we do create a `&mut Option<F>` in `force`, but this is
 // properly synchronized, so it only happens once
 // so it also does not contribute to this impl.
-#[unstable(feature = "once_cell", issue = "68198")]
 unsafe impl<T, F: Send> Sync for SyncLazy<T, F> where SyncOnceCell<T>: Sync {}
 // auto-derived `Send` impl is OK.
 
-#[unstable(feature = "once_cell", issue = "68198")]
+#[cfg(feature = "std")]
 impl<T, F: RefUnwindSafe> RefUnwindSafe for SyncLazy<T, F> where SyncOnceCell<T>: RefUnwindSafe {}
 
 impl<T, F> SyncLazy<T, F> {
     /// Creates a new lazy value with the given initializing
     /// function.
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub const fn new(f: F) -> SyncLazy<T, F> {
         SyncLazy { cell: SyncOnceCell::new(), init: Cell::new(Some(f)) }
     }
@@ -576,11 +970,8 @@ impl<T, F: FnOnce() -> T> SyncLazy<T, F> {
     /// returns a reference to result. This is equivalent
     /// to the `Deref` impl, but is explicit.
     ///
-    /// # Examples
-    ///
+    /// # Example
     /// ```
-    /// #![feature(once_cell)]
-    ///
     /// use std::lazy::SyncLazy;
     ///
     /// let lazy = SyncLazy::new(|| 92);
@@ -588,16 +979,14 @@ impl<T, F: FnOnce() -> T> SyncLazy<T, F> {
     /// assert_eq!(SyncLazy::force(&lazy), &92);
     /// assert_eq!(&*lazy, &92);
     /// ```
-    #[unstable(feature = "once_cell", issue = "68198")]
     pub fn force(this: &SyncLazy<T, F>) -> &T {
         this.cell.get_or_init(|| match this.init.take() {
             Some(f) => f(),
-            None => panic!("Lazy instance has previously been poisoned"),
+            None => panic!("SyncLazy instance has previously been poisoned"),
         })
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T, F: FnOnce() -> T> Deref for SyncLazy<T, F> {
     type Target = T;
     fn deref(&self) -> &T {
@@ -605,348 +994,9 @@ impl<T, F: FnOnce() -> T> Deref for SyncLazy<T, F> {
     }
 }
 
-#[unstable(feature = "once_cell", issue = "68198")]
 impl<T: Default> Default for SyncLazy<T> {
     /// Creates a new lazy value using `Default` as the initializing function.
     fn default() -> SyncLazy<T> {
         SyncLazy::new(T::default)
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use crate::{
-        lazy::{Lazy, SyncLazy, SyncOnceCell},
-        panic,
-        sync::{
-            atomic::{AtomicUsize, Ordering::SeqCst},
-            mpsc::channel,
-            Mutex,
-        },
-    };
-
-    #[test]
-    fn lazy_default() {
-        static CALLED: AtomicUsize = AtomicUsize::new(0);
-
-        struct Foo(u8);
-        impl Default for Foo {
-            fn default() -> Self {
-                CALLED.fetch_add(1, SeqCst);
-                Foo(42)
-            }
-        }
-
-        let lazy: Lazy<Mutex<Foo>> = <_>::default();
-
-        assert_eq!(CALLED.load(SeqCst), 0);
-
-        assert_eq!(lazy.lock().unwrap().0, 42);
-        assert_eq!(CALLED.load(SeqCst), 1);
-
-        lazy.lock().unwrap().0 = 21;
-
-        assert_eq!(lazy.lock().unwrap().0, 21);
-        assert_eq!(CALLED.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn lazy_poisoning() {
-        let x: Lazy<String> = Lazy::new(|| panic!("kaboom"));
-        for _ in 0..2 {
-            let res = panic::catch_unwind(panic::AssertUnwindSafe(|| x.len()));
-            assert!(res.is_err());
-        }
-    }
-
-    // miri doesn't support threads
-    #[cfg(not(miri))]
-    fn spawn_and_wait<R: Send + 'static>(f: impl FnOnce() -> R + Send + 'static) -> R {
-        crate::thread::spawn(f).join().unwrap()
-    }
-
-    #[cfg(not(miri))]
-    fn spawn(f: impl FnOnce() + Send + 'static) {
-        let _ = crate::thread::spawn(f);
-    }
-
-    // "stub threads" for Miri
-    #[cfg(miri)]
-    fn spawn_and_wait<R: Send + 'static>(f: impl FnOnce() -> R + Send + 'static) -> R {
-        f(())
-    }
-
-    #[cfg(miri)]
-    fn spawn(f: impl FnOnce() + Send + 'static) {
-        f(())
-    }
-
-    #[test]
-    fn sync_once_cell() {
-        static ONCE_CELL: SyncOnceCell<i32> = SyncOnceCell::new();
-
-        assert!(ONCE_CELL.get().is_none());
-
-        spawn_and_wait(|| {
-            ONCE_CELL.get_or_init(|| 92);
-            assert_eq!(ONCE_CELL.get(), Some(&92));
-        });
-
-        ONCE_CELL.get_or_init(|| panic!("Kabom!"));
-        assert_eq!(ONCE_CELL.get(), Some(&92));
-    }
-
-    #[test]
-    fn sync_once_cell_get_mut() {
-        let mut c = SyncOnceCell::new();
-        assert!(c.get_mut().is_none());
-        c.set(90).unwrap();
-        *c.get_mut().unwrap() += 2;
-        assert_eq!(c.get_mut(), Some(&mut 92));
-    }
-
-    #[test]
-    fn sync_once_cell_get_unchecked() {
-        let c = SyncOnceCell::new();
-        c.set(92).unwrap();
-        unsafe {
-            assert_eq!(c.get_unchecked(), &92);
-        }
-    }
-
-    #[test]
-    fn sync_once_cell_drop() {
-        static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
-        struct Dropper;
-        impl Drop for Dropper {
-            fn drop(&mut self) {
-                DROP_CNT.fetch_add(1, SeqCst);
-            }
-        }
-
-        let x = SyncOnceCell::new();
-        spawn_and_wait(move || {
-            x.get_or_init(|| Dropper);
-            assert_eq!(DROP_CNT.load(SeqCst), 0);
