Auto merge of #76912 - RalfJung:rollup-q9ur56h, r=RalfJung

Rollup of 14 pull requests

Successful merges:

 - #73963 (deny(unsafe_op_in_unsafe_fn) in libstd/path.rs)
 - #75099 (lint/ty: move fns to avoid abstraction violation)
 - #75502 (Use implicit (not explicit) rules for promotability by default in `const fn`)
 - #75580 (Add test for checking duplicated branch or-patterns)
 - #76310 (Add `[T; N]: TryFrom<Vec<T>>` (insta-stable))
 - #76400 (Clean up vec benches bench_in_place style)
 - #76434 (do not inline black_box when building for Miri)
 - #76492 (Add associated constant `BITS` to all integer types)
 - #76525 (Add as_str() to string::Drain.)
 - #76636 (assert ScalarMaybeUninit size)
 - #76749 (give *even better* suggestion when matching a const range)
 - #76757 (don't convert types to the same type with try_into (clippy::useless_conversion))
 - #76796 (Give a better error message when x.py uses the wrong stage for CI)
 - #76798 (Build fixes for RISC-V 32-bit Linux support)

Failed merges:

r? `@ghost`

Author: bors

compiler/rustc_data_structures/src/lib.rs

@@ -14,6 +14,7 @@
 #![feature(generators)]
 #![feature(generator_trait)]
 #![feature(fn_traits)]
+#![feature(int_bits_const)]
 #![feature(min_specialization)]
 #![feature(optin_builtin_traits)]
 #![feature(nll)]

compiler/rustc_data_structures/src/tagged_ptr/copy.rs

@@ -48,7 +48,7 @@ where
     P: Pointer,
     T: Tag,
 {
-    const TAG_BIT_SHIFT: usize = (8 * std::mem::size_of::<usize>()) - T::BITS;
+    const TAG_BIT_SHIFT: usize = usize::BITS as usize - T::BITS;
     const ASSERTION: () = {
         assert!(T::BITS <= P::BITS);
         // Used for the transmute_copy's below

compiler/rustc_lint/src/builtin.rs

@@ -21,7 +21,8 @@
 //! `late_lint_methods!` invocation in `lib.rs`.
 
 use crate::{
-    types::CItemKind, EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
+    types::{transparent_newtype_field, CItemKind},
+    EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
 };
 use rustc_ast::attr::{self, HasAttrs};
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
@@ -2688,8 +2689,7 @@ impl ClashingExternDeclarations {
                         if is_transparent && !is_non_null {
                             debug_assert!(def.variants.len() == 1);
                             let v = &def.variants[VariantIdx::new(0)];
-                            ty = v
-                                .transparent_newtype_field(tcx)
+                            ty = transparent_newtype_field(tcx, v)
                                 .expect(
                                     "single-variant transparent structure with zero-sized field",
                                 )

compiler/rustc_lint/src/types.rs

@@ -639,6 +639,26 @@ crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtD
         .any(|a| tcx.sess.check_name(a, sym::rustc_nonnull_optimization_guaranteed))
 }
 
+/// `repr(transparent)` structs can have a single non-ZST field, this function returns that
+/// field.
+pub fn transparent_newtype_field<'a, 'tcx>(
+    tcx: TyCtxt<'tcx>,
+    variant: &'a ty::VariantDef,
+) -> Option<&'a ty::FieldDef> {
+    let param_env = tcx.param_env(variant.def_id);
+    for field in &variant.fields {
+        let field_ty = tcx.type_of(field.did);
+        let is_zst =
+            tcx.layout_of(param_env.and(field_ty)).map(|layout| layout.is_zst()).unwrap_or(false);
+
+        if !is_zst {
+            return Some(field);
+        }
+    }
+
+    None
+}
+
 /// Is type known to be non-null?
 crate fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
     let tcx = cx.tcx;
@@ -654,7 +674,7 @@ crate fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: C
             }
 
             for variant in &def.variants {
-                if let Some(field) = variant.transparent_newtype_field(tcx) {
+                if let Some(field) = transparent_newtype_field(cx.tcx, variant) {
                     if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) {
                         return true;
                     }
@@ -675,7 +695,7 @@ fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'t
         ty::Adt(field_def, field_substs) => {
             let inner_field_ty = {
                 let first_non_zst_ty =
-                    field_def.variants.iter().filter_map(|v| v.transparent_newtype_field(tcx));
+                    field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v));
                 debug_assert_eq!(
                     first_non_zst_ty.clone().count(),
                     1,
@@ -816,7 +836,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         if def.repr.transparent() {
             // Can assume that only one field is not a ZST, so only check
             // that field's type for FFI-safety.
-            if let Some(field) = variant.transparent_newtype_field(self.cx.tcx) {
+            if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
                 self.check_field_type_for_ffi(cache, field, substs)
             } else {
                 bug!("malformed transparent type");

