rebar3/bootstrap

#!/usr/bin/env escript
%% -*- mode: erlang;erlang-indent-level: 4;indent-tabs-mode: nil -*-
%% ex: ft=erlang ts=4 sw=4 et

main(_) ->
    application:start(crypto),
    application:start(asn1),
    application:start(public_key),
    application:start(ssl),
    inets:start(),
    inets:start(httpc, [{profile, rebar}]),
    set_httpc_options(),

    %% Fetch and build deps required to build rebar3
    BaseDeps = [{providers, []}
               ,{getopt, []}
               ,{cf, []}
               ,{erlware_commons, ["ec_dictionary.erl", "ec_vsn.erl"]}
               ,{certifi, ["certifi_pt.erl"]}],
    Deps = get_deps(),
    [fetch_and_compile(Dep, Deps) || Dep <- BaseDeps],

    %% Build rebar3 modules with compile:file
    bootstrap_rebar3(),

    %% Build rebar.app from rebar.app.src
    {ok, App} = rebar_app_info:new(rebar, "3.5.0", filename:absname("_build/default/lib/rebar/")),
    rebar_otp_app:compile(rebar_state:new(), App),

    %% Because we are compiling files that are loaded already we want to silence
    %% not_purged errors in rebar_erlc_compiler:opts_changed/1
    error_logger:tty(false),

    setup_env(),
    os:putenv("REBAR_PROFILE", "bootstrap"),
    RegistryFile = default_registry_file(),
    case filelib:is_file(RegistryFile) of
        true ->
            ok;
        false ->
            rebar3:run(["update"])
    end,

    {ok, State} = rebar3:run(["compile"]),
    reset_env(),
    os:putenv("REBAR_PROFILE", ""),

    DepsPaths = rebar_state:code_paths(State, all_deps),
    code:add_pathsa(DepsPaths),

    rebar3:run(["clean", "-a"]),
    rebar3:run(["as", "prod", "escriptize"]),

    %% Done with compile, can turn back on error logger
    error_logger:tty(true).

default_registry_file() ->
    {ok, [[Home]]} = init:get_argument(home),
    CacheDir = filename:join([Home, ".cache", "rebar3"]),
    filename:join([CacheDir, "hex", "default", "registry"]).

fetch_and_compile({Name, ErlFirstFiles}, Deps) ->
    case lists:keyfind(Name, 1, Deps) of
        {Name, Vsn} ->
            ok = fetch({pkg, atom_to_binary(Name, utf8), list_to_binary(Vsn)}, Name);
        {Name, _, Source} ->
            ok = fetch(Source, Name)
    end,

    %% Hack: erlware_commons depends on a .script file to check if it is being built with
    %% rebar2 or rebar3. But since rebar3 isn't built yet it can't get the vsn with get_key.
    %% So we simply make sure that file is deleted before compiling
    file:delete("_build/default/lib/erlware_commons/rebar.config.script"),

    compile(Name, ErlFirstFiles).

fetch({pkg, Name, Vsn}, App) ->
    Dir = filename:join([filename:absname("_build/default/lib/"), App]),
    case filelib:is_dir(Dir) of
        false ->
            CDN = "https://repo.hex.pm/tarballs",
            Package = binary_to_list(<<Name/binary, "-", Vsn/binary, ".tar">>),
            Url = join([CDN, Package], "/"),
            case request(Url) of
                {ok, Binary} ->
                    {ok, Contents} = extract(Binary),
                    ok = erl_tar:extract({binary, Contents}, [{cwd, Dir}, compressed]);
                {error, {Reason, _}} ->
                    ReasonText = re:replace(atom_to_list(Reason), "_", " ", [global,{return,list}]),
                    io:format("Error: Unable to fetch package ~s ~s: ~s~n", [Name, Vsn, ReasonText])
            end;
        true ->
            io:format("Dependency ~s already exists~n", [Name])
    end.

extract(Binary) ->
    {ok, Files} = erl_tar:extract({binary, Binary}, [memory]),
    {"contents.tar.gz", Contents} = lists:keyfind("contents.tar.gz", 1, Files),
    {ok, Contents}.

request(Url) ->
    HttpOptions = [{relaxed, true} | get_proxy_auth()],

    case httpc:request(get, {Url, []},
                       HttpOptions,
                       [{body_format, binary}],
                       rebar) of
        {ok, {{_Version, 200, _Reason}, _Headers, Body}} ->
            {ok, Body};
        Error ->
            Error
    end.