-            drop(x);
-        });
-
-        assert_eq!(DROP_CNT.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn sync_once_cell_drop_empty() {
-        let x = SyncOnceCell::<String>::new();
-        drop(x);
-    }
-
-    #[test]
-    fn clone() {
-        let s = SyncOnceCell::new();
-        let c = s.clone();
-        assert!(c.get().is_none());
-
-        s.set("hello".to_string()).unwrap();
-        let c = s.clone();
-        assert_eq!(c.get().map(String::as_str), Some("hello"));
-    }
-
-    #[test]
-    fn get_or_try_init() {
-        let cell: SyncOnceCell<String> = SyncOnceCell::new();
-        assert!(cell.get().is_none());
-
-        let res = panic::catch_unwind(|| cell.get_or_try_init(|| -> Result<_, ()> { panic!() }));
-        assert!(res.is_err());
-        assert!(cell.get().is_none());
-
-        assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
-
-        assert_eq!(
-            cell.get_or_try_init(|| Ok::<_, ()>("hello".to_string())),
-            Ok(&"hello".to_string())
-        );
-        assert_eq!(cell.get(), Some(&"hello".to_string()));
-    }
-
-    #[test]
-    fn from_impl() {
-        assert_eq!(SyncOnceCell::from("value").get(), Some(&"value"));
-        assert_ne!(SyncOnceCell::from("foo").get(), Some(&"bar"));
-    }
-
-    #[test]
-    fn partialeq_impl() {
-        assert!(SyncOnceCell::from("value") == SyncOnceCell::from("value"));
-        assert!(SyncOnceCell::from("foo") != SyncOnceCell::from("bar"));
-
-        assert!(SyncOnceCell::<String>::new() == SyncOnceCell::new());
-        assert!(SyncOnceCell::<String>::new() != SyncOnceCell::from("value".to_owned()));
-    }
-
-    #[test]
-    fn into_inner() {
-        let cell: SyncOnceCell<String> = SyncOnceCell::new();
-        assert_eq!(cell.into_inner(), None);
-        let cell = SyncOnceCell::new();
-        cell.set("hello".to_string()).unwrap();
-        assert_eq!(cell.into_inner(), Some("hello".to_string()));
-    }
-
-    #[test]
-    fn sync_lazy_new() {
-        static CALLED: AtomicUsize = AtomicUsize::new(0);
-        static SYNC_LAZY: SyncLazy<i32> = SyncLazy::new(|| {
-            CALLED.fetch_add(1, SeqCst);
-            92
-        });
-
-        assert_eq!(CALLED.load(SeqCst), 0);
-
-        spawn_and_wait(|| {
-            let y = *SYNC_LAZY - 30;
-            assert_eq!(y, 62);
-            assert_eq!(CALLED.load(SeqCst), 1);
-        });
-
-        let y = *SYNC_LAZY - 30;
-        assert_eq!(y, 62);
-        assert_eq!(CALLED.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn sync_lazy_default() {
-        static CALLED: AtomicUsize = AtomicUsize::new(0);
-
-        struct Foo(u8);
-        impl Default for Foo {
-            fn default() -> Self {
-                CALLED.fetch_add(1, SeqCst);
-                Foo(42)
-            }
-        }
-
-        let lazy: SyncLazy<Mutex<Foo>> = <_>::default();
-
-        assert_eq!(CALLED.load(SeqCst), 0);
-
-        assert_eq!(lazy.lock().unwrap().0, 42);
-        assert_eq!(CALLED.load(SeqCst), 1);
-
-        lazy.lock().unwrap().0 = 21;
-
-        assert_eq!(lazy.lock().unwrap().0, 21);
-        assert_eq!(CALLED.load(SeqCst), 1);
-    }
-
-    #[test]
-    #[cfg_attr(miri, ignore)] // leaks memory
-    fn static_sync_lazy() {
-        static XS: SyncLazy<Vec<i32>> = SyncLazy::new(|| {
-            let mut xs = Vec::new();
-            xs.push(1);
-            xs.push(2);
-            xs.push(3);
-            xs
-        });
-
-        spawn_and_wait(|| {
-            assert_eq!(&*XS, &vec![1, 2, 3]);
-        });
-
-        assert_eq!(&*XS, &vec![1, 2, 3]);
-    }
-
-    #[test]
-    #[cfg_attr(miri, ignore)] // leaks memory
-    fn static_sync_lazy_via_fn() {
-        fn xs() -> &'static Vec<i32> {
-            static XS: SyncOnceCell<Vec<i32>> = SyncOnceCell::new();
-            XS.get_or_init(|| {
-                let mut xs = Vec::new();
-                xs.push(1);
-                xs.push(2);
-                xs.push(3);
-                xs
-            })
-        }
-        assert_eq!(xs(), &vec![1, 2, 3]);
-    }
-
-    #[test]
-    fn sync_lazy_poisoning() {
-        let x: SyncLazy<String> = SyncLazy::new(|| panic!("kaboom"));
-        for _ in 0..2 {
-            let res = panic::catch_unwind(|| x.len());
-            assert!(res.is_err());
-        }
-    }
-
-    #[test]
-    fn is_sync_send() {
-        fn assert_traits<T: Send + Sync>() {}
-        assert_traits::<SyncOnceCell<String>>();
-        assert_traits::<SyncLazy<String>>();
-    }
-
-    #[test]
-    fn eval_once_macro() {
-        macro_rules! eval_once {
-            (|| -> $ty:ty {
-                $($body:tt)*
-            }) => {{
-                static ONCE_CELL: SyncOnceCell<$ty> = SyncOnceCell::new();
-                fn init() -> $ty {
-                    $($body)*
-                }
-                ONCE_CELL.get_or_init(init)
-            }};
-        }
-
-        let fib: &'static Vec<i32> = eval_once! {
-            || -> Vec<i32> {
-                let mut res = vec![1, 1];
-                for i in 0..10 {
-                    let next = res[i] + res[i + 1];
-                    res.push(next);
-                }
-                res
-            }
-        };
