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

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

[Ethan Plant]

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.

Suggested-by: Benno Lossin <lossin@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1172
Signed-off-by: Ethan Plant <plant.ethan@gmail.com>
---
 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@gmail.com>

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@kernel.org>
> Link: https://github.com/Rust-for-Linux/linux/issues/1172
> Signed-off-by: Ethan Plant <plant.ethan@gmail.com>
> ---
>  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@gmail.com>

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

[Miguel Ojeda]

On Thu, Aug 6, 2026 at 1:54 PM Gary Guo <gary@garyguo.net> wrote:
>
> 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.

Yeah, it also means inconsistency can be introduced for little gain.

Cheers,
Miguel