Rollup of 8 pull requests

src/liballoc/boxed.rs

@@ -4,16 +4,6 @@
 //! heap allocation in Rust. Boxes provide ownership for this allocation, and
 //! drop their contents when they go out of scope.
 //!
-//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for
-//! its allocation. It is valid to convert both ways between a [`Box`] and a
-//! raw pointer allocated with the [`Global`] allocator, given that the
-//! [`Layout`] used with the allocator is correct for the type. More precisely,
-//! a `value: *mut T` that has been allocated with the [`Global`] allocator
-//! with `Layout::for_value(&*value)` may be converted into a box using
-//! `Box::<T>::from_raw(value)`. Conversely, the memory backing a `value: *mut
-//! T` obtained from `Box::<T>::into_raw` may be deallocated using the
-//! [`Global`] allocator with `Layout::for_value(&*value)`.
-//!
 //! # Examples
 //!
 //! Move a value from the stack to the heap by creating a [`Box`]:
@@ -61,6 +51,19 @@
 //! for a `Cons`. By introducing a `Box`, which has a defined size, we know how
 //! big `Cons` needs to be.
 //!
+//! # Memory layout
+//!
+//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for
+//! its allocation. It is valid to convert both ways between a [`Box`] and a
+//! raw pointer allocated with the [`Global`] allocator, given that the
+//! [`Layout`] used with the allocator is correct for the type. More precisely,
+//! a `value: *mut T` that has been allocated with the [`Global`] allocator
+//! with `Layout::for_value(&*value)` may be converted into a box using
+//! `Box::<T>::from_raw(value)`. Conversely, the memory backing a `value: *mut
+//! T` obtained from `Box::<T>::into_raw` may be deallocated using the
+//! [`Global`] allocator with `Layout::for_value(&*value)`.
+//!
+//!
 //! [dereferencing]: ../../std/ops/trait.Deref.html
 //! [`Box`]: struct.Box.html
 //! [`Global`]: ../alloc/struct.Global.html
@@ -127,24 +130,38 @@ impl<T: ?Sized> Box<T> {
     ///
     /// After calling this function, the raw pointer is owned by the
     /// resulting `Box`. Specifically, the `Box` destructor will call
-    /// the destructor of `T` and free the allocated memory. Since the
-    /// way `Box` allocates and releases memory is unspecified, the
-    /// only valid pointer to pass to this function is the one taken
-    /// from another `Box` via the [`Box::into_raw`] function.
+    /// the destructor of `T` and free the allocated memory. For this
+    /// to be safe, the memory must have been allocated in accordance
+    /// with the [memory layout] used by `Box` .
+    ///
+    /// # Safety
     ///
     /// This function is unsafe because improper use may lead to
     /// memory problems. For example, a double-free may occur if the
     /// function is called twice on the same raw pointer.
     ///
-    /// [`Box::into_raw`]: struct.Box.html#method.into_raw
-    ///
     /// # Examples
-    ///
+    /// Recreate a `Box` which was previously converted to a raw pointer
+    /// using [`Box::into_raw`]:
     /// ```
     /// let x = Box::new(5);
     /// let ptr = Box::into_raw(x);
     /// let x = unsafe { Box::from_raw(ptr) };
     /// ```
+    /// Manually create a `Box` from scratch by using the global allocator:
+    /// ```
+    /// use std::alloc::{alloc, Layout};
+    ///
+    /// unsafe {
+    ///     let ptr = alloc(Layout::new::<i32>()) as *mut i32;
+    ///     *ptr = 5;
+    ///     let x = Box::from_raw(ptr);
+    /// }
+    /// ```
+    ///
+    /// [memory layout]: index.html#memory-layout
+    /// [`Layout`]: ../alloc/struct.Layout.html
+    /// [`Box::into_raw`]: struct.Box.html#method.into_raw
     #[stable(feature = "box_raw", since = "1.4.0")]
     #[inline]
     pub unsafe fn from_raw(raw: *mut T) -> Self {
@@ -157,22 +174,40 @@ impl<T: ?Sized> Box<T> {
     ///
     /// After calling this function, the caller is responsible for the
     /// memory previously managed by the `Box`. In particular, the
-    /// caller should properly destroy `T` and release the memory. The
-    /// proper way to do so is to convert the raw pointer back into a
-    /// `Box` with the [`Box::from_raw`] function.
+    /// caller should properly destroy `T` and release the memory, taking
+    /// into account the [memory layout] used by `Box`. The easiest way to
+    /// do this is to convert the raw pointer back into a `Box` with the
+    /// [`Box::from_raw`] function, allowing the `Box` destructor to perform
+    /// the cleanup.
     ///
     /// Note: this is an associated function, which means that you have
     /// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This
     /// is so that there is no conflict with a method on the inner type.
     ///
-    /// [`Box::from_raw`]: struct.Box.html#method.from_raw
-    ///
     /// # Examples
-    ///
+    /// Converting the raw pointer back into a `Box` with [`Box::from_raw`]
+    /// for automatic cleanup:
     /// ```
-    /// let x = Box::new(5);
+    /// let x = Box::new(String::from("Hello"));
     /// let ptr = Box::into_raw(x);
+    /// let x = unsafe { Box::from_raw(ptr) };
+    /// ```
+    /// Manual cleanup by explicitly running the destructor and deallocating
+    /// the memory:
     /// ```
+    /// use std::alloc::{dealloc, Layout};
+    /// use std::ptr;
+    ///
+    /// let x = Box::new(String::from("Hello"));
+    /// let p = Box::into_raw(x);
+    /// unsafe {
+    ///     ptr::drop_in_place(p);
+    ///     dealloc(p as *mut u8, Layout::new::<String>());
+    /// }
+    /// ```
+    ///
+    /// [memory layout]: index.html#memory-layout
+    /// [`Box::from_raw`]: struct.Box.html#method.from_raw
     #[stable(feature = "box_raw", since = "1.4.0")]
     #[inline]
     pub fn into_raw(b: Box<T>) -> *mut T {
@@ -184,7 +219,7 @@ impl<T: ?Sized> Box<T> {
     /// After calling this function, the caller is responsible for the
     /// memory previously managed by the `Box`. In particular, the
     /// caller should properly destroy `T` and release the memory. The
-    /// proper way to do so is to convert the `NonNull<T>` pointer
+    /// easiest way to do so is to convert the `NonNull<T>` pointer
     /// into a raw pointer and back into a `Box` with the [`Box::from_raw`]
     /// function.
     ///
@@ -203,6 +238,10 @@ impl<T: ?Sized> Box<T> {
     /// fn main() {
     ///     let x = Box::new(5);
     ///     let ptr = Box::into_raw_non_null(x);
+    ///
+    ///     // Clean up the memory by converting the NonNull pointer back
+    ///     // into a Box and letting the Box be dropped.
+    ///     let x = unsafe { Box::from_raw(ptr.as_ptr()) };
     /// }
     /// ```
     #[unstable(feature = "box_into_raw_non_null", issue = "47336")]

