Auto merge of #67560 - Centril:rollup-fzdpu9c, r=Centril

Rollup of 8 pull requests

Successful merges:

 - #67233 (Add PartialEq and Eq to Cursor)
 - #67466 (Require const stability attributes on intrinsics to be able to use them in constant contexts)
 - #67507 (Remove mem::uninitalized from tests)
 - #67527 (Results show too much)
 - #67536 (Move `{hir::lowering -> hir}::is_range_literal`)
 - #67538 (Improve diagnostics for invalid assignment)
 - #67546 (Fix ICE in mir interpretation)
 - #67559 (Document that calling Drop, even after it panics, is UB)

Failed merges:

r? @ghost

src/libcore/intrinsics.rs

@@ -1,6 +1,22 @@
 //! Compiler intrinsics.
 //!
 //! The corresponding definitions are in `librustc_codegen_llvm/intrinsic.rs`.
+//! The corresponding const implementations are in `librustc_mir/interpret/intrinsics.rs`
+//!
+//! # Const intrinsics
+//!
+//! Note: any changes to the constness of intrinsics should be discussed with the language team.
+//! This includes changes in the stability of the constness.
+//!
+//! In order to make an intrinsic usable at compile-time, one needs to copy the implementation
+//! from https://github.com/rust-lang/miri/blob/master/src/shims/intrinsics.rs to
+//! `librustc_mir/interpret/intrinsics.rs` and add a
+//! `#[rustc_const_unstable(feature = "foo", issue = "01234")]` to the intrinsic.
+//!
+//! If an intrinsic is supposed to be used from a `const fn` with a `rustc_const_stable` attribute,
+//! the intrinsic's attribute must be `rustc_const_stable`, too. Such a change should not be done
+//! without T-lang consulation, because it bakes a feature into the language that cannot be
+//! replicated in user code without compiler support.
 //!
 //! # Volatiles
 //!
@@ -671,14 +687,17 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`std::mem::size_of`](../../std/mem/fn.size_of.html).
+    #[rustc_const_stable(feature = "const_size_of", since = "1.40.0")]
     pub fn size_of<T>() -> usize;
 
     /// Moves a value to an uninitialized memory location.
     ///
     /// Drop glue is not run on the destination.
     pub fn move_val_init<T>(dst: *mut T, src: T);
 
+    #[rustc_const_stable(feature = "const_min_align_of", since = "1.40.0")]
     pub fn min_align_of<T>() -> usize;
+    #[rustc_const_unstable(feature = "const_pref_align_of", issue = "0")]
     pub fn pref_align_of<T>() -> usize;
 
     /// The size of the referenced value in bytes.
@@ -689,18 +708,21 @@ extern "rust-intrinsic" {
     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 
     /// Gets a static string slice containing the name of a type.
+    #[rustc_const_unstable(feature = "const_type_name", issue = "0")]
     pub fn type_name<T: ?Sized>() -> &'static str;
 
     /// Gets an identifier which is globally unique to the specified type. This
     /// function will return the same value for a type regardless of whichever
     /// crate it is invoked in.
+    #[rustc_const_unstable(feature = "const_type_id", issue = "0")]
     pub fn type_id<T: ?Sized + 'static>() -> u64;
 
     /// A guard for unsafe functions that cannot ever be executed if `T` is uninhabited:
     /// This will statically either panic, or do nothing.
     pub fn panic_if_uninhabited<T>();
 
     /// Gets a reference to a static `Location` indicating where it was called.
+    #[rustc_const_unstable(feature = "const_caller_location", issue = "47809")]
     pub fn caller_location() -> &'static crate::panic::Location<'static>;
 
     /// Creates a value initialized to zero.
@@ -957,6 +979,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`std::mem::needs_drop`](../../std/mem/fn.needs_drop.html).
+    #[rustc_const_stable(feature = "const_needs_drop", since = "1.40.0")]
     pub fn needs_drop<T>() -> bool;
 
     /// Calculates the offset from a pointer.
@@ -1154,6 +1177,7 @@ extern "rust-intrinsic" {
     pub fn float_to_int_approx_unchecked<Float, Int>(value: Float) -> Int;
 
