Better logging when backfilling ancient blocks fail (#10796)

* Better logging when backfilling ancient blocks fail
Print total blocks imported, closes #10792

* `finalize()` doesn't need Engine
Pull out call to migrated_blocks() from replace_client_db()

* More logs

* Clarify that the percentage may be misleading

* Remove replace_client_db() and replace with a straight call to restore_db()

* Include the parent_hash in UnlinkedAncientBlockChain errors

* Add a new RestorationStatus varian: Finalizing (as it can take a loooong while)
Call abort_restore() when restoration fails

* Add missing cases for new variant

* typos

* Typo and derive Debug

* Do not attempt to salvage existing blocks unless they form a complete chain back to genesis

* Fix test

* Revert "Fix test"

This reverts commit f027d4b4cb7b6c23fceec528c1711886ba9cfe4e.

* Fix test again

* Update comment

* Be careful about locks

* fix test failure

* Do not defer returning an error when the chain is broken

* Review feedback

* no hex formatting for Option

parity/informant.rs

@@ -319,9 +319,16 @@ impl<T: InformantData> Informant<T> {
 								RestorationStatus::Ongoing { state_chunks, block_chunks, state_chunks_done, block_chunks_done } => {
 									format!("Syncing snapshot {}/{}", state_chunks_done + block_chunks_done, state_chunks + block_chunks)
 								},
-								RestorationStatus::Initializing { chunks_done } => {
-									format!("Snapshot initializing ({} chunks restored)", chunks_done)
+								RestorationStatus::Initializing { chunks_done, state_chunks, block_chunks } => {
+									let total_chunks = state_chunks + block_chunks;
+									// Note that the percentage here can be slightly misleading when
+									// they have chunks already on disk: we'll import the local
+									// chunks first and then download the rest.
+									format!("Snapshot initializing ({}/{} chunks restored, {:.0}%)", chunks_done, total_chunks, (chunks_done as f32 / total_chunks as f32) * 100.0)
 								},
+								RestorationStatus::Finalizing => {
+									format!("Snapshot finalization under way")
+								}
 								_ => String::new(),
 							}
 						)

parity/snapshot.rs

@@ -123,6 +123,7 @@ fn restore_using<R: SnapshotReader>(snapshot: Arc<SnapshotService>, reader: &R,
 	match snapshot.status() {
 		RestorationStatus::Ongoing { .. } => Err("Snapshot file is incomplete and missing chunks.".into()),
 		RestorationStatus::Initializing { .. } => Err("Snapshot restoration is still initializing.".into()),
+		RestorationStatus::Finalizing => Err("Snapshot restoration is still finalizing.".into()),
 		RestorationStatus::Failed => Err("Snapshot restoration failed.".into()),
 		RestorationStatus::Inactive => {
 			info!("Restoration complete.");