WIP

components/salsa-macros/src/db.rs

@@ -1,11 +1,11 @@
 use proc_macro2::TokenStream;
-use syn::{parse::Nothing, ItemStruct};
+use syn::parse::Nothing;
 
 use crate::hygiene::Hygiene;
 
 // Source:
 //
-// #[salsa::db(Jar0, Jar1, Jar2)]
+// #[salsa::db]
 // pub struct Database {
 //    storage: salsa::Storage<Self>,
 // }
@@ -15,34 +15,54 @@ pub(crate) fn db(
     input: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
     let _nothing = syn::parse_macro_input!(args as Nothing);
-    let db_macro = DbMacro {
-        hygiene: Hygiene::from(&input),
-        input: syn::parse_macro_input!(input as syn::ItemStruct),
-    };
-    match db_macro.try_db() {
+    let hygiene = Hygiene::from(&input);
+    let input = syn::parse_macro_input!(input as syn::Item);
+    let db_macro = DbMacro { hygiene };
+    match db_macro.try_db(input) {
         Ok(v) => v.into(),
         Err(e) => e.to_compile_error().into(),
     }
 }
 
 struct DbMacro {
     hygiene: Hygiene,
-    input: ItemStruct,
 }
 
+#[allow(non_snake_case)]
 impl DbMacro {
-    fn try_db(self) -> syn::Result<TokenStream> {
-        let has_storage_impl = self.has_storage_impl()?;
-        let input = self.input;
-        Ok(quote! {
-            #has_storage_impl
-            #input
-        })
+    fn try_db(self, input: syn::Item) -> syn::Result<TokenStream> {
+        match input {
+            syn::Item::Struct(input) => {
+                let has_storage_impl = self.has_storage_impl(&input)?;
+                Ok(quote! {
+                    #has_storage_impl
+                    #input
+                })
+            }
+            syn::Item::Trait(mut input) => {
+                self.add_salsa_view_method(&mut input)?;
+                Ok(quote! {
+                    #input
+                })
+            }
+            syn::Item::Impl(mut input) => {
+                self.add_salsa_view_method_impl(&mut input)?;
+                Ok(quote! {
+                    #input
+                })
+            }
+            _ => {
+                return Err(syn::Error::new_spanned(
+                    input,
+                    "`db` must be applied to a struct, trait, or impl",
+                ));
+            }
+        }
     }
 
-    fn find_storage_field(&self) -> syn::Result<syn::Ident> {
+    fn find_storage_field(&self, input: &syn::ItemStruct) -> syn::Result<syn::Ident> {
         let storage = "storage";
-        for field in self.input.fields.iter() {
+        for field in input.fields.iter() {
             if let Some(i) = &field.ident {
                 if i == storage {
                     return Ok(i.clone());
@@ -56,15 +76,14 @@ impl DbMacro {
         }
 
         return Err(syn::Error::new_spanned(
-            &self.input.ident,
+            &input.ident,
             "database struct must be a braced struct (`{}`) with a field named `storage`",
         ));
     }
 
-    #[allow(non_snake_case)]
-    fn has_storage_impl(&self) -> syn::Result<TokenStream> {
-        let storage = self.find_storage_field()?;
-        let db = &self.input.ident;
+    fn has_storage_impl(&self, input: &syn::ItemStruct) -> syn::Result<TokenStream> {
+        let storage = self.find_storage_field(input)?;
+        let db = &input.ident;
 
         let SalsaHasStorage = self.hygiene.ident("SalsaHasStorage");
         let SalsaStorage = self.hygiene.ident("SalsaStorage");
@@ -86,4 +105,26 @@ impl DbMacro {
             };
         })
     }
+
+    fn add_salsa_view_method(&self, input: &mut syn::ItemTrait) -> syn::Result<()> {
+        input.items.push(parse_quote! {
+            fn __salsa_add_view__(&self);
+        });
+        Ok(())
+    }
+
+    fn add_salsa_view_method_impl(&self, input: &mut syn::ItemImpl) -> syn::Result<()> {
+        let Some((_, TraitPath, _)) = &input.trait_ else {
+            return Err(syn::Error::new_spanned(
+                &input.self_ty,
+                "impl must be on a trait",
+            ));
+        };
+        input.items.push(parse_quote! {
+            fn __salsa_add_view__(&self) {
+                salsa::storage::views(self).add::<dyn #TraitPath>(|t| t, |t| t);
+            }
+        });
+        Ok(())
+    }
 }

components/salsa-macros/src/lib.rs

@@ -42,7 +42,6 @@ mod accumulator;
 mod configuration;
 mod db;
 mod db_lifetime;
-mod db_view;
 mod debug;
 mod debug_with_db;
 mod input;

src/lib.rs

@@ -41,7 +41,6 @@ pub use self::runtime::Runtime;
 pub use self::storage::Storage;
 pub use salsa_macros::accumulator;
 pub use salsa_macros::db;
-pub use salsa_macros::db_view;
 pub use salsa_macros::input;
 pub use salsa_macros::interned;
 pub use salsa_macros::jar;

src/storage.rs

@@ -14,6 +14,10 @@ use crate::Database;
 
 use super::ParallelDatabase;
 
+pub fn views<Db: ?Sized + Database>(db: &Db) -> &Views {
+    DatabaseGen::views(db)
+}
+
 /// Salsa database methods whose implementation is generated by
 /// the `#[salsa::database]` procedural macro.
 ///
@@ -43,11 +47,6 @@ pub unsafe trait DatabaseGen: Any + Send + Sync {
     /// Returns a reference to the underlying.
     fn views(&self) -> &Views;
 
-    /// Returns the upcasts database, tied to the type of `Self`; cannot be used from `dyn DatabaseGen` objects.
-    fn views_of_self(&self) -> &ViewsOf<Self>
-    where
-        Self: Sized + Database;
-
     /// Returns the nonce for the underyling storage.
     ///
     /// # Safety