Auto merge of #55635 - oli-obk:min_const_unsafe_fn, r=nikomatsakis

Allow calling `const unsafe fn` in `const fn` behind a feature gate cc #55607 r? @Centril

Author: bors

src/libcore/marker.rs

@@ -596,7 +596,7 @@ mod impls {
 /// This affects, for example, whether a `static` of that type is
 /// placed in read-only static memory or writable static memory.
 #[lang = "freeze"]
-unsafe auto trait Freeze {}
+pub(crate) unsafe auto trait Freeze {}
 
 impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
 unsafe impl<T: ?Sized> Freeze for PhantomData<T> {}

src/libcore/nonzero.rs

@@ -11,14 +11,23 @@
 //! Exposes the NonZero lang item which provides optimization hints.
 
 use ops::{CoerceUnsized, DispatchFromDyn};
+use marker::Freeze;
 
 /// A wrapper type for raw pointers and integers that will never be
 /// NULL or 0 that might allow certain optimizations.
 #[rustc_layout_scalar_valid_range_start(1)]
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[derive(Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
 #[repr(transparent)]
-pub(crate) struct NonZero<T>(pub(crate) T);
+pub(crate) struct NonZero<T: Freeze>(pub(crate) T);
 
-impl<T: CoerceUnsized<U>, U> CoerceUnsized<NonZero<U>> for NonZero<T> {}
+// Do not call `T::clone` as theoretically it could turn the field into `0`
+// invalidating `NonZero`'s invariant.
+impl<T: Copy + Freeze> Clone for NonZero<T> {
+ fn clone(&self) -> Self {
+ unsafe { NonZero(self.0) }
+ }
+}
 
-impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<NonZero<U>> for NonZero<T> {}
+impl<T: CoerceUnsized<U> + Freeze, U: Freeze> CoerceUnsized<NonZero<U>> for NonZero<T> {}
+
+impl<T: DispatchFromDyn<U> + Freeze, U: Freeze> DispatchFromDyn<NonZero<U>> for NonZero<T> {}

src/libcore/num/mod.rs

@@ -70,15 +70,15 @@ assert_eq!(size_of::<Option<std::num::", stringify!($Ty), ">>(), size_of::<", st
  #[stable(feature = "nonzero", since = "1.28.0")]
  #[inline]
  pub const unsafe fn new_unchecked(n: $Int) -> Self {
- $Ty(NonZero(n))
+ $Ty(unsafe { NonZero(n) })
  }
 
  /// Create a non-zero if the given value is not zero.
  #[stable(feature = "nonzero", since = "1.28.0")]
  #[inline]
  pub fn new(n: $Int) -> Option<Self> {
  if n != 0 {
- Some($Ty(NonZero(n)))
+ Some($Ty(unsafe { NonZero(n) }))
  } else {
  None
  }

src/libcore/ptr.rs

@@ -2759,7 +2759,7 @@ impl<T: ?Sized> Unique<T> {
  /// Creates a new `Unique` if `ptr` is non-null.
  pub fn new(ptr: *mut T) -> Option<Self> {
  if !ptr.is_null() {
- Some(Unique { pointer: NonZero(ptr as _), _marker: PhantomData })
+ Some(Unique { pointer: unsafe { NonZero(ptr as _) }, _marker: PhantomData })
  } else {
  None
  }
@@ -2815,14 +2815,14 @@ impl<T: ?Sized> fmt::Pointer for Unique<T> {
 #[unstable(feature = "ptr_internals", issue = "0")]
 impl<'a, T: ?Sized> From<&'a mut T> for Unique<T> {
  fn from(reference: &'a mut T) -> Self {
- Unique { pointer: NonZero(reference as _), _marker: PhantomData }
+ Unique { pointer: unsafe { NonZero(reference as _) }, _marker: PhantomData }
  }
 }
 
