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, 29 insertions, 0 deletions

diff --git a/rust/proc-macro2/location.rs b/rust/proc-macro2/location.rs
new file mode 100644
index 000000000000..7190e2d05255
--- /dev/null
+++ b/rust/proc-macro2/location.rs
@@ -0,0 +1,29 @@
+use core::cmp::Ordering;
+
+/// A line-column pair representing the start or end of a `Span`.
+///
+/// This type is semver exempt and not exposed by default.
+#[cfg_attr(docsrs, doc(cfg(feature = "span-locations")))]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct LineColumn {
+    /// The 1-indexed line in the source file on which the span starts or ends
+    /// (inclusive).
+    pub line: usize,
+    /// The 0-indexed column (in UTF-8 characters) in the source file on which
+    /// the span starts or ends (inclusive).
+    pub column: usize,
+}
+
+impl Ord for LineColumn {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.line
+            .cmp(&other.line)
+            .then(self.column.cmp(&other.column))
+    }
+}
+
+impl PartialOrd for LineColumn {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}