src/libcore/mem.rs

@@ -466,7 +466,7 @@ pub unsafe fn zeroed<T>() -> T {
 /// [`MaybeUninit<T>`]: union.MaybeUninit.html
 /// [inv]: union.MaybeUninit.html#initialization-invariant
 #[inline]
-#[rustc_deprecated(since = "1.40.0", reason = "use `mem::MaybeUninit` instead")]
+#[rustc_deprecated(since = "1.38.0", reason = "use `mem::MaybeUninit` instead")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn uninitialized<T>() -> T {
     intrinsics::panic_if_uninhabited::<T>();

src/librustc/middle/intrinsicck.rs

@@ -6,7 +6,7 @@ use crate::ty::query::Providers;
 
 use rustc_target::spec::abi::Abi::RustIntrinsic;
 use rustc_data_structures::indexed_vec::Idx;
-use syntax_pos::Span;
+use syntax_pos::{Span, sym};
 use crate::hir::intravisit::{self, Visitor, NestedVisitorMap};
 use crate::hir;
 
@@ -69,7 +69,7 @@ fn unpack_option_like<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 impl<'a, 'tcx> ExprVisitor<'a, 'tcx> {
     fn def_id_is_transmute(&self, def_id: DefId) -> bool {
         self.tcx.fn_sig(def_id).abi() == RustIntrinsic &&
-        self.tcx.item_name(def_id) == "transmute"
+        self.tcx.item_name(def_id) == sym::transmute
     }
 
