rust: proc-macro2: import crate

This is a subset of the Rust `proc-macro2` crate, version 1.0.101
(released 2025-08-16), licensed under "Apache-2.0 OR MIT", from:

    https://github.com/dtolnay/proc-macro2/raw/1.0.101/src

The files are copied as-is, with no modifications whatsoever (not even
adding the SPDX identifiers).

For copyright details, please see:

    https://github.com/dtolnay/proc-macro2/blob/1.0.101/README.md#license
    https://github.com/dtolnay/proc-macro2/blob/1.0.101/LICENSE-APACHE
    https://github.com/dtolnay/proc-macro2/blob/1.0.101/LICENSE-MIT

The next two patches modify these files as needed for use within the
kernel. This patch split allows reviewers to double-check the import
and to clearly see the differences introduced.

The following script may be used to verify the contents:

    for path in $(cd rust/proc-macro2/ && find . -type f -name '*.rs'); do
        curl --silent --show-error --location \
            https://github.com/dtolnay/proc-macro2/raw/1.0.101/src/$path \
            | diff --unified rust/proc-macro2/$path - && echo $path: OK
    done

Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20251124151837.2184382-7-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/rust/proc-macro2/marker.rs b/rust/proc-macro2/marker.rs
new file mode 100644
index 000000000000..23b94ce6fa85
--- /dev/null
+++ b/rust/proc-macro2/marker.rs
@@ -0,0 +1,17 @@
+use alloc::rc::Rc;
+use core::marker::PhantomData;
+use core::panic::{RefUnwindSafe, UnwindSafe};
+
+// Zero sized marker with the correct set of autotrait impls we want all proc
+// macro types to have.
+#[derive(Copy, Clone)]
+#[cfg_attr(
+    all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)),
+    derive(PartialEq, Eq)
+)]
+pub(crate) struct ProcMacroAutoTraits(PhantomData<Rc<()>>);
+
+pub(crate) const MARKER: ProcMacroAutoTraits = ProcMacroAutoTraits(PhantomData);
+
+impl UnwindSafe for ProcMacroAutoTraits {}
+impl RefUnwindSafe for ProcMacroAutoTraits {}