index: remove supersedes field

Using the field with its current semantics is nearly impossible to get
right. Remove it as it will be replaced anyways in repository format 3.

internal/index/index.go

@@ -50,10 +50,9 @@ type Index struct {
 	byType [restic.NumBlobTypes]indexMap
 	packs  restic.IDs
 
-	final      bool       // set to true for all indexes read from the backend ("finalized")
-	ids        restic.IDs // set to the IDs of the contained finalized indexes
-	supersedes restic.IDs
-	created    time.Time
+	final   bool       // set to true for all indexes read from the backend ("finalized")
+	ids     restic.IDs // set to the IDs of the contained finalized indexes
+	created time.Time
 }
 
 // NewIndex returns a new index.
@@ -197,25 +196,6 @@ func (idx *Index) LookupSize(bh restic.BlobHandle) (plaintextLength uint, found
 	return uint(crypto.PlaintextLength(int(e.length))), true
 }
 
-// Supersedes returns the list of indexes this index supersedes, if any.
-func (idx *Index) Supersedes() restic.IDs {
-	return idx.supersedes
-}
-
-// AddToSupersedes adds the ids to the list of indexes superseded by this
-// index. If the index has already been finalized, an error is returned.
-func (idx *Index) AddToSupersedes(ids ...restic.ID) error {
-	idx.m.Lock()
-	defer idx.m.Unlock()
-
-	if idx.final {
-		return errors.New("index already finalized")
-	}
-
-	idx.supersedes = append(idx.supersedes, ids...)
-	return nil
-}
-
 // Each passes all blobs known to the index to the callback fn. This blocks any
 // modification of the index.
 func (idx *Index) Each(ctx context.Context, fn func(restic.PackedBlob)) error {
@@ -356,8 +336,8 @@ func (idx *Index) generatePackList() ([]packJSON, error) {
 }
 
 type jsonIndex struct {
-	Supersedes restic.IDs `json:"supersedes,omitempty"`
-	Packs      []packJSON `json:"packs"`
+	// removed: Supersedes restic.IDs `json:"supersedes,omitempty"`
+	Packs []packJSON `json:"packs"`
 }
 
 // Encode writes the JSON serialization of the index to the writer w.
@@ -373,8 +353,7 @@ func (idx *Index) Encode(w io.Writer) error {
 
 	enc := json.NewEncoder(w)
 	idxJSON := jsonIndex{
-		Supersedes: idx.supersedes,
-		Packs:      list,
+		Packs: list,
 	}
 	return enc.Encode(idxJSON)
 }
@@ -433,8 +412,7 @@ func (idx *Index) Dump(w io.Writer) error {
 	}
 
 	outer := jsonIndex{
-		Supersedes: idx.Supersedes(),
-		Packs:      list,
+		Packs: list,
 	}
 
 	buf, err := json.MarshalIndent(outer, "", "  ")
@@ -495,7 +473,6 @@ func (idx *Index) merge(idx2 *Index) error {
 	}
 
 	idx.ids = append(idx.ids, idx2.ids...)
-	idx.supersedes = append(idx.supersedes, idx2.supersedes...)
 
 	return nil
 }
@@ -545,7 +522,6 @@ func DecodeIndex(buf []byte, id restic.ID) (idx *Index, oldFormat bool, err erro
 			})
 		}
 	}
-	idx.supersedes = idxJSON.Supersedes
 	idx.ids = append(idx.ids, id)
 	idx.final = true
 

internal/index/index_test.go

@@ -309,8 +309,6 @@ func TestIndexUnserialize(t *testing.T) {
 		{docExampleV1, 1},
 		{docExampleV2, 2},
 	} {
-		oldIdx := restic.IDs{restic.TestParseID("ed54ae36197f4745ebc4b54d10e0f623eaaaedd03013eb7ae90df881b7781452")}
-
 		idx, oldFormat, err := index.DecodeIndex(task.idxBytes, restic.NewRandomID())
 		rtest.OK(t, err)
 		rtest.Assert(t, !oldFormat, "new index format recognized as old format")
@@ -337,8 +335,6 @@ func TestIndexUnserialize(t *testing.T) {
 			}
 		}
 
-		rtest.Equals(t, oldIdx, idx.Supersedes())
-
 		blobs := listPack(t, idx, exampleLookupTest.packID)
 		if len(blobs) != len(exampleLookupTest.blobs) {
 			t.Fatalf("expected %d blobs in pack, got %d", len(exampleLookupTest.blobs), len(blobs))
@@ -446,8 +442,6 @@ func TestIndexUnserializeOld(t *testing.T) {
 		rtest.Equals(t, test.offset, blob.Offset)
 		rtest.Equals(t, test.length, blob.Length)
 	}
-
-	rtest.Equals(t, 0, len(idx.Supersedes()))
 }
 
 func TestIndexPacks(t *testing.T) {

internal/index/master_index.go

@@ -332,7 +332,7 @@ func (mi *MasterIndex) Save(ctx context.Context, repo restic.SaverRemoverUnpacke
 	debug.Log("start rebuilding index of %d indexes, excludePacks: %v", len(mi.idx), excludePacks)
 
 	newIndex := NewIndex()
-	obsolete := restic.NewIDSet()
+	obsolete := restic.NewIDSet(extraObsolete...)
 
 	// track spawned goroutines using wg, create a new context which is
 	// cancelled as soon as an error occurs.
@@ -351,11 +351,6 @@ func (mi *MasterIndex) Save(ctx context.Context, repo restic.SaverRemoverUnpacke
 				}
 
 				debug.Log("adding index ids %v to supersedes field", ids)
-
-				err = newIndex.AddToSupersedes(ids...)
-				if err != nil {
-					return err
-				}
 				obsolete.Merge(restic.NewIDSet(ids...))
 			} else {
 				debug.Log("index %d isn't final, don't add to supersedes field", i)
@@ -380,12 +375,6 @@ func (mi *MasterIndex) Save(ctx context.Context, repo restic.SaverRemoverUnpacke
 			}
 		}
 
-		err := newIndex.AddToSupersedes(extraObsolete...)
-		if err != nil {
-			return err
-		}
-		obsolete.Merge(restic.NewIDSet(extraObsolete...))
-
 		select {
 		case ch <- newIndex:
 		case <-wgCtx.Done():