[PATCH v1 05/28] rust: macros: add `concat_idents!` proc macro

Miguel Ojeda
2022-11-10T16:42:48Z

From: Björn Roy Baron <bjorn3_gh@protonmail.com>

This macro provides similar functionality to the unstable feature
`concat_idents` without having to rely on it.

For instance:

let x_1 = 42;
let x_2 = concat_idents!(x, _1);
assert!(x_1 == x_2);

It has different behavior with respect to macro hygiene. Unlike
the unstable `concat_idents!` macro, it allows, for example,
referring to local variables by taking the span of the second
macro as span for the output identifier.

Signed-off-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
rust/macros/concat_idents.rs | 23 +++++++++++++++++++
rust/macros/lib.rs | 44 ++++++++++++++++++++++++++++++++++++
2 files changed, 67 insertions(+)
create mode 100644 rust/macros/concat_idents.rs

diff --git a/rust/macros/concat_idents.rs b/rust/macros/concat_idents.rs
new file mode 100644
index 000000000000..3b5a9dd70e8a
--- /dev/null
+++ b/rust/macros/concat_idents.rs
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro::{token_stream, Ident, TokenStream, TokenTree};
+
+use crate::helpers::expect_punct;
+
+fn expect_ident(it: &mut token_stream::IntoIter) -> Ident {
+ if let Some(TokenTree::Ident(ident)) = it.next() {
+ ident
+ } else {
+ panic!("Expected Ident")
+ }
+}
+
+pub(crate) fn concat_idents(ts: TokenStream) -> TokenStream {
+ let mut it = ts.into_iter();
+ let a = expect_ident(&mut it);
+ assert_eq!(expect_punct(&mut it), ',');
+ let b = expect_ident(&mut it);
+ assert!(it.next().is_none(), "only two idents can be concatenated");
+ let res = Ident::new(&(a.to_string() + &b.to_string()), b.span());
+ TokenStream::from_iter([TokenTree::Ident(res)])
+}
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index 91764bfb1f89..15555e7ff487 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -2,6 +2,7 @@

//! Crate for all kernel procedural macros.

+mod concat_idents;
mod helpers;
mod module;

@@ -70,3 +71,46 @@ use proc_macro::TokenStream;
pub fn module(ts: TokenStream) -> TokenStream {
module::module(ts)
}
+
+/// Concatenate two identifiers.
+///
+/// This is useful in macros that need to declare or reference items with names
+/// starting with a fixed prefix and ending in a user specified name. The resulting
+/// identifier has the span of the second argument.
+///
+/// # Examples
+///
+/// ```ignore
+/// use kernel::macro::concat_idents;
+///
+/// macro_rules! pub_no_prefix {
+/// ($prefix:ident, $($newname:ident),+) => {
+/// $(pub(crate) const $newname: u32 = kernel::macros::concat_idents!($prefix, $newname);)+
+/// };
+/// }
+///
+/// pub_no_prefix!(
+/// binder_driver_return_protocol_,
+/// BR_OK,
+/// BR_ERROR,
+/// BR_TRANSACTION,
+/// BR_REPLY,
+/// BR_DEAD_REPLY,
+/// BR_TRANSACTION_COMPLETE,
+/// BR_INCREFS,
+/// BR_ACQUIRE,
+/// BR_RELEASE,
+/// BR_DECREFS,
+/// BR_NOOP,
+/// BR_SPAWN_LOOPER,
+/// BR_DEAD_BINDER,
+/// BR_CLEAR_DEATH_NOTIFICATION_DONE,
+/// BR_FAILED_REPLY
+/// );
+///
+/// assert_eq!(BR_OK, binder_driver_return_protocol_BR_OK);
+/// ```
+#[proc_macro]
+pub fn concat_idents(ts: TokenStream) -> TokenStream {
+ concat_idents::concat_idents(ts)
+}
--
2.38.1