Elixir LS not showing warnings

Just for the record the elixir part of that issue will not likely be fixed on 1.12 patch Pass annotation to arguments, closes #11107 · elixir-lang/elixir@49bac68 · GitHub

https://github.com/elixir-lang/elixir/issues/11107

I will try 24.0.3 and hopefully get some of those lovely warnings back.

Hi, I think describing that Dialyzer is not showing some of warnings for Elixir code since Erlang 24 and linking to this thread is enough In your code snippet there is Elixir’s AST, and Elixir does not store line number for some (all?) literals at all. so 11111111 is just represented directly. The fix would be to ensure that the line 3 from the context gets passed down as this tree is being translated to Erlang forms and eventually makes its way to Ann here

I would be glad to create that issue but I really don’t know how what I would say.

I ran this code:

defmodule MyApp do
  def hello do
    default(11_111_111)
  end

  @spec default(binary) :: binary
  def default(bin) when is_binary(bin) do
    "test #{bin}"
  end

  def debug do
    __MODULE__
    |> :code.which()
    |> :beam_lib.chunks([:debug_info])
    |> IO.inspect(label: "debug")
  end
end

And it gave me the following result:

:ok,                                                                                                                                                                                                               
 {MyApp,                                                                                                                                                                                                            
  [                                                                                                                                                                                                                 
    debug_info: {:debug_info_v1, :elixir_erl,                                                                                                                                                                       
     {:elixir_v1,                                                                                                                                                                                                   
      %{                                                                                                                                                                                                            
        attributes: [],                                                                                                                                                                                             
        compile_opts: [],                                                                                                                                                                                           
        definitions: [                                                                                                                                                                                              
          {{:hello, 0}, :def, [line: 2],                                                                                                                                                                            
           [{[line: 2], [], [], {:default, [line: 3], [11111111]}}]},                                                                                                                                               
          {{:default, 1}, :def, [line: 7],                                                                                                                                                                          
           [                                                                                                                                                                                                        
             {[line: 7], [{:bin, [version: 0, line: 7], nil}],                                                                                                                                                      
              [                                                                                                                                                                                                     
                {{:., [line: 7], [:erlang, :is_binary]}, [line: 7],                                                                                                                                                 
                 [{:bin, [version: 0, line: 7], nil}]}                                                                                                                                                              
              ],                                                                                                                                                                                                    
              {:<<>>, [alignment: 0, line: 8],
               [
                 {:"::", [inferred_bitstring_spec: true, line: 8],
                  ["test ", {:binary, [line: 8], []}]},
                 {:"::", [line: 8],
                  [
                    {{:., [line: 8], [String.Chars, :to_string]}, [line: 8],
                     [{:bin, [version: 0, line: 8], nil}]},
                    {:binary, [], []}
                  ]}
               ]}}
           ]},
          {{:debug, 0}, :def, [line: 11],
           [
             {[line: 11], [], [],
              {{:., [line: 15], [IO, :inspect]}, [line: 15],
               [
                 {{:., [line: 14], [:beam_lib, :chunks]}, [line: 14],
                  [
                    {{:., [line: 13], [:code, :which]}, [line: 13], [MyApp]},
                    [:debug_info]
                  ]},
                 [label: "debug"]
               ]}}
           ]}
        ],

 # ...

I do not have knowledge about the compiler but to me it looks like the line numbers are set.

In case of the previous issue I discovered with Elixir <> Dialyzer integration, the root cause was the same - Elixir setting location to 0 for some forms. Erlang to pick the line number was trying to pick the lowest number in the AST, so when some of forms inside the tree had it set to 0, 0 was being picked.

It was fine to “fix” it on the Erlang side, because it didn’t require much hassle (my fix was just a 1 line change, but the Erlang/OTP team decided to merge an alternative PR with a small cleanup as well).

At this point, after discovering this second issue that has the same root cause, I believe Elixir should be a better BEAM citizen and generate Erlang AST that integrates more nicely with the tooling, by correctly adding code location where it can (it would just require passing down location in a few places in the compiler).

Someone should open an issue in the Elixir repo to see what the Elixir team thinks, (I am spending enough time on making Elixir work well with Dialyzer already )

I spent some time debugging and the second, more helpful warning is correctly detected by Dialyzer but not added to list of warnings because Elixir is not generating the Erlang AST as nicely as Dialyzer expects it to be. (Line numbers are missing for literals (are set to 0), and other nodes as well, which makes them be interpreted as generated and Dialyzer decides not to add a warning at all because it would be confusing to point to line number 0).

