Auto merge of #73486 - Manishearth:rollup-11iyqpc, r=Manishearth

Rollup of 17 pull requests

Successful merges:

 - #70551 (Make all uses of ty::Error delay a span bug)
 - #71338 (Expand "recursive opaque type" diagnostic)
 - #71976 (Improve diagnostics for `let x += 1`)
 - #72279 (add raw_ref macros)
 - #72628 (Add tests for 'impl Default for [T; N]')
 - #72804 (Further tweak lifetime errors involving `dyn Trait` and `impl Trait` in return position)
 - #72814 (remove visit_terminator_kind from MIR visitor)
 - #72836 (Complete the std::time documentation to warn about the inconsistencies between OS)
 - #72968 (Only highlight doc search results via mouseover if mouse has moved)
 - #73034 (Export `#[inline]` fns with extern indicators)
 - #73315 (Clean up some weird command strings)
 - #73320 (Make new type param suggestion more targetted)
 - #73361 (Tweak "non-primitive cast" error)
 - #73425 (Mention functions pointers in the documentation)
 - #73428 (Fix typo in librustc_ast docs)
 - #73447 (Improve document for `Result::as_deref(_mut)` methods)
 - #73476 (Added tooltip for should_panic code examples)

Failed merges:

r? @ghost

Author: bors

src/libcore/convert/mod.rs

@@ -374,6 +374,7 @@ pub trait Into<T>: Sized {
 /// [`Into`]: trait.Into.html
 /// [`from`]: trait.From.html#tymethod.from
 /// [book]: ../../book/ch09-00-error-handling.html
+#[rustc_diagnostic_item = "from_trait"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(on(
     all(_Self = "&str", T = "std::string::String"),

src/libcore/mem/mod.rs

@@ -581,11 +581,12 @@ pub const fn needs_drop<T>() -> bool {
 /// This means that, for example, the padding byte in `(u8, u16)` is not
 /// necessarily zeroed.
 ///
-/// There is no guarantee that an all-zero byte-pattern represents a valid value of
-/// some type `T`. For example, the all-zero byte-pattern is not a valid value
-/// for reference types (`&T` and `&mut T`). Using `zeroed` on such types
-/// causes immediate [undefined behavior][ub] because [the Rust compiler assumes][inv]
-/// that there always is a valid value in a variable it considers initialized.
+/// There is no guarantee that an all-zero byte-pattern represents a valid value
+/// of some type `T`. For example, the all-zero byte-pattern is not a valid value
+/// for reference types (`&T`, `&mut T`) and functions pointers. Using `zeroed`
+/// on such types causes immediate [undefined behavior][ub] because [the Rust
+/// compiler assumes][inv] that there always is a valid value in a variable it
+/// considers initialized.
 ///
 /// This has the same effect as [`MaybeUninit::zeroed().assume_init()`][zeroed].
 /// It is useful for FFI sometimes, but should generally be avoided.
@@ -612,6 +613,7 @@ pub const fn needs_drop<T>() -> bool {
 /// use std::mem;
 ///
 /// let _x: &i32 = unsafe { mem::zeroed() }; // Undefined behavior!
+/// let _y: fn() = unsafe { mem::zeroed() }; // And again!
 /// ```
 #[inline(always)]
 #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/ptr/mod.rs

