fix(quasar/compression): unwrap RemainingAccount to AccountView

Newer quasar-lang (post-PR-solana-developers#195 era) changed RemainingAccounts::iter() to
yield Result<RemainingAccount, _> instead of Result<AccountView, _>, so the
existing 'proof_views[i] = result?' assignments stopped compiling.

RemainingAccount is a safe wrapper around AccountView. We only need the
inner view to forward to the bubblegum / spl-account-compression CPI as
read-only proof nodes (no data borrows, no aliasing risk), so reach for
'as_account_view_unchecked' inside an unsafe block.

Affects:
- compression/cnft-burn/quasar (burn CPI proof nodes)
- compression/cnft-vault/quasar (withdraw / withdraw_two transfer CPI)
- compression/cutils/quasar (verify_leaf CPI)

Author: mikemaccana-edwardbot

compression/cnft-burn/quasar/src/instructions/burn_cnft.rs

@@ -43,7 +43,12 @@ pub fn handle_burn_cnft(accounts: &mut BurnCnft, data: &[u8], remaining: Remaini
     ix_data[0..8].copy_from_slice(&BURN_DISCRIMINATOR);
     ix_data[8..116].copy_from_slice(&data[0..108]);
 
-    // Collect remaining accounts (proof nodes) into a stack buffer
+    // Collect remaining accounts (proof nodes) into a stack buffer.
+    //
+    // `remaining.iter()` yields `Result<RemainingAccount, _>` in newer
+    // quasar-lang. Reach the inner `AccountView` via the unchecked accessor
+    // — this CPI only reads proof addresses and views, never touching the
+    // accounts' data, so the aliasing/borrow invariants are upheld.
     let placeholder = accounts.system_program.to_account_view().clone();
     let mut proof_views: [AccountView; MAX_PROOF_NODES] =
         core::array::from_fn(|_| placeholder.clone());
@@ -52,7 +57,10 @@ pub fn handle_burn_cnft(accounts: &mut BurnCnft, data: &[u8], remaining: Remaini
         if proof_count >= MAX_PROOF_NODES {
             break;
         }
-        proof_views[proof_count] = result?;
+        let account = result?;
+        // SAFETY: We only read the AccountView's address and pass an immutable
+        // view to the bubblegum CPI as a proof node; no aliased data access.
+        proof_views[proof_count] = unsafe { account.as_account_view_unchecked() }.clone();
         proof_count += 1;
     }
 

compression/cnft-vault/quasar/src/instructions/withdraw.rs

@@ -50,7 +50,12 @@ pub fn handle_withdraw_cnft(accounts: &mut Withdraw, data: &[u8], remaining: Rem
 
     let ix_data = build_transfer_data(&data[0..TRANSFER_ARGS_LEN]);
 
-    // Collect proof nodes
+    // Collect proof nodes.
+    //
+    // `remaining.iter()` yields `Result<RemainingAccount, _>` in newer
+    // quasar-lang. Reach the inner `AccountView` via the unchecked accessor
+    // — we only read addresses/views to forward to the bubblegum CPI as
+    // proof nodes; no aliased data access.
     let placeholder = accounts.system_program.to_account_view().clone();
     let mut proof_views: [AccountView; MAX_PROOF_NODES] =
         core::array::from_fn(|_| placeholder.clone());
@@ -59,7 +64,9 @@ pub fn handle_withdraw_cnft(accounts: &mut Withdraw, data: &[u8], remaining: Rem
         if proof_count >= MAX_PROOF_NODES {
             break;
         }
-        proof_views[proof_count] = result?;
+        let account = result?;
+        // SAFETY: Only reads address and forwards an immutable view to CPI.
+        proof_views[proof_count] = unsafe { account.as_account_view_unchecked() }.clone();
         proof_count += 1;
     }
 

compression/cnft-vault/quasar/src/instructions/withdraw_two.rs

@@ -65,7 +65,12 @@ pub fn handle_withdraw_two_cnfts(accounts: &mut WithdrawTwo, data: &[u8], remain
     ];
     let signer = Signer::from(&seeds as &[Seed]);
 
-    // Collect all remaining accounts (proof1 ++ proof2)
+    // Collect all remaining accounts (proof1 ++ proof2).
+    //
+    // `remaining.iter()` yields `Result<RemainingAccount, _>` in newer
+    // quasar-lang. Reach the inner `AccountView` via the unchecked accessor
+    // — we only read addresses/views to forward to the bubblegum CPIs as
+    // proof nodes; no aliased data access.
     let placeholder = accounts.system_program.to_account_view().clone();
     let mut all_proofs: [AccountView; MAX_PROOF_NODES * 2] =
         core::array::from_fn(|_| placeholder.clone());
@@ -74,7 +79,9 @@ pub fn handle_withdraw_two_cnfts(accounts: &mut WithdrawTwo, data: &[u8], remain
         if total_proofs >= MAX_PROOF_NODES * 2 {
             break;
         }
-        all_proofs[total_proofs] = result?;
+        let account = result?;
+        // SAFETY: Only reads address and forwards an immutable view to CPI.
+        all_proofs[total_proofs] = unsafe { account.as_account_view_unchecked() }.clone();
         total_proofs += 1;
     }
 

compression/cutils/quasar/src/instructions/verify.rs

@@ -55,7 +55,12 @@ pub fn handle_verify(accounts: &mut Verify, data: &[u8], remaining: RemainingAcc
     ix_data[40..72].copy_from_slice(&leaf_hash);
     ix_data[72..76].copy_from_slice(&index.to_le_bytes());
 
-    // Collect proof nodes
+    // Collect proof nodes.
+    //
+    // `remaining.iter()` yields `Result<RemainingAccount, _>` in newer
+    // quasar-lang. Reach the inner `AccountView` via the unchecked accessor
+    // — we only read addresses/views to forward to the compression CPI as
+    // proof nodes; no aliased data access.
     let placeholder = accounts.compression_program.to_account_view().clone();
     let mut proof_views: [AccountView; MAX_PROOF_NODES] =
         core::array::from_fn(|_| placeholder.clone());
@@ -64,7 +69,9 @@ pub fn handle_verify(accounts: &mut Verify, data: &[u8], remaining: RemainingAcc
         if proof_count >= MAX_PROOF_NODES {
             break;
         }
-        proof_views[proof_count] = result?;
+        let account = result?;
+        // SAFETY: Only reads address and forwards an immutable view to CPI.
+        proof_views[proof_count] = unsafe { account.as_account_view_unchecked() }.clone();
         proof_count += 1;
     }