get_rebar_config() ->
    {ok, [[Home]]} = init:get_argument(home),
    ConfDir = filename:join(Home, ".config/rebar3"),
    case file:consult(filename:join(ConfDir, "rebar.config")) of
        {ok, Config} ->
            Config;
        _ ->
            []
    end.

get_http_vars(Scheme) ->
    OS = case os:getenv(atom_to_list(Scheme)) of
        Str when is_list(Str) -> Str;
        _ -> []
    end,
    proplists:get_value(Scheme, get_rebar_config(), OS).

set_httpc_options() ->
    set_httpc_options(https_proxy, get_http_vars(https_proxy)),
    set_httpc_options(proxy, get_http_vars(http_proxy)).

set_httpc_options(_, []) ->
    ok;

set_httpc_options(Scheme, Proxy) ->
    {ok, {_, UserInfo, Host, Port, _, _}} = http_uri:parse(Proxy),
    httpc:set_options([{Scheme, {{Host, Port}, []}}], rebar),
    set_proxy_auth(UserInfo).

compile(App, FirstFiles) ->
    Dir = filename:join(filename:absname("_build/default/lib/"), App),
    filelib:ensure_dir(filename:join([Dir, "ebin", "dummy.beam"])),
    code:add_path(filename:join(Dir, "ebin")),
    FirstFilesPaths = [filename:join([Dir, "src", Module]) || Module <- FirstFiles],
    Sources = FirstFilesPaths ++ filelib:wildcard(filename:join([Dir, "src", "*.erl"])),
    [compile_file(X, [{i, filename:join(Dir, "include")}
                     ,debug_info
                     ,{outdir,  filename:join(Dir, "ebin")}
                     ,return | additional_defines()]) || X <- Sources].

compile_file(File, Opts) ->
    case compile:file(File, Opts) of
        {ok, _Mod} ->
            ok;
        {ok, _Mod, []} ->
            ok;
        {ok, _Mod, Ws} ->
            io:format("~s~n", [format_warnings(File, Ws)]),
            halt(1);
        {error, Es, Ws} ->
            io:format("~s ~s~n", [format_errors(File, Es), format_warnings(File, Ws)]),
            halt(1)
    end.

bootstrap_rebar3() ->
    filelib:ensure_dir("_build/default/lib/rebar/ebin/dummy.beam"),
    code:add_path("_build/default/lib/rebar/ebin/"),
    Res = symlink_or_copy(filename:absname("src"),
                          filename:absname("_build/default/lib/rebar/src")),
    true = Res == ok orelse Res == exists,
    Sources = ["src/rebar_resource.erl" | filelib:wildcard("src/*.erl")],
    [compile_file(X, [{outdir, "_build/default/lib/rebar/ebin/"}
                     ,return | additional_defines()]) || X <- Sources],
    code:add_patha(filename:absname("_build/default/lib/rebar/ebin")).

%%rebar.hrl
-define(FMT(Str, Args), lists:flatten(io_lib:format(Str, Args))).
%%/rebar.hrl
%%rebar_file_utils
-include_lib("kernel/include/file.hrl").

symlink_or_copy(Source, Target) ->
    Link = case os:type() of
               {win32, _} ->
                   Source;
               _ ->
                   make_relative_path(Source, Target)
           end,
    case file:make_symlink(Link, Target) of
        ok ->
            ok;
        {error, eexist} ->
            exists;
        {error, _} ->
            case os:type() of
                {win32, _} ->
                    S = unicode:characters_to_list(Source),
                    T = unicode:characters_to_list(Target),
                    case filelib:is_dir(S) of
                        true ->
                            win32_symlink_or_copy(S, T);
                        false ->
                            cp_r([S], T)
                    end;
                _ ->
                    case filelib:is_dir(Target) of
                        true ->
                            ok;
                        false ->
                            cp_r([Source], Target)
                    end
            end
    end.

-spec cp_r(list(string()), file:filename()) -> 'ok'.
cp_r([], _Dest) ->
    ok;
cp_r(Sources, Dest) ->
    case os:type() of
        {unix, _} ->
            EscSources = [escape_chars(Src) || Src <- Sources],
            SourceStr = join(EscSources, " "),
            {ok, []} = sh(?FMT("cp -Rp ~ts \"~ts\"",
                          [SourceStr, escape_double_quotes(Dest)]),
                          [{use_stdout, false}, abort_on_error]),
            ok;
        {win32, _} ->
            lists:foreach(fun(Src) -> ok = cp_r_win32(Src,Dest) end, Sources),
            ok
    end.

