rust: add trace crate

The trace crate is a minimal container for dependencies of tracepoints
(so that they do not have to be imported in all the crates that use
tracepoints); it also contains a macro called "include_trace!" that is
able to find the right include file from the trace/ directory.

[Write commit message, add #[allow()]. - Paolo]

Signed-off-by: Tanish Desai <tanishdesai37@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20250929154938.594389-10-pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

rust/trace/src/lib.rs

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! This crate provides macros that aid in using QEMU's tracepoint
+//! functionality.
+
+#[macro_export]
+/// Define the trace-points from the named directory (which should have slashes
+/// replaced by underscore characters) as functions in a module called `trace`.
+///
+/// ```ignore
+/// ::trace::include_trace!("hw_char");
+/// // ...
+/// trace::trace_pl011_read_fifo_rx_full();
+/// ```
+macro_rules! include_trace {
+    ($name:literal) => {
+        #[allow(
+            clippy::ptr_as_ptr,
+            clippy::cast_lossless,
+            clippy::used_underscore_binding
+        )]
+        mod trace {
+            #[cfg(not(MESON))]
+            include!(concat!(
+                env!("MESON_BUILD_ROOT"),
+                "/trace/trace-",
+                $name,
+                ".rs"
+            ));
+
+            #[cfg(MESON)]
+            include!(concat!("@MESON_BUILD_ROOT@/trace/trace-", $name, ".rs"));
+        }
+    };
+}