Add the DomainBlockDescendants storage item to pallet-domains

This storage item is used to keek track of the immediate descendants of an
ER, it is used during fraud proof processing to prune all the descendants of
the targetted fraudulent ER. This storage item can be removed after this task
#1731 is implemented, by then every
ER should only have one immediate descendant

Signed-off-by: linning <linningde25@gmail.com>

crates/pallet-domains/src/block_tree.rs

@@ -2,8 +2,8 @@
 
 use crate::pallet::StateRoots;
 use crate::{
-    BalanceOf, BlockTree, Config, ConsensusBlockHash, DomainBlocks, ExecutionInbox,
-    ExecutionReceiptOf, HeadReceiptNumber, InboxedBundle,
+    BalanceOf, BlockTree, Config, ConsensusBlockHash, DomainBlockDescendants, DomainBlocks,
+    ExecutionInbox, ExecutionReceiptOf, HeadReceiptNumber, InboxedBundle,
 };
 use codec::{Decode, Encode};
 use frame_support::{ensure, PalletError};
@@ -257,18 +257,19 @@ pub(crate) fn process_execution_receipt<T: Config>(
                     return Err(Error::MultipleERsAfterChallengePeriod);
                 }
 
-                let receipt = receipts_at_number
+                let receipt_hash = receipts_at_number
                     .first()
                     .cloned()
                     .expect("should always have a value due to check above");
 
                 let domain_block =
-                    DomainBlocks::<T>::take(receipt).ok_or(Error::MissingDomainBlock)?;
+                    DomainBlocks::<T>::take(receipt_hash).ok_or(Error::MissingDomainBlock)?;
                 _ = StateRoots::<T>::take((
                     domain_id,
                     domain_block.execution_receipt.domain_block_number,
                     domain_block.execution_receipt.domain_block_hash,
                 ));
+                _ = DomainBlockDescendants::<T>::take(receipt_hash);
 
                 // Remove the block's `ExecutionInbox` and `InboxedBundle` as the block is pruned and
                 // does not need to verify its receipt's `extrinsics_root` anymore.
@@ -323,13 +324,19 @@ fn add_new_receipt_to_block_tree<T: Config>(
         execution_receipt.final_state_root,
     );
 
+    BlockTree::<T>::mutate(domain_id, domain_block_number, |er_hashes| {
+        er_hashes.insert(er_hash);
+    });
+    DomainBlockDescendants::<T>::mutate(
+        execution_receipt.parent_domain_block_receipt_hash,
+        |er_hashes| {
+            er_hashes.insert(er_hash);
+        },
+    );
     let domain_block = DomainBlock {
         execution_receipt,
         operator_ids: sp_std::vec![submitter],
     };
-    BlockTree::<T>::mutate(domain_id, domain_block_number, |er_hashes| {
-        er_hashes.insert(er_hash);
-    });
     DomainBlocks::<T>::insert(er_hash, domain_block);
 }
 
@@ -631,6 +638,7 @@ mod tests {
                 pruned_receipt.consensus_block_number,
             )
             .is_none());
+            assert!(DomainBlockDescendants::<Test>::get(pruned_receipt.hash()).is_empty());
         });
     }
 

crates/pallet-domains/src/lib.rs

@@ -447,6 +447,13 @@ mod pallet {
         OptionQuery,
     >;
 
+    // Mapping of the parent ER to all its immediate descendants ER
+    // TODO: remove this mapping once https://github.com/subspace/subspace/issues/1731 is implemented
+    // by then every parent ER should only have one immediate descendants ER
+    #[pallet::storage]
+    pub(super) type DomainBlockDescendants<T: Config> =
+        StorageMap<_, Identity, ReceiptHash, BTreeSet<ReceiptHash>, ValueQuery>;
+
     /// The head receipt number of each domain
     #[pallet::storage]
     pub(super) type HeadReceiptNumber<T: Config> =