Auto merge of #52268 - Mark-Simulacrum:rollup, r=Mark-Simulacrum

Rollup of 14 pull requests

Successful merges:

 - #51614 (Correct suggestion for println)
 - #51952 ( hygiene: Decouple transparencies from expansion IDs)
 - #52193 (step_by: leave time of item skip unspecified)
 - #52207 (improve error message shown for unsafe operations)
 - #52223 (Deny bare trait objects in in src/liballoc)
 - #52224 (Deny bare trait objects in in src/libsyntax)
 - #52239 (Remove sync::Once::call_once 'static bound)
 - #52247 (Deny bare trait objects in in src/librustc)
 - #52248 (Deny bare trait objects in in src/librustc_allocator)
 - #52252 (Deny bare trait objects in in src/librustc_codegen_llvm)
 - #52253 (Deny bare trait objects in in src/librustc_data_structures)
 - #52254 (Deny bare trait objects in in src/librustc_metadata)
 - #52261 (Deny bare trait objects in in src/libpanic_unwind)
 - #52265 (Deny bare trait objects in in src/librustc_codegen_utils)

Failed merges:

r? @ghost

src/liballoc/boxed.rs

@@ -446,7 +446,7 @@ impl From<Box<str>> for Box<[u8]> {
     }
 }
 
-impl Box<Any> {
+impl Box<dyn Any> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     /// Attempt to downcast the box to a concrete type.
@@ -468,10 +468,10 @@ impl Box<Any> {
     ///     print_if_string(Box::new(0i8));
     /// }
     /// ```
-    pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any>> {
+    pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<dyn Any>> {
         if self.is::<T>() {
             unsafe {
-                let raw: *mut Any = Box::into_raw(self);
+                let raw: *mut dyn Any = Box::into_raw(self);
                 Ok(Box::from_raw(raw as *mut T))
             }
         } else {
@@ -480,7 +480,7 @@ impl Box<Any> {
     }
 }
 
-impl Box<Any + Send> {
+impl Box<dyn Any + Send> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     /// Attempt to downcast the box to a concrete type.
@@ -502,10 +502,10 @@ impl Box<Any + Send> {
     ///     print_if_string(Box::new(0i8));
     /// }
     /// ```
-    pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any + Send>> {
-        <Box<Any>>::downcast(self).map_err(|s| unsafe {
+    pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<dyn Any + Send>> {
+        <Box<dyn Any>>::downcast(self).map_err(|s| unsafe {
             // reapply the Send marker
-            Box::from_raw(Box::into_raw(s) as *mut (Any + Send))
+            Box::from_raw(Box::into_raw(s) as *mut (dyn Any + Send))
         })
     }
 }
@@ -643,7 +643,7 @@ impl<A, F> FnBox<A> for F
 
 #[unstable(feature = "fnbox",
            reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
-impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + 'a> {
+impl<'a, A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + 'a> {
     type Output = R;
 
     extern "rust-call" fn call_once(self, args: A) -> R {
@@ -653,7 +653,7 @@ impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + 'a> {
 
 #[unstable(feature = "fnbox",
            reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
-impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + Send + 'a> {
+impl<'a, A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + Send + 'a> {
     type Output = R;
 
     extern "rust-call" fn call_once(self, args: A) -> R {

src/liballoc/boxed_test.rs

@@ -31,8 +31,8 @@ struct Test;
 
 #[test]
 fn any_move() {
-    let a = Box::new(8) as Box<Any>;
-    let b = Box::new(Test) as Box<Any>;
+    let a = Box::new(8) as Box<dyn Any>;
+    let b = Box::new(Test) as Box<dyn Any>;
 
     match a.downcast::<i32>() {
         Ok(a) => {
@@ -47,26 +47,26 @@ fn any_move() {
         Err(..) => panic!(),
     }
 
-    let a = Box::new(8) as Box<Any>;
-    let b = Box::new(Test) as Box<Any>;
+    let a = Box::new(8) as Box<dyn Any>;
+    let b = Box::new(Test) as Box<dyn Any>;
 
     assert!(a.downcast::<Box<Test>>().is_err());
     assert!(b.downcast::<Box<i32>>().is_err());
 }
 