     /// Returns the number of bits set in an integer type `T`
+    #[rustc_const_stable(feature = "const_ctpop", since = "1.40.0")]
     pub fn ctpop<T>(x: T) -> T;
 
     /// Returns the number of leading unset bits (zeroes) in an integer type `T`.
@@ -1181,6 +1205,7 @@ extern "rust-intrinsic" {
     /// let num_leading = ctlz(x);
     /// assert_eq!(num_leading, 16);
     /// ```
+    #[rustc_const_stable(feature = "const_ctlz", since = "1.40.0")]
     pub fn ctlz<T>(x: T) -> T;
 
     /// Like `ctlz`, but extra-unsafe as it returns `undef` when
@@ -1197,6 +1222,7 @@ extern "rust-intrinsic" {
     /// let num_leading = unsafe { ctlz_nonzero(x) };
     /// assert_eq!(num_leading, 3);
     /// ```
+    #[rustc_const_unstable(feature = "constctlz", issue = "0")]
     pub fn ctlz_nonzero<T>(x: T) -> T;
 
     /// Returns the number of trailing unset bits (zeroes) in an integer type `T`.
@@ -1224,6 +1250,7 @@ extern "rust-intrinsic" {
     /// let num_trailing = cttz(x);
     /// assert_eq!(num_trailing, 16);
     /// ```
+    #[rustc_const_stable(feature = "const_cttz", since = "1.40.0")]
     pub fn cttz<T>(x: T) -> T;
 
     /// Like `cttz`, but extra-unsafe as it returns `undef` when
@@ -1240,30 +1267,36 @@ extern "rust-intrinsic" {
     /// let num_trailing = unsafe { cttz_nonzero(x) };
     /// assert_eq!(num_trailing, 3);
     /// ```
+    #[rustc_const_unstable(feature = "const_cttz", issue = "0")]
     pub fn cttz_nonzero<T>(x: T) -> T;
 
     /// Reverses the bytes in an integer type `T`.
+    #[rustc_const_stable(feature = "const_bswap", since = "1.40.0")]
     pub fn bswap<T>(x: T) -> T;
 
     /// Reverses the bits in an integer type `T`.
+    #[rustc_const_stable(feature = "const_bitreverse", since = "1.40.0")]
     pub fn bitreverse<T>(x: T) -> T;
 
     /// Performs checked integer addition.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `overflowing_add` method. For example,
     /// [`std::u32::overflowing_add`](../../std/primitive.u32.html#method.overflowing_add)
+    #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
     pub fn add_with_overflow<T>(x: T, y: T) -> (T, bool);
 
     /// Performs checked integer subtraction
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `overflowing_sub` method. For example,
     /// [`std::u32::overflowing_sub`](../../std/primitive.u32.html#method.overflowing_sub)
+    #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
     pub fn sub_with_overflow<T>(x: T, y: T) -> (T, bool);
 
     /// Performs checked integer multiplication
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `overflowing_mul` method. For example,
     /// [`std::u32::overflowing_mul`](../../std/primitive.u32.html#method.overflowing_mul)
+    #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
     pub fn mul_with_overflow<T>(x: T, y: T) -> (T, bool);
 
     /// Performs an exact division, resulting in undefined behavior where
@@ -1279,9 +1312,11 @@ extern "rust-intrinsic" {
 
     /// Performs an unchecked left shift, resulting in undefined behavior when
     /// y < 0 or y >= N, where N is the width of T in bits.
+    #[rustc_const_stable(feature = "const_int_unchecked", since = "1.40.0")]
     pub fn unchecked_shl<T>(x: T, y: T) -> T;
     /// Performs an unchecked right shift, resulting in undefined behavior when
     /// y < 0 or y >= N, where N is the width of T in bits.
+    #[rustc_const_stable(feature = "const_int_unchecked", since = "1.40.0")]
     pub fn unchecked_shr<T>(x: T, y: T) -> T;
 
     /// Returns the result of an unchecked addition, resulting in
@@ -1300,39 +1335,46 @@ extern "rust-intrinsic" {
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `rotate_left` method. For example,
     /// [`std::u32::rotate_left`](../../std/primitive.u32.html#method.rotate_left)
+    #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
     pub fn rotate_left<T>(x: T, y: T) -> T;
 
