program: Add optional rent sysvar account (#138)

Add optional rent sysvar account

Author: febo

interface/src/instruction.rs

@@ -372,8 +372,14 @@ pub enum TokenInstruction<'a> {
     ///
     /// Accounts expected by this instruction:
     ///
+    ///   * Using runtime Rent sysvar
     ///   0. `[writable]`  The native token account to sync with its underlying
     ///      lamports.
+    ///
+    ///   * Using Rent sysvar account
+    ///   0. `[writable]`  The native token account to sync with its underlying
+    ///      lamports.
+    ///   1. `[]` Rent sysvar.
     SyncNative,
     /// Like [`TokenInstruction::InitializeAccount2`], but does not require the
     /// Rent sysvar to be provided

program/src/processor.rs

@@ -759,8 +759,13 @@ impl Processor {
         let native_account_info = next_account_info(account_info_iter)?;
         Self::check_account_owner(program_id, native_account_info)?;
 
-        let rent = Rent::get()?;
-        let rent_exempt_reserve = rent.minimum_balance(native_account_info.data_len());
+        let rent_exempt_reserve = if let Ok(rent_sysvar_info) = next_account_info(account_info_iter)
+        {
+            let rent = Rent::from_account_info(rent_sysvar_info)?;
+            rent.minimum_balance(native_account_info.data_len())
+        } else {
+            Rent::get()?.minimum_balance(native_account_info.data_len())
+        };
 
         let mut native_account = Account::unpack(&native_account_info.data.borrow())?;