From ecc3e89dd072ed20d9aa6d53be0ab1c44d160232 Mon Sep 17 00:00:00 2001
From: Charles Lew <crlf0710@gmail.com>
Date: Mon, 11 Feb 2019 11:09:26 +0900
Subject: [PATCH] Stabilize boxed_closure_impls in 1.35.0.

---
 .../library-features/boxed-closure-impls.md   | 98 -------------------
 src/liballoc/boxed.rs                         | 12 +--
 .../run-pass/unsized-locals/box-fnonce.rs     |  2 -
 3 files changed, 3 insertions(+), 109 deletions(-)
 delete mode 100644 src/doc/unstable-book/src/library-features/boxed-closure-impls.md

diff --git a/src/doc/unstable-book/src/library-features/boxed-closure-impls.md b/src/doc/unstable-book/src/library-features/boxed-closure-impls.md
deleted file mode 100644
index 5ceb54ff3b9..00000000000
--- a/src/doc/unstable-book/src/library-features/boxed-closure-impls.md
+++ /dev/null
@@ -1,98 +0,0 @@
-# `boxed_closure_impls`
-
-The tracking issue for this feature is [#48055]
-
-[#48055]: https://github.com/rust-lang/rust/issues/48055
-
-------------------------
-
-This includes the following blanket impls for closure traits:
-
-```rust,ignore
-impl<A, F: FnOnce<A> + ?Sized> FnOnce for Box<F> {
-    // ...
-}
-impl<A, F: FnMut<A> + ?Sized> FnMut for Box<F> {
-    // ...
-}
-impl<A, F: Fn<A> + ?Sized> Fn for Box<F> {
-    // ...
-}
-```
-
-## Usage
-
-`Box` can be used almost transparently. You can even use `Box<dyn FnOnce>` now.
-
-```rust
-#![feature(boxed_closure_impls)]
-
-fn main() {
-    let resource = "hello".to_owned();
-    // Create a boxed once-callable closure
-    let f: Box<dyn FnOnce(&i32)> = Box::new(|x| {
-        let s = resource;
-        println!("{}", x);
-        println!("{}", s);
-    });
-
-    // Call it
-    f(&42);
-}
-```
-
-## The reason for instability
-
-This is unstable because of the first impl.
-
-It would have been easy if we're allowed to tighten the bound:
-
-```rust,ignore
-impl<A, F: FnMut<A> + ?Sized> FnOnce for Box<F> {
-    // ...
-}
-```
-
-However, `Box<dyn FnOnce()>` drops out of the modified impl.
-To rescue this, we had had a temporary solution called [`fnbox`][fnbox].
-
-[fnbox]: library-features/fnbox.html
-
-Unfortunately, due to minor coherence reasons, `fnbox` and
-`FnOnce for Box<impl FnMut>` had not been able to coexist.
-We had preferred `fnbox` for the time being.
-
-Now, as [`unsized_locals`][unsized_locals] is implemented, we can just write the
-original impl:
-
-[unsized_locals]: language-features/unsized-locals.html
-
-```rust,ignore
-impl<A, F: FnOnce<A> + ?Sized> FnOnce for Box<F> {
-    type Output = <F as FnOnce<A>>::Output;
-
-    extern "rust-call" fn call_once(self, args: A) -> Self::Output {
-        // *self is an unsized rvalue
-        <F as FnOnce<A>>::call_once(*self, args)
-    }
-}
-```
-
-However, since `unsized_locals` is a very young feature, we're careful about
-this `FnOnce` impl now.
-
-There's another reason for instability: for compatibility with `fnbox`,
-we currently allow specialization of the `Box<impl FnOnce>` impl:
-
-```rust,ignore
-impl<A, F: FnOnce<A> + ?Sized> FnOnce for Box<F> {
-    type Output = <F as FnOnce<A>>::Output;
-
-    // we have "default" here
-    default extern "rust-call" fn call_once(self, args: A) -> Self::Output {
-        <F as FnOnce<A>>::call_once(*self, args)
-    }
-}
-```
-
-This isn't what we desire in the long term.
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index d4fe8be36d6..f6dee7c9eef 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -694,9 +694,7 @@ impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {
 #[stable(feature = "fused", since = "1.26.0")]
 impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
 
-#[unstable(feature = "boxed_closure_impls",
-           reason = "Box<FnOnce> relies on unsized rvalues and needs to be tested more",
-           issue = "48055")]
+#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
 impl<A, F: FnOnce<A> + ?Sized> FnOnce<A> for Box<F> {
     type Output = <F as FnOnce<A>>::Output;
 
@@ -705,18 +703,14 @@ impl<A, F: FnOnce<A> + ?Sized> FnOnce<A> for Box<F> {
     }
 }
 
-#[unstable(feature = "boxed_closure_impls",
-           reason = "Box<FnOnce> relies on unsized rvalues and needs to be tested more",
-           issue = "48055")]
+#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
 impl<A, F: FnMut<A> + ?Sized> FnMut<A> for Box<F> {
     extern "rust-call" fn call_mut(&mut self, args: A) -> Self::Output {
         <F as FnMut<A>>::call_mut(self, args)
     }
 }
 
-#[unstable(feature = "boxed_closure_impls",
-           reason = "Box<FnOnce> relies on unsized rvalues and needs to be tested more",
-           issue = "48055")]
+#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
 impl<A, F: Fn<A> + ?Sized> Fn<A> for Box<F> {
     extern "rust-call" fn call(&self, args: A) -> Self::Output {
         <F as Fn<A>>::call(self, args)
diff --git a/src/test/run-pass/unsized-locals/box-fnonce.rs b/src/test/run-pass/unsized-locals/box-fnonce.rs
index 97007a94239..16bdeae4fad 100644
--- a/src/test/run-pass/unsized-locals/box-fnonce.rs
+++ b/src/test/run-pass/unsized-locals/box-fnonce.rs
@@ -1,5 +1,3 @@
-#![feature(boxed_closure_impls)]
-
 fn call_it<T>(f: Box<dyn FnOnce() -> T>) -> T {
     f()
 }