Function getfpfunc 

pub fn getfpfunc(
    name: &str,
    dir_path_out: &mut Option<String>,
    spec_path: Option<&[String]>,
    _all_loaded: i32,
) -> Option<String>

Port of getfpfunc(char *s, int *ksh, char **fdir, char **alt_path, int test_only) from Src/exec.c:5260. Walks $fpath (or the supplied spec_path slice) for a file named name and writes the resolved directory through *dir_path_out (matching the C char **dir_path). Returns Some(file_contents_path) on success, None when not found.