@@ -1399,3 +1399,70 @@ fnptr_impls_args! { A, B, C, D, E, F, G, H, I }
 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J }
 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K }
 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L }
+
+/// Create a `const` raw pointer to a place, without creating an intermediate reference.
+///
+/// Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned
+/// and points to initialized data. For cases where those requirements do not hold,
+/// raw pointers should be used instead. However, `&expr as *const _` creates a reference
+/// before casting it to a raw pointer, and that reference is subject to the same rules
+/// as all other references. This macro can create a raw pointer *without* creating
+/// a reference first.
+///
+/// # Example
+///
+/// ```
+/// #![feature(raw_ref_macros)]
+/// use std::ptr;
+///
+/// #[repr(packed)]
+/// struct Packed {
+///     f1: u8,
+///     f2: u16,
+/// }
+///
+/// let packed = Packed { f1: 1, f2: 2 };
+/// // `&packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
+/// let raw_f2 = ptr::raw_const!(packed.f2);
+/// assert_eq!(unsafe { raw_f2.read_unaligned() }, 2);
+/// ```
+#[unstable(feature = "raw_ref_macros", issue = "73394")]
+#[rustc_macro_transparency = "semitransparent"]
+#[allow_internal_unstable(raw_ref_op)]
+pub macro raw_const($e:expr) {
+    &raw const $e
+}
+
+/// Create a `mut` raw pointer to a place, without creating an intermediate reference.
+///
+/// Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned
+/// and points to initialized data. For cases where those requirements do not hold,
+/// raw pointers should be used instead. However, `&mut expr as *mut _` creates a reference
+/// before casting it to a raw pointer, and that reference is subject to the same rules
+/// as all other references. This macro can create a raw pointer *without* creating
+/// a reference first.
+///
+/// # Example
+///
+/// ```
+/// #![feature(raw_ref_macros)]
+/// use std::ptr;
+///
+/// #[repr(packed)]
+/// struct Packed {
+///     f1: u8,
+///     f2: u16,
+/// }
+///
+/// let mut packed = Packed { f1: 1, f2: 2 };
+/// // `&mut packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
+/// let raw_f2 = ptr::raw_mut!(packed.f2);
+/// unsafe { raw_f2.write_unaligned(42); }
+/// assert_eq!({packed.f2}, 42); // `{...}` forces copying the field instead of creating a reference.
+/// ```
+#[unstable(feature = "raw_ref_macros", issue = "73394")]
+#[rustc_macro_transparency = "semitransparent"]
+#[allow_internal_unstable(raw_ref_op)]
+pub macro raw_mut($e:expr) {
+    &raw mut $e
+}

src/libcore/result.rs

@@ -1145,45 +1145,69 @@ impl<T, E: Into<!>> Result<T, E> {
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T: Deref, E> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T::Target, &E>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&<T as Deref>::Target, &E>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a reference to the
-    /// `Ok` type's `Deref::Target` type.
+    /// Coerces the [`Ok`] variant of the original [`Result`] via [`Deref`](crate::ops::Deref)
+    /// and returns the new [`Result`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<String, u32> = Ok("hello".to_string());
+    /// let y: Result<&str, &u32> = Ok("hello");
+    /// assert_eq!(x.as_deref(), y);
+    ///
+    /// let x: Result<String, u32> = Err(42);
+    /// let y: Result<&str, &u32> = Err(&42);
+    /// assert_eq!(x.as_deref(), y);
+    /// ```
     pub fn as_deref(&self) -> Result<&T::Target, &E> {
         self.as_ref().map(|t| t.deref())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T, E: Deref> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T, &E::Target>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T, &<E as Deref>::Target>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a reference to the
-    /// `Err` type's `Deref::Target` type.
+    /// Coerces the [`Err`] variant of the original [`Result`] via [`Deref`](crate::ops::Deref)
+    /// and returns the new [`Result`].
     pub fn as_deref_err(&self) -> Result<&T, &E::Target> {
         self.as_ref().map_err(|e| e.deref())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T: DerefMut, E> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T::Target, &mut E>`.
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut <T as DerefMut>::Target, &mut E>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
-    /// the `Ok` type's `Deref::Target` type.
+    /// Coerces the [`Ok`] variant of the original [`Result`] via [`DerefMut`](crate::ops::DerefMut)
+    /// and returns the new [`Result`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut x: Result<String, u32> = Ok("hello".to_string());
+    /// let y: Result<&mut str, &mut u32> = Ok("HELLO");
+    /// assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);
+    ///
+    /// let mut x: Result<String, u32> = Err(42);
+    /// let y: Result<&mut str, &mut u32> = Err(&42);
+    /// assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);
+    /// ```
     pub fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E> {
         self.as_mut().map(|t| t.deref_mut())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T, E: DerefMut> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T, &mut E::Target>`.
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T, &mut <E as DerefMut>::Target>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
-    /// the `Err` type's `Deref::Target` type.
+    /// Coerces the [`Err`] variant of the original [`Result`] via [`DerefMut`](crate::ops::DerefMut)
+    /// and returns the new [`Result`].
     pub fn as_deref_mut_err(&mut self) -> Result<&mut T, &mut E::Target> {
         self.as_mut().map_err(|e| e.deref_mut())
     }

