Auto merge of rust-lang#126297 - jhpratt:rollup-ntic8q6, r=jhpratt

Rollup of 6 pull requests

Successful merges:

 - rust-lang#123374 (DOC: Add FFI example for slice::from_raw_parts())
 - rust-lang#126127 (Spell out other trait diagnostic)
 - rust-lang#126228 (Provide correct parent for nested anon const)
 - rust-lang#126249 (Simplify `[T; N]::try_map` signature)
 - rust-lang#126256 (Add {{target}} substitution to compiletest)
 - rust-lang#126263 (Make issue-122805.rs big endian compatible)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -11,6 +11,7 @@ use rustc_session::lint;
 use rustc_span::symbol::{kw, Symbol};
 use rustc_span::Span;
 
+#[instrument(level = "debug", skip(tcx))]
 pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
     use rustc_hir::*;
 
@@ -66,7 +67,22 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         // FIXME(#43408) always enable this once `lazy_normalization` is
         // stable enough and does not need a feature gate anymore.
         Node::AnonConst(_) => {
-            let parent_def_id = tcx.hir().get_parent_item(hir_id);
+            let parent_did = tcx.parent(def_id.to_def_id());
+
+            // We don't do this unconditionally because the `DefId` parent of an anon const
+            // might be an implicitly created closure during `async fn` desugaring. This would
+            // have the wrong generics.
+            //
+            // i.e. `async fn foo<'a>() { let a = [(); { 1 + 2 }]; bar().await() }`
+            // would implicitly have a closure in its body that would be the parent of
+            // the `{ 1 + 2 }` anon const. This closure's generics is simply a witness
+            // instead of `['a]`.
+            let parent_did = if let DefKind::AnonConst = tcx.def_kind(parent_did) {
+                parent_did
+            } else {
+                tcx.hir().get_parent_item(hir_id).to_def_id()
+            };
+            debug!(?parent_did);
 
             let mut in_param_ty = false;
             for (_parent, node) in tcx.hir().parent_iter(hir_id) {
@@ -121,7 +137,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                     //
                     // This has some implications for how we get the predicates available to the anon const
                     // see `explicit_predicates_of` for more information on this
-                    let generics = tcx.generics_of(parent_def_id.to_def_id());
+                    let generics = tcx.generics_of(parent_did);
                     let param_def_idx = generics.param_def_id_to_index[&param_id.to_def_id()];
                     // In the above example this would be .params[..N#0]
                     let own_params = generics.params_to(param_def_idx as usize, tcx).to_owned();
@@ -147,7 +163,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                     //
                     // Note that we do not supply the parent generics when using
                     // `min_const_generics`.
-                    Some(parent_def_id.to_def_id())
+                    Some(parent_did)
                 }
             } else {
                 let parent_node = tcx.parent_hir_node(hir_id);
@@ -159,7 +175,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                     Node::Expr(Expr { kind: ExprKind::Repeat(_, constant), .. })
                         if constant.hir_id() == hir_id =>
                     {
-                        Some(parent_def_id.to_def_id())
+                        Some(parent_did)
                     }
                     // Exclude `GlobalAsm` here which cannot have generics.
                     Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
@@ -171,7 +187,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                             _ => false,
                         }) =>
                     {
-                        Some(parent_def_id.to_def_id())
+                        Some(parent_did)
                     }
                     _ => None,
                 }

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -2064,7 +2064,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     if all_traits_equal {
                         format!("\n  {}", c.self_ty())
                     } else {
-                        format!("\n  {c}")
+                        format!("\n  `{}` implements `{}`", c.self_ty(), c.print_only_trait_path())
                     }
                 })
                 .collect();

library/core/src/array/mod.rs

@@ -533,11 +533,9 @@ impl<T, const N: usize> [T; N] {
     /// assert_eq!(c, Some(a));
     /// ```
     #[unstable(feature = "array_try_map", issue = "79711")]
-    pub fn try_map<F, R>(self, f: F) -> ChangeOutputType<R, [R::Output; N]>
+    pub fn try_map<R>(self, f: impl FnMut(T) -> R) -> ChangeOutputType<R, [R::Output; N]>
     where
-        F: FnMut(T) -> R,
-        R: Try,
-        R::Residual: Residual<[R::Output; N]>,
+        R: Try<Residual: Residual<[R::Output; N]>>,
     {
         drain_array_with(self, |iter| try_from_trusted_iterator(iter.map(f)))
     }

library/core/src/ops/try_trait.rs

@@ -363,7 +363,9 @@ pub trait Residual<O> {
 }
 
 #[unstable(feature = "pub_crate_should_not_need_unstable_attr", issue = "none")]
-pub(crate) type ChangeOutputType<T, V> = <<T as Try>::Residual as Residual<V>>::TryType;
+#[allow(type_alias_bounds)]
+pub(crate) type ChangeOutputType<T: Try<Residual: Residual<V>>, V> =
+    <T::Residual as Residual<V>>::TryType;
 
