repository: Do not report ignored packs in EachByPack

Ignored packs were reported as an empty pack by EachByPack. The most
immediate effect of this is that the progress bar for rebuilding the
index reports processing more packs than actually exist.

internal/repository/index.go

@@ -276,10 +276,10 @@ func (idx *Index) EachByPack(ctx context.Context, packBlacklist restic.IDSet) <-
 			m := &idx.byType[typ]
 			m.foreach(func(e *indexEntry) bool {
 				packID := idx.packs[e.packIndex]
-				if _, ok := byPack[packID]; !ok {
-					byPack[packID] = make([][]*indexEntry, restic.NumBlobTypes)
-				}
 				if !idx.final || !packBlacklist.Has(packID) {
+					if _, ok := byPack[packID]; !ok {
+						byPack[packID] = make([][]*indexEntry, restic.NumBlobTypes)
+					}
 					byPack[packID][typ] = append(byPack[packID][typ], e)
 				}
 				return true

internal/repository/index_test.go

@@ -613,3 +613,37 @@ func TestMixedEachByPack(t *testing.T) {
 	}
 	rtest.Equals(t, expected, reported)
 }
+
+func TestEachByPackIgnoes(t *testing.T) {
+	idx := repository.NewIndex()
+
+	ignores := restic.NewIDSet()
+	expected := make(map[restic.ID]int)
+	// create 50 packs with one blob each
+	for i := 0; i < 50; i++ {
+		packID := restic.NewRandomID()
+		if i < 3 {
+			ignores.Insert(packID)
+		} else {
+			expected[packID] = 1
+		}
+		blobs := []restic.Blob{
+			{
+				BlobHandle: restic.BlobHandle{Type: restic.DataBlob, ID: restic.NewRandomID()},
+				Offset:     0,
+				Length:     42,
+			},
+		}
+		idx.StorePack(packID, blobs)
+	}
+	idx.Finalize()
+
+	reported := make(map[restic.ID]int)
+	for bp := range idx.EachByPack(context.TODO(), ignores) {
+		reported[bp.PackID]++
+		rtest.Equals(t, 1, len(bp.Blobs)) // correct blob count
+		b0 := bp.Blobs[0]
+		rtest.Assert(t, b0.Type == restic.DataBlob && b0.Offset == 0 && b0.Length == 42, "wrong blob", b0)
+	}
+	rtest.Equals(t, expected, reported)
+}