feat!: make compute_nullifier_without_context unconstrained (#8742)

With noir-lang/noir#5717 closed, we can now
make `compute_nullifier_without_context` `unconstrained`, as it should
have been. This clears the multiple warnings caused by calling
`get_nsk_app` without an `unsafe` block.

I also moved the implementation of `TransparentNote` around, since we
were calling the now unconstrained version. This nicely would've
resulted in a warning about a missing `unsafe` block had I not changed
it 😁

---------

Co-authored-by: Tom French <15848336+TomAFrench@users.noreply.github.com>

Author: 2 people

docs/docs/migration_notes.md

@@ -8,6 +8,16 @@ Aztec is in full-speed development. Literally every version breaks compatibility
 
 ## TBD
 
+### [Aztec.nr] Changes to `NullifiableNote`
+
+The `compute_nullifier_without_context` function is now `unconstrained`. It had always been meant to be called in unconstrained contexts (which is why it did not receive the `context` object), but now that Noir supports trait functions being `unconstrained` this can be implemented properly. Users must add the `unconstrained` keyword to their implementations of the trait:
+
+```diff
+impl NullifiableNote for MyCustomNote {
+-    fn compute_nullifier_without_context(self) -> Field {
++    unconstrained fn compute_nullifier_without_context(self) -> Field {
+```
+
 ### [Aztec.nr] Make `TestEnvironment` unconstrained
 
 All of `TestEnvironment`'s functions are now `unconstrained`, preventing accidentally calling them in a constrained circuit, among other kinds of user error. Becuase they work with mutable references, and these are not allowed to cross the constrained/unconstrained barrier, tests that use `TestEnvironment` must also become `unconstrained`. The recommended practice is to make _all_ Noir tests and test helper functions be `unconstrained:

noir-projects/aztec-nr/address-note/src/address_note.nr

@@ -30,7 +30,7 @@ impl NullifiableNote for AddressNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/aztec-nr/aztec/src/encrypted_logs/incoming_body.nr

@@ -63,7 +63,7 @@ mod test {
             1
         }
 
-        fn compute_nullifier_without_context(_self: Self) -> Field {
+        unconstrained fn compute_nullifier_without_context(_self: Self) -> Field {
             1
         }
     }

noir-projects/aztec-nr/aztec/src/note/note_interface.nr

@@ -19,7 +19,7 @@ pub trait NullifiableNote {
 
     // Unlike compute_nullifier, this function does not take a note hash since it'll only be invoked in unconstrained
     // contexts, where there is no gate count.
-    fn compute_nullifier_without_context(self) -> Field;
+    unconstrained fn compute_nullifier_without_context(self) -> Field;
 }
 
 // docs:start:note_interface
@@ -48,4 +48,3 @@ pub trait NoteInterface<let N: u32> {
     fn compute_note_hash(self) -> Field;
 }
 // docs:end:note_interface
-

noir-projects/aztec-nr/aztec/src/test/mocks/mock_note.nr

@@ -24,7 +24,7 @@ impl NullifiableNote for MockNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         // We don't use any kind of secret here since this is only a mock note and having it here would make tests
         // more cumbersome
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);

noir-projects/aztec-nr/uint-note/src/uint_note.nr

@@ -26,7 +26,7 @@ impl NullifiableNote for UintNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/aztec-nr/value-note/src/value_note.nr

@@ -36,7 +36,7 @@ impl NullifiableNote for ValueNote {
 
     // docs:end:nullifier
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/app_subscription_contract/src/subscription_note.nr

@@ -27,7 +27,7 @@ impl NullifiableNote for SubscriptionNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/docs_example_contract/src/types/card_note.nr

@@ -38,7 +38,7 @@ impl NullifiableNote for CardNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/ecdsa_public_key_note/src/lib.nr

@@ -136,7 +136,7 @@ impl NullifiableNote for EcdsaPublicKeyNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/nft_contract/src/types/nft_note.nr

@@ -27,7 +27,7 @@ impl NullifiableNote for NFTNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/schnorr_account_contract/src/public_key_note.nr

@@ -27,7 +27,7 @@ impl NullifiableNote for PublicKeyNote {
         )
     }
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/spam_contract/src/types/token_note.nr

@@ -35,7 +35,7 @@ impl NullifiableNote for TokenNote {
     }
     // docs:end:nullifier
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/test_contract/src/test_note.nr

@@ -19,7 +19,7 @@ impl NullifiableNote for TestNote {
         0
     }
 
-    fn compute_nullifier_without_context(_self: Self) -> Field {
+    unconstrained fn compute_nullifier_without_context(_self: Self) -> Field {
         // This note is expected to be shared between users and for this reason can't be nullified using a secret.
         0
     }

noir-projects/noir-contracts/contracts/token_blacklist_contract/src/types/token_note.nr