 /// An adapter for implementing non-try methods via the `Try` implementation.
 ///

library/core/src/slice/raw.rs

@@ -82,6 +82,39 @@ use crate::ub_checks;
 /// }
 /// ```
 ///
+/// ### FFI: Handling null pointers
+///
+/// In languages such as C++, pointers to empty collections are not guaranteed to be non-null.
+/// When accepting such pointers, they have to be checked for null-ness to avoid undefined
+/// behavior.
+///
+/// ```
+/// use std::slice;
+///
+/// /// Sum the elements of an FFI slice.
+/// ///
+/// /// # Safety
+/// ///
+/// /// If ptr is not NULL, it must be correctly aligned and
+/// /// point to `len` initialized items of type `f32`.
+/// unsafe extern "C" fn sum_slice(ptr: *const f32, len: usize) -> f32 {
+///     let data = if ptr.is_null() {
+///         // `len` is assumed to be 0.
+///         &[]
+///     } else {
+///         // SAFETY: see function docstring.
+///         unsafe { slice::from_raw_parts(ptr, len) }
+///     };
+///     data.into_iter().sum()
+/// }
+///
+/// // This could be the result of C++'s std::vector::data():
+/// let ptr = std::ptr::null();
+/// // And this could be std::vector::size():
+/// let len = 0;
+/// assert_eq!(unsafe { sum_slice(ptr, len) }, 0.0);
+/// ```
+///
 /// [valid]: ptr#safety
 /// [`NonNull::dangling()`]: ptr::NonNull::dangling
 #[inline]

src/tools/compiletest/src/header.rs

@@ -1281,6 +1281,7 @@ fn expand_variables(mut value: String, config: &Config) -> String {
     const BUILD_BASE: &str = "{{build-base}}";
     const SYSROOT_BASE: &str = "{{sysroot-base}}";
     const TARGET_LINKER: &str = "{{target-linker}}";
+    const TARGET: &str = "{{target}}";
 
     if value.contains(CWD) {
         let cwd = env::current_dir().unwrap();
@@ -1303,6 +1304,10 @@ fn expand_variables(mut value: String, config: &Config) -> String {
         value = value.replace(TARGET_LINKER, config.target_linker.as_deref().unwrap_or(""));
     }
 
+    if value.contains(TARGET) {
+        value = value.replace(TARGET, &config.target);
+    }
+
     value
 }
 

src/tools/tidy/src/target_specific_tests.rs

@@ -53,9 +53,9 @@ pub fn check(path: &Path, bad: &mut bool) {
             } else if directive.starts_with(COMPILE_FLAGS_HEADER) {
                 let compile_flags = &directive[COMPILE_FLAGS_HEADER.len()..];
                 if let Some((_, v)) = compile_flags.split_once("--target") {
-                    if let Some((arch, _)) =
-                        v.trim_start_matches(|c| c == ' ' || c == '=').split_once("-")
-                    {
+                    let v = v.trim_start_matches(|c| c == ' ' || c == '=');
+                    let v = if v == "{{target}}" { Some((v, v)) } else { v.split_once("-") };
+                    if let Some((arch, _)) = v {
                         let info = header_map.entry(revision).or_insert(RevisionInfo::default());
                         info.target_arch.replace(arch);
                     } else {

tests/codegen/issues/issue-122805.rs

@@ -39,17 +39,20 @@
 // OPT3WINX64-NEXT: store <8 x i16>
 // CHECK-NEXT: ret void
 #[no_mangle]
-#[cfg(target_endian = "little")]
 pub fn convert(value: [u16; 8]) -> [u8; 16] {
+    #[cfg(target_endian = "little")]
+    let bswap = u16::to_be;
+    #[cfg(target_endian = "big")]
+    let bswap = u16::to_le;
     let addr16 = [
-        value[0].to_be(),
-        value[1].to_be(),
-        value[2].to_be(),
-        value[3].to_be(),
-        value[4].to_be(),
-        value[5].to_be(),
-        value[6].to_be(),
-        value[7].to_be(),
+        bswap(value[0]),
+        bswap(value[1]),
+        bswap(value[2]),
+        bswap(value[3]),
+        bswap(value[4]),
+        bswap(value[5]),
+        bswap(value[6]),
+        bswap(value[7]),
     ];
     unsafe { core::mem::transmute::<_, [u8; 16]>(addr16) }
 }

