UpdateRules: add TODOs

This logic turns out to be even more messy and buggy than it seems.

internal/buffer/buffer.go

@@ -690,6 +690,7 @@ func parseDefFromFile(f config.RuntimeFile, header *highlight.Header) *highlight
 	}
 
 	if header == nil {
+		// TODO: use faster highlight.MakeHeader() when possible
 		header, err = highlight.MakeHeaderYaml(data)
 		if err != nil {
 			screen.TermMessage("Error parsing header for syntax file " + f.Name() + ": " + err.Error())
@@ -926,6 +927,7 @@ func (b *Buffer) UpdateRules() {
 		includes := highlight.GetIncludes(b.SyntaxDef)
 
 		var files []*highlight.File
+		// TODO: search in the user's custom syntax files first
 		for _, f := range config.ListRuntimeFiles(config.RTSyntax) {
 			data, err := f.Data()
 			if err != nil {
@@ -950,6 +952,8 @@ func (b *Buffer) UpdateRules() {
 					break
 				}
 			}
+			// TODO: fix this mess. For each include, we should include
+			// exactly one file: either a built-in one or a user's custom one
 			if len(files) >= len(includes) {
 				break
 			}