-        assert_eq!(fib[5], 8)
-    }
-
-    #[test]
-    #[cfg_attr(miri, ignore)] // deadlocks without real threads
-    fn sync_once_cell_does_not_leak_partially_constructed_boxes() {
-        static ONCE_CELL: SyncOnceCell<String> = SyncOnceCell::new();
-
-        let n_readers = 10;
-        let n_writers = 3;
-        const MSG: &str = "Hello, World";
-
-        let (tx, rx) = channel();
-
-        for _ in 0..n_readers {
-            let tx = tx.clone();
-            spawn(move || {
-                loop {
-                    if let Some(msg) = ONCE_CELL.get() {
-                        tx.send(msg).unwrap();
-                        break;
-                    }
-                }
-            });
-        }
-        for _ in 0..n_writers {
-            spawn(move || {
-                let _ = ONCE_CELL.set(MSG.to_owned());
-            });
-        }
-
-        for _ in 0..n_readers {
-            let msg = rx.recv().unwrap();
-            assert_eq!(msg, MSG);
-        }
-    }
-}
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 21978f0d936f4..9feefd4e242a1 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -284,7 +284,6 @@
 #![feature(linkage)]
 #![feature(llvm_asm)]
 #![feature(log_syntax)]
-#![feature(maybe_uninit_extra)]
 #![feature(maybe_uninit_ref)]
 #![feature(maybe_uninit_slice)]
 #![feature(min_specialization)]
@@ -292,7 +291,6 @@
 #![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(nll)]
-#![feature(once_cell)]
 #![feature(optin_builtin_traits)]
 #![feature(or_patterns)]
 #![feature(panic_info_message)]
@@ -477,7 +475,10 @@ pub mod process;
 pub mod sync;
 pub mod time;
 
-#[unstable(feature = "once_cell", issue = "68198")]
+#[unstable(
+    feature = "std_lazy",
+    issue = "99",
+)]
 pub mod lazy;
 
 #[stable(feature = "futures_api", since = "1.36.0")]

From 6eaaff4f1f24c8d512ab1d9ecd0295add1683a7e Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 24 Jul 2020 09:59:16 -0400
Subject: [PATCH 7/7] Revert "First cut of `std::lazy` module"

This reverts commit cac1768b03c8d6673c51605dca03997876979d68.
---
 src/libstd/lazy.rs | 1002 --------------------------------------------
 src/libstd/lib.rs  |    6 -
 2 files changed, 1008 deletions(-)
 delete mode 100644 src/libstd/lazy.rs

diff --git a/src/libstd/lazy.rs b/src/libstd/lazy.rs
deleted file mode 100644
index bcac2dc311aff..0000000000000
--- a/src/libstd/lazy.rs
+++ /dev/null
@@ -1,1002 +0,0 @@
-//! `lazy` modules provides lazy values and one-time initialization of static data.
-//!
-//! `lazy` provides two new cell-like types, `OnceCell` and `SyncOnceCell`. `OnceCell`
-//! might store arbitrary non-`Copy` types, can be assigned to at most once and provide direct access
-//! to the stored contents. In a nutshell, API looks *roughly* like this:
-//!
-//! ```rust,ignore
-//! impl<T> OnceCell<T> {
-//!     fn new() -> OnceCell<T> { ... }
-//!     fn set(&self, value: T) -> Result<(), T> { ... }
-//!     fn get(&self) -> Option<&T> { ... }
-//! }
-//! ```
-//!
-//! Note that, like with `RefCell` and `Mutex`, the `set` method requires only a shared reference.
-//! Because of the single assignment restriction `get` can return an `&T` instead of `Ref<T>`
-//! or `MutexGuard<T>`.
-//!
-//! The `SyncOnceCell` flavor is thread-safe (that is, implements [`Sync`]) trait, while  `OnceCell` one is not.
-//!
-//! [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html
-//!
-//! # Patterns
-//!
-//! `OnceCell` might be useful for a variety of patterns.
-//!
-//! ## Safe Initialization of global data
-//!
-//! ```rust
-//! use std::{env, io};
-//! use std::lazy::SyncOnceCell;
-//!
-//! #[derive(Debug)]
-//! pub struct Logger {
-//!     // ...
-//! }
-//! static INSTANCE: OnceCell<Logger> = OnceCell::new();
-//!
-//! impl Logger {
-//!     pub fn global() -> &'static Logger {
-//!         INSTANCE.get().expect("logger is not initialized")
-//!     }
-//!
-//!     fn from_cli(args: env::Args) -> Result<Logger, std::io::Error> {
-//!        // ...
-//! #      Ok(Logger {})
-//!     }
-//! }
-//!
-//! fn main() {
-//!     let logger = Logger::from_cli(env::args()).unwrap();
-//!     INSTANCE.set(logger).unwrap();
-//!     // use `Logger::global()` from now on
-//! }
-//! ```
-//!
-//! ## Lazy initialized global data
-//!
-//! This is essentially `lazy_static!` macro, but without a macro.
-//!
-//! ```rust
-//! use std::{sync::Mutex, collections::HashMap};
-//! use lazy::SyncOnceCell;
-//!
-//! fn global_data() -> &'static Mutex<HashMap<i32, String>> {
-//!     static INSTANCE: OnceCell<Mutex<HashMap<i32, String>>> = OnceCell::new();
-//!     INSTANCE.get_or_init(|| {
-//!         let mut m = HashMap::new();
-//!         m.insert(13, "Spica".to_string());
-//!         m.insert(74, "Hoyten".to_string());
-//!         Mutex::new(m)
-//!     })
-//! }
-//! ```
-//!
-//! There are also `sync::Lazy` and `unsync::Lazy` convenience types to streamline this pattern:
-//!
-//! ```rust
-//! use std::{sync::Mutex, collections::HashMap};
-//! use lazy::SyncLazy;
-//!
-//! static GLOBAL_DATA: Lazy<Mutex<HashMap<i32, String>>> = Lazy::new(|| {
-//!     let mut m = HashMap::new();
-//!     m.insert(13, "Spica".to_string());
-//!     m.insert(74, "Hoyten".to_string());
-//!     Mutex::new(m)
-//! });
-//!
