refactor: make Note a marker trait

Author: olehmisar

packages/contracts/noir/common/src/erc20_note.nr

@@ -1,5 +1,3 @@
-use protocol_types::hash::poseidon2_hash_with_separator;
-
 // fails to compile if this file is moved to erc20 crate
 
 pub struct Erc20Note {
@@ -8,6 +6,8 @@ pub struct Erc20Note {
     pub randomness: Field,
 }
 
+impl crate::Note for Erc20Note {}
+
 impl Erc20Note {
     pub fn sub_and_emit_change<let N: u32>(
         context: &mut crate::Context,
@@ -41,13 +41,6 @@ impl crate::Serialize<6> for Erc20Note {
     }
 }
 
-impl crate::Note for Erc20Note {
-    fn hash(self) -> Field {
-        let serialized = self.serialize();
-        poseidon2_hash_with_separator(serialized, crate::GENERATOR_INDEX__NOTE_HASH)
-    }
-}
-
 impl crate::OwnedNote for Erc20Note {
     fn owner(self) -> crate::WaAddress {
         self.owner

packages/contracts/noir/common/src/lib.nr

@@ -8,7 +8,7 @@ mod owned_note;
 
 pub use context::{Context, Result};
 pub use erc20_note::{Erc20Note, Erc20NoteConsumptionInputs};
-pub use note::Note;
+pub use note::{compute_note_hash, Note};
 pub use owned_note::{NoteConsumptionInputs, OwnedNote};
 pub use protocol_types::{address::EthAddress, traits::Serialize};
 

packages/contracts/noir/common/src/note.nr

@@ -1,7 +1,17 @@
-pub trait Note {
-    fn hash(self) -> Field;
+use protocol_types::hash::poseidon2_hash_with_separator;
+
+/// A marker trait to mark structs as notes
+pub trait Note: crate::Serialize<_> {
 
     pub fn emit(self, context: &mut crate::Context) {
-        context.push_note_hash(self.hash());
+        context.push_note_hash(crate::compute_note_hash(self));
     }
 }
+
+pub fn compute_note_hash<T>(note: T) -> Field
+where
+    T: Note,
+{
+    let serialized = note.serialize();
+    poseidon2_hash_with_separator(serialized, crate::GENERATOR_INDEX__NOTE_HASH)
+}

packages/contracts/noir/common/src/owned_note.nr

@@ -11,9 +11,10 @@ fn compute_nullifier_of_owned_note<T>(note: T, secret_key: Field) -> Field
 where
     T: OwnedNote,
 {
+    // TODO(perf): pass note hash as an argument to avoid hashing twice?
     assert_eq(note.owner(), crate::WaAddress::from_secret_key(secret_key), "invalid secret key");
     poseidon2_hash_with_separator(
-        [note.hash(), secret_key],
+        [crate::compute_note_hash(note), secret_key],
         crate::GENERATOR_INDEX__NOTE_NULLIFIER,
     )
 }
@@ -32,7 +33,7 @@ where
 {
     pub fn consume(self, context: &mut crate::Context, secret_key: Field) {
         merkle_tree::assert_check_membership(
-            self.note.hash(),
+            crate::compute_note_hash(self.note),
             self.note_index,
             self.note_sibling_path,
             context.tree_roots().note_hash_root,