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Message-ID: <20260108135127.3153925-6-lossin@kernel.org>
Date: Thu, 8 Jan 2026 14:50:43 +0100
From: Benno Lossin <lossin@...nel.org>
To: Benno Lossin <lossin@...nel.org>,
Gary Guo <gary@...yguo.net>,
Miguel Ojeda <ojeda@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Andreas Hindborg <a.hindborg@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>,
Fiona Behrens <me@...enk.dev>,
Tamir Duberstein <tamird@...il.com>,
Alban Kurti <kurti@...icto.ai>
Cc: rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 05/12] rust: pin-init: rewrite the `#[pinned_drop]` attribute macro using `syn`
Rewrite the attribute macro for implementing `PinnedDrop` using `syn`.
Otherwise no functional changes intended aside from improved error
messages on syntactic and semantical errors. For example:
When missing the `drop` function in the implementation, the old error
was:
error: no rules expected `)`
--> tests/ui/compile-fail/pinned_drop/no_fn.rs:6:1
|
6 | #[pinned_drop]
| ^^^^^^^^^^^^^^ no rules expected this token in macro call
|
note: while trying to match keyword `fn`
--> src/macros.rs
|
| fn drop($($sig:tt)*) {
| ^^
= note: this error originates in the attribute macro `pinned_drop` (in Nightly builds, run with -Z macro-backtrace for more info)
And the new one is:
error[E0046]: not all trait items implemented, missing: `drop`
--> tests/ui/compile-fail/pinned_drop/no_fn.rs:7:1
|
7 | impl PinnedDrop for Foo {}
| ^^^^^^^^^^^^^^^^^^^^^^^ missing `drop` in implementation
|
= help: implement the missing item: `fn drop(self: Pin<&mut Self>, _: OnlyCallFromDrop) { todo!() }`
Signed-off-by: Benno Lossin <lossin@...nel.org>
---
rust/pin-init/internal/src/lib.rs | 6 +-
rust/pin-init/internal/src/pinned_drop.rs | 87 ++++++++++++-----------
rust/pin-init/src/macros.rs | 28 --------
3 files changed, 52 insertions(+), 69 deletions(-)
diff --git a/rust/pin-init/internal/src/lib.rs b/rust/pin-init/internal/src/lib.rs
index ec593362c5ac..d0156b82b5d3 100644
--- a/rust/pin-init/internal/src/lib.rs
+++ b/rust/pin-init/internal/src/lib.rs
@@ -25,7 +25,11 @@ pub fn pin_data(inner: TokenStream, item: TokenStream) -> TokenStream {
#[proc_macro_attribute]
pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
- pinned_drop::pinned_drop(args.into(), input.into()).into()
+ pinned_drop::pinned_drop(
+ parse_macro_input!(args as _),
+ parse_macro_input!(input as _),
+ )
+ .into()
}
#[proc_macro_derive(Zeroable)]
diff --git a/rust/pin-init/internal/src/pinned_drop.rs b/rust/pin-init/internal/src/pinned_drop.rs
index cf8cd1c42984..4df2cb9959fb 100644
--- a/rust/pin-init/internal/src/pinned_drop.rs
+++ b/rust/pin-init/internal/src/pinned_drop.rs
@@ -1,49 +1,56 @@
// SPDX-License-Identifier: Apache-2.0 OR MIT
-use proc_macro2::{TokenStream, TokenTree};
-use quote::quote;
+use proc_macro2::TokenStream;
+use quote::{quote, quote_spanned};
+use syn::{parse::Nothing, parse_quote, spanned::Spanned, ImplItem, ItemImpl, Token};
-pub(crate) fn pinned_drop(_args: TokenStream, input: TokenStream) -> TokenStream {
- let mut toks = input.into_iter().collect::<Vec<_>>();
- assert!(!toks.is_empty());
- // Ensure that we have an `impl` item.
- assert!(matches!(&toks[0], TokenTree::Ident(i) if i == "impl"));
- // Ensure that we are implementing `PinnedDrop`.
