rust: macros: convert `#[export]` to use `syn`

This eliminates the custom `function_name` 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/20260112170919.1888584-7-gary@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

3 files changed, 12 insertions, 35 deletions

diff --git a/rust/macros/export.rs b/rust/macros/export.rs
index 92d9b3097192..6d53521f62fc 100644
--- a/rust/macros/export.rs
+++ b/rust/macros/export.rs
@@ -3,19 +3,14 @@
 use proc_macro2::TokenStream;
 use quote::quote;
 
-use crate::helpers::function_name;
-
 /// Please see [`crate::export`] for documentation.
-pub(crate) fn export(_attr: TokenStream, ts: TokenStream) -> TokenStream {
-    let Some(name) = function_name(ts.clone()) else {
-        return "::core::compile_error!(\"The #[export] attribute must be used on a function.\");"
-            .parse::<TokenStream>()
-            .unwrap();
-    };
+pub(crate) fn export(f: syn::ItemFn) -> TokenStream {
+    let name = &f.sig.ident;
 
-    // This verifies that the function has the same signature as the declaration generated by
-    // bindgen. It makes use of the fact that all branches of an if/else must have the same type.
-    let signature_check = quote!(
+    quote! {
+        // This verifies that the function has the same signature as the declaration generated by
+        // bindgen. It makes use of the fact that all branches of an if/else must have the same
+        // type.
         const _: () = {
             if true {
                 ::kernel::bindings::#name
@@ -23,9 +18,8 @@ pub(crate) fn export(_attr: TokenStream, ts: TokenStream) -> TokenStream {
                 #name
             };
         };
-    );
-
-    let no_mangle = quote!(#[no_mangle]);
 
-    TokenStream::from_iter([signature_check, no_mangle, ts])
+        #[no_mangle]
+        #f
+    }
 }
diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
index fa66ef6eb0f3..754c827cc21e 100644
--- a/rust/macros/helpers.rs
+++ b/rust/macros/helpers.rs
@@ -2,7 +2,6 @@
 
 use proc_macro2::{
     token_stream,
-    Ident,
     TokenStream,
     TokenTree, //
 };
@@ -50,23 +49,6 @@ impl AsciiLitStr {
     }
 }
 
-/// Given a function declaration, finds the name of the function.
-pub(crate) fn function_name(input: TokenStream) -> Option<Ident> {
-    let mut input = input.into_iter();
-    while let Some(token) = input.next() {
-        match token {
-            TokenTree::Ident(i) if i == "fn" => {
-                if let Some(TokenTree::Ident(i)) = input.next() {
-                    return Some(i);
-                }
-                return None;
-            }
-            _ => continue,
-        }
-    }
-    None
-}
-
 pub(crate) fn file() -> String {
     #[cfg(not(CONFIG_RUSTC_HAS_SPAN_FILE))]
     {
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index 9ce250cbf7ea..027ddaa2d710 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -234,8 +234,9 @@ pub fn vtable(attr: TokenStream, input: TokenStream) -> TokenStream {
 /// This macro is *not* the same as the C macros `EXPORT_SYMBOL_*`. All Rust symbols are currently
 /// automatically exported with `EXPORT_SYMBOL_GPL`.
 #[proc_macro_attribute]
-pub fn export(attr: TokenStream, ts: TokenStream) -> TokenStream {
-    export::export(attr.into(), ts.into()).into()
+pub fn export(attr: TokenStream, input: TokenStream) -> TokenStream {
+    parse_macro_input!(attr as syn::parse::Nothing);
+    export::export(parse_macro_input!(input)).into()
 }
 
 /// Like [`core::format_args!`], but automatically wraps arguments in [`kernel::fmt::Adapter`].