public String groomQualifiedFileName(String outputDir, String fileName) {
        if (outputDir.equals(".")) {
            return fileName;
        }
		else if (outputDir.indexOf(' ') >= 0) { // has spaces?
            String escSpaces = outputDir.replace(" ", "\\ ");
            return escSpaces + File.separator + fileName;
        }
		else {
            return outputDir + File.separator + fileName;
        }
    }
Return a list of File objects that name files ANTLR will read
to process T.g; This can only be .tokens files and only
if they use the tokenVocab option.

@return List of dependencies other than imported grammars
tool/src/org/antlr/v4/tool/BuildDependencyGenerator.java