-//! fn main() {
-//!     println!("{:?}", GLOBAL_DATA.lock().unwrap());
-//! }
-//! ```
-//!
-//! ## General purpose lazy evaluation
-//!
-//! `Lazy` also works with local variables.
-//!
-//! ```rust
-//! use std::lazy::Lazy;
-//!
-//! fn main() {
-//!     let ctx = vec![1, 2, 3];
-//!     let thunk = Lazy::new(|| {
-//!         ctx.iter().sum::<i32>()
-//!     });
-//!     assert_eq!(*thunk, 6);
-//! }
-//! ```
-//!
-//! If you need a lazy field in a struct, you probably should use `OnceCell`
-//! directly, because that will allow you to access `self` during initialization.
-//!
-//! ```rust
-//! use std::{fs, path::PathBuf};
-//!
-//! use std::lazy::OnceCell;
-//!
-//! struct Ctx {
-//!     config_path: PathBuf,
-//!     config: OnceCell<String>,
-//! }
-//!
-//! impl Ctx {
-//!     pub fn get_config(&self) -> Result<&str, std::io::Error> {
-//!         let cfg = self.config.get_or_try_init(|| {
-//!             fs::read_to_string(&self.config_path)
-//!         })?;
-//!         Ok(cfg.as_str())
-//!     }
-//! }
-//! ```
-//!
-//! ## Building block
-//!
-//! Naturally, it is  possible to build other abstractions on top of `OnceCell`.
-//! For example, this is a `regex!` macro which takes a string literal and returns an
-//! *expression* that evaluates to a `&'static Regex`:
-//!
-//! ```
-//! macro_rules! regex {
-//!     ($re:literal $(,)?) => {{
-//!         static RE: std::lazy::SyncOnceCell<regex::Regex> = std::lazy::SyncOnceCell::new();
-//!         RE.get_or_init(|| regex::Regex::new($re).unwrap())
-//!     }};
-//! }
-//! ```
-//!
-//! This macro can be useful to avoid "compile regex on every loop iteration" problem.
-//!
-//! # Comparison with other interior mutatbility types
-//!
-//! |`!Sync` types         | Access Mode            | Drawbacks                                     |
-//! |----------------------|------------------------|-----------------------------------------------|
-//! |`Cell<T>`             | `T`                    | requires `T: Copy` for `get`                  |
-//! |`RefCell<T>`          | `RefMut<T>` / `Ref<T>` | may panic at runtime                          |
-//! |`OnceCell<T>`         | `&T`                   | assignable only once                          |
-//!
-//! |`Sync` types          | Access Mode            | Drawbacks                                     |
-//! |----------------------|------------------------|-----------------------------------------------|
-//! |`AtomicT`             | `T`                    | works only with certain `Copy` types          |
-//! |`Mutex<T>`            | `MutexGuard<T>`        | may deadlock at runtime, may block the thread |
-//! |`SyncOnceCell<T>`     | `&T`                   | assignable only once, may block the thread    |
-//!
-//! Technically, calling `get_or_init` will also cause a panic or a deadlock if it recursively calls
-//! itself. However, because the assignment can happen only once, such cases should be more rare than
-//! equivalents with `RefCell` and `Mutex`.
-
-use crate::{
-    cell::{Cell, UnsafeCell},
-    fmt,
-    hint::unreachable_unchecked,
-    marker::PhantomData,
-    ops::Deref,
-    panic::{RefUnwindSafe, UnwindSafe},
-    sync::atomic::{AtomicBool, AtomicUsize, Ordering},
-    thread::{self, Thread},
-};
-
-/// A cell which can be written to only once. Not thread safe.
-///
-/// Unlike `:td::cell::RefCell`, a `OnceCell` provides simple `&`
-/// references to the contents.
-///
-/// # Example
-/// ```
-/// use std::lazy::OnceCell;
-///
-/// let cell = OnceCell::new();
-/// assert!(cell.get().is_none());
-///
-/// let value: &String = cell.get_or_init(|| {
-///     "Hello, World!".to_string()
-/// });
-/// assert_eq!(value, "Hello, World!");
-/// assert!(cell.get().is_some());
-/// ```
-pub struct OnceCell<T> {
-    // Invariant: written to at most once.
-    inner: UnsafeCell<Option<T>>,
-}
-
-// Similarly to a `Sync` bound on `SyncOnceCell`, we can use
-// `&OnceCell` to sneak a `T` through `catch_unwind`,
-// by initializing the cell in closure and extracting the value in the
-// `Drop`.
-#[cfg(feature = "std")]
-impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T> {}
-#[cfg(feature = "std")]
-impl<T: UnwindSafe> UnwindSafe for OnceCell<T> {}
-
-impl<T> Default for OnceCell<T> {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
-impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.get() {
-            Some(v) => f.debug_tuple("OnceCell").field(v).finish(),
-            None => f.write_str("OnceCell(Uninit)"),
-        }
-    }
-}
-
-impl<T: Clone> Clone for OnceCell<T> {
-    fn clone(&self) -> OnceCell<T> {
-        let res = OnceCell::new();
-        if let Some(value) = self.get() {
-            match res.set(value.clone()) {
-                Ok(()) => (),
-                Err(_) => unreachable!(),
-            }
-        }
-        res
-    }
-}
-
-impl<T: PartialEq> PartialEq for OnceCell<T> {
-    fn eq(&self, other: &Self) -> bool {
-        self.get() == other.get()
-    }
-}
-
-impl<T: Eq> Eq for OnceCell<T> {}
-
-impl<T> From<T> for OnceCell<T> {
-    fn from(value: T) -> Self {
-        OnceCell { inner: UnsafeCell::new(Some(value)) }
-    }
-}
-
-impl<T> OnceCell<T> {
-    /// Creates a new empty cell.
-    pub const fn new() -> OnceCell<T> {
-        OnceCell { inner: UnsafeCell::new(None) }
-    }
-
-    /// Gets the reference to the underlying value.
