fix: Preserve not_synchronized_on on shared dirs

  When a member of a sharing modifies a directory within this sharing
  then the `io.cozy.files` doc on the other members' Cozy will lose
  their `not_synchronized_on` attribute.

  This means the directory will get synchronized with their Desktop
  client again while they haven't modified the configuration themselves.

  This is because we forgot to keep the existing attribute when updating
  the document in the sharing indexer.

model/sharing/files_test.go

@@ -1,6 +1,7 @@
 package sharing
 
 import (
+	"strings"
 	"testing"
 	"time"
 
@@ -215,13 +216,22 @@ func TestFiles(t *testing.T) {
 			assert.Equal(t, "/Tree Shared with me/Test update dir/Foo", dir.Fullpath)
 		}
 
+		// Exclude dir from synchronization on a Desktop client
+		dir.NotSynchronizedOn = append(dir.NotSynchronizedOn,
+			couchdb.DocReference{ID: "ea24f891a41bf1f433460d20706d22c9", Type: "io.cozy.oauth.clients"},
+		)
+		err = couchdb.UpdateDoc(inst, dir)
+		require.NoError(t, err)
+		newTargetRev := strings.SplitN(dir.Rev(), "-", 2)[1]
+
 		target = map[string]interface{}{
 			"_id":  idFoo,
-			"_rev": "2-96c72d35f3ad802484a61df501b0f1bb",
+			"_rev": "3-96c72d35f3ad802484a61df501b0f1bb",
 			"_revisions": map[string]interface{}{
-				"start": float64(2),
+				"start": float64(3),
 				"ids": []interface{}{
 					"96c72d35f3ad802484a61df501b0f1bb",
+					newTargetRev,
 					"4fff5291a41bf1f493460d2070694c5a",
 				},
 			},
@@ -244,6 +254,7 @@ func TestFiles(t *testing.T) {
 			assert.Equal(t, "2018-04-13 15:06:00.012345678 +0100 +0100", dir.CreatedAt.String())
 			assert.Equal(t, "2018-04-13 15:10:57.364765745 +0100 +0100", dir.UpdatedAt.String())
 			assert.Equal(t, []string{"quux", "courge"}, dir.Tags)
+			assert.Equal(t, []couchdb.DocReference{{ID: "ea24f891a41bf1f433460d20706d22c9", Type: "io.cozy.oauth.clients"}}, dir.NotSynchronizedOn)
 		}
 	})
 

model/sharing/indexer.go

@@ -312,6 +312,9 @@ func (s *sharingIndexer) UpdateDirDoc(olddoc, doc *vfs.DirDoc) error {
 	if len(doc.ReferencedBy) > 0 {
 		docs[0][couchdb.SelectorReferencedBy] = doc.ReferencedBy
 	}
+	if len(doc.NotSynchronizedOn) > 0 {
+		docs[0]["not_synchronized_on"] = doc.NotSynchronizedOn
+	}
 	if doc.Metadata != nil {
 		docs[0]["metadata"] = doc.Metadata
 	}