- let mut nesting: usize = 0;
- let mut pinned_drop_idx = None;
- for (i, tt) in toks.iter().enumerate() {
- match tt {
- TokenTree::Punct(p) if p.as_char() == '<' => {
- nesting += 1;
+pub(crate) fn pinned_drop(_args: Nothing, mut input: ItemImpl) -> TokenStream {
+ let mut errors = vec![];
+ if let Some(unsafety) = input.unsafety {
+ errors.push(quote_spanned! {unsafety.span=>
+ ::core::compile_error!("implementing `PinnedDrop` is safe");
+ });
+ }
+ input.unsafety = Some(Token);
+ match &mut input.trait_ {
+ Some((not, path, _for)) => {
+ if let Some(not) = not {
+ errors.push(quote_spanned! {not.span=>
+ ::core::compile_error!("cannot implement `!PinnedDrop`");
+ });
}
- TokenTree::Punct(p) if p.as_char() == '>' => {
- nesting = nesting.checked_sub(1).unwrap();
- continue;
+ for (seg, expected) in path
+ .segments
+ .iter()
+ .rev()
+ .zip(["PinnedDrop", "pin_init", ""])
+ {
+ if expected.is_empty() || seg.ident != expected {
+ errors.push(quote_spanned! {seg.span()=>
+ ::core::compile_error!("bad import path for `PinnedDrop`");
+ });
+ }
+ if !seg.arguments.is_none() {
+ errors.push(quote_spanned! {seg.arguments.span()=>
+ ::core::compile_error!("unexpected arguments for `PinnedDrop` path");
+ });
+ }
}
- _ => {}
- }
- if i >= 1 && nesting == 0 {
- // Found the end of the generics, this should be `PinnedDrop`.
- assert!(
- matches!(tt, TokenTree::Ident(i) if i == "PinnedDrop"),
- "expected 'PinnedDrop', found: '{tt:?}'"
- );
- pinned_drop_idx = Some(i);
- break;
+ *path = parse_quote!(::pin_init::PinnedDrop);
}
+ None => errors.push(quote_spanned! {input.impl_token.span=>
+ ::core::compile_error!("expected `impl ... PinnedDrop for ...`, got inherent impl");
+ }),
}
- let idx = pinned_drop_idx
- .unwrap_or_else(|| panic!("Expected an `impl` block implementing `PinnedDrop`."));
- // Fully qualify the `PinnedDrop`, as to avoid any tampering.
- toks.splice(idx..idx, quote!(::pin_init::));
- // Take the `{}` body and call the declarative macro.
- if let Some(TokenTree::Group(last)) = toks.pop() {
- let last = last.stream();
- quote!(::pin_init::__pinned_drop! {
- @impl_sig(#(#toks)*),
- @impl_body(#last),
- })
- } else {
- TokenStream::from_iter(toks)
+ for item in &mut input.items {
+ if let ImplItem::Fn(fn_item) = item {
+ if fn_item.sig.ident == "drop" {
+ fn_item
+ .sig
+ .inputs
+ .push(parse_quote!(_: ::pin_init::__internal::OnlyCallFromDrop));
+ }
+ }
}
+ quote!(#(#errors)* #input)
}
diff --git a/rust/pin-init/src/macros.rs b/rust/pin-init/src/macros.rs
index 53ed5ce860fc..b80c95612fd6 100644
--- a/rust/pin-init/src/macros.rs
+++ b/rust/pin-init/src/macros.rs
@@ -503,34 +503,6 @@
#[cfg(not(kernel))]
pub use ::paste::paste;
-/// Creates a `unsafe impl<...> PinnedDrop for $type` block.
-///
-/// See [`PinnedDrop`] for more information.
-///
-/// [`PinnedDrop`]: crate::PinnedDrop
-#[doc(hidden)]
-#[macro_export]
-macro_rules! __pinned_drop {
- (
- @impl_sig($($impl_sig:tt)*),
- @impl_body(
- $(#[$($attr:tt)*])*
- fn drop($($sig:tt)*) {
- $($inner:tt)*
- }
- ),
- ) => {
- // SAFETY: TODO.
- unsafe $($impl_sig)* {
- // Inherit all attributes and the type/ident tokens for the signature.
- $(#[$($attr)*])*
- fn drop($($sig)*, _: $crate::__internal::OnlyCallFromDrop) {
- $($inner)*
- }
- }
- }
-}
-
/// This macro first parses the struct definition such that it separates pinned and not pinned
/// fields. Afterwards it declares the struct and implement the `PinData` trait safely.
#[doc(hidden)]
--
2.51.2
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