-    ///
-    /// Returns `None` if the cell is empty.
-    pub fn get(&self) -> Option<&T> {
-        // Safe due to `inner`'s invariant
-        unsafe { &*self.inner.get() }.as_ref()
-    }
-
-    /// Gets the mutable reference to the underlying value.
-    ///
-    /// Returns `None` if the cell is empty.
-    pub fn get_mut(&mut self) -> Option<&mut T> {
-        // Safe because we have unique access
-        unsafe { &mut *self.inner.get() }.as_mut()
-    }
-
-    /// Sets the contents of this cell to `value`.
-    ///
-    /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was
-    /// full.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell = OnceCell::new();
-    /// assert!(cell.get().is_none());
-    ///
-    /// assert_eq!(cell.set(92), Ok(()));
-    /// assert_eq!(cell.set(62), Err(62));
-    ///
-    /// assert!(cell.get().is_some());
-    /// ```
-    pub fn set(&self, value: T) -> Result<(), T> {
-        let slot = unsafe { &*self.inner.get() };
-        if slot.is_some() {
-            return Err(value);
-        }
-        let slot = unsafe { &mut *self.inner.get() };
-        // This is the only place where we set the slot, no races
-        // due to reentrancy/concurrency are possible, and we've
-        // checked that slot is currently `None`, so this write
-        // maintains the `inner`'s invariant.
-        *slot = Some(value);
-        Ok(())
-    }
-
-    /// Gets the contents of the cell, initializing it with `f`
-    /// if the cell was empty.
-    ///
-    /// # Panics
-    ///
-    /// If `f` panics, the panic is propagated to the caller, and the cell
-    /// remains uninitialized.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`. Doing
-    /// so results in a panic.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell = OnceCell::new();
-    /// let value = cell.get_or_init(|| 92);
-    /// assert_eq!(value, &92);
-    /// let value = cell.get_or_init(|| unreachable!());
-    /// assert_eq!(value, &92);
-    /// ```
-    pub fn get_or_init<F>(&self, f: F) -> &T
-    where
-        F: FnOnce() -> T,
-    {
-        match self.get_or_try_init(|| Ok::<T, !>(f())) {
-            Ok(val) => val,
-        }
-    }
-
-    /// Gets the contents of the cell, initializing it with `f` if
-    /// the cell was empty. If the cell was empty and `f` failed, an
-    /// error is returned.
-    ///
-    /// # Panics
-    ///
-    /// If `f` panics, the panic is propagated to the caller, and the cell
-    /// remains uninitialized.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`. Doing
-    /// so results in a panic.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell = OnceCell::new();
-    /// assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
-    /// assert!(cell.get().is_none());
-    /// let value = cell.get_or_try_init(|| -> Result<i32, ()> {
-    ///     Ok(92)
-    /// });
-    /// assert_eq!(value, Ok(&92));
-    /// assert_eq!(cell.get(), Some(&92))
-    /// ```
-    pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
-    where
-        F: FnOnce() -> Result<T, E>,
-    {
-        if let Some(val) = self.get() {
-            return Ok(val);
-        }
-        let val = f()?;
-        // Note that *some* forms of reentrant initialization might lead to
-        // UB (see `reentrant_init` test). I believe that just removing this
-        // `assert`, while keeping `set/get` would be sound, but it seems
-        // better to panic, rather than to silently use an old value.
-        assert!(self.set(val).is_ok(), "reentrant init");
-        Ok(self.get().unwrap())
-    }
-
-    /// Consumes the `OnceCell`, returning the wrapped value.
-    ///
-    /// Returns `None` if the cell was empty.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::lazy::OnceCell;
-    ///
-    /// let cell: OnceCell<String> = OnceCell::new();
-    /// assert_eq!(cell.into_inner(), None);
-    ///
-    /// let cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
-    /// ```
-    pub fn into_inner(self) -> Option<T> {
-        // Because `into_inner` takes `self` by value, the compiler statically verifies
-        // that it is not currently borrowed. So it is safe to move out `Option<T>`.
-        self.inner.into_inner()
-    }
-}
-
-/// A value which is initialized on the first access.
-///
-/// # Example
-/// ```
-/// use std::lazy::Lazy;
-///
-/// let lazy: Lazy<i32> = Lazy::new(|| {
-///     println!("initializing");
-///     92
-/// });
-/// println!("ready");
-/// println!("{}", *lazy);
-/// println!("{}", *lazy);
-///
-/// // Prints:
-/// //   ready
-/// //   initializing
-/// //   92
-/// //   92
-/// ```
-pub struct Lazy<T, F = fn() -> T> {
-    cell: OnceCell<T>,
-    init: Cell<Option<F>>,
-}
-
-#[cfg(feature = "std")]
-impl<T, F: RefUnwindSafe> RefUnwindSafe for Lazy<T, F> where OnceCell<T>: RefUnwindSafe {}
-
-impl<T: fmt::Debug, F: fmt::Debug> fmt::Debug for Lazy<T, F> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
-    }
-}
-
-impl<T, F> Lazy<T, F> {
-    /// Creates a new lazy value with the given initializing function.
-    ///
-    /// # Example
-    /// ```
-    /// # fn main() {
-    /// use std::lazy::Lazy;
-    ///
-    /// let hello = "Hello, World!".to_string();
-    ///
-    /// let lazy = Lazy::new(|| hello.to_uppercase());
-    ///
-    /// assert_eq!(&*lazy, "HELLO, WORLD!");
-    /// # }
-    /// ```
-    pub const fn new(init: F) -> Lazy<T, F> {
-        Lazy { cell: OnceCell::new(), init: Cell::new(Some(init)) }
-    }
-}
-
-impl<T, F: FnOnce() -> T> Lazy<T, F> {
-    /// Forces the evaluation of this lazy value and returns a reference to
-    /// the result.
