scanner: Allow disabling weak hash in scanning (fixes #3891)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3905

lib/scanner/walk.go

@@ -72,6 +72,8 @@ type Config struct {
 	ProgressTickIntervalS int
 	// Signals cancel from the outside - when closed, we should stop walking.
 	Cancel chan struct{}
+	// Wether or not we should also compute weak hashes
+	UseWeakHashes bool
 }
 
 type CurrentFiler interface {
@@ -129,7 +131,7 @@ func (w *walker) walk() (chan protocol.FileInfo, error) {
 	// We're not required to emit scan progress events, just kick off hashers,
 	// and feed inputs directly from the walker.
 	if w.ProgressTickIntervalS < 0 {
-		newParallelHasher(w.Dir, w.BlockSize, w.Hashers, finishedChan, toHashChan, nil, nil, w.Cancel)
+		newParallelHasher(w.Dir, w.BlockSize, w.Hashers, finishedChan, toHashChan, nil, nil, w.Cancel, w.UseWeakHashes)
 		return finishedChan, nil
 	}
 
@@ -160,7 +162,7 @@ func (w *walker) walk() (chan protocol.FileInfo, error) {
 		done := make(chan struct{})
 		progress := newByteCounter()
 
-		newParallelHasher(w.Dir, w.BlockSize, w.Hashers, finishedChan, realToHashChan, progress, done, w.Cancel)
+		newParallelHasher(w.Dir, w.BlockSize, w.Hashers, finishedChan, realToHashChan, progress, done, w.Cancel, w.UseWeakHashes)
 
 		// A routine which actually emits the FolderScanProgress events
 		// every w.ProgressTicker ticks, until the hasher routines terminate.