%% @private Compatibility function for windows
win32_symlink_or_copy(Source, Target) ->
    Res = sh(?FMT("cmd /c mklink /j \"~ts\" \"~ts\"",
             [escape_double_quotes(filename:nativename(Target)),
              escape_double_quotes(filename:nativename(Source))]),
             [{use_stdout, false}, return_on_error]),
    case win32_mklink_ok(Res, Target) of
        true -> ok;
        false -> cp_r_win32(Source, drop_last_dir_from_path(Target))
    end.

cp_r_win32({true, SourceDir}, {true, DestDir}) ->
    %% from directory to directory
     ok = case file:make_dir(DestDir) of
             {error, eexist} -> ok;
             Other -> Other
         end,
    ok = xcopy_win32(SourceDir, DestDir);
cp_r_win32({false, Source} = S,{true, DestDir}) ->
    %% from file to directory
    cp_r_win32(S, {false, filename:join(DestDir, filename:basename(Source))});
cp_r_win32({false, Source},{false, Dest}) ->
    %% from file to file
    {ok,_} = file:copy(Source, Dest),
    ok;
cp_r_win32({true, SourceDir}, {false, DestDir}) ->
    case filelib:is_regular(DestDir) of
        true ->
            %% From directory to file? This shouldn't happen
            {error, lists:flatten(
                      io_lib:format("Cannot copy dir (~p) to file (~p)\n",
                                    [SourceDir, DestDir]))};
        false ->
            %% Specifying a target directory that doesn't currently exist.
            %% So let's attempt to create this directory
            case filelib:ensure_dir(filename:join(DestDir, "dummy")) of
                ok ->
                    ok = xcopy_win32(SourceDir, DestDir);
                {error, Reason} ->
                    {error, lists:flatten(
                              io_lib:format("Unable to create dir ~p: ~p\n",
                                            [DestDir, Reason]))}
            end
    end;
cp_r_win32(Source,Dest) ->
    Dst = {filelib:is_dir(Dest), Dest},
    lists:foreach(fun(Src) ->
                          ok = cp_r_win32({filelib:is_dir(Src), Src}, Dst)
                  end, filelib:wildcard(Source)),
    ok.

%% drops the last 'node' of the filename, presumably the last dir such as 'src'
%% this is because cp_r_win32/2 automatically adds the dir name, to appease
%% robocopy and be more uniform with POSIX
drop_last_dir_from_path([]) ->
    [];
drop_last_dir_from_path(Path) ->
    case lists:droplast(filename:split(Path)) of
        [] -> [];
        Dirs -> filename:join(Dirs)
    end.

%% @private specifically pattern match against the output
%% of the windows 'mklink' shell call; different values from
%% what win32_ok/1 handles
win32_mklink_ok({ok, _}, _) ->
    true;
win32_mklink_ok({error,{1,"Local NTFS volumes are required to complete the operation.\n"}}, _) ->
    false;
win32_mklink_ok({error,{1,"Cannot create a file when that file already exists.\n"}}, Target) ->
    % File or dir is already in place; find if it is already a symlink (true) or
    % if it is a directory (copy-required; false)
    is_symlink(Target);
win32_mklink_ok(_, _) ->
    false.

xcopy_win32(Source,Dest)->
    %% "xcopy \"~ts\" \"~ts\" /q /y /e 2> nul", Changed to robocopy to
    %% handle long names. May have issues with older windows.
    Cmd = case filelib:is_dir(Source) of
              true ->
                  %% For robocopy, copying /a/b/c/ to /d/e/f/ recursively does not
                  %% create /d/e/f/c/*, but rather copies all files to /d/e/f/*.
                  %% The usage we make here expects the former, not the later, so we
                  %% must manually add the last fragment of a directory to the `Dest`
                  %% in order to properly replicate POSIX platforms
                  NewDest = filename:join([Dest, filename:basename(Source)]),
                  ?FMT("robocopy \"~ts\" \"~ts\" /e 1> nul",
                       [escape_double_quotes(filename:nativename(Source)),
                        escape_double_quotes(filename:nativename(NewDest))]);
              false ->
                  ?FMT("robocopy \"~ts\" \"~ts\" \"~ts\" /e 1> nul",
                       [escape_double_quotes(filename:nativename(filename:dirname(Source))),
                        escape_double_quotes(filename:nativename(Dest)),
                        escape_double_quotes(filename:basename(Source))])
          end,
    Res = sh(Cmd, [{use_stdout, false}, return_on_error]),
    case win32_ok(Res) of
        true -> ok;
        false ->
            {error, lists:flatten(
                      io_lib:format("Failed to copy ~ts to ~ts~n",
                                    [Source, Dest]))}
    end.

