posixExecv

fn posixExecv(
    arg0_expand: process.ArgExpansion,
    file: [*:0]const u8,
    child_argv: [*:null]?[*:0]const u8,
    env_block: process.Environ.PosixBlock,
    PATH: []const u8,
) process.ReplaceError {
    const file_slice = std.mem.sliceTo(file, 0);
    if (std.mem.findScalar(u8, file_slice, '/') != null) return posixExecvPath(file, child_argv, env_block);

    // Use of PATH_MAX here is valid as the path_buf will be passed
    // directly to the operating system in posixExecvPath.
    var path_buf: [posix.PATH_MAX]u8 = undefined;
    var it = std.mem.tokenizeScalar(u8, PATH, ':');
    var seen_eacces = false;
    var err: process.ReplaceError = error.FileNotFound;

    // In case of expanding arg0 we must put it back if we return with an error.
    const prev_arg0 = child_argv[0];
    defer switch (arg0_expand) {
        .expand => child_argv[0] = prev_arg0,
        .no_expand => {},
    };

    while (it.next()) |search_path| {
        const path_len = search_path.len + file_slice.len + 1;
        if (path_buf.len < path_len + 1) return error.NameTooLong;
        @memcpy(path_buf[0..search_path.len], search_path);
        path_buf[search_path.len] = '/';
        @memcpy(path_buf[search_path.len + 1 ..][0..file_slice.len], file_slice);
        path_buf[path_len] = 0;
        const full_path = path_buf[0..path_len :0].ptr;
        switch (arg0_expand) {
            .expand => child_argv[0] = full_path,
            .no_expand => {},
        }
        err = posixExecvPath(full_path, child_argv, env_block);
        switch (err) {
            error.AccessDenied => seen_eacces = true,
            error.FileNotFound, error.NotDir => {},
            else => |e| return e,
        }
    }
    if (seen_eacces) return error.AccessDenied;
    return err;
}