Merge tag 'rust-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull Rust updates from Miguel Ojeda:
 "Toolchain and infrastructure:

   - Add support for 'syn'.

     Syn is a parsing library for parsing a stream of Rust tokens into a
     syntax tree of Rust source code.

     Currently this library is geared toward use in Rust procedural
     macros, but contains some APIs that may be useful more generally.

     'syn' allows us to greatly simplify writing complex macros such as
     'pin-init' (Benno has already prepared the 'syn'-based version). We
     will use it in the 'macros' crate too.

     'syn' is the most downloaded Rust crate (according to crates.io),
     and it is also used by the Rust compiler itself. While the amount
     of code is substantial, there should not be many updates needed for
     these crates, and even if there are, they should not be too big,
     e.g. +7k -3k lines across the 3 crates in the last year.

     'syn' requires two smaller dependencies: 'quote' and 'proc-macro2'.
     I only modified their code to remove a third dependency
     ('unicode-ident') and to add the SPDX identifiers. The code can be
     easily verified to exactly match upstream with the provided
     scripts.

     They are all licensed under "Apache-2.0 OR MIT", like the other
     vendored 'alloc' crate we had for a while.

     Please see the merge commit with the cover letter for more context.

   - Allow 'unreachable_pub' and 'clippy::disallowed_names' for
     doctests.

     Examples (i.e. doctests) may want to do things like show public
     items and use names such as 'foo'.

     Nevertheless, we still try to keep examples as close to real code
     as possible (this is part of why running Clippy on doctests is
     important for us, e.g. for safety comments, which userspace Rust
     does not support yet but we are stricter).

  'kernel' crate:

   - Replace our custom 'CStr' type with 'core::ffi::CStr'.

     Using the standard library type reduces our custom code footprint,
     and we retain needed custom functionality through an extension
     trait and a new 'fmt!' macro which replaces the previous 'core'
     import.

     This started in 6.17 and continued in 6.18, and we finally land the
     replacement now. This required quite some stamina from Tamir, who
     split the changes in steps to prepare for the flag day change here.

   - Replace 'kernel::c_str!' with C string literals.

     C string literals were added in Rust 1.77, which produce '&CStr's
     (the 'core' one), so now we can write:

         c"hi"

     instead of:

         c_str!("hi")

   - Add 'num' module for numerical features.

     It includes the 'Integer' trait, implemented for all primitive
     integer types.

     It also includes the 'Bounded' integer wrapping type: an integer
     value that requires only the 'N' least significant bits of the
     wrapped type to be encoded:

         // An unsigned 8-bit integer, of which only the 4 LSBs are used.
         let v = Bounded::<u8, 4>::new::<15>();
         assert_eq!(v.get(), 15);

     'Bounded' is useful to e.g. enforce guarantees when working with
     bitfields that have an arbitrary number of bits.

     Values can also be constructed from simple non-constant expressions
     or, for more complex ones, validated at runtime.

     'Bounded' also comes with comparison and arithmetic operations
     (with both their backing type and other 'Bounded's with a
     compatible backing type), casts to change the backing type,
     extending/shrinking and infallible/fallible conversions from/to
     primitives as applicable.

   - 'rbtree' module: add immutable cursor ('Cursor').

     It enables to use just an immutable tree reference where
     appropriate. The existing fully-featured mutable cursor is renamed
     to 'CursorMut'.

  kallsyms:

   - Fix wrong "big" kernel symbol type read from procfs.

  'pin-init' crate:

   - A couple minor fixes (Benno asked me to pick these patches up for
     him this cycle).

  Documentation:

   - Quick Start guide: add Debian 13 (Trixie).

     Debian Stable is now able to build Linux, since Debian 13 (released
     2025-08-09) packages Rust 1.85.0, which is recent enough.

     We are planning to propose that the minimum supported Rust version
     in Linux follows Debian Stable releases, with Debian 13 being the
     first one we upgrade to, i.e. Rust 1.85.

  MAINTAINERS:

   - Add entry for the new 'num' module.

   - Remove Alex as Rust maintainer: he hasn't had the time to
     contribute for a few years now, so it is a no-op change in
     practice.

  And a few other cleanups and improvements"

* tag 'rust-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux: (53 commits)
  rust: macros: support `proc-macro2`, `quote` and `syn`
  rust: syn: enable support in kbuild
  rust: syn: add `README.md`
  rust: syn: remove `unicode-ident` dependency
  rust: syn: add SPDX License Identifiers
  rust: syn: import crate
  rust: quote: enable support in kbuild
  rust: quote: add `README.md`
  rust: quote: add SPDX License Identifiers
  rust: quote: import crate
  rust: proc-macro2: enable support in kbuild
  rust: proc-macro2: add `README.md`
  rust: proc-macro2: remove `unicode_ident` dependency
  rust: proc-macro2: add SPDX License Identifiers
  rust: proc-macro2: import crate
  rust: kbuild: support using libraries in `rustc_procmacro`
  rust: kbuild: support skipping flags in `rustc_test_library`
  rust: kbuild: add proc macro library support
  rust: kbuild: simplify `--cfg` handling
  rust: kbuild: introduce `core-flags` and `core-skip_flags`
  ...

