[Rust] Add possibility to be generic over DbContext

crates/bindings/src/lib.rs

@@ -1457,9 +1457,14 @@ pub trait DbContext {
     ///
     /// This method is provided for times when a programmer wants to be generic over the `DbContext` type.
     /// Concrete-typed code is expected to read the `.db` field off the particular `DbContext` implementor.
-    /// Currently, being this generic is only meaningful in clients,
-    /// as `ReducerContext` is the only implementor of `DbContext` within modules.
     fn db(&self) -> &Self::DbView;
+
+    /// Get a read-only view into the tables.
+    ///
+    /// This method is provided for times when a programmer wants to be generic over the `DbContext` type.
+    /// Concrete-typed code is expected to read the `.db` field off the particular `DbContext` implementor.
+    #[cfg(feature = "unstable")]
+    fn db_read_only(&self) -> &LocalReadOnly;
 }
 
 impl DbContext for AnonymousViewContext {
@@ -1468,6 +1473,11 @@ impl DbContext for AnonymousViewContext {
     fn db(&self) -> &Self::DbView {
         &self.db
     }
+
+    #[cfg(feature = "unstable")]
+    fn db_read_only(&self) -> &LocalReadOnly {
+        &self.db
+    }
 }
 
 impl DbContext for ReducerContext {
@@ -1476,6 +1486,11 @@ impl DbContext for ReducerContext {
     fn db(&self) -> &Self::DbView {
         &self.db
     }
+
+    #[cfg(feature = "unstable")]
+    fn db_read_only(&self) -> &LocalReadOnly {
+        self.db.get_read_only()
+    }
 }
 
 #[cfg(feature = "unstable")]
@@ -1485,6 +1500,10 @@ impl DbContext for TxContext {
     fn db(&self) -> &Self::DbView {
         &self.db
     }
+
+    fn db_read_only(&self) -> &LocalReadOnly {
+        self.db.get_read_only()
+    }
 }
 
 impl DbContext for ViewContext {
@@ -1493,6 +1512,11 @@ impl DbContext for ViewContext {
     fn db(&self) -> &Self::DbView {
         &self.db
     }
+
+    #[cfg(feature = "unstable")]
+    fn db_read_only(&self) -> &LocalReadOnly {
+        &self.db
+    }
 }
 
 // `ProcedureContext` is *not* a `DbContext`
@@ -1506,6 +1530,13 @@ impl DbContext for ViewContext {
 #[non_exhaustive]
 pub struct Local {}
 
+impl Local {
+    #[cfg(feature = "unstable")]
+    fn get_read_only(&self) -> &LocalReadOnly {
+        &LocalReadOnly {}
+    }
+}
+
 /// The [JWT] of an [`AuthCtx`].
 ///
 /// [JWT]: https://en.wikipedia.org/wiki/JSON_Web_Token