Re: [PATCH v3 06/15] rust: pin-init: rewrite the `#[pinned_drop]` attribute macro using `syn`

[Gary Guo]

On Wed Jan 14, 2026 at 6:18 PM GMT, Benno Lossin wrote:
> 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!() }`
> 
> Tested-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> Signed-off-by: Benno Lossin <lossin@xxxxxxxxxx>

Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>

> ---
> Changes in v3:
> * use DiagCtxt error handling
> Changes in v2:
> * improved error handling
> * improved error span
> ---
>  rust/pin-init/internal/src/lib.rs         |  4 +-
>  rust/pin-init/internal/src/pinned_drop.rs | 86 +++++++++++++----------
>  rust/pin-init/src/macros.rs               | 28 --------
>  3 files changed, 52 insertions(+), 66 deletions(-)