Re: [PATCH] rust: macros: Allow omitting trailing commas in module!

[Gary Guo]

On Thu Aug 6, 2026 at 11:14 AM BST, Ethan Plant wrote:
> The module! macro currently requires a trailing comma after the final
> argument, despite using syntax modeled on Rust struct initializers,
> where trailing commas are optional.
>
> Allow parsing to finish after the final field when the input stream is
> empty. If more input remains, continue requiring a comma, so missing
> separators between fields are still rejected.
>
> Document that the final trailing comma is optional and update an existing
> module! doctest to exercise the syntax without one.

Hmm, I am not sure if we really want this.

`module!` invocation usually spans multiple lines so the formatting rules would
always prefer adding trailing comma for this case.

Allowing omitting sounds like encouraging bad practice.

Best,
Gary

>
> Suggested-by: Benno Lossin <lossin@xxxxxxxxxx>
> Link: https://github.com/Rust-for-Linux/linux/issues/1172
> Signed-off-by: Ethan Plant <plant.ethan@xxxxxxxxx>
> ---
>  rust/macros/lib.rs    | 4 +++-
>  rust/macros/module.rs | 7 ++++++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
> index 4a48fabbc2682..f6474b194687f 100644
> --- a/rust/macros/lib.rs
> +++ b/rust/macros/lib.rs
> @@ -61,6 +61,8 @@
>  ///
>  /// [`Module`]: ../kernel/trait.Module.html
>  ///
> +/// The trailing comma after the final field is optional.
> +///
>  /// # Examples
>  ///
>  /// ```ignore
> @@ -112,7 +114,7 @@
>  ///     authors: ["Rust for Linux Contributors"],
>  ///     description: "My device driver requires firmware",
>  ///     license: "GPL",
> -///     firmware: ["my_device_firmware1.bin", "my_device_firmware2.bin"],
> +///     firmware: ["my_device_firmware1.bin", "my_device_firmware2.bin"]
>  /// }
>  ///
>  /// struct MyDeviceDriverModule;
> diff --git a/rust/macros/module.rs b/rust/macros/module.rs
> index 06c18e2075083..57ee79b49a7ec 100644
> --- a/rust/macros/module.rs
> +++ b/rust/macros/module.rs
> @@ -261,8 +261,13 @@ macro_rules! parse_ordered_fields {
>                  }
>              }
>  
> -            $input.parse::<Token![,]>()?;
>              seen_keys.push(key);
> +
> +            if $input.is_empty() {
> +                break;
> +            }
> +
> +            $input.parse::<Token![,]>()?;
>          }
>  
>          for key in REQUIRED_KEYS {
>
> ---
> base-commit: dc01dfb37b34beeefcfe1c3055364d41a4070c7e
> change-id: 20260806-module-optional-trailing-comma-44a336ddf649
>
> Best regards,
> --  
> Ethan Plant <plant.ethan@xxxxxxxxx>