is_symlink(Filename) ->
    {ok, Info} = file:read_link_info(Filename),
    Info#file_info.type == symlink.

win32_ok({ok, _}) -> true;
win32_ok({error, {Rc, _}}) when Rc<9; Rc=:=16 -> true;
win32_ok(_) -> false.

%%/rebar_file_utils

%%rebar_utils

%% escape\ as\ a\ shell\?
escape_chars(Str) when is_atom(Str) ->
    escape_chars(atom_to_list(Str));
escape_chars(Str) ->
    re:replace(Str, "([ ()?`!$&;\"\'])", "\\\\&",
               [global, {return, list}, unicode]).

%% "escape inside these"
escape_double_quotes(Str) ->
    re:replace(Str, "([\"\\\\`!$&*;])", "\\\\&",
               [global, {return, list}, unicode]).

sh(Command0, Options0) ->
    DefaultOptions = [{use_stdout, false}],
    Options = [expand_sh_flag(V)
               || V <- proplists:compact(Options0 ++ DefaultOptions)],

    ErrorHandler = proplists:get_value(error_handler, Options),
    OutputHandler = proplists:get_value(output_handler, Options),

    Command = lists:flatten(patch_on_windows(Command0, proplists:get_value(env, Options, []))),
    PortSettings = proplists:get_all_values(port_settings, Options) ++
        [exit_status, {line, 16384}, use_stdio, stderr_to_stdout, hide, eof],
    Port = open_port({spawn, Command}, PortSettings),

    try
        case sh_loop(Port, OutputHandler, []) of
            {ok, _Output} = Ok ->
                Ok;
            {error, {_Rc, _Output}=Err} ->
                ErrorHandler(Command, Err)
        end
    after
        port_close(Port)
    end.

sh_loop(Port, Fun, Acc) ->
    receive
        {Port, {data, {eol, Line}}} ->
            sh_loop(Port, Fun, Fun(Line ++ "\n", Acc));
        {Port, {data, {noeol, Line}}} ->
            sh_loop(Port, Fun, Fun(Line, Acc));
        {Port, eof} ->
            Data = lists:flatten(lists:reverse(Acc)),
            receive
                {Port, {exit_status, 0}} ->
                    {ok, Data};
                {Port, {exit_status, Rc}} ->
                    {error, {Rc, Data}}
            end
    end.

expand_sh_flag(return_on_error) ->
    {error_handler,
     fun(_Command, Err) ->
             {error, Err}
     end};
expand_sh_flag(abort_on_error) ->
    {error_handler,
     fun log_and_abort/2};
expand_sh_flag({use_stdout, false}) ->
    {output_handler,
     fun(Line, Acc) ->
             [Line | Acc]
     end};
expand_sh_flag({cd, _CdArg} = Cd) ->
    {port_settings, Cd};
expand_sh_flag({env, _EnvArg} = Env) ->
    {port_settings, Env}.

%% We do the shell variable substitution ourselves on Windows and hope that the
%% command doesn't use any other shell magic.
patch_on_windows(Cmd, Env) ->
    case os:type() of
        {win32,nt} ->
            Cmd1 = "cmd /q /c "
                ++ lists:foldl(fun({Key, Value}, Acc) ->
                                       expand_env_variable(Acc, Key, Value)
                               end, Cmd, Env),
            %% Remove left-over vars
            re:replace(Cmd1, "\\\$\\w+|\\\${\\w+}", "",
                       [global, {return, list}, unicode]);
        _ ->
            Cmd
    end.

