Import scopeguard 1.1.0 am: 3ba109e9da am: 96a4bb4586 am: a7271b14bd am: e3629448a8

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/scopeguard/+/1460402

Change-Id: Iac87fac442791945b62ab90ba35ca60cedcd29be

14 files changed, 1036 insertions, 0 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
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index 0000000..55e0c60
--- /dev/null
+++ b/.cargo_vcs_info.json
@@ -0,0 +1,5 @@
+{
+  "git": {
+    "sha1": "c1ae9969f7c9bc9013602b4bf29bb789e6e7eb16"
+  }
+}
diff --git a/.gitignore b/.gitignore
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index 0000000..fa8d85a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+Cargo.lock
+target
diff --git a/.travis.yml b/.travis.yml
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index 0000000..a803d58
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,20 @@
+language: rust
+sudo: false
+
+rust:
+  - 1.20.0
+  - stable
+  - beta
+  - nightly
+
+branches:
+  only:
+    - master
+
+# the main build
+script:
+  - |
+      cargo build --no-default-features &&
+      cargo test --no-default-features &&
+      cargo build &&
+      cargo test
diff --git a/Cargo.toml b/Cargo.toml
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--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,28 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+name = "scopeguard"
+version = "1.1.0"
+authors = ["bluss"]
+description = "A RAII scope guard that will run a given closure when it goes out of scope,\neven if the code between panics (assuming unwinding panic).\n\nDefines the macros `defer!`, `defer_on_unwind!`, `defer_on_success!` as\nshorthands for guards with one of the implemented strategies.\n"
+documentation = "https://docs.rs/scopeguard/"
+keywords = ["scope-guard", "defer", "panic", "unwind"]
+categories = ["rust-patterns", "no-std"]
+license = "MIT/Apache-2.0"
+repository = "https://github.com/bluss/scopeguard"
+[package.metadata.release]
+no-dev-version = true
+
+[features]
+default = ["use_std"]
+use_std = []
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
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--- /dev/null
+++ b/Cargo.toml.orig
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+[package]
+name = "scopeguard"
+version = "1.1.0"
+
+license = "MIT/Apache-2.0"
+repository = "https://github.com/bluss/scopeguard"
+documentation = "https://docs.rs/scopeguard/"
+authors = ["bluss"]
+
+description = """
+A RAII scope guard that will run a given closure when it goes out of scope,
+even if the code between panics (assuming unwinding panic).
+
+Defines the macros `defer!`, `defer_on_unwind!`, `defer_on_success!` as
+shorthands for guards with one of the implemented strategies.
+"""
+
+keywords = ["scope-guard", "defer", "panic", "unwind"]
+categories = ["rust-patterns", "no-std"]
+
+[features]
+default = ["use_std"]
+use_std = []
+
+[package.metadata.release]
+no-dev-version = true
diff --git a/LICENSE b/LICENSE
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index 0000000..6b579aa
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+LICENSE-APACHE
\ No newline at end of file
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..16fe87b
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,201 @@
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diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..8514471
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,25 @@
+Copyright (c) 2016-2019 Ulrik Sverdrup "bluss" and scopeguard developers
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
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+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
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+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
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+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
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+DEALINGS IN THE SOFTWARE.
diff --git a/METADATA b/METADATA
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--- /dev/null
+++ b/METADATA
@@ -0,0 +1,19 @@
+name: "scopeguard"
+description: "A RAII scope guard that will run a given closure when it goes out of scope, even if the code between panics (assuming unwinding panic).  Defines the macros `defer!`, `defer_on_unwind!`, `defer_on_success!` as shorthands for guards with one of the implemented strategies."
