Add ink_env::pay_with_call! helper macro for off-chain emulation of…

… sending payments with contract msg calls (#1379)

* first ver.: transfer_in api function implememted but we can't have it in on-chain env

* transfer_in moved to test_api

* doc + example updated

* Update examples/contract-transfer/lib.rs

Co-authored-by: Hernando Castano <[email protected]>

* use stmt moved to macro

* docs and nitty gritties

* moved the macro to the test mod

* spell fix

* next review round suggestions applied

* Use four spaces for macro indentation

Co-authored-by: Hernando Castano <[email protected]>
Co-authored-by: Hernando Castano <[email protected]>

crates/env/src/engine/off_chain/test_api.rs

@@ -200,6 +200,8 @@ where
 }
 
 /// Sets the value transferred from the caller to the callee as part of the call.
+///
+/// Please note that the acting accounts should be set with [`set_caller()`] and [`set_callee()`] beforehand.
 pub fn set_value_transferred<T>(value: T::Balance)
 where
     T: Environment<Balance = u128>, // Just temporary for the MVP!
@@ -209,6 +211,44 @@ where
     })
 }
 
+/// Transfers value from the caller account to the contract.
+///
+/// Please note that the acting accounts should be set with [`set_caller()`] and [`set_callee()`] beforehand.
+pub fn transfer_in<T>(value: T::Balance)
+where
+    T: Environment<Balance = u128>, // Just temporary for the MVP!
+{
+    <EnvInstance as OnInstance>::on_instance(|instance| {
+        let caller = instance
+            .engine
+            .exec_context
+            .caller
+            .as_ref()
+            .expect("no caller has been set")
+            .as_bytes()
+            .to_vec();
+
+        let caller_old_balance = instance
+            .engine
+            .get_balance(caller.clone())
+            .unwrap_or_default();
+
+        let callee = instance.engine.get_callee();
+        let contract_old_balance = instance
+            .engine
+            .get_balance(callee.clone())
+            .unwrap_or_default();
+
+        instance
+            .engine
+            .set_balance(caller, caller_old_balance - value);
+        instance
+            .engine
+            .set_balance(callee, contract_old_balance + value);
+        instance.engine.set_value_transferred(value);
+    });
+}
+
 /// Returns the amount of storage cells used by the account `account_id`.
 ///
 /// Returns `None` if the `account_id` is non-existent.
@@ -355,3 +395,12 @@ pub fn assert_contract_termination<T, F>(
     assert_eq!(value_transferred, expected_value_transferred_to_beneficiary);
     assert_eq!(beneficiary, expected_beneficiary);
 }
+
+/// Prepend contract message call with value transfer. Used for tests in off-chain environment.
+#[macro_export]
+macro_rules! pay_with_call {
+    ($contract:ident . $message:ident ( $($params:ty)? ) , $amount:expr) => {{
+        $crate::test::transfer_in::<Environment>($amount);
+        $contract.$message($($params:ty)?)
+    }}
+}

examples/contract-transfer/lib.rs

@@ -101,20 +101,31 @@ pub mod give_me {
 
         #[ink::test]
         fn test_transferred_value() {
+            use ink_lang::codegen::Env;
             // given
             let accounts = default_accounts();
             let give_me = create_contract(100);
+            let contract_account = give_me.env().account_id();
 
             // when
-            // Push the new execution context which sets Eve as caller and
-            // the `mock_transferred_value` as the value which the contract
-            // will see as transferred to it.
+            // Push the new execution context which sets initial balances and
+            // sets Eve as the caller
+            set_balance(accounts.eve, 100);
+            set_balance(contract_account, 0);
             set_sender(accounts.eve);
-            ink_env::test::set_value_transferred::<ink_env::DefaultEnvironment>(10);
 
             // then
-            // there must be no panic
-            give_me.was_it_ten();
+            // we use helper macro to emulate method invocation coming with payment,
+            // and there must be no panic
+            ink_env::pay_with_call!(give_me.was_it_ten(), 10);
+
+            // and
+            // balances should be changed properly
+            let contract_new_balance = get_balance(contract_account);
+            let caller_new_balance = get_balance(accounts.eve);
+
+            assert_eq!(caller_new_balance, 100 - 10);
+            assert_eq!(contract_new_balance, 10);
         }
 
         #[ink::test]