%% @doc Given env. variable `FOO' we want to expand all references to
%% it in `InStr'. References can have two forms: `$FOO' and `${FOO}'
%% The end of form `$FOO' is delimited with whitespace or EOL
-spec expand_env_variable(string(), string(), term()) -> string().
expand_env_variable(InStr, VarName, RawVarValue) ->
    case chr(InStr, $$) of
        0 ->
            %% No variables to expand
            InStr;
        _ ->
            ReOpts = [global, unicode, {return, list}],
            VarValue = re:replace(RawVarValue, "\\\\", "\\\\\\\\", ReOpts),
            %% Use a regex to match/replace:
            %% Given variable "FOO": match $FOO\s | $FOOeol | ${FOO}
            RegEx = io_lib:format("\\\$(~ts(\\W|$)|{~ts})", [VarName, VarName]),
            re:replace(InStr, RegEx, [VarValue, "\\2"], ReOpts)
    end.

-spec log_and_abort(string(), {integer(), string()}) -> no_return().
log_and_abort(Command, {Rc, Output}) ->
    io:format("sh(~ts)~n"
              "failed with return code ~w and the following output:~n"
              "~ts", [Command, Rc, Output]),
    throw(bootstrap_abort).

%%/rebar_utils

%%rebar_dir
make_relative_path(Source, Target) ->
    AbsSource = make_normalized_path(Source),
    AbsTarget = make_normalized_path(Target),
    do_make_relative_path(filename:split(AbsSource), filename:split(AbsTarget)).

%% @private based on fragments of paths, replace the number of common
%% segments by `../' bits, and add the rest of the source alone after it
-spec do_make_relative_path([string()], [string()]) -> file:filename().
do_make_relative_path([H|T1], [H|T2]) ->
    do_make_relative_path(T1, T2);
do_make_relative_path(Source, Target) ->
    Base = lists:duplicate(max(length(Target) - 1, 0), ".."),
    filename:join(Base ++ Source).

make_normalized_path(Path) ->
    AbsPath = make_absolute_path(Path),
    Components = filename:split(AbsPath),
    make_normalized_path(Components, []).
    
make_absolute_path(Path) ->
    case filename:pathtype(Path) of
        absolute ->
            Path;
        relative ->
            {ok, Dir} = file:get_cwd(),
            filename:join([Dir, Path]);
        volumerelative ->
            Volume = hd(filename:split(Path)),
            {ok, Dir} = file:get_cwd(Volume),
            filename:join([Dir, Path])
    end.

-spec make_normalized_path([string()], [string()]) -> file:filename().
make_normalized_path([], NormalizedPath) ->
    filename:join(lists:reverse(NormalizedPath));
make_normalized_path([H|T], NormalizedPath) ->
    case H of
        "." when NormalizedPath == [], T == [] -> make_normalized_path(T, ["."]);
        "."  -> make_normalized_path(T, NormalizedPath);
        ".." when NormalizedPath == [] -> make_normalized_path(T, [".."]);
        ".." when hd(NormalizedPath) =/= ".." -> make_normalized_path(T, tl(NormalizedPath));
        _    -> make_normalized_path(T, [H|NormalizedPath])
    end.
%%/rebar_dir

setup_env() ->
    %% We don't need or want relx providers loaded yet
    application:load(rebar),
    {ok, Providers} = application:get_env(rebar, providers),
    Providers1 = Providers -- [rebar_prv_release,
                               rebar_prv_relup,
                               rebar_prv_tar],
    application:set_env(rebar, providers, Providers1).

reset_env() ->
    %% Reset the env so we get all providers
    application:unset_env(rebar, providers),
    application:unload(rebar),
    application:load(rebar).

get_deps() ->
    case file:consult("rebar.lock") of
        {ok, [[]]} ->
            %% Something went wrong in a previous build, lock file shouldn't be empty
            io:format("Empty list in lock file, deleting rebar.lock~n"),
            ok = file:delete("rebar.lock"),
            {ok, Config} = file:consult("rebar.config"),
            proplists:get_value(deps, Config);
        {ok, [Deps]} ->
            [{binary_to_atom(Name, utf8), "", Source} || {Name, Source, _Level} <- Deps];
        _ ->
            {ok, Config} = file:consult("rebar.config"),
            proplists:get_value(deps, Config)
    end.

format_errors(Source, Errors) ->
    format_errors(Source, "", Errors).

format_warnings(Source, Warnings) ->
    format_warnings(Source, Warnings, []).

format_warnings(Source, Warnings, Opts) ->
    Prefix = case lists:member(warnings_as_errors, Opts) of
                 true -> "";
                 false -> "Warning: "
             end,
    format_errors(Source, Prefix, Warnings).

