[erlang-bugs] Unused variable causing v3_kernel crash

[José Valim]

Hello everyone,

The following module fails to compile using both R15B03-01 and R16A:

    -module(sample).
    -export([hello/1]).

    hello(X) ->
      case do_something(X) of
        false ->
          A = false;
        Res ->
          { A, B } = Res,
          do_something(A),
          do_something(B)
      end,
      ThisShouldNotFail = A,
      ok.

    do_something(X) ->
      external:do_something(X).

With the following exception:

    crash reason: {function_clause,
                      [{v3_kernel,lit_vars,
                           [{ivalues,
                                [11,{file,"sample.erl"}],
                                [{k_var,[],ker4},{k_atom,[],ok}]}],
                           [{file,"v3_kernel.erl"},{line,1749}]},

 {v3_kernel,uexpr,3,[{file,"v3_kernel.erl"},{line,1628}]},

 {v3_kernel,ubody,3,[{file,"v3_kernel.erl"},{line,1408}]},

 {v3_kernel,ubody,3,[{file,"v3_kernel.erl"},{line,1409}]},

 {v3_kernel,umatch,3,[{file,"v3_kernel.erl"},{line,1716}]},
                       {v3_kernel,'-umatch_list/3-anonymous-0-',3,
                           [{file,"v3_kernel.erl"},{line,1735}]},

 {v3_kernel,umatch,3,[{file,"v3_kernel.erl"},{line,1711}]},
                       {v3_kernel,'-umatch_list/3-anonymous-0-',3,
                           [{file,"v3_kernel.erl"},{line,1735}]}]}

The code and exceptions are also available here:
https://gist.github.com/7bd4eea30cd187e68caa

Removing the `ThisShouldNotFail` assignment makes it work correctly,
although I wouldn't expect it to explode with that line and just output a
couple warnings instead.

This snippet was extract from a more complex code. The name of the
functions, module and variables do not seem to affect the failure.

I tried to further debug the issue but I could not pinpoint the
failure. Let me know if I can help any further.

Thank you for your time,


*
José Valim
www.plataformatec.com.br
Founder and Lead Developer
*
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