[erlang-bugs] bogus 'unsafe variable' warning with try-else

[Mikael Pettersson]

The following, adapted from an example in the online Erlang
Reference Manual, looks like a bug to me:

> cat bug.erl
-module(bug).
-compile(export_all).

termize_file(Name) ->
  {ok,F} = file:open(Name, [read,binary]),
  try
    {ok,Bin} = file:read(F, 1024*1024)
  after
    file:close(F)
  end,
  binary_to_term(Bin).
> erlc bug.erl
bug.erl:11: variable 'Bin' unsafe in 'try' (line 6)

Unless I'm missing something, there is no way to reach the
binary_to_term/1 call without successfully evaluating the
{ok,Bin} = ... match expression; therefore the use is not
unsafe.  If the file:read/2 call or the {ok,Bin} match fails,
the after clause runs and the entire try expression fails,
and the binary_to_term/1 is not reached.

Reproduced with 17.3 and r15b03-1.

Workaround: match on the value of the try itself:
"{ok,Bin} = try file:read(...) after ... end".

/Mikael