Eliminate FnBox usages from libstd.

src/libstd/sys/cloudabi/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::cmp;
 use crate::ffi::CStr;
 use crate::io;
@@ -22,7 +21,7 @@ unsafe impl Sync for Thread {}
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(stack: usize, p: Box<dyn FnBox()>) -> io::Result<Thread> {
+    pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
         let p = box p;
         let mut native: libc::pthread_t = mem::zeroed();
         let mut attr: libc::pthread_attr_t = mem::zeroed();

src/libstd/sys/redox/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
@@ -19,7 +18,7 @@ unsafe impl Sync for Thread {}
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, p: Box<dyn FnBox()>) -> io::Result<Thread> {
+    pub unsafe fn new(_stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
         let p = box p;
 
         let id = cvt(syscall::clone(syscall::CLONE_VM | syscall::CLONE_FS | syscall::CLONE_FILES))?;

src/libstd/sys/sgx/thread.rs

@@ -1,5 +1,4 @@
 #![cfg_attr(test, allow(dead_code))] // why is this necessary?
-use crate::boxed::FnBox;
 use crate::ffi::CStr;
 use crate::io;
 use crate::time::Duration;
@@ -13,17 +12,16 @@ pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 mod task_queue {
     use crate::sync::{Mutex, MutexGuard, Once};
     use crate::sync::mpsc;
-    use crate::boxed::FnBox;
 
     pub type JoinHandle = mpsc::Receiver<()>;
 
     pub(super) struct Task {
-        p: Box<dyn FnBox()>,
+        p: Box<dyn FnOnce()>,
         done: mpsc::Sender<()>,
     }
 
     impl Task {
-        pub(super) fn new(p: Box<dyn FnBox()>) -> (Task, JoinHandle) {
+        pub(super) fn new(p: Box<dyn FnOnce()>) -> (Task, JoinHandle) {
             let (done, recv) = mpsc::channel();
             (Task { p, done }, recv)
         }
@@ -51,7 +49,7 @@ mod task_queue {
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, p: Box<dyn FnBox()>)
+    pub unsafe fn new(_stack: usize, p: Box<dyn FnOnce()>)
         -> io::Result<Thread>
     {
         let mut queue_lock = task_queue::lock();

src/libstd/sys/unix/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::cmp;
 use crate::ffi::CStr;
 use crate::io;
@@ -39,7 +38,7 @@ unsafe fn pthread_attr_setstacksize(_attr: *mut libc::pthread_attr_t,
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(stack: usize, p: Box<dyn FnBox()>)
+    pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>)
                           -> io::Result<Thread> {
         let p = box p;
         let mut native: libc::pthread_t = mem::zeroed();

src/libstd/sys/wasi/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::cmp;
 use crate::ffi::CStr;
 use crate::io;
@@ -13,7 +12,7 @@ pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, _p: Box<dyn FnBox()>)
+    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>)
         -> io::Result<Thread>
     {
         unsupported()

src/libstd/sys/wasm/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::ffi::CStr;
 use crate::io;
 use crate::sys::{unsupported, Void};
@@ -10,7 +9,7 @@ pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, _p: Box<dyn FnBox()>)
+    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>)
         -> io::Result<Thread>
     {
         unsupported()

src/libstd/sys/windows/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::io;
 use crate::ffi::CStr;
 use crate::mem;
@@ -20,7 +19,7 @@ pub struct Thread {
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(stack: usize, p: Box<dyn FnBox()>)
+    pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>)
                           -> io::Result<Thread> {
         let p = box p;
 

src/libstd/sys_common/at_exit_imp.rs

@@ -2,12 +2,11 @@
 //!
 //! Documentation can be found on the `rt::at_exit` function.
 
-use crate::boxed::FnBox;
 use crate::ptr;
 use crate::mem;
 use crate::sys_common::mutex::Mutex;
 
-type Queue = Vec<Box<dyn FnBox()>>;
+type Queue = Vec<Box<dyn FnOnce()>>;
 
 // NB these are specifically not types from `std::sync` as they currently rely
 // on poisoning and this module needs to operate at a lower level than requiring
@@ -61,7 +60,7 @@ pub fn cleanup() {
     }
 }
 
-pub fn push(f: Box<dyn FnBox()>) -> bool {
+pub fn push(f: Box<dyn FnOnce()>) -> bool {
     unsafe {
         let _guard = LOCK.lock();
         if init() {

src/libstd/sys_common/thread.rs

@@ -1,4 +1,3 @@
-use crate::boxed::FnBox;
 use crate::env;
 use crate::sync::atomic::{self, Ordering};
 use crate::sys::stack_overflow;
@@ -11,7 +10,7 @@ pub unsafe fn start_thread(main: *mut u8) {
     let _handler = stack_overflow::Handler::new();
 
     // Finally, let's run some code.
-    Box::from_raw(main as *mut Box<dyn FnBox()>)()
+    Box::from_raw(main as *mut Box<dyn FnOnce()>)()
 }
 
 pub fn min_stack() -> usize {

src/libstd/thread/mod.rs

@@ -157,7 +157,6 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::any::Any;
-use crate::boxed::FnBox;
 use crate::cell::UnsafeCell;
 use crate::ffi::{CStr, CString};
 use crate::fmt;
@@ -488,7 +487,9 @@ impl Builder {
             // returning.
             native: Some(imp::Thread::new(
                 stack_size,
-                mem::transmute::<Box<dyn FnBox() + 'a>, Box<dyn FnBox() + 'static>>(Box::new(main))
+                mem::transmute::<Box<dyn FnOnce() + 'a>, Box<dyn FnOnce() + 'static>>(Box::new(
+                    main,
+                )),
             )?),
             thread: my_thread,
             packet: Packet(my_packet),