More concretely, this happens because for the 1 integer literal at line 3 Elixir generates something that later is seen by Dialyzer as:

{c_literal,[0,{file,"0"}],1}

so it has line number set to 0 so returns is_generated true here

can confirm that there are no warnings with erlang 24.0 and 24.0.2. But still there is a warning missing for 24.0.3

I think Elixir version doesn’t make a difference, to reproduce just use erlang 24.0 (without any patches) or erlang 24.0.2 and there will be no warnings shown. Dialyzer returns

{:warn_return_no_exit, {'lib/my_app.ex', 0}, {:no_return, [:only_normal, :hello, 0]}}

so this is probably related to Fix lost line numbers in Dialyzer warnings for Elixir code by michallepicki · Pull Request #4890 · erlang/otp · GitHub. With 24.0.3 I also see only one warning.

I can partially reproduce with OTP 22 and 24 (switched between these 3 times and always the same behaviour). 22 shows both warnings, 24 only one.

$ asdf global erlang 22.3.4.20 
$ asdf global elixir 1.11.4-otp-22

--> Function hello/0 has no local return.
--> The function call will not succeed. (MyApp.default(1))

$ asdf global erlang 24.0.3 
$ asdf global elixir 1.12.2-otp-24 

--> Function hello/0 has no local return.

also showing both:

erlang 23.3.4.1  
elixir 1.12.1-otp-23 

Which Elixir version?

EDIT:
I installed erlang 24.0. and can confirm, that I also do not get any warnings displayed.
Also the output of ElixirLS differs.

Output with 24.0.3:

Started ElixirLS v0.7.0
Elixir version: "1.12.2 (compiled with Erlang/OTP 24)"
Erlang version: "24" # 24.0.3
ElixirLS compiled with Elixir 1.8.2 and erlang 21
MIX_ENV: test
MIX_TARGET: 
[Info  - 1:54:55 PM] Compile took 732 milliseconds
[Info  - 1:54:55 PM] [ElixirLS Dialyzer] Checking for stale beam files
[Info  - 1:54:55 PM] [ElixirLS WorkspaceSymbols] Indexing...
[Info  - 1:54:55 PM] [ElixirLS Dialyzer] Found 32 changed files in 26 milliseconds
[Info  - 1:54:55 PM] [ElixirLS Dialyzer] Analyzing 0 modules: []
[Info  - 1:54:55 PM] [ElixirLS Dialyzer] Analysis finished in 28 milliseconds
[Info  - 1:54:55 PM] [ElixirLS WorkspaceSymbols] Module discovery complete
[Info  - 1:54:55 PM] Dialyzer analysis is up to date
[Info  - 1:54:55 PM] [ElixirLS WorkspaceSymbols] 181 modules added to index
[Info  - 1:54:55 PM] [ElixirLS WorkspaceSymbols] 22 callbacks added to index
[Info  - 1:54:56 PM] [ElixirLS Dialyzer] Writing manifest...
[Info  - 1:54:56 PM] [ElixirLS WorkspaceSymbols] 280 types added to index
[Info  - 1:54:58 PM] [ElixirLS Dialyzer] Done writing manifest in 3144 milliseconds.
[Info  - 1:55:02 PM] [ElixirLS WorkspaceSymbols] 3971 functions added to index

Output with 24.0:

Started ElixirLS v0.7.0
Elixir version: "1.12.2 (compiled with Erlang/OTP 24)"
Erlang version: "24" # 24.0
ElixirLS compiled with Elixir 1.8.2 and erlang 21
MIX_ENV: test
MIX_TARGET: 
[Info  - 1:56:52 PM] Compile took 605 milliseconds
[Info  - 1:56:52 PM] [ElixirLS WorkspaceSymbols] Indexing...
[Info  - 1:56:52 PM] [ElixirLS Dialyzer] Checking for stale beam files
[Info  - 1:56:52 PM] [ElixirLS Dialyzer] Found 32 changed files in 21 milliseconds
[Info  - 1:56:52 PM] [ElixirLS WorkspaceSymbols] Module discovery complete
[Info  - 1:56:52 PM] [ElixirLS WorkspaceSymbols] 26 callbacks added to index
[Info  - 1:56:52 PM] [ElixirLS WorkspaceSymbols] 185 modules added to index
[Info  - 1:56:52 PM] [ElixirLS WorkspaceSymbols] 285 types added to index
[Info  - 1:56:55 PM] [ElixirLS WorkspaceSymbols] 3990 functions added to index

I can see the issue with Erlang 24.0. Switching to Erlang 24.0.3 fixes it.