 #[test]
 fn test_show() {
-    let a = Box::new(8) as Box<Any>;
-    let b = Box::new(Test) as Box<Any>;
+    let a = Box::new(8) as Box<dyn Any>;
+    let b = Box::new(Test) as Box<dyn Any>;
     let a_str = format!("{:?}", a);
     let b_str = format!("{:?}", b);
     assert_eq!(a_str, "Any");
     assert_eq!(b_str, "Any");
 
     static EIGHT: usize = 8;
     static TEST: Test = Test;
-    let a = &EIGHT as &Any;
-    let b = &TEST as &Any;
+    let a = &EIGHT as &dyn Any;
+    let b = &TEST as &dyn Any;
     let s = format!("{:?}", a);
     assert_eq!(s, "Any");
     let s = format!("{:?}", b);
@@ -110,12 +110,12 @@ fn raw_trait() {
         }
     }
 
-    let x: Box<Foo> = Box::new(Bar(17));
+    let x: Box<dyn Foo> = Box::new(Bar(17));
     let p = Box::into_raw(x);
     unsafe {
         assert_eq!(17, (*p).get());
         (*p).set(19);
-        let y: Box<Foo> = Box::from_raw(p);
+        let y: Box<dyn Foo> = Box::from_raw(p);
         assert_eq!(19, y.get());
     }
 }

src/liballoc/lib.rs

@@ -72,6 +72,7 @@
        test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 #![no_std]
 #![needs_allocator]
+#![deny(bare_trait_objects)]
 #![deny(missing_debug_implementations)]
 
 #![cfg_attr(test, allow(deprecated))] // rand

src/liballoc/rc.rs

@@ -618,7 +618,7 @@ impl<T: Clone> Rc<T> {
     }
 }
 
-impl Rc<Any> {
+impl Rc<dyn Any> {
     #[inline]
     #[stable(feature = "rc_downcast", since = "1.29.0")]
     /// Attempt to downcast the `Rc<Any>` to a concrete type.
@@ -641,7 +641,7 @@ impl Rc<Any> {
     ///     print_if_string(Rc::new(0i8));
     /// }
     /// ```
-    pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<Any>> {
+    pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<dyn Any>> {
         if (*self).is::<T>() {
             let ptr = self.ptr.cast::<RcBox<T>>();
             forget(self);
@@ -1554,7 +1554,7 @@ mod tests {
         assert_eq!(unsafe { &*ptr }, "foo");
         assert_eq!(rc, rc2);
 
-        let rc: Rc<Display> = Rc::new(123);
+        let rc: Rc<dyn Display> = Rc::new(123);
 
         let ptr = Rc::into_raw(rc.clone());
         let rc2 = unsafe { Rc::from_raw(ptr) };
@@ -1755,8 +1755,8 @@ mod tests {
         use std::fmt::Display;
         use std::string::ToString;
 
-        let b: Box<Display> = box 123;
-        let r: Rc<Display> = Rc::from(b);
+        let b: Box<dyn Display> = box 123;
+        let r: Rc<dyn Display> = Rc::from(b);
 
         assert_eq!(r.to_string(), "123");
     }
@@ -1765,8 +1765,8 @@ mod tests {
     fn test_from_box_trait_zero_sized() {
         use std::fmt::Debug;
 
-        let b: Box<Debug> = box ();
-        let r: Rc<Debug> = Rc::from(b);
+        let b: Box<dyn Debug> = box ();
+        let r: Rc<dyn Debug> = Rc::from(b);
 
         assert_eq!(format!("{:?}", r), "()");
     }
@@ -1783,8 +1783,8 @@ mod tests {
     fn test_downcast() {
         use std::any::Any;
 
-        let r1: Rc<Any> = Rc::new(i32::max_value());
-        let r2: Rc<Any> = Rc::new("abc");
+        let r1: Rc<dyn Any> = Rc::new(i32::max_value());
+        let r2: Rc<dyn Any> = Rc::new("abc");
 
         assert!(r1.clone().downcast::<u32>().is_err());
 

src/liballoc/sync.rs

@@ -978,18 +978,18 @@ unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> {
     }
 }
 
