sync: overlap check is now filter-sensitive

Previously, the overlap check was based on simple prefix checks of the source and destination paths. Now it actually checks whether the destination is excluded via any filter rule or a "--exclude-if-present"-file.

fs/operations/operations.go

@@ -796,6 +796,47 @@ func Overlapping(fdst, fsrc fs.Info) bool {
 	return strings.HasPrefix(fdstRoot, fsrcRoot) || strings.HasPrefix(fsrcRoot, fdstRoot)
 }
 
+// OverlappingFilterCheck returns true if fdst and fsrc point to the same
+// underlying Fs and they overlap without fdst being excluded by any filter rule.
+func OverlappingFilterCheck(ctx context.Context, fdst fs.Fs, fsrc fs.Fs) bool {
+	if !SameConfig(fdst, fsrc) {
+		return false
+	}
+	fdstRoot := fixRoot(fdst)
+	fsrcRoot := fixRoot(fsrc)
+	if strings.HasPrefix(fdstRoot, fsrcRoot) {
+		fdstRelative := fdstRoot[len(fsrcRoot):]
+		return filterCheckR(ctx, fdstRelative, 0, fsrc)
+	}
+	return strings.HasPrefix(fsrcRoot, fdstRoot)
+}
+
+// filterCheckR checks if fdst would be included in the sync
+func filterCheckR(ctx context.Context, fdstRelative string, pos int, fsrc fs.Fs) bool {
+	include := true
+	fi := filter.GetConfig(ctx)
+	includeDirectory := fi.IncludeDirectory(ctx, fsrc)
+	dirs := strings.SplitAfterN(fdstRelative, "/", pos+2)
+	newPath := ""
+	for i := 0; i <= pos; i++ {
+		newPath += dirs[i]
+	}
+	if !strings.HasSuffix(newPath, "/") {
+		newPath += "/"
+	}
+	if strings.HasPrefix(fdstRelative, newPath) {
+		include, _ = includeDirectory(newPath)
+		if include {
+			if newPath == fdstRelative {
+				return true
+			}
+			pos++
+			include = filterCheckR(ctx, fdstRelative, pos, fsrc)
+		}
+	}
+	return include
+}
+
 // SameDir returns true if fdst and fsrc point to the same
 // underlying Fs and they are the same directory.
 func SameDir(fdst, fsrc fs.Info) bool {