Rollup merge of #61113 - SimonSapin:fnbox, r=alexcrichton

Deprecate `FnBox`. `Box<dyn FnOnce()>` can be called directly, since 1.35

FCP completion: https://github.com/rust-lang/rust/issues/28796#issuecomment-439731515

src/liballoc/boxed.rs

@@ -759,13 +759,14 @@ impl<A, F: Fn<A> + ?Sized> Fn<A> for Box<F> {
     }
 }
 
+/// `FnBox` is deprecated and will be removed.
+/// `Box<dyn FnOnce()>` can be called directly, since Rust 1.35.0.
+///
 /// `FnBox` is a version of the `FnOnce` intended for use with boxed
-/// closure objects. The idea is that where one would normally store a
+/// closure objects. The idea was that where one would normally store a
-/// `Box<dyn FnOnce()>` in a data structure, you should use
+/// `Box<dyn FnOnce()>` in a data structure, you whould use
 /// `Box<dyn FnBox()>`. The two traits behave essentially the same, except
-/// that a `FnBox` closure can only be called if it is boxed. (Note
+/// that a `FnBox` closure can only be called if it is boxed.
-/// that `FnBox` may be deprecated in the future if `Box<dyn FnOnce()>`
-/// closures become directly usable.)
 ///
 /// # Examples
 ///
@@ -777,6 +778,7 @@ impl<A, F: Fn<A> + ?Sized> Fn<A> for Box<F> {
 ///
 /// ```
 /// #![feature(fnbox)]
+/// #![allow(deprecated)]
 ///
 /// use std::boxed::FnBox;
 /// use std::collections::HashMap;
@@ -796,16 +798,38 @@ impl<A, F: Fn<A> + ?Sized> Fn<A> for Box<F> {
 ///     }
 /// }
 /// ```
+///
+/// In Rust 1.35.0 or later, use `FnOnce`, `FnMut`, or `Fn` instead:
+///
+/// ```
+/// use std::collections::HashMap;
+///
+/// fn make_map() -> HashMap<i32, Box<dyn FnOnce() -> i32>> {
+///     let mut map: HashMap<i32, Box<dyn FnOnce() -> i32>> = HashMap::new();
+///     map.insert(1, Box::new(|| 22));
+///     map.insert(2, Box::new(|| 44));
+///     map
+/// }
+///
+/// fn main() {
+///     let mut map = make_map();
+///     for i in &[1, 2] {
+///         let f = map.remove(&i).unwrap();
+///         assert_eq!(f(), i * 22);
+///     }
+/// }
+/// ```
 #[rustc_paren_sugar]
-#[unstable(feature = "fnbox",
+#[unstable(feature = "fnbox", issue = "28796")]
-           reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
+#[rustc_deprecated(reason = "use `FnOnce`, `FnMut`, or `Fn` instead", since = "1.37.0")]
 pub trait FnBox<A>: FnOnce<A> {
     /// Performs the call operation.
     fn call_box(self: Box<Self>, args: A) -> Self::Output;
 }
 
-#[unstable(feature = "fnbox",
+#[unstable(feature = "fnbox", issue = "28796")]
-           reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
+#[rustc_deprecated(reason = "use `FnOnce`, `FnMut`, or `Fn` instead", since = "1.37.0")]
+#[allow(deprecated, deprecated_in_future)]
 impl<A, F> FnBox<A> for F
     where F: FnOnce<A>
 {

src/libtest/lib.rs

@@ -22,7 +22,6 @@
 #![unstable(feature = "test", issue = "27812")]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/", test(attr(deny(warnings))))]
 #![feature(asm)]
-#![feature(fnbox)]
 #![cfg_attr(any(unix, target_os = "cloudabi"), feature(libc, rustc_private))]
 #![feature(nll)]
 #![feature(set_stdio)]
@@ -56,7 +55,6 @@ pub use self::TestResult::*;
 
 use std::any::Any;
 use std::borrow::Cow;
-use std::boxed::FnBox;
 use std::cmp;
 use std::collections::BTreeMap;
 use std::env;
@@ -174,7 +172,7 @@ pub trait TDynBenchFn: Send {
 pub enum TestFn {
     StaticTestFn(fn()),
     StaticBenchFn(fn(&mut Bencher)),
-    DynTestFn(Box<dyn FnBox() + Send>),
+    DynTestFn(Box<dyn FnOnce() + Send>),
     DynBenchFn(Box<dyn TDynBenchFn + 'static>),
 }
 