 #[unstable(feature = "ptr_internals", issue = "0")]
 impl<'a, T: ?Sized> From<&'a T> for Unique<T> {
  fn from(reference: &'a T) -> Self {
- Unique { pointer: NonZero(reference as _), _marker: PhantomData }
+ Unique { pointer: unsafe { NonZero(reference as _) }, _marker: PhantomData }
  }
 }
 
@@ -2895,15 +2895,15 @@ impl<T: ?Sized> NonNull<T> {
  #[stable(feature = "nonnull", since = "1.25.0")]
  #[inline]
  pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
- NonNull { pointer: NonZero(ptr as _) }
+ NonNull { pointer: unsafe { NonZero(ptr as _) } }
  }
 
  /// Creates a new `NonNull` if `ptr` is non-null.
  #[stable(feature = "nonnull", since = "1.25.0")]
  #[inline]
  pub fn new(ptr: *mut T) -> Option<Self> {
  if !ptr.is_null() {
- Some(NonNull { pointer: NonZero(ptr as _) })
+ Some(unsafe { Self::new_unchecked(ptr) })
  } else {
  None
  }
@@ -3025,14 +3025,14 @@ impl<T: ?Sized> From<Unique<T>> for NonNull<T> {
 impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T> {
  #[inline]
  fn from(reference: &'a mut T) -> Self {
- NonNull { pointer: NonZero(reference as _) }
+ NonNull { pointer: unsafe { NonZero(reference as _) } }
  }
 }
 
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<'a, T: ?Sized> From<&'a T> for NonNull<T> {
  #[inline]
  fn from(reference: &'a T) -> Self {
- NonNull { pointer: NonZero(reference as _) }
+ NonNull { pointer: unsafe { NonZero(reference as _) } }
  }
 }

src/librustc/ich/impls_mir.rs

@@ -46,7 +46,8 @@ impl_stable_hash_for!(enum mir::BorrowKind {
 
 impl_stable_hash_for!(enum mir::UnsafetyViolationKind {
  General,
- MinConstFn,
+ GeneralAndConstFn,
+ GatedConstFnCall,
  ExternStatic(lint_node_id),
  BorrowPacked(lint_node_id),
 });

src/librustc/mir/mod.rs

@@ -25,7 +25,7 @@ use rustc_data_structures::graph::{self, GraphPredecessors, GraphSuccessors};
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::sync::MappedReadGuard;
-use rustc_serialize as serialize;
+use rustc_serialize::{self as serialize};
 use smallvec::SmallVec;
 use std::borrow::Cow;
 use std::fmt::{self, Debug, Formatter, Write};
@@ -2778,8 +2778,11 @@ impl Location {
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum UnsafetyViolationKind {
  General,
- /// unsafety is not allowed at all in min const fn
- MinConstFn,
+ /// Right now function calls to `const unsafe fn` are only permitted behind a feature gate
+ /// Also, even `const unsafe fn` need an `unsafe` block to do the allowed operations.
+ GatedConstFnCall,
+ /// Permitted in const fn and regular fns
+ GeneralAndConstFn,
  ExternStatic(ast::NodeId),
  BorrowPacked(ast::NodeId),
 }

src/librustc/ty/constness.rs

@@ -5,7 +5,6 @@ use ty::TyCtxt;
 use syntax_pos::symbol::Symbol;
 use hir::map::blocks::FnLikeNode;
 use syntax::attr;
-use rustc_target::spec::abi;
 
 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
  /// Whether the `def_id` counts as const fn in your current crate, considering all active
@@ -40,19 +39,12 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 
  /// Returns true if this function must conform to `min_const_fn`
  pub fn is_min_const_fn(self, def_id: DefId) -> bool {
+ // Bail out if the signature doesn't contain `const`
+ if !self.is_const_fn_raw(def_id) {
+ return false;
+ }
+
  if self.features().staged_api {
- // some intrinsics are waved through if called inside the
- // standard library. Users never need to call them directly
- if let abi::Abi::RustIntrinsic = self.fn_sig(def_id).abi() {
- assert!(!self.is_const_fn(def_id));
- match &self.item_name(def_id).as_str()[..] {
- | "size_of"
- | "min_align_of"
- | "needs_drop"
- => return true,
- _ => {},
- }
- }
  // in order for a libstd function to be considered min_const_fn
  // it needs to be stable and have no `rustc_const_unstable` attribute
  match self.lookup_stability(def_id) {