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://crates.io/crates/scopeguard"
+  }
+  url {
+    type: ARCHIVE
+    value: "https://static.crates.io/crates/scopeguard/scopeguard-1.1.0.crate"
+  }
+  version: "1.1.0"
+  license_type: NOTICE
+  last_upgrade_date {
+    year: 2020
+    month: 10
+    day: 14
+  }
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
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index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/OWNERS b/OWNERS
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--- /dev/null
+++ b/OWNERS
@@ -0,0 +1 @@
+include platform/prebuilts/rust:/OWNERS
diff --git a/README.rst b/README.rst
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--- /dev/null
+++ b/README.rst
@@ -0,0 +1,103 @@
+
+scopeguard
+==========
+
+Rust crate for a convenient RAII scope guard that will run a given closure when
+it goes out of scope, even if the code between panics (assuming unwinding panic).
+
+The `defer!` macro and `guard` are `no_std` compatible (require only core),
+but the on unwinding / not on uwinding strategies requires linking to `std`.
+
+Requires Rust 1.20.
+
+
+Please read the `API documentation here`__
+
+__ https://docs.rs/scopeguard/
+
+|build_status|_ |crates|_
+
+.. |build_status| image:: https://travis-ci.org/bluss/scopeguard.svg
+.. _build_status: https://travis-ci.org/bluss/scopeguard
+
+.. |crates| image:: http://meritbadge.herokuapp.com/scopeguard
+.. _crates: https://crates.io/crates/scopeguard
+
+How to use
+----------
+
+.. code:: rust
+
+    #[macro_use(defer)] extern crate scopeguard;
+
+    use scopeguard::guard;
+
+    fn f() {
+        defer!(println!("Called at return or panic"));
+        panic!();
+    }
+
+    use std::fs::File;
+    use std::io::Write;
+
+    fn g() {
+        let f = File::create("newfile.txt").unwrap();
+        let mut file = guard(f, |f| {
+            // write file at return or panic
+            let _ = f.sync_all();
+        });
+        // Access the file through the scope guard itself
+        file.write_all(b"test me\n").unwrap();
+    }
+
+Recent Changes
+--------------
+
+- 1.1.0
+
+  - Change macros (``defer!``, ``defer_on_success!`` and ``defer_on_unwind!``)
+    to accept statements. (by @konsumlamm)
+
+- 1.0.0
+
+  - Change the closure type from ``FnMut(&mut T)`` to ``FnOnce(T)``:
+    Passing the inner value by value instead of a mutable reference is a
+    breaking change, but allows the guard closure to consume it. (by @tormol)
+
+  - Add ``defer_on_success!{}``, ``guard_on_success()`` and ``OnSuccess``
+    strategy, which triggers when scope is exited *without* panic. It's the
+    opposite to ``OnUnwind`` / ``guard_on_unwind()`` / ``defer_on_unwind!{}``.
+
+  - Add ``ScopeGuard::into_inner()``, which "defuses" the guard and returns the
+    guarded value. (by @tormol)
+
+  - Implement ``Sync`` for guards with non-``Sync`` closures.
+
+  - Require Rust 1.20
+
+- 0.3.3
+
+  - Use ``#[inline]`` on a few more functions by @stjepang (#14)
+  - Add examples to crate documentation
+
+- 0.3.2
+
+  - Add crate categories
+
+- 0.3.1
+
+  - Add ``defer_on_unwind!``, ``Strategy`` trait
+  - Rename ``Guard`` → ``ScopeGuard``
+  - Add ``ScopeGuard::with_strategy``.
+  - ``ScopeGuard`` now implements ``Debug``.
+  - Require Rust 1.11
+
+- 0.2.0
+
+  - Require Rust 1.6
+  - Use `no_std` unconditionally
+  - No other changes
+
+- 0.1.2
+
+  - Add macro ``defer!()``
diff --git a/examples/readme.rs b/examples/readme.rs
new file mode 100644
index 0000000..0710f9f
--- /dev/null
+++ b/examples/readme.rs
@@ -0,0 +1,27 @@
+
+#[macro_use(defer)] extern crate scopeguard;
+
+use scopeguard::guard;
+
+fn f() {
+    defer!(println!("Called at return or panic"));
+    panic!();
+}
+
+use std::fs::File;
+use std::io::Write;
+
+fn g() {
+    let f = File::create("newfile.txt").unwrap();
+    let mut file = guard(f, |f| {
+        // write file at return or panic
+        let _ = f.sync_all();
+    });
+    // Access the file through the scope guard itself
+    file.write_all(b"test me\n").unwrap();
+}
+
+fn main() {
+    f();
+    g();
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..d33c2b6
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,578 @@
+#![cfg_attr(not(any(test, feature = "use_std")), no_std)]
+#![doc(html_root_url = "https://docs.rs/scopeguard/1/")]
+
+//! A scope guard will run a given closure when it goes out of scope,
+//! even if the code between panics.