     /// Performs rotate right.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `rotate_right` method. For example,
     /// [`std::u32::rotate_right`](../../std/primitive.u32.html#method.rotate_right)
+    #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
     pub fn rotate_right<T>(x: T, y: T) -> T;
 
     /// Returns (a + b) mod 2<sup>N</sup>, where N is the width of T in bits.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `wrapping_add` method. For example,
     /// [`std::u32::wrapping_add`](../../std/primitive.u32.html#method.wrapping_add)
+    #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
     pub fn wrapping_add<T>(a: T, b: T) -> T;
     /// Returns (a - b) mod 2<sup>N</sup>, where N is the width of T in bits.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `wrapping_sub` method. For example,
     /// [`std::u32::wrapping_sub`](../../std/primitive.u32.html#method.wrapping_sub)
+    #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
     pub fn wrapping_sub<T>(a: T, b: T) -> T;
     /// Returns (a * b) mod 2<sup>N</sup>, where N is the width of T in bits.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `wrapping_mul` method. For example,
     /// [`std::u32::wrapping_mul`](../../std/primitive.u32.html#method.wrapping_mul)
+    #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
     pub fn wrapping_mul<T>(a: T, b: T) -> T;
 
     /// Computes `a + b`, while saturating at numeric bounds.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `saturating_add` method. For example,
     /// [`std::u32::saturating_add`](../../std/primitive.u32.html#method.saturating_add)
+    #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
     pub fn saturating_add<T>(a: T, b: T) -> T;
     /// Computes `a - b`, while saturating at numeric bounds.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `saturating_sub` method. For example,
     /// [`std::u32::saturating_sub`](../../std/primitive.u32.html#method.saturating_sub)
+    #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
     pub fn saturating_sub<T>(a: T, b: T) -> T;
 
     /// Returns the value of the discriminant for the variant in 'v',
@@ -1354,6 +1396,7 @@ extern "rust-intrinsic" {
     pub fn nontemporal_store<T>(ptr: *mut T, val: T);
 
     /// See documentation of `<*const T>::offset_from` for details.
+    #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "0")]
     pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
 
     /// Internal hook used by Miri to implement unwinding.

src/libcore/lib.rs

@@ -127,6 +127,8 @@
 #![feature(maybe_uninit_slice)]
 #![feature(external_doc)]
 #![feature(associated_type_bounds)]
+#![feature(const_type_id)]
+#![feature(const_caller_location)]
 
 #[prelude_import]
 #[allow(unused)]

src/libcore/macros/mod.rs

@@ -5,6 +5,7 @@
     // the `caller_location` intrinsic, but once  `#[track_caller]` is implemented,
     // `panicking::{panic, panic_fmt}` can use that instead of a `Location` argument.
     core_intrinsics,
+    const_caller_location,
 )]
 #[stable(feature = "core", since = "1.6.0")]
 macro_rules! panic {

src/libcore/ops/drop.rs

@@ -99,9 +99,15 @@ pub trait Drop {
     /// Given that a [`panic!`] will call `drop` as it unwinds, any [`panic!`]
     /// in a `drop` implementation will likely abort.
     ///
+    /// Note that even if this panics, the value is considered to be dropped;
+    /// you must not cause `drop` to be called again. This is normally automatically
+    /// handled by the compiler, but when using unsafe code, can sometimes occur
+    /// unintentionally, particularly when using [`std::ptr::drop_in_place`].
+    ///
     /// [E0040]: ../../error-index.html#E0040
     /// [`panic!`]: ../macro.panic.html
     /// [`std::mem::drop`]: ../../std/mem/fn.drop.html
+    /// [`std::ptr::drop_in_place`]: ../../std/ptr/fn.drop_in_place.html
     #[stable(feature = "rust1", since = "1.0.0")]
     fn drop(&mut self);
 }