tests/ui/binop/binary-op-suggest-deref.stderr

@@ -303,10 +303,10 @@ LL |     let _ = FOO & (*"Sized".to_string().into_boxed_str());
    |
    = help: the trait `BitAnd<str>` is not implemented for `i32`
    = help: the following other types implement trait `BitAnd<Rhs>`:
-             <&'a i32 as BitAnd<i32>>
-             <&i32 as BitAnd<&i32>>
-             <i32 as BitAnd<&i32>>
-             <i32 as BitAnd>
+             `&'a i32` implements `BitAnd<i32>`
+             `&i32` implements `BitAnd<&i32>`
+             `i32` implements `BitAnd<&i32>`
+             `i32` implements `BitAnd`
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/binary-op-suggest-deref.rs:78:17

tests/ui/binop/binop-mul-i32-f32.stderr

@@ -6,10 +6,10 @@ LL |     x * y
    |
    = help: the trait `Mul<f32>` is not implemented for `i32`
    = help: the following other types implement trait `Mul<Rhs>`:
-             <&'a i32 as Mul<i32>>
-             <&i32 as Mul<&i32>>
-             <i32 as Mul<&i32>>
-             <i32 as Mul>
+             `&'a i32` implements `Mul<i32>`
+             `&i32` implements `Mul<&i32>`
+             `i32` implements `Mul<&i32>`
+             `i32` implements `Mul`
 
 error: aborting due to 1 previous error
 

tests/ui/binop/shift-various-bad-types.stderr

@@ -6,14 +6,14 @@ LL |     22 >> p.char;
    |
    = help: the trait `Shr<char>` is not implemented for `{integer}`
    = help: the following other types implement trait `Shr<Rhs>`:
-             <&'a i128 as Shr<i128>>
-             <&'a i128 as Shr<i16>>
-             <&'a i128 as Shr<i32>>
-             <&'a i128 as Shr<i64>>
-             <&'a i128 as Shr<i8>>
-             <&'a i128 as Shr<isize>>
-             <&'a i128 as Shr<u128>>
-             <&'a i128 as Shr<u16>>
+             `&'a i128` implements `Shr<i128>`
+             `&'a i128` implements `Shr<i16>`
+             `&'a i128` implements `Shr<i32>`
+             `&'a i128` implements `Shr<i64>`
+             `&'a i128` implements `Shr<i8>`
+             `&'a i128` implements `Shr<isize>`
+             `&'a i128` implements `Shr<u128>`
+             `&'a i128` implements `Shr<u16>`
            and 568 others
 
 error[E0277]: no implementation for `{integer} >> &str`
@@ -24,14 +24,14 @@ LL |     22 >> p.str;
    |
    = help: the trait `Shr<&str>` is not implemented for `{integer}`
    = help: the following other types implement trait `Shr<Rhs>`:
-             <&'a i128 as Shr<i128>>
-             <&'a i128 as Shr<i16>>
-             <&'a i128 as Shr<i32>>
-             <&'a i128 as Shr<i64>>
-             <&'a i128 as Shr<i8>>
-             <&'a i128 as Shr<isize>>
-             <&'a i128 as Shr<u128>>
-             <&'a i128 as Shr<u16>>
+             `&'a i128` implements `Shr<i128>`
+             `&'a i128` implements `Shr<i16>`
+             `&'a i128` implements `Shr<i32>`
+             `&'a i128` implements `Shr<i64>`
+             `&'a i128` implements `Shr<i8>`
+             `&'a i128` implements `Shr<isize>`
+             `&'a i128` implements `Shr<u128>`
+             `&'a i128` implements `Shr<u16>`
            and 568 others
 
 error[E0277]: no implementation for `{integer} >> &Panolpy`
@@ -42,14 +42,14 @@ LL |     22 >> p;
    |
    = help: the trait `Shr<&Panolpy>` is not implemented for `{integer}`
    = help: the following other types implement trait `Shr<Rhs>`:
-             <&'a i128 as Shr<i128>>
-             <&'a i128 as Shr<i16>>
-             <&'a i128 as Shr<i32>>
-             <&'a i128 as Shr<i64>>
-             <&'a i128 as Shr<i8>>
-             <&'a i128 as Shr<isize>>
-             <&'a i128 as Shr<u128>>
-             <&'a i128 as Shr<u16>>
+             `&'a i128` implements `Shr<i128>`
+             `&'a i128` implements `Shr<i16>`
+             `&'a i128` implements `Shr<i32>`
+             `&'a i128` implements `Shr<i64>`
+             `&'a i128` implements `Shr<i8>`
+             `&'a i128` implements `Shr<isize>`
+             `&'a i128` implements `Shr<u128>`
+             `&'a i128` implements `Shr<u16>`
            and 568 others
 
 error[E0308]: mismatched types

tests/ui/const-generics/exhaustive-value.stderr

@@ -5,14 +5,14 @@ LL |     <() as Foo<N>>::test()
    |      ^^ the trait `Foo<N>` is not implemented for `()`
    |
    = help: the following other types implement trait `Foo<N>`:
-             <() as Foo<0>>
-             <() as Foo<100>>
-             <() as Foo<101>>
-             <() as Foo<102>>
-             <() as Foo<103>>
-             <() as Foo<104>>
-             <() as Foo<105>>
-             <() as Foo<106>>
+             `()` implements `Foo<0>`
+             `()` implements `Foo<100>`
+             `()` implements `Foo<101>`
+             `()` implements `Foo<102>`
+             `()` implements `Foo<103>`
+             `()` implements `Foo<104>`
+             `()` implements `Foo<105>`
+             `()` implements `Foo<106>`
            and 248 others
 
 error: aborting due to 1 previous error

tests/ui/const-generics/repeat_expr_hack_gives_right_generics.rs

@@ -0,0 +1,20 @@
+// Given an anon const `a`: `{ N }` and some anon const `b` which references the
+// first anon const: `{ [1; a] }`. `b` should not have any generics as it is not
+// a simple `N` argument nor is it a repeat expr count.
+//
+// On the other hand `b` *is* a repeat expr count and so it should inherit its
+// parents generics as part of the `const_evaluatable_unchecked` fcw (#76200).
+//
+// In this specific case however `b`'s parent should be `a` and so it should wind
+// up not having any generics after all. If `a` were to inherit its generics from
+// the enclosing item then the reference to `a` from `b` would contain generic
+// parameters not usable by `b` which would cause us to ICE.
+
+fn bar<const N: usize>() {}
+
+fn foo<const N: usize>() {
+    bar::<{ [1; N] }>();
+    //~^ ERROR: generic parameters may not be used in const operations
+}
+
+fn main() {}

tests/ui/const-generics/repeat_expr_hack_gives_right_generics.stderr

@@ -0,0 +1,11 @@
+error: generic parameters may not be used in const operations
+  --> $DIR/repeat_expr_hack_gives_right_generics.rs:16:17
+   |
+LL |     bar::<{ [1; N] }>();
+   |                 ^ cannot perform const operation using `N`
+   |
+   = help: const parameters may only be used as standalone arguments, i.e. `N`
+   = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
+
+error: aborting due to 1 previous error
+

tests/ui/consts/const-eval/const-eval-overflow-3b.stderr

@@ -12,10 +12,10 @@ LL |     = [0; (i8::MAX + 1u8) as usize];
    |
    = help: the trait `Add<u8>` is not implemented for `i8`
    = help: the following other types implement trait `Add<Rhs>`:
-             <&'a i8 as Add<i8>>
-             <&i8 as Add<&i8>>
-             <i8 as Add<&i8>>
-             <i8 as Add>
+             `&'a i8` implements `Add<i8>`
+             `&i8` implements `Add<&i8>`
+             `i8` implements `Add<&i8>`
+             `i8` implements `Add`
 
 error: aborting due to 2 previous errors
 

tests/ui/consts/const-eval/const-eval-overflow-4b.stderr

@@ -12,10 +12,10 @@ LL |     : [u32; (i8::MAX as i8 + 1u8) as usize]
    |
    = help: the trait `Add<u8>` is not implemented for `i8`
    = help: the following other types implement trait `Add<Rhs>`:
-             <&'a i8 as Add<i8>>
-             <&i8 as Add<&i8>>
-             <i8 as Add<&i8>>
-             <i8 as Add>
+             `&'a i8` implements `Add<i8>`
+             `&i8` implements `Add<&i8>`
+             `i8` implements `Add<&i8>`
+             `i8` implements `Add`
 
 error[E0604]: only `u8` can be cast as `char`, not `i8`
   --> $DIR/const-eval-overflow-4b.rs:22:13