format_errors(_MainSource, Extra, Errors) ->
    [begin
         [format_error(Source, Extra, Desc) || Desc <- Descs]
     end
     || {Source, Descs} <- Errors].

format_error(AbsSource, Extra, {{Line, Column}, Mod, Desc}) ->
    ErrorDesc = Mod:format_error(Desc),
    io_lib:format("~s:~w:~w: ~s~s~n", [AbsSource, Line, Column, Extra, ErrorDesc]);
format_error(AbsSource, Extra, {Line, Mod, Desc}) ->
    ErrorDesc = Mod:format_error(Desc),
    io_lib:format("~s:~w: ~s~s~n", [AbsSource, Line, Extra, ErrorDesc]);
format_error(AbsSource, Extra, {Mod, Desc}) ->
    ErrorDesc = Mod:format_error(Desc),
    io_lib:format("~s: ~s~s~n", [AbsSource, Extra, ErrorDesc]).

additional_defines() ->
    [{d, D} || {Re, D} <- [{"^[0-9]+", namespaced_types},
                           {"^R1[4|5]", deprecated_crypto},
                           {"^2", unicode_str},
                           {"^((1[8|9])|2)", rand_module}],
               is_otp_release(Re)].

is_otp_release(ArchRegex) ->
    case re:run(otp_release(), ArchRegex, [{capture, none}]) of
        match ->
            true;
        nomatch ->
            false
    end.

otp_release() ->
    otp_release1(erlang:system_info(otp_release)).

%% If OTP <= R16, otp_release is already what we want.
otp_release1([$R,N|_]=Rel) when is_integer(N) ->
    Rel;
%% If OTP >= 17.x, erlang:system_info(otp_release) returns just the
%% major version number, we have to read the full version from
%% a file. See http://www.erlang.org/doc/system_principles/versions.html
%% Read vsn string from the 'OTP_VERSION' file and return as list without
%% the "\n".
otp_release1(Rel) ->
    File = filename:join([code:root_dir(), "releases", Rel, "OTP_VERSION"]),
    case file:read_file(File) of
        {error, _} ->
            Rel;
        {ok, Vsn} ->
            %% It's fine to rely on the binary module here because we can
            %% be sure that it's available when the otp_release string does
            %% not begin with $R.
            Size = byte_size(Vsn),
            %% The shortest vsn string consists of at least two digits
            %% followed by "\n". Therefore, it's safe to assume Size >= 3.
            case binary:part(Vsn, {Size, -3}) of
                <<"**\n">> ->
                    %% The OTP documentation mentions that a system patched
                    %% using the otp_patch_apply tool available to licensed
                    %% customers will leave a '**' suffix in the version as a
                    %% flag saying the system consists of application versions
                    %% from multiple OTP versions. We ignore this flag and
                    %% drop the suffix, given for all intents and purposes, we
                    %% cannot obtain relevant information from it as far as
                    %% tooling is concerned.
                    binary:bin_to_list(Vsn, {0, Size - 3});
                _ ->
                    binary:bin_to_list(Vsn, {0, Size - 1})
            end
    end.

set_proxy_auth([]) ->
    ok;
set_proxy_auth(UserInfo) ->
    [Username, Password] = re:split(UserInfo, ":",
                                    [{return, list}, {parts,2}, unicode]),
    %% password may contain url encoded characters, need to decode them first
    put(proxy_auth, [{proxy_auth, {Username, http_uri:decode(Password)}}]).

get_proxy_auth() ->
    case get(proxy_auth) of
        undefined -> [];
        ProxyAuth -> ProxyAuth
    end.

%% string:join/2 copy; string:join/2 is getting obsoleted
%% and replaced by lists:join/2, but lists:join/2 is too new
%% for version support (only appeared in 19.0) so it cannot be
%% used. Instead we just adopt join/2 locally and hope it works
%% for most unicode use cases anyway.
join([], Sep) when is_list(Sep) ->
        [];
join([H|T], Sep) ->
    H ++ lists:append([Sep ++ X || X <- T]).

%% Same for chr; no non-deprecated equivalent in OTP20+ 
chr(S, C) when is_integer(C) -> chr(S, C, 1).
chr([C|_Cs], C, I) -> I;
chr([_|Cs], C, I) -> chr(Cs, C, I+1);
chr([], _C, _I) -> 0.