-impl Arc<Any + Send + Sync> {
+impl Arc<dyn Any + Send + Sync> {
     #[inline]
     #[stable(feature = "rc_downcast", since = "1.29.0")]
-    /// Attempt to downcast the `Arc<Any + Send + Sync>` to a concrete type.
+    /// Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::any::Any;
     /// use std::sync::Arc;
     ///
-    /// fn print_if_string(value: Arc<Any + Send + Sync>) {
+    /// fn print_if_string(value: Arc<dyn Any + Send + Sync>) {
     ///     if let Ok(string) = value.downcast::<String>() {
     ///         println!("String ({}): {}", string.len(), string);
     ///     }
@@ -1574,7 +1574,7 @@ mod tests {
         assert_eq!(unsafe { &*ptr }, "foo");
         assert_eq!(arc, arc2);
 
-        let arc: Arc<Display> = Arc::new(123);
+        let arc: Arc<dyn Display> = Arc::new(123);
 
         let ptr = Arc::into_raw(arc.clone());
         let arc2 = unsafe { Arc::from_raw(ptr) };
@@ -1879,8 +1879,8 @@ mod tests {
         use std::fmt::Display;
         use std::string::ToString;
 
-        let b: Box<Display> = box 123;
-        let r: Arc<Display> = Arc::from(b);
+        let b: Box<dyn Display> = box 123;
+        let r: Arc<dyn Display> = Arc::from(b);
 
         assert_eq!(r.to_string(), "123");
     }
@@ -1889,8 +1889,8 @@ mod tests {
     fn test_from_box_trait_zero_sized() {
         use std::fmt::Debug;
 
-        let b: Box<Debug> = box ();
-        let r: Arc<Debug> = Arc::from(b);
+        let b: Box<dyn Debug> = box ();
+        let r: Arc<dyn Debug> = Arc::from(b);
 
         assert_eq!(format!("{:?}", r), "()");
     }
@@ -1907,8 +1907,8 @@ mod tests {
     fn test_downcast() {
         use std::any::Any;
 
-        let r1: Arc<Any + Send + Sync> = Arc::new(i32::max_value());
-        let r2: Arc<Any + Send + Sync> = Arc::new("abc");
+        let r1: Arc<dyn Any + Send + Sync> = Arc::new(i32::max_value());
+        let r2: Arc<dyn Any + Send + Sync> = Arc::new("abc");
 
         assert!(r1.clone().downcast::<u32>().is_err());
 

src/libcore/iter/iterator.rs

@@ -271,9 +271,30 @@ pub trait Iterator {
     /// Creates an iterator starting at the same point, but stepping by
     /// the given amount at each iteration.
     ///
-    /// Note that it will always return the first element of the iterator,
+    /// Note 1: The first element of the iterator will always be returned,
     /// regardless of the step given.
     ///
+    /// Note 2: The time at which ignored elements are pulled is not fixed.
+    /// `StepBy` behaves like the sequence `next(), nth(step-1), nth(step-1), …`,
+    /// but is also free to behave like the sequence
+    /// `advance_n_and_return_first(step), advance_n_and_return_first(step), …`
+    /// Which way is used may change for some iterators for performance reasons.
+    /// The second way will advance the iterator earlier and may consume more items.
+    ///
+    /// `advance_n_and_return_first` is the equivalent of:
+    /// ```
+    /// fn advance_n_and_return_first<I>(iter: &mut I, total_step: usize) -> Option<I::Item>
+    /// where
+    ///     I: Iterator,
+    /// {
+    ///     let next = iter.next();
+    ///     if total_step > 1 {
+    ///         iter.nth(total_step-2);
+    ///     }
+    ///     next
+    /// }
+    /// ```
+    ///
     /// # Panics
     ///
     /// The method will panic if the given step is `0`.

src/libpanic_unwind/dwarf/eh.rs

@@ -48,8 +48,8 @@ pub const DW_EH_PE_indirect: u8 = 0x80;
 pub struct EHContext<'a> {
     pub ip: usize, // Current instruction pointer
     pub func_start: usize, // Address of the current function
-    pub get_text_start: &'a Fn() -> usize, // Get address of the code section
-    pub get_data_start: &'a Fn() -> usize, // Get address of the data section
+    pub get_text_start: &'a dyn Fn() -> usize, // Get address of the code section
+    pub get_data_start: &'a dyn Fn() -> usize, // Get address of the data section
 }
 
 pub enum EHAction {

src/libpanic_unwind/emcc.rs

@@ -29,20 +29,20 @@ pub fn payload() -> *mut u8 {
     ptr::null_mut()
 }
 
-pub unsafe fn cleanup(ptr: *mut u8) -> Box<Any + Send> {
+pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     assert!(!ptr.is_null());
     let ex = ptr::read(ptr as *mut _);
     __cxa_free_exception(ptr as *mut _);
     ex
 }
 
