rust: macros: convert concat_idents! to use syn

This eliminates the need for `expect_punct` helper.

Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260112170919.1888584-8-gary@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/macros/concat_idents.rs

@@ -1,23 +1,36 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro2::{token_stream, Ident, TokenStream, TokenTree};
+use proc_macro2::{
+    Ident,
+    TokenStream,
+    TokenTree, //
+};
+use syn::{
+    parse::{
+        Parse,
+        ParseStream, //
+    },
+    Result,
+    Token, //
+};
 
-use crate::helpers::expect_punct;
+pub(crate) struct Input {
+    a: Ident,
+    _comma: Token![,],
+    b: Ident,
+}
 
-fn expect_ident(it: &mut token_stream::IntoIter) -> Ident {
-    if let Some(TokenTree::Ident(ident)) = it.next() {
-        ident
-    } else {
-        panic!("Expected Ident")
+impl Parse for Input {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        Ok(Self {
+            a: input.parse()?,
+            _comma: input.parse()?,
+            b: input.parse()?,
+        })
     }
 }
 
-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");
+pub(crate) fn concat_idents(Input { a, b, .. }: Input) -> TokenStream {
     let res = Ident::new(&format!("{a}{b}"), b.span());
     TokenStream::from_iter([TokenTree::Ident(res)])
 }

rust/macros/helpers.rs

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro2::{
-    token_stream,
-    TokenStream,
-    TokenTree, //
-};
+use proc_macro2::TokenStream;
 use quote::ToTokens;
 use syn::{
     parse::{
@@ -16,14 +12,6 @@ use syn::{
     Result, //
 };
 
-pub(crate) fn expect_punct(it: &mut token_stream::IntoIter) -> char {
-    if let TokenTree::Punct(punct) = it.next().expect("Reached end of token stream for Punct") {
-        punct.as_char()
-    } else {
-        panic!("Expected Punct");
-    }
-}
-
 /// A string literal that is required to have ASCII value only.
 pub(crate) struct AsciiLitStr(LitStr);
 

rust/macros/lib.rs

@@ -311,8 +311,8 @@ pub fn fmt(input: TokenStream) -> TokenStream {
 /// assert_eq!(BR_OK, binder_driver_return_protocol_BR_OK);
 /// ```
 #[proc_macro]
-pub fn concat_idents(ts: TokenStream) -> TokenStream {
-    concat_idents::concat_idents(ts.into()).into()
+pub fn concat_idents(input: TokenStream) -> TokenStream {
+    concat_idents::concat_idents(parse_macro_input!(input)).into()
 }
 
 /// Paste identifiers together.