@@ -1447,7 +1445,7 @@ pub fn run_test(
         desc: TestDesc,
         monitor_ch: Sender<MonitorMsg>,
         nocapture: bool,
-        testfn: Box<dyn FnBox() + Send>,
+        testfn: Box<dyn FnOnce() + Send>,
         concurrency: Concurrent,
     ) {
         // Buffer for capturing standard I/O

src/test/run-pass/unsized-locals/fnbox-compat.rs

@@ -1,4 +1,5 @@
 #![feature(fnbox)]
+#![allow(deprecated, deprecated_in_future)]
 
 use std::boxed::FnBox;
 

src/test/ui/confuse-field-and-method/issue-2392.rs

@@ -1,7 +1,3 @@
-#![feature(core, fnbox)]
-
-use std::boxed::FnBox;
-
 struct FuncContainer {
     f1: fn(data: u8),
     f2: extern "C" fn(data: u8),
@@ -18,7 +14,7 @@ struct Obj<F> where F: FnOnce() -> u32 {
 }
 
 struct BoxedObj {
-    boxed_closure: Box<FnBox() -> u32>,
+    boxed_closure: Box<FnOnce() -> u32>,
 }
 
 struct Wrapper<F> where F: FnMut() -> u32 {
@@ -29,8 +25,8 @@ fn func() -> u32 {
     0
 }
 
-fn check_expression() -> Obj<Box<FnBox() -> u32>> {
+fn check_expression() -> Obj<Box<FnOnce() -> u32>> {
-    Obj { closure: Box::new(|| 42_u32) as Box<FnBox() -> u32>, not_closure: 42 }
+    Obj { closure: Box::new(|| 42_u32) as Box<FnOnce() -> u32>, not_closure: 42 }
 }
 
 fn main() {
@@ -48,7 +44,7 @@ fn main() {
     let boxed_fn = BoxedObj { boxed_closure: Box::new(func) };
     boxed_fn.boxed_closure();//~ ERROR no method named `boxed_closure` found
 
-    let boxed_closure = BoxedObj { boxed_closure: Box::new(|| 42_u32) as Box<FnBox() -> u32> };
+    let boxed_closure = BoxedObj { boxed_closure: Box::new(|| 42_u32) as Box<FnOnce() -> u32> };
     boxed_closure.boxed_closure();//~ ERROR no method named `boxed_closure` found
 
     // test expression writing in the notes

src/test/ui/confuse-field-and-method/issue-2392.stderr

@@ -1,5 +1,5 @@
-error[E0599]: no method named `closure` found for type `Obj<[closure@$DIR/issue-2392.rs:39:36: 39:41]>` in the current scope
+error[E0599]: no method named `closure` found for type `Obj<[closure@$DIR/issue-2392.rs:35:36: 35:41]>` in the current scope
-  --> $DIR/issue-2392.rs:40:15
+  --> $DIR/issue-2392.rs:36:15
    |
 LL | struct Obj<F> where F: FnOnce() -> u32 {
    | -------------------------------------- method `closure` not found for this
@@ -11,8 +11,8 @@ help: to call the function stored in `closure`, surround the field access with p
 LL |     (o_closure.closure)();
    |     ^                 ^
 
