Add salsa::Update trait bounds to generics when deriving salsa::Update

components/salsa-macros/src/update.rs

@@ -130,7 +130,10 @@ pub(crate) fn update_derive(input: syn::DeriveInput) -> syn::Result<TokenStream>
         .collect::<syn::Result<_>>()?;
 
     let ident = &input.ident;
-    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+    let generics = input.generics;
+    let generics = add_trait_bounds(generics);
+
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
     let tokens = quote! {
         #[allow(clippy::all)]
         #[automatically_derived]
@@ -148,6 +151,16 @@ pub(crate) fn update_derive(input: syn::DeriveInput) -> syn::Result<TokenStream>
     Ok(crate::debug::dump_tokens(&input.ident, tokens))
 }
 
+// Add a bound `T: salsa::Update` to every type parameter T
+fn add_trait_bounds(mut generics: syn::Generics) -> syn::Generics {
+    for param in &mut generics.params {
+        if let syn::GenericParam::Type(type_param) = param {
+            type_param.bounds.push(syn::parse_quote!(::salsa::Update));
+        }
+    }
+    generics
+}
+
 pub(crate) fn assert_update(
     db_lt: &syn::Lifetime,
     zalsa: &syn::Ident,

tests/interned-structs.rs

@@ -78,6 +78,14 @@ struct InternedStringWithCustomIdAndNoLifetime<'db> {
     data: String,
 }
 
+#[derive(salsa::Update, Clone, Eq, PartialEq, Hash, Debug)]
+struct Generic<T>(T);
+
+#[salsa::interned(debug)]
+struct InternedOverGeneric {
+    value: Generic<String>,
+}
+
 #[salsa::tracked]
 fn intern_stuff(db: &dyn salsa::Database) -> String {
     let s1 = InternedString::new(db, "Hello, ".to_string());
@@ -217,3 +225,12 @@ fn interning_reference() {
     let s2 = InternedFoo::new(&db, &Foo);
     assert_eq!(s1, s2);
 }
+
+#[test]
+fn interned_generic() {
+    let db = salsa::DatabaseImpl::new();
+
+    let s1 = InternedOverGeneric::new(&db, Generic("test".to_string()));
+    let s2 = InternedOverGeneric::new(&db, Generic("test".to_string()));
+    assert_eq!(s1, s2);
+}