src/libcore/tests/array.rs

@@ -241,3 +241,52 @@ fn iterator_drops() {
     }
     assert_eq!(i.get(), 5);
 }
+
+// This test does not work on targets without panic=unwind support.
+// To work around this problem, test is marked is should_panic, so it will
+// be automagically skipped on unsuitable targets, such as
+// wasm32-unknown-unkown.
+//
+// It means that we use panic for indicating success.
+#[test]
+#[should_panic(expected = "test succeeded")]
+fn array_default_impl_avoids_leaks_on_panic() {
+    use core::sync::atomic::{AtomicUsize, Ordering::Relaxed};
+    static COUNTER: AtomicUsize = AtomicUsize::new(0);
+    #[derive(Debug)]
+    struct Bomb(usize);
+
+    impl Default for Bomb {
+        fn default() -> Bomb {
+            if COUNTER.load(Relaxed) == 3 {
+                panic!("bomb limit exceeded");
+            }
+
+            COUNTER.fetch_add(1, Relaxed);
+            Bomb(COUNTER.load(Relaxed))
+        }
+    }
+
+    impl Drop for Bomb {
+        fn drop(&mut self) {
+            COUNTER.fetch_sub(1, Relaxed);
+        }
+    }
+
+    let res = std::panic::catch_unwind(|| <[Bomb; 5]>::default());
+    let panic_msg = match res {
+        Ok(_) => unreachable!(),
+        Err(p) => p.downcast::<&'static str>().unwrap(),
+    };
+    assert_eq!(*panic_msg, "bomb limit exceeded");
+    // check that all bombs are successfully dropped
+    assert_eq!(COUNTER.load(Relaxed), 0);
+    panic!("test succeeded")
+}
+
+#[test]
+fn empty_array_is_always_default() {
+    struct DoesNotImplDefault;
+
+    let _arr = <[DoesNotImplDefault; 0]>::default();
+}

src/librustc_ast/ast.rs

@@ -5,7 +5,7 @@
 //! additional metadata), and [`ItemKind`] (which represents a concrete type and contains
 //! information specific to the type of the item).
 //!
-//! Other module items that worth mentioning:
+//! Other module items worth mentioning:
 //! - [`Ty`] and [`TyKind`]: A parsed Rust type.
 //! - [`Expr`] and [`ExprKind`]: A parsed Rust expression.
 //! - [`Pat`] and [`PatKind`]: A parsed Rust pattern. Patterns are often dual to expressions.

src/librustc_codegen_ssa/back/symbol_export.rs

@@ -89,10 +89,12 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<
                 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
                     let def_id = tcx.hir().local_def_id(hir_id);
                     let generics = tcx.generics_of(def_id);
-                    if !generics.requires_monomorphization(tcx) &&
-                        // Functions marked with #[inline] are only ever codegened
-                        // with "internal" linkage and are never exported.
-                        !Instance::mono(tcx, def_id.to_def_id()).def.generates_cgu_internal_copy(tcx)
+                    if !generics.requires_monomorphization(tcx)
+                        // Functions marked with #[inline] are codegened with "internal"
+                        // linkage and are not exported unless marked with an extern
+                        // inidicator
+                        && (!Instance::mono(tcx, def_id.to_def_id()).def.generates_cgu_internal_copy(tcx)
+                            || tcx.codegen_fn_attrs(def_id.to_def_id()).contains_extern_indicator())
                     {
                         Some(def_id)
                     } else {

src/librustc_codegen_ssa/debuginfo/type_names.rs

@@ -195,7 +195,7 @@ pub fn push_debuginfo_type_name<'tcx>(
                 tcx.def_key(def_id).disambiguated_data.disambiguator
             ));
         }
-        ty::Error
+        ty::Error(_)
         | ty::Infer(_)
         | ty::Placeholder(..)
         | ty::Projection(..)

