public List<File> getDependenciesFileList() {
        // Find all the things other than imported grammars
        List<File> files = getNonImportDependenciesFileList();

        // Handle imported grammars
        List<Grammar> imports = g.getAllImportedGrammars();
        if ( imports!=null ) {
			for (Grammar g : imports) {
				String libdir = tool.libDirectory;
				String fileName = groomQualifiedFileName(libdir, g.fileName);
				files.add(new File(fileName));
			}
		}

        if (files.isEmpty()) {
            return null;
        }
        return files;
    }
Return a list of File objects that name files ANTLR will read
to process T.g; This can be .tokens files if the grammar uses the tokenVocab option
as well as any imported grammar files.
tool/src/org/antlr/v4/tool/BuildDependencyGenerator.java