+//! (as long as panic doesn't abort)
+//!
+//! # Examples
+//!
+//! ## Hello World
+//!
+//! This example creates a scope guard with an example function:
+//!
+//! ```
+//! extern crate scopeguard;
+//!
+//! fn f() {
+//!     let _guard = scopeguard::guard((), |_| {
+//!         println!("Hello Scope Exit!");
+//!     });
+//!
+//!     // rest of the code here.
+//!
+//!     // Here, at the end of `_guard`'s scope, the guard's closure is called.
+//!     // It is also called if we exit this scope through unwinding instead.
+//! }
+//! # fn main() {
+//! #    f();
+//! # }
+//! ```
+//!
+//! ## `defer!`
+//!
+//! Use the `defer` macro to run an operation at scope exit,
+//! either regular scope exit or during unwinding from a panic.
+//!
+//! ```
+//! #[macro_use(defer)] extern crate scopeguard;
+//!
+//! use std::cell::Cell;
+//!
+//! fn main() {
+//!     // use a cell to observe drops during and after the scope guard is active
+//!     let drop_counter = Cell::new(0);
+//!     {
+//!         // Create a scope guard using `defer!` for the current scope
+//!         defer! {
+//!             drop_counter.set(1 + drop_counter.get());
+//!         }
+//!
+//!         // Do regular operations here in the meantime.
+//!
+//!         // Just before scope exit: it hasn't run yet.
+//!         assert_eq!(drop_counter.get(), 0);
+//!
+//!         // The following scope end is where the defer closure is called
+//!     }
+//!     assert_eq!(drop_counter.get(), 1);
+//! }
+//! ```
+//!
+//! ## Scope Guard with Value
+//!
+//! If the scope guard closure needs to access an outer value that is also
+//! mutated outside of the scope guard, then you may want to use the scope guard
+//! with a value. The guard works like a smart pointer, so the inner value can
+//! be accessed by reference or by mutable reference.
+//!
+//! ### 1. The guard owns a file
+//!
+//! In this example, the scope guard owns a file and ensures pending writes are
+//! synced at scope exit.
+//!
+//! ```
+//! extern crate scopeguard;
+//!
+//! use std::fs::*;
+//! use std::io::{self, Write};
+//! # // Mock file so that we don't actually write a file
+//! # struct MockFile;
+//! # impl MockFile {
+//! #     fn create(_s: &str) -> io::Result<Self> { Ok(MockFile) }
+//! #     fn write_all(&self, _b: &[u8]) -> io::Result<()> { Ok(()) }
+//! #     fn sync_all(&self) -> io::Result<()> { Ok(()) }
+//! # }
+//! # use self::MockFile as File;
+//!
+//! fn try_main() -> io::Result<()> {
+//!     let f = File::create("newfile.txt")?;
+//!     let mut file = scopeguard::guard(f, |f| {
+//!         // ensure we flush file at return or panic
+//!         let _ = f.sync_all();
+//!     });
+//!     // Access the file through the scope guard itself
+//!     file.write_all(b"test me\n").map(|_| ())
+//! }
+//!
+//! fn main() {
+//!     try_main().unwrap();
+//! }
+//!
+//! ```
+//!
+//! ### 2. The guard restores an invariant on scope exit
+//!
+//! ```
+//! extern crate scopeguard;
+//!
