Function describe_symbol_cross_file 

pub fn describe_symbol_cross_file(
    files: &HashMap<PathBuf, String>,
    current_uri: &Url,
    name: &str,
) -> Option<(Url, String)>

Markdown hover content for name from any project file other than current_uri, plus the URI of the file that contributed it. See bynk_ide::symbols::describe_symbol_cross_file for the pure logic.