[PATCH v2 2/7] rust: macros: auto-insert ThisModule in #[vtable]

[Alvin Sun]

Auto-add `type ThisModule: ::kernel::ModuleMetadata;` as a required
associated type on the trait side if not already defined, and
auto-insert `type ThisModule = crate::LocalModule;` on the impl side
if not explicitly provided, eliminating the need to manually declare
and implement `ThisModule` in every vtable trait and impl.

Signed-off-by: Alvin Sun <alvi...@linux.dev>
---
rust/macros/lib.rs | 6 ++++++
rust/macros/vtable.rs | 38 +++++++++++++++++++++++++++++++++++++-
2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index 2cfd59e0f9e7c..d35e45ea745c0 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -176,6 +176,12 @@ pub fn module(input: TokenStream) -> TokenStream {
///
/// This macro should not be used when all functions are required.
///
+/// Additionally, this macro automatically handles the `ThisModule`
+/// associated type: on the trait side, `type ThisModule: ModuleMetadata;`
+/// is added as a required associated type if not already defined; on the
+/// impl side, `type ThisModule = LocalModule;` is automatically inserted
+/// if not explicitly defined.
+///
/// # Examples
///
/// ```
diff --git a/rust/macros/vtable.rs b/rust/macros/vtable.rs
index c6510b0c4ea1d..d3d0e9cbd7172 100644
--- a/rust/macros/vtable.rs
+++ b/rust/macros/vtable.rs
@@ -23,6 +23,7 @@

fn handle_trait(mut item: ItemTrait) -> Result<ItemTrait> {
let mut gen_items = Vec::new();
+ let mut has_this_module = false;

gen_items.push(parse_quote! {
/// A marker to prevent implementors from forgetting to use [`#[vtable]`](vtable)
@@ -30,6 +31,28 @@ fn handle_trait(mut item: ItemTrait) -> Result<ItemTrait> {
const USE_VTABLE_ATTR: ();
});

+ // Detect existing type ThisModule so we don't add a duplicate.
+ for i in &item.items {
+ if let TraitItem::Type(type_item) = i {
+ if type_item.ident == "ThisModule" {
+ has_this_module = true;
+ }
+ }
+ }
+
+ // Add `type ThisModule: ModuleMetadata` as a required associated type if
+ // the trait does not already define it. No default is used because
+ // `associated_type_defaults` is unstable (issue #29661).
+ if !has_this_module {
+ gen_items.push(parse_quote! {
+ /// The module implementing this vtable trait.
+ ///
+ /// Automatically set to `crate::LocalModule` by the `#[vtable]`
+ /// impl macro.
+ type ThisModule: ::kernel::ModuleMetadata;
+ });
+ }
+
for item in &item.items {
if let TraitItem::Fn(fn_item) = item {
let name = &fn_item.sig.ident;
@@ -58,18 +81,31 @@ fn handle_trait(mut item: ItemTrait) -> Result<ItemTrait> {
fn handle_impl(mut item: ItemImpl) -> Result<ItemImpl> {
let mut gen_items = Vec::new();
let mut defined_consts = HashSet::new();
+ let mut defined_types = HashSet::new();

- // Iterate over all user-defined constants to gather any possible explicit overrides.
+ // Iterate over all user-defined constants and types to gather any possible explicit overrides.
for item in &item.items {
if let ImplItem::Const(const_item) = item {
defined_consts.insert(const_item.ident.clone());
}
+ if let ImplItem::Type(type_item) = item {
+ defined_types.insert(type_item.ident.clone());
+ }
}

gen_items.push(parse_quote! {
const USE_VTABLE_ATTR: () = ();
});

+ // Auto-insert `type ThisModule = crate::LocalModule` if not explicitly defined.
+ // `crate::LocalModule` resolves to the real module type (via `module!`) or a
+ // dummy fallback in non-module contexts (e.g., doctests).
+ if !defined_types.contains(&parse_quote!(ThisModule)) {
+ gen_items.push(parse_quote! {
+ type ThisModule = crate::LocalModule;
+ });
+ }
+
for item in &item.items {
if let ImplItem::Fn(fn_item) = item {
let name = &fn_item.sig.ident;

--
2.43.0

[Andreas Hindborg]

Alvin Sun <alvi...@linux.dev> writes:

> Auto-add `type ThisModule: ::kernel::ModuleMetadata;` as a required
> associated type on the trait side if not already defined, and
> auto-insert `type ThisModule = crate::LocalModule;` on the impl side
> if not explicitly provided, eliminating the need to manually declare
> and implement `ThisModule` in every vtable trait and impl.
>
> Signed-off-by: Alvin Sun <alvi...@linux.dev>

Reviewed-by: Andreas Hindborg <a.hin...@kernel.org>


Best regards,
Andreas Hindborg

[Gary Guo]

On Thu May 21, 2026 at 8:52 AM BST, Alvin Sun wrote:
> Auto-add `type ThisModule: ::kernel::ModuleMetadata;` as a required
> associated type on the trait side if not already defined, and
> auto-insert `type ThisModule = crate::LocalModule;` on the impl side
> if not explicitly provided, eliminating the need to manually declare
> and implement `ThisModule` in every vtable trait and impl.
>
> Signed-off-by: Alvin Sun <alvi...@linux.dev>

Suggested-by: Gary Guo <ga...@garyguo.net>
Link: https://lore.kernel.org/all/DIMMWHUOLPSH....@garyguo.net

I don't think this is relevant. What's the sensible default anyway?

> + if !has_this_module {

Perhaps just make this an one liner :

if !item.items.iter().any(|i| matches!(item, TraitItem::Type(t) if t.ident == "ThisModule")) {

> + gen_items.push(parse_quote! {
> + /// The module implementing this vtable trait.
> + ///
> + /// Automatically set to `crate::LocalModule` by the `#[vtable]`
> + /// impl macro.
> + type ThisModule: ::kernel::ModuleMetadata;
> + });
> + }
> +
> for item in &item.items {
> if let TraitItem::Fn(fn_item) = item {
> let name = &fn_item.sig.ident;
> @@ -58,18 +81,31 @@ fn handle_trait(mut item: ItemTrait) -> Result<ItemTrait> {
> fn handle_impl(mut item: ItemImpl) -> Result<ItemImpl> {
> let mut gen_items = Vec::new();
> let mut defined_consts = HashSet::new();
> + let mut defined_types = HashSet::new();

I'd just rename `defined_consts` to `defined_items` to reuse the same set as
there cannot be assoc items with same name anyway.

Best,
Gary