1 files changed, 153 insertions, 0 deletions

diff --git a/rust/proc-macro2/extra.rs b/rust/proc-macro2/extra.rs
new file mode 100644
index 000000000000..55feb5ec7526
--- /dev/null
+++ b/rust/proc-macro2/extra.rs
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! Items which do not have a correspondence to any API in the proc_macro crate,
+//! but are necessary to include in proc-macro2.
+
+use crate::fallback;
+use crate::imp;
+use crate::marker::{ProcMacroAutoTraits, MARKER};
+use crate::Span;
+use core::fmt::{self, Debug};
+
+/// Invalidate any `proc_macro2::Span` that exist on the current thread.
+///
+/// The implementation of `Span` uses thread-local data structures and this
+/// function clears them. Calling any method on a `Span` on the current thread
+/// created prior to the invalidation will return incorrect values or crash.
+///
+/// This function is useful for programs that process more than 2<sup>32</sup>
+/// bytes of Rust source code on the same thread. Just like rustc, proc-macro2
+/// uses 32-bit source locations, and these wrap around when the total source
+/// code processed by the same thread exceeds 2<sup>32</sup> bytes (4
+/// gigabytes). After a wraparound, `Span` methods such as `source_text()` can
+/// return wrong data.
+///
+/// # Example
+///
+/// As of late 2023, there is 200 GB of Rust code published on crates.io.
+/// Looking at just the newest version of every crate, it is 16 GB of code. So a
+/// workload that involves parsing it all would overflow a 32-bit source
+/// location unless spans are being invalidated.
+///
+/// ```
+/// use flate2::read::GzDecoder;
+/// use std::ffi::OsStr;
+/// use std::io::{BufReader, Read};
+/// use std::str::FromStr;
+/// use tar::Archive;
+///
+/// rayon::scope(|s| {
+///     for krate in every_version_of_every_crate() {
+///         s.spawn(move |_| {
+///             proc_macro2::extra::invalidate_current_thread_spans();
+///
+///             let reader = BufReader::new(krate);
+///             let tar = GzDecoder::new(reader);
+///             let mut archive = Archive::new(tar);
+///             for entry in archive.entries().unwrap() {
+///                 let mut entry = entry.unwrap();
+///                 let path = entry.path().unwrap();
+///                 if path.extension() != Some(OsStr::new("rs")) {
+///                     continue;
+///                 }
+///                 let mut content = String::new();
+///                 entry.read_to_string(&mut content).unwrap();
+///                 match proc_macro2::TokenStream::from_str(&content) {
+///                     Ok(tokens) => {/* ... */},
+///                     Err(_) => continue,
+///                 }
+///             }
+///         });
+///     }
+/// });
+/// #
+/// # fn every_version_of_every_crate() -> Vec<std::fs::File> {
+/// #     Vec::new()
+/// # }
+/// ```
+///
+/// # Panics
+///
+/// This function is not applicable to and will panic if called from a
+/// procedural macro.
+#[cfg(span_locations)]
+#[cfg_attr(docsrs, doc(cfg(feature = "span-locations")))]
+pub fn invalidate_current_thread_spans() {
+    crate::imp::invalidate_current_thread_spans();
+}
+
+/// An object that holds a [`Group`]'s `span_open()` and `span_close()` together
+/// in a more compact representation than holding those 2 spans individually.
+///
+/// [`Group`]: crate::Group
+#[derive(Copy, Clone)]
+pub struct DelimSpan {
+    inner: DelimSpanEnum,
+    _marker: ProcMacroAutoTraits,
+}
+
+#[derive(Copy, Clone)]
+enum DelimSpanEnum {
+    #[cfg(wrap_proc_macro)]
+    Compiler {
+        join: proc_macro::Span,
+        open: proc_macro::Span,
+        close: proc_macro::Span,
+    },
+    Fallback(fallback::Span),
+}
+
+impl DelimSpan {
+    pub(crate) fn new(group: &imp::Group) -> Self {
+        #[cfg(wrap_proc_macro)]
+        let inner = match group {
+            imp::Group::Compiler(group) => DelimSpanEnum::Compiler {
+                join: group.span(),
+                open: group.span_open(),
+                close: group.span_close(),
+            },
+            imp::Group::Fallback(group) => DelimSpanEnum::Fallback(group.span()),
+        };
+
+        #[cfg(not(wrap_proc_macro))]
+        let inner = DelimSpanEnum::Fallback(group.span());
+
+        DelimSpan {
+            inner,
+            _marker: MARKER,
+        }
+    }
+
+    /// Returns a span covering the entire delimited group.
+    pub fn join(&self) -> Span {
+        match &self.inner {
+            #[cfg(wrap_proc_macro)]
+            DelimSpanEnum::Compiler { join, .. } => Span::_new(imp::Span::Compiler(*join)),
+            DelimSpanEnum::Fallback(span) => Span::_new_fallback(*span),
+        }
+    }
+
+    /// Returns a span for the opening punctuation of the group only.
+    pub fn open(&self) -> Span {
+        match &self.inner {
+            #[cfg(wrap_proc_macro)]
+            DelimSpanEnum::Compiler { open, .. } => Span::_new(imp::Span::Compiler(*open)),
+            DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.first_byte()),
+        }
+    }
+
+    /// Returns a span for the closing punctuation of the group only.
+    pub fn close(&self) -> Span {
+        match &self.inner {
+            #[cfg(wrap_proc_macro)]
+            DelimSpanEnum::Compiler { close, .. } => Span::_new(imp::Span::Compiler(*close)),
+            DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.last_byte()),
+        }
+    }
+}
+
+impl Debug for DelimSpan {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Debug::fmt(&self.join(), f)
+    }
+}