[PATCH v3 3/6] rust: macros: auto-insert OwnerModule in #[vtable]

[Alvin Sun <alvin.sun@linux.dev>]

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

Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Suggested-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/all/DIMMWHUOLPSH.13JFRHDKDQJGO@garyguo.net
Signed-off-by: Alvin Sun <alvin.sun@linux.dev>
---
 rust/macros/lib.rs    |  6 ++++++
 rust/macros/vtable.rs | 41 ++++++++++++++++++++++++++++++++++++-----
 2 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index 2cfd59e0f9e7c..bc7ded353c5ca 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 `OwnerModule`
+/// associated type: on the trait side, `type OwnerModule: ModuleMetadata;`
+/// is added as a required associated type if not already defined; on the
+/// impl side, `type OwnerModule = LocalModule;` is automatically inserted
+/// if not explicitly defined.
+///
 /// # Examples
 ///
 /// ```
diff --git a/rust/macros/vtable.rs b/rust/macros/vtable.rs
index c6510b0c4ea1d..be9a5ed8abe5e 100644
--- a/rust/macros/vtable.rs
+++ b/rust/macros/vtable.rs
@@ -30,6 +30,22 @@ fn handle_trait(mut item: ItemTrait) -> Result<ItemTrait> {
          const USE_VTABLE_ATTR: ();
     });
 
+    // Add `type OwnerModule: ModuleMetadata` as a required associated type if
+    // the trait does not already define it.
+    if !item
+        .items
+        .iter()
+        .any(|i| matches!(i, TraitItem::Type(t) if t.ident == "OwnerModule"))
+    {
+        gen_items.push(parse_quote! {
+            /// The module implementing this vtable trait.
+            ///
+            /// Automatically set to `crate::LocalModule` by the `#[vtable]`
+            /// impl macro.
+            type OwnerModule: ::kernel::ModuleMetadata;
+        });
+    }
+
     for item in &item.items {
         if let TraitItem::Fn(fn_item) = item {
             let name = &fn_item.sig.ident;
@@ -57,12 +73,18 @@ 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_items = HashSet::new();
 
-    // Iterate over all user-defined constants to gather any possible explicit overrides.
+    // Iterate over all user-defined items 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());
+        match item {
+            ImplItem::Const(const_item) => {
+                defined_items.insert(const_item.ident.clone());
+            }
+            ImplItem::Type(type_item) => {
+                defined_items.insert(type_item.ident.clone());
+            }
+            _ => {}
         }
     }
 
@@ -70,6 +92,15 @@ fn handle_impl(mut item: ItemImpl) -> Result<ItemImpl> {
         const USE_VTABLE_ATTR: () = ();
     });
 
+    // Auto-insert `type OwnerModule = 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_items.contains(&parse_quote!(OwnerModule)) {
+        gen_items.push(parse_quote! {
+            type OwnerModule = crate::LocalModule;
+        });
+    }
+
     for item in &item.items {
         if let ImplItem::Fn(fn_item) = item {
             let name = &fn_item.sig.ident;
@@ -78,7 +109,7 @@ fn handle_impl(mut item: ItemImpl) -> Result<ItemImpl> {
                 name.span(),
             );
             // Skip if it's declared already -- this allows user override.
-            if defined_consts.contains(&gen_const_name) {
+            if defined_items.contains(&gen_const_name) {
                 continue;
             }
             let cfg_attrs = crate::helpers::gather_cfg_attrs(&fn_item.attrs);

-- 
2.43.0