-    ///
-    /// This is equivalent to the `Deref` impl, but is explicit.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::Lazy;
-    ///
-    /// let lazy = Lazy::new(|| 92);
-    ///
-    /// assert_eq!(Lazy::force(&lazy), &92);
-    /// assert_eq!(&*lazy, &92);
-    /// ```
-    pub fn force(this: &Lazy<T, F>) -> &T {
-        this.cell.get_or_init(|| match this.init.take() {
-            Some(f) => f(),
-            None => panic!("Lazy instance has previously been poisoned"),
-        })
-    }
-}
-
-impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
-    type Target = T;
-    fn deref(&self) -> &T {
-        Lazy::force(self)
-    }
-}
-
-impl<T: Default> Default for Lazy<T> {
-    /// Creates a new lazy value using `Default` as the initializing function.
-    fn default() -> Lazy<T> {
-        Lazy::new(T::default)
-    }
-}
-
-/// A thread-safe cell which can be written to only once.
-///
-/// `OnceCell` provides `&` references to the contents without RAII guards.
-///
-/// Reading a non-`None` value out of `OnceCell` establishes a
-/// happens-before relationship with a corresponding write. For example, if
-/// thread A initializes the cell with `get_or_init(f)`, and thread B
-/// subsequently reads the result of this call, B also observes all the side
-/// effects of `f`.
-///
-/// # Example
-/// ```
-/// use std::lazy::SyncOnceCell;
-///
-/// static CELL: OnceCell<String> = OnceCell::new();
-/// assert!(CELL.get().is_none());
-///
-/// std::thread::spawn(|| {
-///     let value: &String = CELL.get_or_init(|| {
-///         "Hello, World!".to_string()
-///     });
-///     assert_eq!(value, "Hello, World!");
-/// }).join().unwrap();
-///
-/// let value: Option<&String> = CELL.get();
-/// assert!(value.is_some());
-/// assert_eq!(value.unwrap().as_str(), "Hello, World!");
-/// ```
-pub struct SyncOnceCell<T> {
-    // This `state` word is actually an encoded version of just a pointer to a
-    // `Waiter`, so we add the `PhantomData` appropriately.
-    state_and_queue: AtomicUsize,
-    _marker: PhantomData<*mut Waiter>,
-    // FIXME: switch to `std::mem::MaybeUninit` once we are ready to bump MSRV
-    // that far. It was stabilized in 1.36.0, so, if you are reading this and
-    // it's higher than 1.46.0 outside, please send a PR! ;) (and do the same
-    // for `Lazy`, while we are at it).
-    pub(crate) value: UnsafeCell<Option<T>>,
-}
-
-// Why do we need `T: Send`?
-// Thread A creates a `OnceCell` and shares it with
-// scoped thread B, which fills the cell, which is
-// then destroyed by A. That is, destructor observes
-// a sent value.
-unsafe impl<T: Sync + Send> Sync for SyncOnceCell<T> {}
-unsafe impl<T: Send> Send for SyncOnceCell<T> {}
-
-impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SyncOnceCell<T> {}
-impl<T: UnwindSafe> UnwindSafe for SyncOnceCell<T> {}
-
-impl<T> Default for SyncOnceCell<T> {
-    fn default() -> SyncOnceCell<T> {
-        SyncOnceCell::new()
-    }
-}
-
-impl<T: fmt::Debug> fmt::Debug for SyncOnceCell<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.get() {
-            Some(v) => f.debug_tuple("SyncOnceCell").field(v).finish(),
-            None => f.write_str("SyncOnceCell(Uninit)"),
-        }
-    }
-}
-
-impl<T: Clone> Clone for SyncOnceCell<T> {
-    fn clone(&self) -> SyncOnceCell<T> {
-        let res = SyncOnceCell::new();
-        if let Some(value) = self.get() {
-            match res.set(value.clone()) {
-                Ok(()) => (),
-                Err(_) => unreachable!(),
-            }
-        }
-        res
-    }
-}
-
-impl<T> From<T> for SyncOnceCell<T> {
-    fn from(value: T) -> Self {
-        let cell = Self::new();
-        cell.get_or_init(|| value);
-        cell
-    }
-}
-
-impl<T: PartialEq> PartialEq for SyncOnceCell<T> {
-    fn eq(&self, other: &SyncOnceCell<T>) -> bool {
-        self.get() == other.get()
-    }
-}
-
-impl<T: Eq> Eq for SyncOnceCell<T> {}
-
-impl<T> SyncOnceCell<T> {
-    /// Creates a new empty cell.
-    pub const fn new() -> SyncOnceCell<T> {
-        SyncOnceCell {
-            state_and_queue: AtomicUsize::new(INCOMPLETE),
-            _marker: PhantomData,
-            value: UnsafeCell::new(None),
-        }
-    }
-
-    /// Gets the reference to the underlying value.
-    ///
-    /// Returns `None` if the cell is empty, or being initialized. This
-    /// method never blocks.
-    pub fn get(&self) -> Option<&T> {
-        if self.is_initialized() {
-            // Safe b/c checked is_initialize
-            Some(unsafe { self.get_unchecked() })
-        } else {
-            None
-        }
-    }
-
-    /// Gets the mutable reference to the underlying value.
-    ///
-    /// Returns `None` if the cell is empty.
-    pub fn get_mut(&mut self) -> Option<&mut T> {
-        // Safe b/c we have a unique access.
-        unsafe { &mut *self.value.get() }.as_mut()
-    }
-
-    /// Get the reference to the underlying value, without checking if the
-    /// cell is initialized.
-    ///
-    /// Safety:
-    ///
-    /// Caller must ensure that the cell is in initialized state, and that
-    /// the contents are acquired by (synchronized to) this thread.
-    pub unsafe fn get_unchecked(&self) -> &T {
-        debug_assert!(self.is_initialized());
-        let slot: &Option<T> = &*self.value.get();
-        match slot {
-            Some(value) => value,
-            // This unsafe does improve performance, see `examples/bench`.
-            None => {
-                debug_assert!(false);
-                unreachable_unchecked()
-            }
-        }
-    }
-
-    /// Sets the contents of this cell to `value`.
