[solana] Add close_vesting_balance instruction (#242)

* Add `close_vesting_balance` ix

* Add rent_payer to `VestingBalance` for rent reclaim on close

* Add total_vesting_balance == 0 constraint

* Only set new `rent_payer` if not initialized already

* Make rent_payer signer and remove unused mut

* Remove unused `globalConfig

* Add vesting test cases

Author: nvsriram

solana/programs/staking/src/contexts/close_vesting_balance.rs

@@ -0,0 +1,44 @@
+use crate::context::{VESTING_BALANCE_SEED, VESTING_CONFIG_SEED};
+use crate::error::VestingError;
+use crate::state::{VestingBalance, VestingConfig};
+use anchor_lang::prelude::*;
+use anchor_spl::associated_token::AssociatedToken;
+use anchor_spl::token_interface::{Mint, TokenAccount, TokenInterface};
+
+#[derive(Accounts)]
+#[instruction()]
+pub struct CloseVestingBalance<'info> {
+    #[account(mut)]
+    /// CHECK: This account is the original rent_payer for the vesting_balance account
+    rent_payer: Signer<'info>,
+    mint: InterfaceAccount<'info, Mint>,
+    #[account(
+        seeds = [VESTING_CONFIG_SEED.as_bytes(), mint.key().as_ref(), config.seed.to_le_bytes().as_ref()],
+        bump = config.bump
+    )]
+    config: Account<'info, VestingConfig>,
+    #[account(
+        mut,
+        has_one = rent_payer,
+        constraint = vesting_balance.total_vesting_balance == 0 @ VestingError::NotFullyVested,
+        seeds = [VESTING_BALANCE_SEED.as_bytes(), config.key().as_ref(), vester_ta.owner.key().as_ref()],
+        bump,
+        close = rent_payer,
+    )]
+    vesting_balance: Account<'info, VestingBalance>,
+    #[account(
+        associated_token::mint = mint,
+        associated_token::authority = vester_ta.owner,
+        associated_token::token_program = token_program
+    )]
+    vester_ta: InterfaceAccount<'info, TokenAccount>,
+    associated_token_program: Program<'info, AssociatedToken>,
+    token_program: Interface<'info, TokenInterface>,
+    system_program: Program<'info, System>,
+}
+
+impl<'info> CloseVestingBalance<'info> {
+    pub fn close_vesting_balance(&mut self) -> Result<()> {
+        Ok(())
+    }
+}

solana/programs/staking/src/contexts/create_vesting_balance.rs

@@ -53,6 +53,7 @@ impl<'info> CreateVestingBalance<'info> {
             stake_account_metadata: Pubkey::default(),
             total_vesting_balance: 0,
             bump,
+            rent_payer: self.admin.key(),
         });
 
         Ok(())

solana/programs/staking/src/contexts/mod.rs

@@ -15,8 +15,10 @@ pub use cancel_vesting::*;
 
 pub mod withdraw_surplus;
 pub use withdraw_surplus::*;
+mod close_vesting_balance;
 mod create_vesting_balance;
 
+pub use close_vesting_balance::*;
 pub use create_vesting_balance::*;
 
 pub mod transfer_vesting;

solana/programs/staking/src/contexts/transfer_vesting.rs

@@ -319,6 +319,11 @@ impl<'info> crate::contexts::TransferVesting<'info> {
                 .checked_add(self.vest.amount)
                 .ok_or(VestingError::Overflow)?,
             bump: new_vesting_balance_bump,
+            rent_payer: if self.new_vesting_balance.rent_payer == Pubkey::default() {
+                self.vester.key()
+            } else {
+                self.new_vesting_balance.rent_payer
+            },
         });
 
         self.vesting_balance.total_vesting_balance = self

solana/programs/staking/src/lib.rs

@@ -704,6 +704,11 @@ pub mod staking {
             .create_vesting_balance(ctx.bumps.vesting_balance)
     }
 
+    // Closes a vesting balance account
+    pub fn close_vesting_balance(ctx: Context<CloseVestingBalance>) -> Result<()> {
+        ctx.accounts.close_vesting_balance()
+    }
+
     // Finalize a Config, disabling any further creation or cancellation of Vesting accounts
     pub fn finalize_vesting_config(ctx: Context<Finalize>) -> Result<()> {
         ctx.accounts.finalize()

solana/programs/staking/src/state/vesting_balance.rs

@@ -9,6 +9,7 @@ pub struct VestingBalance {
     pub total_vesting_balance: u64,
     pub bump: u8,
     pub stake_account_metadata: Pubkey,
+    pub rent_payer: Pubkey,
 }
 
 impl VestingBalance {
@@ -21,6 +22,6 @@ pub mod tests {
 
     #[test]
     fn check_size() {
-        assert!(VestingBalance::LEN == 8 + 32 + 8 + 1 + 32); // 81
+        assert!(VestingBalance::LEN == 8 + 32 + 8 + 1 + 32 + 32); // 113
     }
 }