Dialyzer giving warnings that make no sense

NobbZ · November 13, 2018, 5:21pm

Its already reported and closed:

github.com/elixir-lang/elixir

Guard test tuple_size(...) can never succeed warning

opened 10:16PM - 31 Aug 18 UTC

closed 07:42PM - 14 Sep 18 UTC

seancribbs

Kind:Bug Level:Intermediate App:Elixir (compiler)

### Environment * Elixir & Erlang/OTP versions (elixir --version): ``` Erl…ang/OTP 21 [erts-10.0.5] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace] Elixir 1.7.2 (compiled with Erlang/OTP 21) ``` * Operating system: Mac OS/X High Sierra 10.13.6 ### Current behavior Dialyzer produces warnings on generated exception-handling code in the `try` macro when a `rescue` clause matches on `ErlangError`. Minimal example: ```elixir defmodule TryTupleSize do def demo do try do :erlang.error(:badarg) rescue e in ErlangError -> {:ok, e} end end end ``` Dialyzer output: ``` try_tuple_size.ex:6: Guard test tuple_size(__@5::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed ``` The decompiled-to-Erlang version of the `demo/0` function: ```erlang demo() -> try error(badarg) catch error:__@3:___STACKTRACE__@1 when not is_map(__@3) -> _e@1 = 'Elixir.Exception':normalize(error, __@3, case __@3 of __@5 when tuple_size(__@5) == 2 andalso element(1, __@5) == badkey; __@5 == undef; __@5 == function_clause -> ___STACKTRACE__@1; _ -> [] end), {ok,_e@1}; error:#{'__struct__' := __@4,'__exception__' := true} = __@3:___STACKTRACE__@1 when __@4 == 'Elixir.ErlangError' -> _e@1 = 'Elixir.Exception':normalize(error, __@3, case __@3 of __@5 when tuple_size(__@5) == 2 andalso element(1, __@5) == badkey; __@5 == undef; __@5 == function_clause -> ___STACKTRACE__@1; _ -> [] end), {ok,_e@1} end. ``` ### Expected behavior In the case where the (second) generated `catch` branch has already matched on an exception map/struct, it should not use `tuple_size/1` in that clause. Furthermore, since it has already established that the error has been normalized, it shouldn't be trying to normalize the error again. This could remove the type warning from the generated code.

I’m not sure though, if the fix is in the 1.7 branch or only for 1.8.