+//! use std::mem::ManuallyDrop;
+//! use std::ptr;
+//!
+//! // This function, just for this example, takes the first element
+//! // and inserts it into the assumed sorted tail of the vector.
+//! //
+//! // For optimization purposes we temporarily violate an invariant of the
+//! // Vec, that it owns all of its elements.
+//! //
+//! // The safe approach is to use swap, which means two writes to memory,
+//! // the optimization is to use a “hole” which uses only one write of memory
+//! // for each position it moves.
+//! //
+//! // We *must* use a scope guard to run this code safely. We
+//! // are running arbitrary user code (comparison operators) that may panic.
+//! // The scope guard ensures we restore the invariant after successful
+//! // exit or during unwinding from panic.
+//! fn insertion_sort_first<T>(v: &mut Vec<T>)
+//!     where T: PartialOrd
+//! {
+//!     struct Hole<'a, T: 'a> {
+//!         v: &'a mut Vec<T>,
+//!         index: usize,
+//!         value: ManuallyDrop<T>,
+//!     }
+//!
+//!     unsafe {
+//!         // Create a moved-from location in the vector, a “hole”.
+//!         let value = ptr::read(&v[0]);
+//!         let mut hole = Hole { v: v, index: 0, value: ManuallyDrop::new(value) };
+//!
+//!         // Use a scope guard with a value.
+//!         // At scope exit, plug the hole so that the vector is fully
+//!         // initialized again.
+//!         // The scope guard owns the hole, but we can access it through the guard.
+//!         let mut hole_guard = scopeguard::guard(hole, |hole| {
+//!             // plug the hole in the vector with the value that was // taken out
+//!             let index = hole.index;
+//!             ptr::copy_nonoverlapping(&*hole.value, &mut hole.v[index], 1);
+//!         });
+//!
+//!         // run algorithm that moves the hole in the vector here
+//!         // move the hole until it's in a sorted position
+//!         for i in 1..hole_guard.v.len() {
+//!             if *hole_guard.value >= hole_guard.v[i] {
+//!                 // move the element back and the hole forward
+//!                 let index = hole_guard.index;
+//!                 ptr::copy_nonoverlapping(&hole_guard.v[index + 1], &mut hole_guard.v[index], 1);
+//!                 hole_guard.index += 1;
+//!             } else {
+//!                 break;
+//!             }
+//!         }
+//!
+//!         // When the scope exits here, the Vec becomes whole again!
+//!     }
+//! }
+//!
+//! fn main() {
+//!     let string = String::from;
+//!     let mut data = vec![string("c"), string("a"), string("b"), string("d")];
+//!     insertion_sort_first(&mut data);
+//!     assert_eq!(data, vec!["a", "b", "c", "d"]);
+//! }
+//!
+//! ```
+//!
+//!
+//! # Crate Features
+//!
+//! - `use_std`
+//!   + Enabled by default. Enables the `OnUnwind` and `OnSuccess` strategies.
+//!   + Disable to use `no_std`.
+//!
+//! # Rust Version
+//!
+//! This version of the crate requires Rust 1.20 or later.
+//!
+//! The scopeguard 1.x release series will use a carefully considered version
+//! upgrade policy, where in a later 1.x version, we will raise the minimum
+//! required Rust version.
+
+#[cfg(not(any(test, feature = "use_std")))]
+extern crate core as std;
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem::{self, ManuallyDrop};
+use std::ops::{Deref, DerefMut};
+use std::ptr;
+
+/// Controls in which cases the associated code should be run
+pub trait Strategy {
+    /// Return `true` if the guard’s associated code should run
+    /// (in the context where this method is called).
+    fn should_run() -> bool;
+}
+
+/// Always run on scope exit.
+///
+/// “Always” run: on regular exit from a scope or on unwinding from a panic.
+/// Can not run on abort, process exit, and other catastrophic events where
+/// destructors don’t run.
+#[derive(Debug)]
+pub enum Always {}
+
+/// Run on scope exit through unwinding.