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -578,6 +578,9 @@ pub enum ScalarMaybeUninit<Tag = ()> {
     Uninit,
 }
 
+#[cfg(target_arch = "x86_64")]
+static_assert_size!(ScalarMaybeUninit, 24);
+
 impl<Tag> From<Scalar<Tag>> for ScalarMaybeUninit<Tag> {
     #[inline(always)]
     fn from(s: Scalar<Tag>) -> Self {

compiler/rustc_middle/src/ty/mod.rs

@@ -1999,7 +1999,7 @@ pub struct VariantDef {
     flags: VariantFlags,
 }
 
-impl<'tcx> VariantDef {
+impl VariantDef {
     /// Creates a new `VariantDef`.
     ///
     /// `variant_did` is the `DefId` that identifies the enum variant (if this `VariantDef`
@@ -2065,19 +2065,6 @@ impl<'tcx> VariantDef {
     pub fn is_recovered(&self) -> bool {
         self.flags.intersects(VariantFlags::IS_RECOVERED)
     }
-
-    /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
-    /// field.
-    pub fn transparent_newtype_field(&self, tcx: TyCtxt<'tcx>) -> Option<&FieldDef> {
-        for field in &self.fields {
-            let field_ty = field.ty(tcx, InternalSubsts::identity_for_item(tcx, self.def_id));
-            if !field_ty.is_zst(tcx, self.def_id) {
-                return Some(field);
-            }
-        }
-
-        None
-    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]

compiler/rustc_middle/src/ty/sty.rs

@@ -2322,9 +2322,4 @@ impl<'tcx> TyS<'tcx> {
             }
         }
     }
-
-    /// Is this a zero-sized type?
-    pub fn is_zst(&'tcx self, tcx: TyCtxt<'tcx>, did: DefId) -> bool {
-        tcx.layout_of(tcx.param_env(did).and(self)).map(|layout| layout.is_zst()).unwrap_or(false)
-    }
 }

compiler/rustc_mir/src/dataflow/move_paths/builder.rs

@@ -4,7 +4,6 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
 use smallvec::{smallvec, SmallVec};
 
-use std::convert::TryInto;
 use std::mem;
 
 use super::abs_domain::Lift;
@@ -481,12 +480,7 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
             };
             let base_ty = base_place.ty(self.builder.body, self.builder.tcx).ty;
             let len: u64 = match base_ty.kind() {
-                ty::Array(_, size) => {
-                    let length = size.eval_usize(self.builder.tcx, self.builder.param_env);
-                    length
-                        .try_into()
-                        .expect("slice pattern of array with more than u32::MAX elements")
-                }
+                ty::Array(_, size) => size.eval_usize(self.builder.tcx, self.builder.param_env),
                 _ => bug!("from_end: false slice pattern of non-array type"),
             };
             for offset in from..to {

compiler/rustc_mir/src/interpret/place.rs

@@ -551,7 +551,7 @@ where
                 let n = base.len(self)?;
                 if n < min_length {
                     // This can only be reached in ConstProp and non-rustc-MIR.
-                    throw_ub!(BoundsCheckFailed { len: min_length.into(), index: n });
+                    throw_ub!(BoundsCheckFailed { len: min_length, index: n });
                 }
 
                 let index = if from_end {
@@ -565,9 +565,7 @@ where
                 self.mplace_index(base, index)?
             }
 
-            Subslice { from, to, from_end } => {
-                self.mplace_subslice(base, u64::from(from), u64::from(to), from_end)?
-            }
+            Subslice { from, to, from_end } => self.mplace_subslice(base, from, to, from_end)?,
         })
     }
 

compiler/rustc_mir/src/transform/promote_consts.rs

@@ -734,7 +734,14 @@ impl<'tcx> Validator<'_, 'tcx> {
     ) -> Result<(), Unpromotable> {
         let fn_ty = callee.ty(self.body, self.tcx);
 
-        if !self.explicit && self.const_kind.is_none() {
+        // `const` and `static` use the explicit rules for promotion regardless of the `Candidate`,
+        // meaning calls to `const fn` can be promoted.
+        let context_uses_explicit_promotion_rules = matches!(
+            self.const_kind,
+            Some(hir::ConstContext::Static(_) | hir::ConstContext::Const)
+        );
+
+        if !self.explicit && !context_uses_explicit_promotion_rules {
             if let ty::FnDef(def_id, _) = *fn_ty.kind() {
                 // Never promote runtime `const fn` calls of
                 // functions without `#[rustc_promotable]`.