Addressed review comments

examples/contracts/src/lib.rs

@@ -1,7 +1,7 @@
 #[cfg(test)]
 mod tests {
-    use fuels::tx::{Bytes32, ContractIdExt};
     use fuels::types::errors::{error, Error, Result};
+    use fuels::types::Bits256;
 
     #[tokio::test]
     async fn instantiate_client() -> Result<()> {
@@ -345,9 +345,7 @@ mod tests {
         let response = contract_methods.mint_coins(1_000_000).call().await?;
         // ANCHOR: variable_outputs
         let address = wallet.address();
-        let asset_id = ContractId::from(contract_id)
-            .asset_id(&Bytes32::zeroed())
-            .into();
+        let asset_id = contract_id.asset_id(&Bits256::zeroed()).into();
 
         // withdraw some tokens to wallet
         let response = contract_methods
@@ -410,7 +408,7 @@ mod tests {
             .await?;
         // ANCHOR_END: dependency_estimation_manual
 
-        let asset_id = ContractId::from(*caller_contract_id.hash()).asset_id(&Bytes32::zeroed());
+        let asset_id = caller_contract_id.asset_id(&Bits256::zeroed());
         let balance = wallet.get_asset_balance(&asset_id).await?;
         assert_eq!(balance, amount);
 

examples/cookbook/src/lib.rs

@@ -1,6 +1,6 @@
 #[cfg(test)]
 mod tests {
-    use fuels::tx::{Bytes32, ContractIdExt};
+    use fuels::types::Bits256;
     use fuels::{
         prelude::Result,
         types::transaction_builders::{ScriptTransactionBuilder, TransactionBuilder},
@@ -66,7 +66,7 @@ mod tests {
         // ANCHOR_END: liquidity_deposit
 
         // ANCHOR: liquidity_withdraw
-        let lp_asset_id = ContractId::from(*contract_id.hash()).asset_id(&Bytes32::zeroed());
+        let lp_asset_id = contract_id.asset_id(&Bits256::zeroed());
         let lp_token_balance = wallet.get_asset_balance(&lp_asset_id).await?;
 
         let call_params = CallParameters::default()

packages/fuels-core/src/types/bech32.rs

@@ -3,8 +3,10 @@ use std::{
     str::FromStr,
 };
 
+use crate::types::Bits256;
 use bech32::{FromBase32, ToBase32, Variant::Bech32m};
-use fuel_tx::{Address, Bytes32, ContractId};
+use fuel_tx::{Address, Bytes32, ContractId, ContractIdExt};
+use fuel_types::AssetId;
 
 use crate::types::errors::{Error, Result};
 
@@ -128,6 +130,14 @@ impl From<ContractId> for Bech32ContractId {
     }
 }
 
+impl Bech32ContractId {
+    /// Creates an `AssetId` from the `Bech32ContractId` and `sub_id`.
+    pub fn asset_id(&self, sub_id: &Bits256) -> AssetId {
+        let sub_id = Bytes32::from(sub_id.0);
+        ContractId::from(self).asset_id(&sub_id)
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

packages/fuels-core/src/types/core/bits.rs

@@ -10,6 +10,11 @@ use crate::types::errors::{error, Error, Result};
 pub struct Bits256(pub [u8; 32]);
 
 impl Bits256 {
+    /// Returns `Self` with zeroes inside.
+    pub fn zeroed() -> Self {
+        Self([0; 32])
+    }
+
     /// Create a new `Bits256` from a string representation of a hex.
     /// Accepts both `0x` prefixed and non-prefixed hex strings.
     pub fn from_hex_str(hex: &str) -> Result<Self> {

packages/fuels/tests/contracts.rs

@@ -3,7 +3,6 @@ use std::future::Future;
 use std::vec;
 
 use fuel_core::chain_config::ChainConfig;
-use fuel_tx::{Bytes32, ContractIdExt};
 use fuels::{
     accounts::{predicate::Predicate, Account},
     core::codec::{calldata, fn_selector},
@@ -662,7 +661,7 @@ async fn setup_output_variable_estimation_test(
     .deploy(&wallets[0], TxParameters::default())
     .await?;
 
-    let mint_asset_id = ContractId::from(&contract_id).asset_id(&Bytes32::zeroed());
+    let mint_asset_id = contract_id.asset_id(&Bits256::zeroed());
     let addresses: [Address; 3] = wallets
         .iter()
         .map(|wallet| wallet.address().into())

packages/fuels/tests/logs.rs

@@ -1,7 +1,5 @@
-use fuel_tx::ContractIdExt;
 use std::fmt::Debug;
 
-use fuels::tx::Bytes32;
 use fuels::{
     prelude::*,
     tx::Receipt,
@@ -1246,9 +1244,7 @@ async fn contract_token_ops_error_messages() -> Result<()> {
 
     {
         let contract_id = contract_instance.contract_id();
-        let asset_id = ContractId::from(contract_id)
-            .asset_id(&Bytes32::zeroed())
-            .into();
+        let asset_id = contract_id.asset_id(&Bits256::zeroed()).into();
         let address = wallet.address();
 
         let error = contract_methods

packages/fuels/tests/providers.rs

@@ -3,7 +3,6 @@ use std::{iter, ops::Add, str::FromStr, vec};
 use chrono::{DateTime, Duration, NaiveDateTime, TimeZone, Utc};
 use fuel_core::service::{Config as CoreConfig, FuelService, ServiceTrait};
 use fuel_core_types::tai64::Tai64;
-use fuel_tx::{Bytes32, ContractIdExt};
 use fuels::{
     accounts::{fuel_crypto::SecretKey, Account},
     client::{PageDirection, PaginationRequest},
@@ -12,6 +11,7 @@ use fuels::{
     tx::Receipt,
     types::{block::Block, coin_type::CoinType, errors::error, message::Message},
 };
+use fuels_core::types::Bits256;
 
 #[tokio::test]
 async fn test_provider_launch_and_connect() -> Result<()> {
@@ -338,6 +338,8 @@ async fn test_gas_forwarded_defaults_to_tx_limit() -> Result<()> {
         ),
     );
 
+    // The gas used by the script to call a contract and forward remaining gas limit.
+    let gas_used_by_script = 161;
     let gas_limit = 225_883;
     let response = contract_instance
         .methods()
@@ -354,7 +356,7 @@ async fn test_gas_forwarded_defaults_to_tx_limit() -> Result<()> {
         .gas()
         .unwrap();
 
-    assert_eq!(gas_limit, gas_forwarded + 161);
+    assert_eq!(gas_limit, gas_forwarded + gas_used_by_script);
 
     Ok(())
 }
@@ -375,9 +377,7 @@ async fn test_amount_and_asset_forwarding() -> Result<()> {
     );
     let contract_id = contract_instance.contract_id();
     let contract_methods = contract_instance.methods();
-    let asset_id = ContractId::from(contract_id)
-        .asset_id(&Bytes32::zeroed())
-        .into();
+    let asset_id = contract_id.asset_id(&Bits256::zeroed()).into();
 
     let mut balance_response = contract_methods
         .get_balance(contract_id, asset_id)