+///
+/// Requires crate feature `use_std`.
+#[cfg(feature = "use_std")]
+#[derive(Debug)]
+pub enum OnUnwind {}
+
+/// Run on regular scope exit, when not unwinding.
+///
+/// Requires crate feature `use_std`.
+#[cfg(feature = "use_std")]
+#[derive(Debug)]
+pub enum OnSuccess {}
+
+impl Strategy for Always {
+    #[inline(always)]
+    fn should_run() -> bool { true }
+}
+
+#[cfg(feature = "use_std")]
+impl Strategy for OnUnwind {
+    #[inline]
+    fn should_run() -> bool { std::thread::panicking() }
+}
+
+#[cfg(feature = "use_std")]
+impl Strategy for OnSuccess {
+    #[inline]
+    fn should_run() -> bool { !std::thread::panicking() }
+}
+
+/// Macro to create a `ScopeGuard` (always run).
+///
+/// The macro takes statements, which are the body of a closure
+/// that will run when the scope is exited.
+#[macro_export]
+macro_rules! defer {
+    ($($t:tt)*) => {
+        let _guard = $crate::guard((), |()| { $($t)* });
+    };
+}
+
+/// Macro to create a `ScopeGuard` (run on successful scope exit).
+///
+/// The macro takes statements, which are the body of a closure
+/// that will run when the scope is exited.
+///
+/// Requires crate feature `use_std`.
+#[cfg(feature = "use_std")]
+#[macro_export]
+macro_rules! defer_on_success {
+    ($($t:tt)*) => {
+        let _guard = $crate::guard_on_success((), |()| { $($t)* });
+    };
+}
+
+/// Macro to create a `ScopeGuard` (run on unwinding from panic).
+///
+/// The macro takes statements, which are the body of a closure
+/// that will run when the scope is exited.
+///
+/// Requires crate feature `use_std`.
+#[cfg(feature = "use_std")]
+#[macro_export]
+macro_rules! defer_on_unwind {
+    ($($t:tt)*) => {
+        let _guard = $crate::guard_on_unwind((), |()| { $($t)* });
+    };
+}
+
+/// `ScopeGuard` is a scope guard that may own a protected value.
+///
+/// If you place a guard in a local variable, the closure can
+/// run regardless how you leave the scope — through regular return or panic
+/// (except if panic or other code aborts; so as long as destructors run).
+/// It is run only once.
+///
+/// The `S` parameter for [`Strategy`](trait.Strategy.html) determines if
+/// the closure actually runs.
+///
+/// The guard's closure will be called with the held value in the destructor.
+///
+/// The `ScopeGuard` implements `Deref` so that you can access the inner value.
+pub struct ScopeGuard<T, F, S = Always>
+    where F: FnOnce(T),
+          S: Strategy,
+{
+    value: ManuallyDrop<T>,
+    dropfn: ManuallyDrop<F>,
+    // fn(S) -> S is used, so that the S is not taken into account for auto traits.
+    strategy: PhantomData<fn(S) -> S>,
+}
+
+impl<T, F, S> ScopeGuard<T, F, S>
+    where F: FnOnce(T),
+          S: Strategy,
+{
+    /// Create a `ScopeGuard` that owns `v` (accessible through deref) and calls
+    /// `dropfn` when its destructor runs.
+    ///
+    /// The `Strategy` decides whether the scope guard's closure should run.
+    #[inline]
+    pub fn with_strategy(v: T, dropfn: F) -> ScopeGuard<T, F, S> {
+        ScopeGuard {
+            value: ManuallyDrop::new(v),
+            dropfn: ManuallyDrop::new(dropfn),
+            strategy: PhantomData,
+        }
+    }
+
+    /// “Defuse” the guard and extract the value without calling the closure.