@@ -34,7 +34,7 @@ impl NullifiableNote for TokenNote {
     }
     // docs:end:nullifier
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/token_blacklist_contract/src/types/transparent_note.nr

@@ -6,6 +6,8 @@ use dep::aztec::{
     macros::notes::note
 };
 
+use dep::std::mem::zeroed;
+
 // Transparent note represents a note that is created in the clear (public execution), but can only be spent by those
 // that know the preimage of the "secret_hash" (the secret). This is typically used when shielding a token balance.
 // Owner of the tokens provides a "secret_hash" as an argument to the public "shield" function and then the tokens
@@ -17,11 +19,6 @@ pub struct TransparentNote {
 }
 
 impl NullifiableNote for TransparentNote {
-
-    fn compute_nullifier(self, _context: &mut PrivateContext, _note_hash_for_nullify: Field) -> Field {
-        self.compute_nullifier_without_context()
-    }
-
     // Computing a nullifier in a transparent note is not guarded by making secret a part of the nullifier preimage (as
     // is common in other cases) and instead is guarded by the functionality of "redeem_shield" function. There we do
     // the following:
@@ -30,13 +27,18 @@ impl NullifiableNote for TransparentNote {
     //      3) the "get_notes" oracle constrains that the secret hash in the returned note matches the one computed in
     //         circuit.
     // This achieves that the note can only be spent by the party that knows the secret.
-    fn compute_nullifier_without_context(self) -> Field {
+    fn compute_nullifier(self, _context: &mut PrivateContext, _note_hash_for_nullify: Field) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         poseidon2_hash_with_separator(
             [note_hash_for_nullify],
             GENERATOR_INDEX__NOTE_NULLIFIER as Field
         )
     }
+
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
+        // compute_nullifier ignores both of its parameters so we can reuse it here
+        self.compute_nullifier(zeroed(), zeroed())
+    }
 }
 
 impl TransparentNote {

noir-projects/noir-contracts/contracts/token_contract/src/types/token_note.nr

@@ -36,7 +36,7 @@ impl NullifiableNote for TokenNote {
     }
     // docs:end:nullifier
 
-    fn compute_nullifier_without_context(self) -> Field {
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         let secret = get_nsk_app(self.npk_m_hash);
         poseidon2_hash_with_separator(

noir-projects/noir-contracts/contracts/token_contract/src/types/transparent_note.nr

@@ -5,6 +5,8 @@ use dep::aztec::{
     macros::notes::note
 };
 
+use dep::std::mem::zeroed;
+
 // Transparent note represents a note that is created in the clear (public execution), but can only be spent by those
 // that know the preimage of the "secret_hash" (the secret). This is typically used when shielding a token balance.
 // Owner of the tokens provides a "secret_hash" as an argument to the public "shield" function and then the tokens
@@ -16,10 +18,6 @@ pub struct TransparentNote {
 }
 
 impl NullifiableNote for TransparentNote {
-    fn compute_nullifier(self, _context: &mut PrivateContext, _note_hash_for_nullify: Field) -> Field {
-        self.compute_nullifier_without_context()
-    }
-
     // Computing a nullifier in a transparent note is not guarded by making secret a part of the nullifier preimage (as
     // is common in other cases) and instead is guarded by the functionality of "redeem_shield" function. There we do
     // the following:
@@ -28,13 +26,18 @@ impl NullifiableNote for TransparentNote {
     //      3) the "get_notes" oracle constrains that the secret hash in the returned note matches the one computed in
     //         circuit.
     // This achieves that the note can only be spent by the party that knows the secret.
-    fn compute_nullifier_without_context(self) -> Field {
+    fn compute_nullifier(self, _context: &mut PrivateContext, _note_hash_for_nullify: Field) -> Field {
         let note_hash_for_nullify = compute_note_hash_for_nullify(self);
         poseidon2_hash_with_separator(
             [note_hash_for_nullify],
             GENERATOR_INDEX__NOTE_NULLIFIER as Field
         )
     }
+
+    unconstrained fn compute_nullifier_without_context(self) -> Field {
+        // compute_nullifier ignores both of its parameters so we can reuse it here
+        self.compute_nullifier(zeroed(), zeroed())
+    }
 }
 
 impl TransparentNote {
@@ -50,4 +53,4 @@ impl Eq for TransparentNote {
     }
 }
 
-// docs:end:token_types_all
+// docs:end:token_types_all