-    ///
-    /// Returns `Ok(())` if the cell was empty and `Err(value)` if it was
-    /// full.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::SyncOnceCell;
-    ///
-    /// static CELL: SyncOnceCell<i32> = SyncOnceCell::new();
-    ///
-    /// fn main() {
-    ///     assert!(CELL.get().is_none());
-    ///
-    ///     std::thread::spawn(|| {
-    ///         assert_eq!(CELL.set(92), Ok(()));
-    ///     }).join().unwrap();
-    ///
-    ///     assert_eq!(CELL.set(62), Err(62));
-    ///     assert_eq!(CELL.get(), Some(&92));
-    /// }
-    /// ```
-    pub fn set(&self, value: T) -> Result<(), T> {
-        let mut value = Some(value);
-        self.get_or_init(|| value.take().unwrap());
-        match value {
-            None => Ok(()),
-            Some(value) => Err(value),
-        }
-    }
-
-    /// Gets the contents of the cell, initializing it with `f` if the cell
-    /// was empty.
-    ///
-    /// Many threads may call `get_or_init` concurrently with different
-    /// initializing functions, but it is guaranteed that only one function
-    /// will be executed.
-    ///
-    /// # Panics
-    ///
-    /// If `f` panics, the panic is propagated to the caller, and the cell
-    /// remains uninitialized.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`. The
-    /// exact outcome is unspecified. Current implementation deadlocks, but
-    /// this may be changed to a panic in the future.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::SyncOnceCell;
-    ///
-    /// let cell = SyncOnceCell::new();
-    /// let value = cell.get_or_init(|| 92);
-    /// assert_eq!(value, &92);
-    /// let value = cell.get_or_init(|| unreachable!());
-    /// assert_eq!(value, &92);
-    /// ```
-    pub fn get_or_init<F>(&self, f: F) -> &T
-    where
-        F: FnOnce() -> T,
-    {
-        match self.get_or_try_init(|| Ok::<T, !>(f())) {
-            Ok(val) => val,
-        }
-    }
-
-    /// Gets the contents of the cell, initializing it with `f` if
-    /// the cell was empty. If the cell was empty and `f` failed, an
-    /// error is returned.
-    ///
-    /// # Panics
-    ///
-    /// If `f` panics, the panic is propagated to the caller, and
-    /// the cell remains uninitialized.
-    ///
-    /// It is an error to reentrantly initialize the cell from `f`.
-    /// The exact outcome is unspecified. Current implementation
-    /// deadlocks, but this may be changed to a panic in the future.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::SyncOnceCell;
-    ///
-    /// let cell = SyncOnceCell::new();
-    /// assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
-    /// assert!(cell.get().is_none());
-    /// let value = cell.get_or_try_init(|| -> Result<i32, ()> {
-    ///     Ok(92)
-    /// });
-    /// assert_eq!(value, Ok(&92));
-    /// assert_eq!(cell.get(), Some(&92))
-    /// ```
-    pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
-    where
-        F: FnOnce() -> Result<T, E>,
-    {
-        // Fast path check
-        if let Some(value) = self.get() {
-            return Ok(value);
-        }
-        self.initialize(f)?;
-
-        // Safe b/c called initialize
-        debug_assert!(self.is_initialized());
-        Ok(unsafe { self.get_unchecked() })
-    }
-
-    /// Consumes the `SyncOnceCell`, returning the wrapped value. Returns
-    /// `None` if the cell was empty.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::lazy::SyncOnceCell;
-    ///
-    /// let cell: SyncOnceCell<String> = SyncOnceCell::new();
-    /// assert_eq!(cell.into_inner(), None);
-    ///
-    /// let cell = SyncOnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
-    /// ```
-    pub fn into_inner(self) -> Option<T> {
-        // Because `into_inner` takes `self` by value, the compiler statically verifies
-        // that it is not currently borrowed. So it is safe to move out `Option<T>`.
-        self.value.into_inner()
-    }
-
-    /// Safety: synchronizes with store to value via Release/(Acquire|SeqCst).
-    #[inline]
-    fn is_initialized(&self) -> bool {
-        // An `Acquire` load is enough because that makes all the initialization
-        // operations visible to us, and, this being a fast path, weaker
-        // ordering helps with performance. This `Acquire` synchronizes with
-        // `SeqCst` operations on the slow path.
-        self.state_and_queue.load(Ordering::Acquire) == COMPLETE
-    }
-
-    /// Safety: synchronizes with store to value via SeqCst read from state,
-    /// writes value only once because we never get to INCOMPLETE state after a
-    /// successful write.
-    #[cold]
-    fn initialize<F, E>(&self, f: F) -> Result<(), E>
-    where
-        F: FnOnce() -> Result<T, E>,
-    {
-        let mut f = Some(f);
-        let mut res: Result<(), E> = Ok(());
-        let slot = &self.value;
-        initialize_inner(&self.state_and_queue, &mut || {
-            let f = f.take().unwrap();
-            match f() {
-                Ok(value) => {
-                    unsafe { *slot.get() = Some(value) };
-                    true
-                }
-                Err(e) => {
-                    res = Err(e);
-                    false
-                }
-            }
-        });
-        res
-    }
-}
-
-// region: copy-paste
-// The following code is copied from `sync::Once`.
-// This should be uncopypasted once we decide the right way to handle panics.