-error[E0599]: no method named `not_closure` found for type `Obj<[closure@$DIR/issue-2392.rs:39:36: 39:41]>` in the current scope
+error[E0599]: no method named `not_closure` found for type `Obj<[closure@$DIR/issue-2392.rs:35:36: 35:41]>` in the current scope
-  --> $DIR/issue-2392.rs:42:15
+  --> $DIR/issue-2392.rs:38:15
    |
 LL | struct Obj<F> where F: FnOnce() -> u32 {
    | -------------------------------------- method `not_closure` not found for this
@@ -23,7 +23,7 @@ LL |     o_closure.not_closure();
    |               field, not a method
 
 error[E0599]: no method named `closure` found for type `Obj<fn() -> u32 {func}>` in the current scope
-  --> $DIR/issue-2392.rs:46:12
+  --> $DIR/issue-2392.rs:42:12
    |
 LL | struct Obj<F> where F: FnOnce() -> u32 {
    | -------------------------------------- method `closure` not found for this
@@ -36,7 +36,7 @@ LL |     (o_func.closure)();
    |     ^              ^
 
 error[E0599]: no method named `boxed_closure` found for type `BoxedObj` in the current scope
-  --> $DIR/issue-2392.rs:49:14
+  --> $DIR/issue-2392.rs:45:14
    |
 LL | struct BoxedObj {
    | --------------- method `boxed_closure` not found for this
@@ -49,7 +49,7 @@ LL |     (boxed_fn.boxed_closure)();
    |     ^                      ^
 
 error[E0599]: no method named `boxed_closure` found for type `BoxedObj` in the current scope
-  --> $DIR/issue-2392.rs:52:19
+  --> $DIR/issue-2392.rs:48:19
    |
 LL | struct BoxedObj {
    | --------------- method `boxed_closure` not found for this
@@ -62,7 +62,7 @@ LL |     (boxed_closure.boxed_closure)();
    |     ^                           ^
 
 error[E0599]: no method named `closure` found for type `Obj<fn() -> u32 {func}>` in the current scope
-  --> $DIR/issue-2392.rs:57:12
+  --> $DIR/issue-2392.rs:53:12
    |
 LL | struct Obj<F> where F: FnOnce() -> u32 {
    | -------------------------------------- method `closure` not found for this
@@ -75,7 +75,7 @@ LL |     (w.wrap.closure)();
    |     ^              ^
 
 error[E0599]: no method named `not_closure` found for type `Obj<fn() -> u32 {func}>` in the current scope
-  --> $DIR/issue-2392.rs:59:12
+  --> $DIR/issue-2392.rs:55:12
    |
 LL | struct Obj<F> where F: FnOnce() -> u32 {
    | -------------------------------------- method `not_closure` not found for this
@@ -85,8 +85,8 @@ LL |     w.wrap.not_closure();
    |            |
    |            field, not a method
 
-error[E0599]: no method named `closure` found for type `Obj<std::boxed::Box<(dyn std::boxed::FnBox<(), Output = u32> + 'static)>>` in the current scope
+error[E0599]: no method named `closure` found for type `Obj<std::boxed::Box<(dyn std::ops::FnOnce() -> u32 + 'static)>>` in the current scope
-  --> $DIR/issue-2392.rs:62:24
+  --> $DIR/issue-2392.rs:58:24
    |
 LL | struct Obj<F> where F: FnOnce() -> u32 {
    | -------------------------------------- method `closure` not found for this
@@ -99,7 +99,7 @@ LL |     (check_expression().closure)();
    |     ^                          ^
 
 error[E0599]: no method named `f1` found for type `FuncContainer` in the current scope
-  --> $DIR/issue-2392.rs:68:31
+  --> $DIR/issue-2392.rs:64:31
    |
 LL | struct FuncContainer {
    | -------------------- method `f1` not found for this
@@ -112,7 +112,7 @@ LL |             ((*self.container).f1)(1);
    |             ^                    ^
 
 error[E0599]: no method named `f2` found for type `FuncContainer` in the current scope
-  --> $DIR/issue-2392.rs:69:31
+  --> $DIR/issue-2392.rs:65:31
    |
 LL | struct FuncContainer {
    | -------------------- method `f2` not found for this
@@ -125,7 +125,7 @@ LL |             ((*self.container).f2)(1);
    |             ^                    ^
 
 error[E0599]: no method named `f3` found for type `FuncContainer` in the current scope
-  --> $DIR/issue-2392.rs:70:31
+  --> $DIR/issue-2392.rs:66:31
    |
 LL | struct FuncContainer {
    | -------------------- method `f3` not found for this