lib/model: More precise deletion detection (fixes #2571, fixes #4573) (#4765)

lib/model/model.go

@@ -2044,33 +2044,32 @@ func (m *Model) internalScanFolderSubdirs(ctx context.Context, folder string, su
 				batchSizeBytes += nf.ProtoSize()
 				changes++
 
+			case f.IsInvalid() && !ignores.Match(f.Name).IsIgnored():
+				// Successfully scanned items are already un-ignored during
+				// the scan, so check whether it is deleted.
+				fallthrough
 			case !f.IsInvalid() && !f.IsDeleted():
 				// The file is valid and not deleted. Lets check if it's
 				// still here.
-
-				if _, err := mtimefs.Lstat(f.Name); err != nil {
-					// We don't specifically verify that the error is
-					// fs.IsNotExist because there is a corner case when a
-					// directory is suddenly transformed into a file. When that
-					// happens, files that were in the directory (that is now a
-					// file) are deleted but will return a confusing error ("not a
-					// directory") when we try to Lstat() them.
-
-					nf := protocol.FileInfo{
-						Name:       f.Name,
-						Type:       f.Type,
-						Size:       0,
-						ModifiedS:  f.ModifiedS,
-						ModifiedNs: f.ModifiedNs,
-						ModifiedBy: m.id.Short(),
-						Deleted:    true,
-						Version:    f.Version.Update(m.shortID),
-					}
-
-					batch = append(batch, nf)
-					batchSizeBytes += nf.ProtoSize()
-					changes++
+				// Simply stating it wont do as there are tons of corner
+				// cases (e.g. parent dir->simlink, missing permissions)
+				if !osutil.IsDeleted(mtimefs, f.Name) {
+					return true
 				}
+				nf := protocol.FileInfo{
+					Name:       f.Name,
+					Type:       f.Type,
+					Size:       0,
+					ModifiedS:  f.ModifiedS,
+					ModifiedNs: f.ModifiedNs,
+					ModifiedBy: m.id.Short(),
+					Deleted:    true,
+					Version:    f.Version.Update(m.shortID),
+				}
+
+				batch = append(batch, nf)
+				batchSizeBytes += nf.ProtoSize()
+				changes++
 			}
 			return true
 		})