fixup! irmin-pack: update GC for chunked suffix

src/irmin-pack/unix/dispatcher.ml

@@ -85,18 +85,18 @@ module Make (Fm : File_manager.S with module Io = Io.Unix) :
 
   module Suffix_arithmetic = struct
     (* Adjust the read in suffix, as the global offset [off] is
-       [off] = [suffix_start_offset] + [suffix_offset]. *)
+       [off] = [suffix_start_offset] + [soff] - [suffix_dead_bytes]. *)
     let soff_of_off t off =
       let open Int63.Syntax in
       let suffix_start_offset = suffix_start_offset t in
       let suffix_dead_bytes = suffix_dead_bytes t in
       off - suffix_start_offset + suffix_dead_bytes
 
-    let off_of_soff t suffix_off =
+    let off_of_soff t soff =
       let open Int63.Syntax in
       let suffix_start_offset = suffix_start_offset t in
       let suffix_dead_bytes = suffix_dead_bytes t in
-      suffix_off - suffix_dead_bytes + suffix_start_offset
+      suffix_start_offset + soff - suffix_dead_bytes
   end
 
   let offset_of_soff = Suffix_arithmetic.off_of_soff

src/irmin-pack/unix/gc.ml

@@ -108,7 +108,7 @@ module Make (Args : Gc_args.S) = struct
       latest_gc_target_offset;
     }
 
-  let swap_and_purge t removable_chunk_num suffix =
+  let swap_and_purge t removable_chunk_num suffix_params =
     let open Result_syntax in
     let { generation; latest_gc_target_offset; _ } = t in
     let Worker.
@@ -117,13 +117,15 @@ module Make (Args : Gc_args.S) = struct
             chunk_start_idx;
             dead_bytes = suffix_dead_bytes;
           } =
-      suffix
+      suffix_params
     in
     (* Calculate chunk num in main process since more chunks could have been
        added while GC was running. GC process only tells us how many chunks are
        to be removed. *)
     let suffix = Fm.suffix t.fm in
     let chunk_num = Fm.Suffix.chunk_num suffix - removable_chunk_num in
+    (* Assert that we have at least one chunk (the appendable chunk), which
+       is guaranteed by the GC process. *)
     assert (chunk_num >= 1);
 
     let* () =
@@ -233,13 +235,16 @@ module Make (Args : Gc_args.S) = struct
             let open Result_syntax in
             match (status, gc_output) with
             | ( `Success,
-                Ok { suffix; removable_chunk_idxs; stats = worker_stats } ) ->
+                Ok { suffix_params; removable_chunk_idxs; stats = worker_stats }
+              ) ->
                 let partial_stats =
                   Gc_stats.Main.finish_current_step partial_stats
                     "swap and purge"
                 in
                 let* () =
-                  swap_and_purge t (List.length removable_chunk_idxs) suffix
+                  swap_and_purge t
+                    (List.length removable_chunk_idxs)
+                    suffix_params
                 in
                 let partial_stats =
                   Gc_stats.Main.finish_current_step partial_stats "unlink"

src/irmin-pack/unix/gc_worker.ml

@@ -118,15 +118,15 @@ module Make (Args : Gc_args.S) = struct
     stats := Gc_stats.Worker.add_file_size !stats "old_prefix" prefix_size;
     stats := Gc_stats.Worker.add_file_size !stats "old_mapping" mapping_size
 
-  type new_suffix = {
+  type suffix_params = {
     start_offset : int63;
     chunk_start_idx : int;
     dead_bytes : int63;
   }
   [@@deriving irmin]
 
   type gc_results = {
-    suffix : new_suffix;
+    suffix_params : suffix_params;
     removable_chunk_idxs : int list;
     stats : Stats.Latest_gc.worker;
   }
@@ -277,8 +277,8 @@ module Make (Args : Gc_args.S) = struct
         (Commit_value.parents commit)
     in
 
-    (* Step 6. Calculate new suffix values. *)
-    let new_suffix, removable_chunk_idxs =
+    (* Step 6. Calculate post-GC suffix parameters. *)
+    let suffix_params, removable_chunk_idxs =
       stats :=
         Gc_stats.Worker.finish_current_step !stats
           "suffix: calculate new values";
@@ -344,7 +344,7 @@ module Make (Args : Gc_args.S) = struct
 
     (* Step 7. Finalise stats and return. *)
     let stats = Gc_stats.Worker.finalise !stats in
-    { suffix = new_suffix; removable_chunk_idxs; stats }
+    { suffix_params; removable_chunk_idxs; stats }
 
   let write_gc_output ~root ~generation output =
     let open Result_syntax in

src/irmin-pack/unix/gc_worker.mli

@@ -25,15 +25,15 @@ module Make (Args : Gc_args.S) : sig
   val run_and_output_result :
     generation:int -> string -> Args.key -> int63 -> unit
 
-  type new_suffix = {
+  type suffix_params = {
     start_offset : int63;
     chunk_start_idx : int;
     dead_bytes : int63;
   }
   [@@deriving irmin]
 
   type gc_results = {
-    suffix : new_suffix;
+    suffix_params : suffix_params;
     removable_chunk_idxs : int list;
     stats : Stats.Latest_gc.worker;
   }

test/irmin-pack/test_gc.ml

@@ -923,28 +923,28 @@ module Split = struct
     let* () = S.Repo.close t.repo in
     S.Repo.close ro_t.repo
 
-  let c t s =
-    let h =
-      match Irmin.Type.(of_string Schema.Hash.t) s with
+  let load_commit t h =
+    let hash =
+      match Irmin.Type.(of_string Schema.Hash.t) h with
       | Error (`Msg s) -> Alcotest.failf "failed hash_of_string %s" s
-      | Ok h -> h
+      | Ok hash -> hash
     in
-    let+ c = S.Commit.of_hash t.repo h in
-    match c with
-    | None -> Alcotest.failf "Commit %s not found" s
+    let+ commit = S.Commit.of_hash t.repo hash in
+    match commit with
+    | None -> Alcotest.failf "Commit %s not found" h
     | Some commit -> commit
 
   let check_preexisting_commit t =
-    let s = "22e159de13b427226e5901defd17f0c14e744205" in
-    let* commit = c t s in
+    let h = "22e159de13b427226e5901defd17f0c14e744205" in
+    let* commit = load_commit t h in
     let tree = S.Commit.tree commit in
     let+ got = S.Tree.find tree [ "step-n01"; "step-b01" ] in
     Alcotest.(check (option string)) "find blob" (Some "b01") got
 
   let v3_migrated_store_splits_and_gc () =
     let root = create_test_env () in
     let* t = init ~readonly:false ~fresh:false ~root () in
-    let* c0 = c t "22e159de13b427226e5901defd17f0c14e744205" in
+    let* c0 = load_commit t "22e159de13b427226e5901defd17f0c14e744205" in
     let* t, c1 = commit_1 t in
     let () = S.split t.repo in
     let* t = checkout_exn t c1 in