     fn check_transmute(&self, span: Span, from: Ty<'tcx>, to: Ty<'tcx>) {

src/librustc/session/config.rs

@@ -1853,7 +1853,7 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
 
 // Convert strings provided as --cfg [cfgspec] into a crate_cfg
 pub fn parse_cfgspecs(cfgspecs: Vec<String>) -> FxHashSet<(String, Option<String>)> {
-    syntax::with_globals(move || {
+    syntax::with_default_globals(move || {
         let cfg = cfgspecs.into_iter().map(|s| {
             let sess = parse::ParseSess::new(FilePathMapping::empty());
             let filename = FileName::cfg_spec_source_code(&s);
@@ -2735,7 +2735,7 @@ mod tests {
     // When the user supplies --test we should implicitly supply --cfg test
     #[test]
     fn test_switch_implies_cfg_test() {
-        syntax::with_globals(|| {
+        syntax::with_default_globals(|| {
             let matches = &match optgroups().parse(&["--test".to_string()]) {
                 Ok(m) => m,
                 Err(f) => panic!("test_switch_implies_cfg_test: {}", f),
@@ -2753,7 +2753,7 @@ mod tests {
     #[test]
     fn test_switch_implies_cfg_test_unless_cfg_test() {
         use syntax::symbol::sym;
-        syntax::with_globals(|| {
+        syntax::with_default_globals(|| {
             let matches = &match optgroups().parse(&["--test".to_string(),
                                                      "--cfg=test".to_string()]) {
                 Ok(m) => m,
@@ -2771,15 +2771,15 @@ mod tests {
 
     #[test]
     fn test_can_print_warnings() {
-        syntax::with_globals(|| {
+        syntax::with_default_globals(|| {
             let matches = optgroups().parse(&["-Awarnings".to_string()]).unwrap();
             let registry = errors::registry::Registry::new(&[]);
             let (sessopts, _) = build_session_options_and_crate_config(&matches);
             let sess = build_session(sessopts, None, registry);
             assert!(!sess.diagnostic().flags.can_emit_warnings);
         });
 
-        syntax::with_globals(|| {
+        syntax::with_default_globals(|| {
             let matches = optgroups()
                 .parse(&["-Awarnings".to_string(), "-Dwarnings".to_string()])
                 .unwrap();
@@ -2789,7 +2789,7 @@ mod tests {
             assert!(sess.diagnostic().flags.can_emit_warnings);
         });
 
-        syntax::with_globals(|| {
+        syntax::with_default_globals(|| {
             let matches = optgroups().parse(&["-Adead_code".to_string()]).unwrap();
             let registry = errors::registry::Registry::new(&[]);
             let (sessopts, _) = build_session_options_and_crate_config(&matches);

src/librustc/traits/on_unimplemented.rs

@@ -243,15 +243,15 @@ impl<'a, 'gcx, 'tcx> OnUnimplementedFormatString {
                     // `{Self}` is allowed
                     Position::ArgumentNamed(s) if s == "Self" => (),
                     // `{ThisTraitsName}` is allowed
-                    Position::ArgumentNamed(s) if s == name => (),
+                    Position::ArgumentNamed(s) if s == name.as_str() => (),
                     // `{from_method}` is allowed
                     Position::ArgumentNamed(s) if s == "from_method" => (),
                     // `{from_desugaring}` is allowed
                     Position::ArgumentNamed(s) if s == "from_desugaring" => (),
                     // So is `{A}` if A is a type parameter
-                    Position::ArgumentNamed(s) => match generics.params.iter().find(|param|
-                        param.name == s
-                    ) {
+                    Position::ArgumentNamed(s) => match generics.params.iter().find(|param| {
+                        param.name.as_str() == s
+                    }) {
                         Some(_) => (),
                         None => {
                             span_err!(tcx.sess, span, E0230,
@@ -301,7 +301,7 @@ impl<'a, 'gcx, 'tcx> OnUnimplementedFormatString {
                 Piece::NextArgument(a) => match a.position {
                     Position::ArgumentNamed(s) => match generic_map.get(s) {
                         Some(val) => val,
-                        None if s == name => {
+                        None if s == name.as_str() => {
                             &trait_str
                         }
                         None => {

src/librustc/ty/mod.rs

@@ -2981,9 +2981,9 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
-    pub fn item_name(self, id: DefId) -> InternedString {
+    pub fn item_name(self, id: DefId) -> Symbol {
         if id.index == CRATE_DEF_INDEX {
-            self.original_crate_name(id.krate).as_interned_str()
+            self.original_crate_name(id.krate)
         } else {
             let def_key = self.def_key(id);
             match def_key.disambiguated_data.data {
@@ -2995,7 +2995,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     }),
                 _ => def_key.disambiguated_data.data.get_opt_name().unwrap_or_else(|| {
                     bug!("item_name: no name for {:?}", self.def_path(id));
-                }),
+                }).as_symbol(),
             }
         }
     }