+    ///
+    /// ```
+    /// extern crate scopeguard;
+    ///
+    /// use scopeguard::{guard, ScopeGuard};
+    ///
+    /// fn conditional() -> bool { true }
+    ///
+    /// fn main() {
+    ///     let mut guard = guard(Vec::new(), |mut v| v.clear());
+    ///     guard.push(1);
+    ///     
+    ///     if conditional() {
+    ///         // a condition maybe makes us decide to
+    ///         // “defuse” the guard and get back its inner parts
+    ///         let value = ScopeGuard::into_inner(guard);
+    ///     } else {
+    ///         // guard still exists in this branch
+    ///     }
+    /// }
+    /// ```
+    #[inline]
+    pub fn into_inner(guard: Self) -> T {
+        // Cannot move out of Drop-implementing types, so
+        // ptr::read the value and forget the guard.
+        unsafe {
+            let value = ptr::read(&*guard.value);
+            // read the closure so that it is dropped, and assign it to a local
+            // variable to ensure that it is only dropped after the guard has
+            // been forgotten. (In case the Drop impl of the closure, or that
+            // of any consumed captured variable, panics).
+            let _dropfn = ptr::read(&*guard.dropfn);
+            mem::forget(guard);
+            value
+        }
+    }
+}
+
+
+/// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.
+#[inline]
+pub fn guard<T, F>(v: T, dropfn: F) -> ScopeGuard<T, F, Always>
+    where F: FnOnce(T)
+{
+    ScopeGuard::with_strategy(v, dropfn)
+}
+
+/// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.
+///
+/// Requires crate feature `use_std`.
+#[cfg(feature = "use_std")]
+#[inline]
+pub fn guard_on_success<T, F>(v: T, dropfn: F) -> ScopeGuard<T, F, OnSuccess>
+    where F: FnOnce(T)
+{
+    ScopeGuard::with_strategy(v, dropfn)
+}
+
+/// Create a new `ScopeGuard` owning `v` and with deferred closure `dropfn`.
+///
+/// Requires crate feature `use_std`.
+///
+/// ## Examples
+///
+/// For performance reasons, or to emulate “only run guard on unwind” in
+/// no-std environments, we can also use the default guard and simply manually
+/// defuse it at the end of scope like the following example. (The performance
+/// reason would be if the [`OnUnwind`]'s call to [std::thread::panicking()] is
+/// an issue.)
+///
+/// ```
+/// extern crate scopeguard;
+///
+/// use scopeguard::ScopeGuard;
+/// # fn main() {
+/// {
+///     let guard = scopeguard::guard((), |_| {});
+///
+///     // rest of the code here
+///
+///     // we reached the end of scope without unwinding - defuse it
+///     ScopeGuard::into_inner(guard);
+/// }
+/// # }
+/// ```
+#[cfg(feature = "use_std")]
+#[inline]
+pub fn guard_on_unwind<T, F>(v: T, dropfn: F) -> ScopeGuard<T, F, OnUnwind>
+    where F: FnOnce(T)
+{
+    ScopeGuard::with_strategy(v, dropfn)
+}
+
+// ScopeGuard can be Sync even if F isn't because the closure is
+// not accessible from references.
+// The guard does not store any instance of S, so it is also irrelevant.
+unsafe impl<T, F, S> Sync for ScopeGuard<T, F, S>
+    where T: Sync,
+          F: FnOnce(T),
+          S: Strategy
+{}
+
+impl<T, F, S> Deref for ScopeGuard<T, F, S>
+    where F: FnOnce(T),
+          S: Strategy
+{
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &*self.value
+    }
+}
+
+impl<T, F, S> DerefMut for ScopeGuard<T, F, S>
+    where F: FnOnce(T),
+          S: Strategy
+{
+    fn deref_mut(&mut self) -> &mut T {
+        &mut *self.value
+    }
+}
+
+impl<T, F, S> Drop for ScopeGuard<T, F, S>
+    where F: FnOnce(T),
+          S: Strategy
+{
+    fn drop(&mut self) {
+        // This is OK because the fields are `ManuallyDrop`s
+        // which will not be dropped by the compiler.