-pub unsafe fn panic(data: Box<Any + Send>) -> u32 {
+pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     let sz = mem::size_of_val(&data);
     let exception = __cxa_allocate_exception(sz);
     if exception == ptr::null_mut() {
         return uw::_URC_FATAL_PHASE1_ERROR as u32;
     }
-    let exception = exception as *mut Box<Any + Send>;
+    let exception = exception as *mut Box<dyn Any + Send>;
     ptr::write(exception, data);
     __cxa_throw(exception as *mut _, ptr::null_mut(), ptr::null_mut());
 

src/libpanic_unwind/gcc.rs

@@ -67,10 +67,10 @@ use dwarf::eh::{self, EHContext, EHAction};
 #[repr(C)]
 struct Exception {
     _uwe: uw::_Unwind_Exception,
-    cause: Option<Box<Any + Send>>,
+    cause: Option<Box<dyn Any + Send>>,
 }
 
-pub unsafe fn panic(data: Box<Any + Send>) -> u32 {
+pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     let exception = Box::new(Exception {
         _uwe: uw::_Unwind_Exception {
             exception_class: rust_exception_class(),
@@ -94,7 +94,7 @@ pub fn payload() -> *mut u8 {
     ptr::null_mut()
 }
 
-pub unsafe fn cleanup(ptr: *mut u8) -> Box<Any + Send> {
+pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     let my_ep = ptr as *mut Exception;
     let cause = (*my_ep).cause.take();
     uw::_Unwind_DeleteException(ptr as *mut _);

src/libpanic_unwind/lib.rs

@@ -22,6 +22,7 @@
 //! More documentation about each implementation can be found in the respective
 //! module.
 
+#![deny(bare_trait_objects)]
 #![no_std]
 #![unstable(feature = "panic_unwind", issue = "32837")]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -117,6 +118,6 @@ pub unsafe extern "C" fn __rust_maybe_catch_panic(f: fn(*mut u8),
 #[no_mangle]
 #[unwind(allowed)]
 pub unsafe extern "C" fn __rust_start_panic(payload: usize) -> u32 {
-    let payload = payload as *mut &mut BoxMeUp;
+    let payload = payload as *mut &mut dyn BoxMeUp;
     imp::panic(Box::from_raw((*payload).box_me_up()))
 }

src/libpanic_unwind/seh.rs

@@ -43,7 +43,7 @@
 //!   throwing. Note that throwing an exception into Rust is undefined behavior
 //!   anyway, so this should be fine.
 //! * We've got some data to transmit across the unwinding boundary,
-//!   specifically a `Box<Any + Send>`. Like with Dwarf exceptions
+//!   specifically a `Box<dyn Any + Send>`. Like with Dwarf exceptions
 //!   these two pointers are stored as a payload in the exception itself. On
 //!   MSVC, however, there's no need for an extra heap allocation because the
 //!   call stack is preserved while filter functions are being executed. This
@@ -243,7 +243,7 @@ static mut TYPE_DESCRIPTOR2: _TypeDescriptor = _TypeDescriptor {
     name: imp::NAME2,
 };
 
-pub unsafe fn panic(data: Box<Any + Send>) -> u32 {
+pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     use core::intrinsics::atomic_store;
 
     // _CxxThrowException executes entirely on this stack frame, so there's no
@@ -297,7 +297,7 @@ pub fn payload() -> [u64; 2] {
     [0; 2]
 }
 
-pub unsafe fn cleanup(payload: [u64; 2]) -> Box<Any + Send> {
+pub unsafe fn cleanup(payload: [u64; 2]) -> Box<dyn Any + Send> {
     mem::transmute(raw::TraitObject {
         data: payload[0] as *mut _,
         vtable: payload[1] as *mut _,