-const INCOMPLETE: usize = 0x0;
-const RUNNING: usize = 0x1;
-const COMPLETE: usize = 0x2;
-
-const STATE_MASK: usize = 0x3;
-
-
-#[repr(align(4))]
-struct Waiter {
-    thread: Cell<Option<Thread>>,
-    signaled: AtomicBool,
-    next: *const Waiter,
-}
-
-struct WaiterQueue<'a> {
-    state_and_queue: &'a AtomicUsize,
-    set_state_on_drop_to: usize,
-}
-
-impl Drop for WaiterQueue<'_> {
-    fn drop(&mut self) {
-        let state_and_queue =
-            self.state_and_queue.swap(self.set_state_on_drop_to, Ordering::AcqRel);
-
-        assert_eq!(state_and_queue & STATE_MASK, RUNNING);
-
-        unsafe {
-            let mut queue = (state_and_queue & !STATE_MASK) as *const Waiter;
-            while !queue.is_null() {
-                let next = (*queue).next;
-                let thread = (*queue).thread.replace(None).unwrap();
-                (*queue).signaled.store(true, Ordering::Release);
-                queue = next;
-                thread.unpark();
-            }
-        }
-    }
-}
-
-fn initialize_inner(my_state_and_queue: &AtomicUsize, init: &mut dyn FnMut() -> bool) -> bool {
-    let mut state_and_queue = my_state_and_queue.load(Ordering::Acquire);
-
-    loop {
-        match state_and_queue {
-            COMPLETE => return true,
-            INCOMPLETE => {
-                let old = my_state_and_queue.compare_and_swap(
-                    state_and_queue,
-                    RUNNING,
-                    Ordering::Acquire,
-                );
-                if old != state_and_queue {
-                    state_and_queue = old;
-                    continue;
-                }
-                let mut waiter_queue = WaiterQueue {
-                    state_and_queue: my_state_and_queue,
-                    set_state_on_drop_to: INCOMPLETE,
-                };
-                let success = init();
-
-                waiter_queue.set_state_on_drop_to = if success { COMPLETE } else { INCOMPLETE };
-                return success;
-            }
-            _ => {
-                assert!(state_and_queue & STATE_MASK == RUNNING);
-                wait(&my_state_and_queue, state_and_queue);
-                state_and_queue = my_state_and_queue.load(Ordering::Acquire);
-            }
-        }
-    }
-}
-
-fn wait(state_and_queue: &AtomicUsize, mut current_state: usize) {
-    loop {
-        if current_state & STATE_MASK != RUNNING {
-            return;
-        }
-
-        let node = Waiter {
-            thread: Cell::new(Some(thread::current())),
-            signaled: AtomicBool::new(false),
-            next: (current_state & !STATE_MASK) as *const Waiter,
-        };
-        let me = &node as *const Waiter as usize;
-
-        let old = state_and_queue.compare_and_swap(current_state, me | RUNNING, Ordering::Release);
-        if old != current_state {
-            current_state = old;
-            continue;
-        }
-
-        while !node.signaled.load(Ordering::Acquire) {
-            thread::park();
-        }
-        break;
-    }
-}
-// endregion: copy-paste
-
-/// A value which is initialized on the first access.
-///
-/// This type is thread-safe and can be used in statics:
-///
-/// # Example
-/// ```
-/// use std::collections::HashMap;
-///
-/// use std::lazy::Lazy;
-///
-/// static HASHMAP: Lazy<HashMap<i32, String>> = Lazy::new(|| {
-///     println!("initializing");
-///     let mut m = HashMap::new();
-///     m.insert(13, "Spica".to_string());
-///     m.insert(74, "Hoyten".to_string());
-///     m
-/// });
-///
-/// fn main() {
-///     println!("ready");
-///     std::thread::spawn(|| {
-///         println!("{:?}", HASHMAP.get(&13));
-///     }).join().unwrap();
-///     println!("{:?}", HASHMAP.get(&74));
-///
-///     // Prints:
-///     //   ready
-///     //   initializing
-///     //   Some("Spica")
-///     //   Some("Hoyten")
-/// }
-/// ```
-pub struct SyncLazy<T, F = fn() -> T> {
-    cell: SyncOnceCell<T>,
-    init: Cell<Option<F>>,
-}
-
-impl<T: fmt::Debug, F: fmt::Debug> fmt::Debug for SyncLazy<T, F> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("SyncLazy").field("cell", &self.cell).field("init", &"..").finish()
-    }
-}
-
-// We never create a `&F` from a `&SyncLazy<T, F>` so it is fine
-// to not impl `Sync` for `F`
-// we do create a `&mut Option<F>` in `force`, but this is
-// properly synchronized, so it only happens once
-// so it also does not contribute to this impl.
-unsafe impl<T, F: Send> Sync for SyncLazy<T, F> where SyncOnceCell<T>: Sync {}
-// auto-derived `Send` impl is OK.
-
-#[cfg(feature = "std")]
-impl<T, F: RefUnwindSafe> RefUnwindSafe for SyncLazy<T, F> where SyncOnceCell<T>: RefUnwindSafe {}
-
-impl<T, F> SyncLazy<T, F> {
-    /// Creates a new lazy value with the given initializing
-    /// function.
-    pub const fn new(f: F) -> SyncLazy<T, F> {
-        SyncLazy { cell: SyncOnceCell::new(), init: Cell::new(Some(f)) }
-    }
-}
-
-impl<T, F: FnOnce() -> T> SyncLazy<T, F> {
-    /// Forces the evaluation of this lazy value and
-    /// returns a reference to result. This is equivalent
-    /// to the `Deref` impl, but is explicit.
-    ///
-    /// # Example
-    /// ```
-    /// use std::lazy::SyncLazy;
-    ///
-    /// let lazy = SyncLazy::new(|| 92);
-    ///
-    /// assert_eq!(SyncLazy::force(&lazy), &92);
-    /// assert_eq!(&*lazy, &92);
-    /// ```
-    pub fn force(this: &SyncLazy<T, F>) -> &T {
-        this.cell.get_or_init(|| match this.init.take() {
-            Some(f) => f(),
-            None => panic!("SyncLazy instance has previously been poisoned"),
-        })
-    }
-}
-
-impl<T, F: FnOnce() -> T> Deref for SyncLazy<T, F> {
-    type Target = T;
-    fn deref(&self) -> &T {
-        SyncLazy::force(self)
-    }
-}
-
-impl<T: Default> Default for SyncLazy<T> {
-    /// Creates a new lazy value using `Default` as the initializing function.
-    fn default() -> SyncLazy<T> {
-        SyncLazy::new(T::default)
-    }
-}
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 9feefd4e242a1..5acc24c34fee6 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -475,12 +475,6 @@ pub mod process;
 pub mod sync;
 pub mod time;
 
-#[unstable(
-    feature = "std_lazy",
-    issue = "99",
-)]
-pub mod lazy;
-
 #[stable(feature = "futures_api", since = "1.36.0")]
 pub mod task {
     //! Types and Traits for working with asynchronous tasks.