+        let (value, dropfn) = unsafe {
+            (ptr::read(&*self.value), ptr::read(&*self.dropfn))
+        };
+        if S::should_run() {
+            dropfn(value);
+        }
+    }
+}
+
+impl<T, F, S> fmt::Debug for ScopeGuard<T, F, S>
+    where T: fmt::Debug,
+          F: FnOnce(T),
+          S: Strategy
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct(stringify!(ScopeGuard))
+         .field("value", &*self.value)
+         .finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::cell::Cell;
+    use std::panic::catch_unwind;
+    use std::panic::AssertUnwindSafe;
+
+    #[test]
+    fn test_defer() {
+        let drops = Cell::new(0);
+        defer!(drops.set(1000));
+        assert_eq!(drops.get(), 0);
+    }
+
+    #[cfg(feature = "use_std")]
+    #[test]
+    fn test_defer_success_1() {
+        let drops = Cell::new(0);
+        {
+            defer_on_success!(drops.set(1));
+            assert_eq!(drops.get(), 0);
+        }
+        assert_eq!(drops.get(), 1);
+    }
+
+    #[cfg(feature = "use_std")]
+    #[test]
+    fn test_defer_success_2() {
+        let drops = Cell::new(0);
+        let _ = catch_unwind(AssertUnwindSafe(|| {
+            defer_on_success!(drops.set(1));
+            panic!("failure")
+        }));
+        assert_eq!(drops.get(), 0);
+    }
+
+    #[cfg(feature = "use_std")]
+    #[test]
+    fn test_defer_unwind_1() {
+        let drops = Cell::new(0);
+        let _ = catch_unwind(AssertUnwindSafe(|| {
+            defer_on_unwind!(drops.set(1));
+            assert_eq!(drops.get(), 0);
+            panic!("failure")
+        }));
+        assert_eq!(drops.get(), 1);
+    }
+
+    #[cfg(feature = "use_std")]
+    #[test]
+    fn test_defer_unwind_2() {
+        let drops = Cell::new(0);
+        {
+            defer_on_unwind!(drops.set(1));
+        }
+        assert_eq!(drops.get(), 0);
+    }
+
+    #[test]
+    fn test_only_dropped_by_closure_when_run() {
+        let value_drops = Cell::new(0);
+        let value = guard((), |()| value_drops.set(1 + value_drops.get()));
+        let closure_drops = Cell::new(0);
+        let guard = guard(value, |_| closure_drops.set(1 + closure_drops.get()));
+        assert_eq!(value_drops.get(), 0);
+        assert_eq!(closure_drops.get(), 0);
+        drop(guard);
+        assert_eq!(value_drops.get(), 1);
+        assert_eq!(closure_drops.get(), 1);
+    }
+
+    #[cfg(feature = "use_std")]
+    #[test]
+    fn test_dropped_once_when_not_run() {
+        let value_drops = Cell::new(0);
+        let value = guard((), |()| value_drops.set(1 + value_drops.get()));
+        let captured_drops = Cell::new(0);
+        let captured = guard((), |()| captured_drops.set(1 + captured_drops.get()));
+        let closure_drops = Cell::new(0);
+        let guard = guard_on_unwind(value, |value| {
+            drop(value);
+            drop(captured);
+            closure_drops.set(1 + closure_drops.get())
+        });
+        assert_eq!(value_drops.get(), 0);
+        assert_eq!(captured_drops.get(), 0);
+        assert_eq!(closure_drops.get(), 0);
+        drop(guard);
+        assert_eq!(value_drops.get(), 1);
+        assert_eq!(captured_drops.get(), 1);
+        assert_eq!(closure_drops.get(), 0);
+    }
+
+    #[test]
+    fn test_into_inner() {
+        let dropped = Cell::new(false);
+        let value = guard(42, |_| dropped.set(true));
+        let guard = guard(value, |_| dropped.set(true));
+        let inner = ScopeGuard::into_inner(guard);
+        assert_eq!(dropped.get(), false);
+        assert_eq!(*inner, 42);
+    }
+}