Merge patch series "refactor Rust proc macros with syn"

Gary writes:

  "This series converts Rust proc macros that we have to use `syn`,
   and replace the custom `quote!` macro that we have with the vendored
   `quote!` macro. The `pin-init` macros are not converted yet; Benno
   has a work in progress in converting them. They're however converted
   to use `quote` and `proc-macro2` crate so our custom `quote!` macro
   can be removed.

   Overall this improves the robustness of the macros as we have precise
   parsing of the AST rather than relying on heuristics to extract needed
   information from there. This is also a quality-of-life improvement
   to those using language servers (e.g. Rust analyzer) as the span
   information of the proc macros are now preserved which allows the
   "jump-to-definition" feature to work, even when used on completely
   custom macros such as `module!`.

   Miguel gave a very good explanation on why `syn` is a good idea in the
   patch series that introduced it [1], which I shall not repeat here."

The `pin-init` rewrite was merged just before this one.

Link: https://lore.kernel.org/rust-for-linux/20251124151837.2184382-1-ojeda@kernel.org/ [1]
Link: https://patch.msgid.link/20260112170919.1888584-1-gary@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/kernel/kunit.rs

@@ -189,9 +189,6 @@ pub fn is_test_result_ok(t: impl TestResult) -> bool {
 }
 
 /// Represents an individual test case.
-///
-/// The [`kunit_unsafe_test_suite!`] macro expects a `NULL`-terminated list of valid test cases.
-/// Use [`kunit_case_null`] to generate such a delimiter.
 #[doc(hidden)]
 pub const fn kunit_case(
     name: &'static kernel::str::CStr,
@@ -212,27 +209,6 @@ pub const fn kunit_case(
     }
 }
 
-/// Represents the `NULL` test case delimiter.
-///
-/// The [`kunit_unsafe_test_suite!`] macro expects a `NULL`-terminated list of test cases. This
-/// function returns such a delimiter.
-#[doc(hidden)]
-pub const fn kunit_case_null() -> kernel::bindings::kunit_case {
-    kernel::bindings::kunit_case {
-        run_case: None,
-        name: core::ptr::null_mut(),
-        generate_params: None,
-        attr: kernel::bindings::kunit_attributes {
-            speed: kernel::bindings::kunit_speed_KUNIT_SPEED_NORMAL,
-        },
-        status: kernel::bindings::kunit_status_KUNIT_SUCCESS,
-        module_name: core::ptr::null_mut(),
-        log: core::ptr::null_mut(),
-        param_init: None,
-        param_exit: None,
-    }
-}
-
 /// Registers a KUnit test suite.
 ///
 /// # Safety
@@ -251,7 +227,7 @@ pub const fn kunit_case_null() -> kernel::bindings::kunit_case {
 ///
 /// static mut KUNIT_TEST_CASES: [kernel::bindings::kunit_case; 2] = [
 ///     kernel::kunit::kunit_case(c"name", test_fn),
-///     kernel::kunit::kunit_case_null(),
+///     pin_init::zeroed(),
 /// ];
 /// kernel::kunit_unsafe_test_suite!(suite_name, KUNIT_TEST_CASES);
 /// ```

rust/macros/concat_idents.rs

@@ -1,23 +1,36 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro::{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/export.rs

@@ -1,29 +1,25 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use crate::helpers::function_name;
-use proc_macro::TokenStream;
+use proc_macro2::TokenStream;
+use quote::quote;
 
 /// 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
             } else {
                 #name
             };
         };
-    );
 
-    let no_mangle = quote!(#[no_mangle]);
-
-    TokenStream::from_iter([signature_check, no_mangle, ts])
+        #[no_mangle]
+        #f
+    }
 }

rust/macros/fmt.rs

@@ -1,8 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro::{Ident, TokenStream, TokenTree};
 use std::collections::BTreeSet;
 
