Function unique_php_source_namespace 

fn unique_php_source_namespace<'a>(
    graph: &'a SymbolGraph,
    symbol_index: &GraphSymbolIndex<'_>,
    source_parent: Option<&str>,
    relation: &SymbolRelation,
    control: &IndexWorkControl,
) -> Result<Option<&'a str>, CliError>

Prove a PHP caller’s namespace, including the empty global namespace.