refactor: Optimize private call stack item hash for gate count

noir-projects/noir-protocol-circuits/crates/types/src/abis/private_call_stack_item.nr

@@ -56,7 +56,17 @@ impl Deserialize<PRIVATE_CALL_STACK_ITEM_LENGTH> for PrivateCallStackItem {
 
 impl Hash for PrivateCallStackItem {
     fn hash(self) -> Field {
-        pedersen_hash(self.serialize(), GENERATOR_INDEX__CALL_STACK_ITEM)
+        // We don't need a hash of the entire private call stack item, just a few pieces.
+        // See Issue(#7092) for more details.
+        pedersen_hash([
+            self.contract_address.to_field(),
+            self.public_inputs.call_context.hash(),
+            self.function_data.hash(),
+            self.public_inputs.args_hash,
+            self.public_inputs.returns_hash,
+            self.public_inputs.start_side_effect_counter as Field,
+            self.public_inputs.end_side_effect_counter as Field,
+        ], GENERATOR_INDEX__CALL_STACK_ITEM)
     }
 }
 
@@ -85,6 +95,6 @@ fn empty_hash() {
     let hash = item.hash();
 
     // Value from private_call_stack_item.test.ts "computes empty item hash" test
-    let test_data_empty_hash = 0x157022d579f892f06461fb895cdf5550b24329e15e7a41df14f9dad582fa1bc5;
+    let test_data_empty_hash = 0x2a876837d4bf400bf6787126331db78e53027a9ba5d91d9c974dbab1d41fe37c;
     assert_eq(hash, test_data_empty_hash);
 }

yarn-project/circuits.js/src/structs/__snapshots__/private_call_stack_item.test.ts.snap

@@ -1,5 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`PrivateCallStackItem computes empty item hash 1`] = `Fr<0x157022d579f892f06461fb895cdf5550b24329e15e7a41df14f9dad582fa1bc5>`;
+exports[`PrivateCallStackItem computes empty item hash 1`] = `Fr<0x2a876837d4bf400bf6787126331db78e53027a9ba5d91d9c974dbab1d41fe37c>`;
 
-exports[`PrivateCallStackItem computes hash 1`] = `Fr<0x029b1573da033e679c68a55e05987602c5e73419c4fdfdd6104e178a9a360834>`;
+exports[`PrivateCallStackItem computes hash 1`] = `Fr<0x12a821d797cdb85d17a98ad9e763334df45f8de9d5e027050ddac007f35fc6ac>`;

yarn-project/circuits.js/src/structs/call_context.ts

@@ -1,10 +1,11 @@
 import { FunctionSelector } from '@aztec/foundation/abi';
 import { AztecAddress } from '@aztec/foundation/aztec-address';
+import { pedersenHash } from '@aztec/foundation/crypto';
 import { Fr } from '@aztec/foundation/fields';
 import { BufferReader, FieldReader, serializeToBuffer, serializeToFields } from '@aztec/foundation/serialize';
 import { type FieldsOf } from '@aztec/foundation/types';
 
-import { CALL_CONTEXT_LENGTH } from '../constants.gen.js';
+import { CALL_CONTEXT_LENGTH, GeneratorIndex } from '../constants.gen.js';
 
 /**
  * Call context.
@@ -125,4 +126,8 @@ export class CallContext {
       callContext.sideEffectCounter === this.sideEffectCounter
     );
   }
+
+  hash(): Fr {
+    return pedersenHash(this.toFields(), GeneratorIndex.CALL_CONTEXT);
+  }
 }

yarn-project/circuits.js/src/structs/private_call_stack_item.ts

@@ -89,6 +89,15 @@ export class PrivateCallStackItem {
    * @returns Hash.
    */
   public hash(): Fr {
-    return pedersenHash(this.toFields(), GeneratorIndex.CALL_STACK_ITEM);
+    const fields = [
+      this.contractAddress.toField(),
+      this.publicInputs.callContext.hash(),
+      this.functionData.hash(),
+      this.publicInputs.argsHash,
+      this.publicInputs.returnsHash,
+      this.publicInputs.startSideEffectCounter,
+      this.publicInputs.endSideEffectCounter,
+    ];
+    return pedersenHash(fields, GeneratorIndex.CALL_STACK_ITEM);
   }
 }