+use proc_macro2::{Ident, TokenStream, TokenTree};
+use quote::quote_spanned;
+
 /// Please see [`crate::fmt`] for documentation.
 pub(crate) fn fmt(input: TokenStream) -> TokenStream {
     let mut input = input.into_iter();

rust/macros/helpers.rs

@@ -1,101 +1,41 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro::{token_stream, Group, Ident, TokenStream, TokenTree};
-
-pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
-    if let Some(TokenTree::Ident(ident)) = it.next() {
-        Some(ident.to_string())
-    } else {
-        None
-    }
-}
-
-pub(crate) fn try_sign(it: &mut token_stream::IntoIter) -> Option<char> {
-    let peek = it.clone().next();
-    match peek {
-        Some(TokenTree::Punct(punct)) if punct.as_char() == '-' => {
-            let _ = it.next();
-            Some(punct.as_char())
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::{
+    parse::{
+        Parse,
+        ParseStream, //
+    },
+    Attribute,
+    Error,
+    LitStr,
+    Result, //
+};
+
+/// A string literal that is required to have ASCII value only.
+pub(crate) struct AsciiLitStr(LitStr);
+
+impl Parse for AsciiLitStr {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let s: LitStr = input.parse()?;
+        if !s.value().is_ascii() {
+            return Err(Error::new_spanned(s, "expected ASCII-only string literal"));
         }
-        _ => None,
-    }
-}
-
-pub(crate) fn try_literal(it: &mut token_stream::IntoIter) -> Option<String> {
-    if let Some(TokenTree::Literal(literal)) = it.next() {
-        Some(literal.to_string())
-    } else {
-        None
+        Ok(Self(s))
     }
 }
 
-pub(crate) fn try_string(it: &mut token_stream::IntoIter) -> Option<String> {
-    try_literal(it).and_then(|string| {
-        if string.starts_with('\"') && string.ends_with('\"') {
-            let content = &string[1..string.len() - 1];
-            if content.contains('\\') {
-                panic!("Escape sequences in string literals not yet handled");
-            }
-            Some(content.to_string())
-        } else if string.starts_with("r\"") {
-            panic!("Raw string literals are not yet handled");
-        } else {
-            None
-        }
-    })
-}
-
-pub(crate) fn expect_ident(it: &mut token_stream::IntoIter) -> String {
-    try_ident(it).expect("Expected Ident")
-}
-
-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");
+impl ToTokens for AsciiLitStr {
+    fn to_tokens(&self, ts: &mut TokenStream) {
+        self.0.to_tokens(ts);
     }
 }
 
-pub(crate) fn expect_string(it: &mut token_stream::IntoIter) -> String {
-    try_string(it).expect("Expected string")
-}
-
-pub(crate) fn expect_string_ascii(it: &mut token_stream::IntoIter) -> String {
-    let string = try_string(it).expect("Expected string");
-    assert!(string.is_ascii(), "Expected ASCII string");
-    string
-}
-
-pub(crate) fn expect_group(it: &mut token_stream::IntoIter) -> Group {
-    if let TokenTree::Group(group) = it.next().expect("Reached end of token stream for Group") {
-        group
-    } else {
-        panic!("Expected Group");
-    }
-}
-
-pub(crate) fn expect_end(it: &mut token_stream::IntoIter) {
-    if it.next().is_some() {
-        panic!("Expected end");
-    }
-}
-
-/// 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.to_string() == "fn" => {
-                if let Some(TokenTree::Ident(i)) = input.next() {
-                    return Some(i);
-                }
-                return None;
-            }
-            _ => continue,
-        }
+impl AsciiLitStr {
+    pub(crate) fn value(&self) -> String {
+        self.0.value()
     }
-    None
 }
 
 pub(crate) fn file() -> String {
@@ -115,16 +55,7 @@ pub(crate) fn file() -> String {
     }
 }
 
-/// Parse a token stream of the form `expected_name: "value",` and return the
-/// string in the position of "value".
-///
-/// # Panics
-///
-/// - On parse error.
-pub(crate) fn expect_string_field(it: &mut token_stream::IntoIter, expected_name: &str) -> String {
-    assert_eq!(expect_ident(it), expected_name);
-    assert_eq!(expect_punct(it), ':');
-    let string = expect_string(it);
-    assert_eq!(expect_punct(it), ',');
-    string
+/// Obtain all `#[cfg]` attributes.
+pub(crate) fn gather_cfg_attrs(attr: &[Attribute]) -> impl Iterator<Item = &Attribute> + '_ {
+    attr.iter().filter(|a| a.path().is_ident("cfg"))
 }