src/librustc/ty/print/pretty.rs

@@ -1140,14 +1140,16 @@ impl<F: fmt::Write> PrettyPrinter<'gcx, 'tcx> for FmtPrinter<'_, 'gcx, 'tcx, F>
 
         match *region {
             ty::ReEarlyBound(ref data) => {
-                data.name != "" && data.name != "'_"
+                data.name.as_symbol() != keywords::Invalid.name() &&
+                data.name.as_symbol() != keywords::UnderscoreLifetime.name()
             }
 
             ty::ReLateBound(_, br) |
             ty::ReFree(ty::FreeRegion { bound_region: br, .. }) |
             ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
                 if let ty::BrNamed(_, name) = br {
-                    if name != "" && name != "'_" {
+                    if name.as_symbol() != keywords::Invalid.name() &&
+                       name.as_symbol() != keywords::UnderscoreLifetime.name() {
                         return true;
                     }
                 }
@@ -1203,7 +1205,7 @@ impl<F: fmt::Write> FmtPrinter<'_, '_, '_, F> {
         // `explain_region()` or `note_and_explain_region()`.
         match *region {
             ty::ReEarlyBound(ref data) => {
-                if data.name != "" {
+                if data.name.as_symbol() != keywords::Invalid.name() {
                     p!(write("{}", data.name));
                     return Ok(self);
                 }
@@ -1212,7 +1214,8 @@ impl<F: fmt::Write> FmtPrinter<'_, '_, '_, F> {
             ty::ReFree(ty::FreeRegion { bound_region: br, .. }) |
             ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
                 if let ty::BrNamed(_, name) = br {
-                    if name != "" && name != "'_" {
+                    if name.as_symbol() != keywords::Invalid.name() &&
+                       name.as_symbol() != keywords::UnderscoreLifetime.name() {
                         p!(write("{}", name));
                         return Ok(self);
                     }

src/librustc_allocator/expand.rs

@@ -14,7 +14,7 @@ use syntax::{
         base::{ExtCtxt, Resolver},
         build::AstBuilder,
         expand::ExpansionConfig,
-        hygiene::{self, Mark, SyntaxContext},
+        hygiene::{Mark, SyntaxContext},
     },
     mut_visit::{self, MutVisitor},
     parse::ParseSess,
@@ -96,7 +96,7 @@ impl MutVisitor for ExpandAllocatorDirectives<'_> {
             ].into()),
             allow_internal_unsafe: false,
             local_inner_macros: false,
-            edition: hygiene::default_edition(),
+            edition: self.sess.edition,
         });
 
         // Tie the span to the macro expansion info we just created

src/librustc_codegen_utils/symbol_names.rs

@@ -264,7 +264,7 @@ fn compute_symbol_name(tcx: TyCtxt<'_, 'tcx, 'tcx>, instance: Instance<'tcx>) ->
             return name.as_interned_str();
         }
         // Don't mangle foreign items.
-        return tcx.item_name(def_id);
+        return tcx.item_name(def_id).as_interned_str();
     }
 
     if let Some(name) = &attrs.export_name {
@@ -274,7 +274,7 @@ fn compute_symbol_name(tcx: TyCtxt<'_, 'tcx, 'tcx>, instance: Instance<'tcx>) ->
 
     if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
         // Don't mangle
-        return tcx.item_name(def_id);
+        return tcx.item_name(def_id).as_interned_str();
     }
 
     // We want to compute the "type" of this item. Unfortunately, some

src/librustc_data_structures/macros.rs

@@ -1,13 +1,12 @@
-/// A simple static assertion macro. The first argument should be a unique
-/// ALL_CAPS identifier that describes the condition.
+/// A simple static assertion macro.
 #[macro_export]
-#[allow_internal_unstable(type_ascription)]
+#[allow_internal_unstable(type_ascription, underscore_const_names)]
 macro_rules! static_assert {
-    ($name:ident: $test:expr) => {
+    ($test:expr) => {
         // Use the bool to access an array such that if the bool is false, the access
         // is out-of-bounds.
         #[allow(dead_code)]
-        static $name: () = [()][!($test: bool) as usize];
+        const _: () = [()][!($test: bool) as usize];
     }
 }