Add typespecs to the elixir code, enough to make dialyzer useful

[dazuma]

See Appendix 2 in Programming Elixir.

[dazuma]

The main point of this task is to decide on some best practices for using type specs in a project like this, and report back to the group.

[BKStephens]

Erlang 18 support is not coming until Elixir 1.2, and I think I am running into some problems with dialyzer due to this. Below are the steps I have taken, and some output.

jeremyjh/dialyxir#26
elixir-lang/elixir#3212

1. Find Elixir libraries
   • iex
   • :code.lib_dir(:elixir)
2. dialyzer --build_plt --apps erts path/to/elixir/libraries/ebin
3. dialyzer _build/dev/lib/tanx/ebin

Step 2 output:

dialyzer --build_plt --apps erts /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin
  Compiling some key modules to native code... done in 0m0.23s
  Creating PLT /Users/benstephens/.dialyzer_plt ...
dialyzer: Analysis failed with error:
Could not scan the following file(s):
  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Version.InvalidVersionError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.UnicodeC
onversionError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Version.InvalidRequirementError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elix
ir/ebin/Elixir.UndefinedFunctionError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Version.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixi
r/ebin/Elixir.Version.Requirement.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.TryClauseError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/el
ixir/ebin/Elixir.TokenMissingError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.URI.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/
Elixir.SystemLimitError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Task.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Syn
taxError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.System.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Supervisor.beam
 Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Stream.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.RuntimeError.beam  Could not g
et core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Regex.CompileError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Regex.beam  Could not get core
 Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Protocol.UndefinedError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Range.beam  Could not get core E
rlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.MatchError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Macro.Env.beam  Could not get core Erlang code
for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.KeyError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Inspect.Opts.beam  Could not get core Erlang code for: /usr/
local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.IO.StreamError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.HashSet.beam  Could not get core Erlang code for: /usr/local/Cel
lar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.HashDict.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.FunctionClauseError.beam  Could not get core Erlang code for: /usr/local/Cellar
/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.IO.Stream.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.File.CopyError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir
/1.0.5/bin/../lib/elixir/ebin/Elixir.File.Error.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.ErlangError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bi
n/../lib/elixir/ebin/Elixir.GenEvent.Stream.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.File.Stream.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/..
/lib/elixir/ebin/Elixir.File.Stat.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Exception.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/
ebin/Elixir.Enum.OutOfBoundsError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.Enum.EmptyError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/e
lixir/ebin/Elixir.CondClauseError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.CompileError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elix
ir/ebin/Elixir.Code.LoadError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.CaseClauseError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixi
r/ebin/Elixir.BadStructError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.BadMapError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebi
n/Elixir.BadFunctionError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.BadArityError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin
/Elixir.ArgumentError.beam  Could not get core Erlang code for: /usr/local/Cellar/elixir/1.0.5/bin/../lib/elixir/ebin/Elixir.ArithmeticError.beam
Last messages in the log cache:
Reading files and computing callgraph...

Step 3 output:

dialyzer _build/dev/lib/tanx/ebin
  Checking whether the PLT /Users/benstephens/.dialyzer_plt is up-to-date...
dialyzer: Could not find the PLT: /Users/benstephens/.dialyzer_plt
Use the options:
   --build_plt   to build a new PLT; or
   --add_to_plt  to add to an existing PLT

For example, use a command like the following:
   dialyzer --build_plt --apps erts kernel stdlib mnesia
Note that building a PLT such as the above may take 20 mins or so

If you later need information about other applications, say crypto,
you can extend the PLT by the command:
  dialyzer --add_to_plt --apps crypto
For applications that are not in Erlang/OTP use an absolute file name.

[dazuma]

Ugh that's annoying.

I did a bit more digging on this. It seems odd to me that it would be claimed that elixir won't support erlang 18 until elixir 1.2, because elixir 1.0.5 clearly runs on erlang 18 (even though it doesn't use erlang 18 features.)

I suspect the issue might boil down to how elixir is built. The homebrew install of elixir 1.0.5 is probably built using erlang 17 (for compatibility). I think there are supposedly some beam file changes between the two erlang releases that would cause dialyzer not to like the erlang-17-built elixir beams. (See e.g. https://www.bountysource.com/issues/25690722-how-to-use-it). Maybe someone can try building elixir from source using erlang 18 and see if that helps.