src/librustc/hir/intravisit.rs

@@ -1043,9 +1043,9 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
             walk_list!(visitor, visit_label, opt_label);
             visitor.visit_block(block);
         }
-        ExprKind::Assign(ref left_hand_expression, ref right_hand_expression) => {
-            visitor.visit_expr(right_hand_expression);
-            visitor.visit_expr(left_hand_expression)
+        ExprKind::Assign(ref lhs, ref rhs, _) => {
+            visitor.visit_expr(rhs);
+            visitor.visit_expr(lhs)
         }
         ExprKind::AssignOp(_, ref left_expression, ref right_expression) => {
             visitor.visit_expr(right_expression);

src/librustc/hir/lowering.rs

@@ -3437,65 +3437,3 @@ fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'hir>>) -> Vec<hir::BodyId>
     body_ids.sort_by_key(|b| bodies[b].value.span);
     body_ids
 }
-
-/// Checks if the specified expression is a built-in range literal.
-/// (See: `LoweringContext::lower_expr()`).
-pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
-    use hir::{Path, QPath, ExprKind, TyKind};
-
-    // Returns whether the given path represents a (desugared) range,
-    // either in std or core, i.e. has either a `::std::ops::Range` or
-    // `::core::ops::Range` prefix.
-    fn is_range_path(path: &Path) -> bool {
-        let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.to_string()).collect();
-        let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
-
-        // "{{root}}" is the equivalent of `::` prefix in `Path`.
-        if let ["{{root}}", std_core, "ops", range] = segs.as_slice() {
-            (*std_core == "std" || *std_core == "core") && range.starts_with("Range")
-        } else {
-            false
-        }
-    };
-
-    // Check whether a span corresponding to a range expression is a
-    // range literal, rather than an explicit struct or `new()` call.
-    fn is_lit(sess: &Session, span: &Span) -> bool {
-        let source_map = sess.source_map();
-        let end_point = source_map.end_point(*span);
-
-        if let Ok(end_string) = source_map.span_to_snippet(end_point) {
-            !(end_string.ends_with("}") || end_string.ends_with(")"))
-        } else {
-            false
-        }
-    };
-
-    match expr.kind {
-        // All built-in range literals but `..=` and `..` desugar to `Struct`s.
-        ExprKind::Struct(ref qpath, _, _) => {
-            if let QPath::Resolved(None, ref path) = **qpath {
-                return is_range_path(&path) && is_lit(sess, &expr.span);
-            }
-        }
-
-        // `..` desugars to its struct path.
-        ExprKind::Path(QPath::Resolved(None, ref path)) => {
-            return is_range_path(&path) && is_lit(sess, &expr.span);
-        }
-
-        // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
-        ExprKind::Call(ref func, _) => {
-            if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.kind {
-                if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.kind {
-                    let new_call = segment.ident.name == sym::new;
-                    return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;
-                }
-            }
-        }
-
-        _ => {}
-    }
-
-    false
-}

src/librustc/hir/lowering/expr.rs

@@ -122,8 +122,8 @@ impl LoweringContext<'_, '_> {
                 self.lower_block(blk, opt_label.is_some()),
                 self.lower_label(opt_label),
             ),
-            ExprKind::Assign(ref el, ref er) => {
-                hir::ExprKind::Assign(P(self.lower_expr(el)), P(self.lower_expr(er)))
+            ExprKind::Assign(ref el, ref er, span) => {
+                hir::ExprKind::Assign(P(self.lower_expr(el)), P(self.lower_expr(er)), span)
             }
             ExprKind::AssignOp(op, ref el, ref er) => hir::ExprKind::AssignOp(
                 self.lower_binop(op),
@@ -994,8 +994,11 @@ impl LoweringContext<'_, '_> {
             let (val_pat, val_pat_hid) = self.pat_ident(pat.span, val_ident);
             let val_expr = P(self.expr_ident(pat.span, val_ident, val_pat_hid));
             let next_expr = P(self.expr_ident(pat.span, next_ident, next_pat_hid));
-            let assign =
-                P(self.expr(pat.span, hir::ExprKind::Assign(next_expr, val_expr), ThinVec::new()));
+            let assign = P(self.expr(
+                pat.span,
+                hir::ExprKind::Assign(next_expr, val_expr, pat.span),
+                ThinVec::new(),
+            ));
             let some_pat = self.pat_some(pat.span, val_pat);
             self.arm(some_pat, assign)
         };