feat: touch account (#488)

closes #455

cairo/ethereum/cancun/state.cairo

@@ -636,6 +636,17 @@ func set_transient_storage{poseidon_ptr: PoseidonBuiltin*, transient_storage: Tr
     return ();
 }
 
+func account_exists{poseidon_ptr: PoseidonBuiltin*, state: State}(address: Address) -> bool {
+    let account = get_account_optional(address);
+
+    if (cast(account.value, felt) == 0) {
+        tempvar result = bool(0);
+        return result;
+    }
+    tempvar result = bool(1);
+    return result;
+}
+
 func account_has_code_or_nonce{poseidon_ptr: PoseidonBuiltin*, state: State}(
     address: Address
 ) -> bool {
@@ -655,17 +666,6 @@ func account_has_code_or_nonce{poseidon_ptr: PoseidonBuiltin*, state: State}(
     return res;
 }
 
-func account_exists{poseidon_ptr: PoseidonBuiltin*, state: State}(address: Address) -> bool {
-    let account = get_account_optional(address);
-
-    if (cast(account.value, felt) == 0) {
-        tempvar result = bool(0);
-        return result;
-    }
-    tempvar result = bool(1);
-    return result;
-}
-
 func is_account_empty{poseidon_ptr: PoseidonBuiltin*, state: State}(address: Address) -> bool {
     // Get the account at the address
     let account = get_account(address);
@@ -983,3 +983,15 @@ func set_account_balance{poseidon_ptr: PoseidonBuiltin*, state: State}(
     set_account(address, new_account);
     return ();
 }
+
+func touch_account{poseidon_ptr: PoseidonBuiltin*, state: State}(address: Address) {
+    let _account_exists = account_exists(address);
+    if (_account_exists.value != 0) {
+        return ();
+    }
+
+    let _empty_account = EMPTY_ACCOUNT();
+    let empty_account = OptionalAccount(_empty_account.value);
+    set_account(address, empty_account);
+    return ();
+}

cairo/tests/ethereum/cancun/test_state.py

@@ -28,6 +28,7 @@
     set_code,
     set_storage,
     set_transient_storage,
+    touch_account,
 )
 from tests.utils.args_gen import State, TransientStorage
 from tests.utils.strategies import address, bytes32, code, state, transient_storage
@@ -197,6 +198,13 @@ def test_increment_nonce(self, cairo_run, data):
         increment_nonce(state, address)
         assert state_cairo == state
 
+    @given(data=state_and_address_and_optional_key())
+    def test_touch_account(self, cairo_run, data):
+        state, address = data
+        state_cairo = cairo_run("touch_account", state, address)
+        touch_account(state, address)
+        assert state_cairo == state
+
 
 class TestStateStorage:
     @given(state_and_address_and_optional_key(key_strategy=bytes32))