src/librustc_codegen_ssa/mir/analyze.rs

@@ -234,8 +234,8 @@ impl<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> Visitor<'tcx>
         self.visit_rvalue(rvalue, location);
     }
 
-    fn visit_terminator_kind(&mut self, kind: &mir::TerminatorKind<'tcx>, location: Location) {
-        let check = match *kind {
+    fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
+        let check = match terminator.kind {
             mir::TerminatorKind::Call { func: mir::Operand::Constant(ref c), ref args, .. } => {
                 match c.literal.ty.kind {
                     ty::FnDef(did, _) => Some((did, args)),
@@ -259,7 +259,7 @@ impl<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> Visitor<'tcx>
             }
         }
 
-        self.super_terminator_kind(kind, location);
+        self.super_terminator(terminator, location);
     }
 
     fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) {

src/librustc_codegen_ssa/mir/block.rs

@@ -998,8 +998,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 bx.unreachable();
             }
 
-            mir::TerminatorKind::Drop { location, target, unwind } => {
-                self.codegen_drop_terminator(helper, bx, location, target, unwind);
+            mir::TerminatorKind::Drop { place, target, unwind } => {
+                self.codegen_drop_terminator(helper, bx, place, target, unwind);
             }
 
             mir::TerminatorKind::Assert { ref cond, expected, ref msg, target, cleanup } => {

src/librustc_error_codes/error_codes.rs

@@ -439,6 +439,7 @@ E0752: include_str!("./error_codes/E0752.md"),
 E0753: include_str!("./error_codes/E0753.md"),
 E0754: include_str!("./error_codes/E0754.md"),
 E0758: include_str!("./error_codes/E0758.md"),
+E0759: include_str!("./error_codes/E0759.md"),
 E0760: include_str!("./error_codes/E0760.md"),
 E0761: include_str!("./error_codes/E0761.md"),
 E0762: include_str!("./error_codes/E0762.md"),

src/librustc_error_codes/error_codes/E0759.md

@@ -0,0 +1,67 @@
+A `'static` requirement in a return type involving a trait is not fulfilled.
+
+Erroneous code examples:
+
+```compile_fail,E0759
+use std::fmt::Debug;
+
+fn foo(x: &i32) -> impl Debug {
+    x
+}
+```
+
+```compile_fail,E0759
+# use std::fmt::Debug;
+fn bar(x: &i32) -> Box<dyn Debug> {
+    Box::new(x)
+}
+```
+
+These examples have the same semantics as the following:
+
+```compile_fail,E0759
+# use std::fmt::Debug;
+fn foo(x: &i32) -> impl Debug + 'static {
+    x
+}
+```
+
+```compile_fail,E0759
+# use std::fmt::Debug;
+fn bar(x: &i32) -> Box<dyn Debug + 'static> {
+    Box::new(x)
+}
+```
+
+Both [`dyn Trait`] and [`impl Trait`] in return types have a an implicit
+`'static` requirement, meaning that the value implementing them that is being
+returned has to be either a `'static` borrow or an owned value.
+
+In order to change the requirement from `'static` to be a lifetime derived from
+its arguments, you can add an explicit bound, either to an anonymous lifetime
+`'_` or some appropriate named lifetime.
+
+```
+# use std::fmt::Debug;
+fn foo(x: &i32) -> impl Debug + '_ {
+    x
+}
+fn bar(x: &i32) -> Box<dyn Debug + '_> {
+    Box::new(x)
+}
+```
+
+These are equivalent to the following explicit lifetime annotations:
+
+```
+# use std::fmt::Debug;
+fn foo<'a>(x: &'a i32) -> impl Debug + 'a {
+    x
+}
+fn bar<'a>(x: &'a i32) -> Box<dyn Debug + 'a> {
+    Box::new(x)
+}
+```
+
+[`dyn Trait`]: https://doc.rust-lang.org/book/ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types
+[`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits