rust: upgrade to Rust 1.66.0

Upgrade the Rust version from 1.62.0 to 1.66.0.

The overwhelming majority of the commit is about upgrading our `alloc`
fork to the new version from upstream [1]. License has not changed [2][3]
(there were changes in the `COPYRIGHT` file, but unrelated to `alloc`).

As in the previous version upgrades (done out of tree so far), upgrading
`alloc` requires checking that our small additions (`try_*`) still match
their original (non`-try_*`) versions.

With this version upgrade, the following unstable Rust features were
stabilized: `bench_black_box` (1.66.0), `const_ptr_offset_from` (1.65.0),
`core_ffi_c` (1.64.0) and `generic_associated_types` (1.65.0). Thus
remove them.

This also implies that only two unstable features remain allowed for
non-`rust/` code: `allocator_api` and `const_refs_to_cell`.

There are some new Clippy warnings that we are triggering (i.e.
introduced since 1.62.0), as well as a few others that were not
triggered before, thus allow them in this commit and clean up or
remove them as needed later on:

  - `borrow_deref_ref` (new in 1.63.0).
  - `explicit_auto_deref` (new in 1.64.0).
  - `bool_to_int_with_if` (new in 1.65.0).
  - `needless_borrow`.
  - `type_complexity`.
  - `unnecessary_cast` (allowed only on `CONFIG_ARM`).

Furthermore, `rustdoc` lint `broken_intra_doc_links` is triggering on
links pointing to `macro_export` `macro_rules` defined in the same
module (i.e. appearing in the crate root).

However, even if the warning appears, the link still gets generated
like in previous versions, thus it is a bit confusing. An issue has
been opened upstream [4], and it appears that the link still being
generated was a compatibility measure, thus we will need to adapt
to the new behavior (done in the next patch).

In addition, there is an added `#[const_trait]` attribute in
`RawDeviceId`, due to 1.66.0's PR "Require `#[const_trait]` on `Trait`
for `impl const Trait`") [5].

Finally, the `-Aunused-imports` was added for compiling `core`. This was
fixed upstream for 1.67.0 in PR "Fix warning when libcore is compiled
with no_fp_fmt_parse" [6], and prevented for the future for that `cfg`
in PR "core: ensure `no_fp_fmt_parse builds` are warning-free" [7].

Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Tested-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Reviewed-by: Alice Ferrazzi <alice.ferrazzi@miraclelinux.com>
Tested-by: Alice Ferrazzi <alice.ferrazzi@miraclelinux.com>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Tested-by: Neal Gompa <neal@gompa.dev>
Link: Rust-for-Linux#947
Link: https://github.com/rust-lang/rust/tree/1.66.0/library/alloc/src [1]
Link: https://github.com/rust-lang/rust/blob/1.66.0/library/alloc/Cargo.toml#L4 [2]
Link: https://github.com/rust-lang/rust/blob/1.66.0/COPYRIGHT [3]
Link: rust-lang/rust#106142 [4]
Link: rust-lang/rust#100982 [5]
Link: rust-lang/rust#105434 [6]
Link: rust-lang/rust#105811 [7]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Documentation/process/changes.rst

@@ -31,7 +31,7 @@ you probably needn't concern yourself with pcmciautils.
 ====================== ===============  ========================================
 GNU C                  5.1              gcc --version
 Clang/LLVM (optional)  11.0.0           clang --version
-Rust (optional)        1.62.0           rustc --version
+Rust (optional)        1.66.0           rustc --version
 bindgen (optional)     0.56.0           bindgen --version
 GNU make               3.82             make --version
 bash                   4.2              bash --version

rust/Makefile

@@ -376,7 +376,7 @@ endif
 $(obj)/core.o: private skip_clippy = 1
 $(obj)/core.o: private skip_flags = -Dunreachable_pub
 $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
-$(obj)/core.o: private rustc_target_flags = $(core-cfgs)
+$(obj)/core.o: private rustc_target_flags = $(core-cfgs) -Aunused-imports
 $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs $(obj)/target.json FORCE
 	$(call if_changed_dep,rustc_library)
 

rust/alloc/alloc.rs

@@ -27,16 +27,23 @@ extern "Rust" {
     // (the code expanding that attribute macro generates those functions), or to call
     // the default implementations in libstd (`__rdl_alloc` etc. in `library/std/src/alloc.rs`)
     // otherwise.
-    // The rustc fork of LLVM also special-cases these function names to be able to optimize them
+    // The rustc fork of LLVM 14 and earlier also special-cases these function names to be able to optimize them
     // like `malloc`, `realloc`, and `free`, respectively.
     #[rustc_allocator]
-    #[rustc_allocator_nounwind]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_alloc(size: usize, align: usize) -> *mut u8;
-    #[rustc_allocator_nounwind]
+    #[rustc_deallocator]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
-    #[rustc_allocator_nounwind]
+    #[rustc_reallocator]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
-    #[rustc_allocator_nounwind]
+    #[rustc_allocator_zeroed]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
 }
 
@@ -72,11 +79,14 @@ pub use std::alloc::Global;
 /// # Examples
 ///
 /// ```
-/// use std::alloc::{alloc, dealloc, Layout};
+/// use std::alloc::{alloc, dealloc, handle_alloc_error, Layout};
 ///
 /// unsafe {
 ///     let layout = Layout::new::<u16>();
 ///     let ptr = alloc(layout);
+///     if ptr.is_null() {
+///         handle_alloc_error(layout);
+///     }
 ///
 ///     *(ptr as *mut u16) = 42;
 ///     assert_eq!(*(ptr as *mut u16), 42);
@@ -400,13 +410,13 @@ pub mod __alloc_error_handler {
 
     // if there is no `#[alloc_error_handler]`
     #[rustc_std_internal_symbol]
-    pub unsafe extern "C-unwind" fn __rdl_oom(size: usize, _align: usize) -> ! {
+    pub unsafe fn __rdl_oom(size: usize, _align: usize) -> ! {
         panic!("memory allocation of {size} bytes failed")
     }
 
     // if there is an `#[alloc_error_handler]`
     #[rustc_std_internal_symbol]
-    pub unsafe extern "C-unwind" fn __rg_oom(size: usize, align: usize) -> ! {
+    pub unsafe fn __rg_oom(size: usize, align: usize) -> ! {
         let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
         extern "Rust" {
             #[lang = "oom"]