src/librustc_data_structures/indexed_vec.rs

@@ -98,12 +98,18 @@ macro_rules! newtype_index {
  @max [$max:expr]
  @vis [$v:vis]
  @debug_format [$debug_format:tt]) => (
- #[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, $($derives),*)]
+ #[derive(Copy, PartialEq, Eq, Hash, PartialOrd, Ord, $($derives),*)]
  #[rustc_layout_scalar_valid_range_end($max)]
  $v struct $type {
  private: u32
  }
 
+ impl Clone for $type {
+ fn clone(&self) -> Self {
+ *self
+ }
+ }
+
  impl $type {
  $v const MAX_AS_U32: u32 = $max;
 
@@ -145,7 +151,7 @@ macro_rules! newtype_index {
 
  #[inline]
  $v const unsafe fn from_u32_unchecked(value: u32) -> Self {
- $type { private: value }
+ unsafe { $type { private: value } }
  }
 
  /// Extract value of this index as an integer.
@@ -328,12 +334,13 @@ macro_rules! newtype_index {
  derive [$($derives:ident,)+]
  $($tokens:tt)*) => (
  newtype_index!(
- @derives [$($derives,)+ RustcDecodable, RustcEncodable,]
+ @derives [$($derives,)+ RustcEncodable,]
  @type [$type]
  @max [$max]
  @vis [$v]
  @debug_format [$debug_format]
  $($tokens)*);
+ newtype_index!(@decodable $type);
  );
 
  // The case where no derives are added, but encodable is overridden. Don't
@@ -360,12 +367,29 @@ macro_rules! newtype_index {
  @debug_format [$debug_format:tt]
  $($tokens:tt)*) => (
  newtype_index!(
- @derives [RustcDecodable, RustcEncodable,]
+ @derives [RustcEncodable,]
  @type [$type]
  @max [$max]
  @vis [$v]
  @debug_format [$debug_format]
  $($tokens)*);
+ newtype_index!(@decodable $type);
+ );
+
+ (@decodable $type:ident) => (
+ impl $type {
+ fn __decodable__impl__hack() {
+ mod __more_hacks_because__self_doesnt_work_in_functions {
+ extern crate serialize;
+ use self::serialize::{Decodable, Decoder};
+ impl Decodable for super::$type {
+ fn decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
+ d.read_u32().map(Self::from)
+ }
+ }
+ }
+ }
+ }
  );
 
  // Rewrite final without comma to one that includes comma

src/librustc_mir/build/mod.rs

@@ -91,8 +91,9 @@ pub fn mir_build<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Mir<'t
  // types/lifetimes replaced)
  let fn_hir_id = tcx.hir.node_to_hir_id(id);
  let fn_sig = cx.tables().liberated_fn_sigs()[fn_hir_id].clone();
+ let fn_def_id = tcx.hir.local_def_id(id);
 
- let ty = tcx.type_of(tcx.hir.local_def_id(id));
+ let ty = tcx.type_of(fn_def_id);
  let mut abi = fn_sig.abi;
  let implicit_argument = match ty.sty {
  ty::Closure(..) => {
@@ -108,9 +109,15 @@ pub fn mir_build<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Mir<'t
  _ => None,
  };
 
- // FIXME: safety in closures
  let safety = match fn_sig.unsafety {
  hir::Unsafety::Normal => Safety::Safe,
+ hir::Unsafety::Unsafe if tcx.is_min_const_fn(fn_def_id) => {
+ // As specified in #55607, a `const unsafe fn` differs
+ // from an `unsafe fn` in that its body is still considered
+ // safe code by default.
+ assert!(implicit_argument.is_none());
+ Safety::Safe
+ },
  hir::Unsafety::Unsafe => Safety::FnUnsafe,
  };