IO.warn diagnostic with not filled metadata

[lukaszsamson]

Elixir and Erlang/OTP versions

Erlang/OTP 26 [erts-14.1.1] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit]

Elixir 1.16.0-rc.1 (81a12b7) (compiled with Erlang/OTP 26)

Operating system

macOS

Current behavior

Repro:

1. Create an empty mix project
2. Add IO.warn("foo") in mix.exs
3. in iex

Mix.start()
Code.with_diagnostics(fn -> Code.compile_file("mix.exs") end)

   %{
     message: "foo",
     position: 0,
     file: nil,
     stacktrace: [
       {:elixir_compiler_0, :__FILE__, 1, [file: ~c"mix.exs", line: 57]},
       {:elixir_compiler, :dispatch, 4,
        [file: ~c"src/elixir_compiler.erl", line: 67]},
       {:elixir_compiler, :compile, 4,
        [file: ~c"src/elixir_compiler.erl", line: 52]},
       {:elixir_compiler, :maybe_fast_compile, 3,
        [file: ~c"src/elixir_compiler.erl", line: 39]},
       {:elixir_lexical, :run, 3, [file: ~c"src/elixir_lexical.erl", line: 15]},
       {:elixir_compiler, :quoted, 3,
        [file: ~c"src/elixir_compiler.erl", line: 17]}
     ],
     span: nil,
     severity: :warning
   }

Mix.start()
Kernel.ParallelCompiler.compile(["mix.exs"], return_diagnostics: true)

compile_warnings: [
     %{
       message: "foo",
       position: 0,
       file: nil,
       stacktrace: [
         {:elixir_compiler_1, :__MODULE__, 1, [file: ~c"mix.exs", line: 57]},
         {:elixir_compiler, :dispatch, 4,
          [file: ~c"src/elixir_compiler.erl", line: 67]},
         {:elixir_compiler, :compile, 4,
          [file: ~c"src/elixir_compiler.erl", line: 52]},
         {:elixir_module, :eval_form, 7,
          [file: ~c"src/elixir_module.erl", line: 426]},
         {:elixir_module, :compile, 7,
          [file: ~c"src/elixir_module.erl", line: 128]},
         {:elixir_compiler_0, :__FILE__, 1, [file: ~c"mix.exs", line: 1]}
       ],
       span: nil,
       severity: :warning
     }
     ]

Similarly, if I put IO.warn in lib/sample.ex and do

Mix.start()
Code.compile_file("mix.exs")
Mix.Task.run("compile", ["--return-errors", "--force"])

the warning will be printed with file and position

warning: foo
  lib/sample.ex:2: (file)
  (elixir 1.16.0-rc.1) src/elixir_compiler.erl:67: :elixir_compiler.dispatch/4
  (elixir 1.16.0-rc.1) src/elixir_compiler.erl:52: :elixir_compiler.compile/4
  (elixir 1.16.0-rc.1) src/elixir_compiler.erl:39: :elixir_compiler.maybe_fast_compile/3
  (elixir 1.16.0-rc.1) src/elixir_lexical.erl:15: :elixir_lexical.run/3
  (elixir 1.16.0-rc.1) src/elixir_compiler.erl:17: :elixir_compiler.quoted/3

but returned diagnostic is not filled

%Mix.Task.Compiler.Diagnostic{
     file: nil,
     severity: :warning,
     message: "foo",
     position: 0,
     compiler_name: "Elixir",
     span: nil,
     details: nil,
     stacktrace: [
       {:elixir_compiler_0, :__FILE__, 1, [file: ~c"lib/sample.ex", line: 2]},
       {:elixir_compiler, :dispatch, 4,
        [file: ~c"src/elixir_compiler.erl", line: 67]},
       {:elixir_compiler, :compile, 4,
        [file: ~c"src/elixir_compiler.erl", line: 52]},
       {:elixir_compiler, :maybe_fast_compile, 3,
        [file: ~c"src/elixir_compiler.erl", line: 39]},
       {:elixir_lexical, :run, 3, [file: ~c"src/elixir_lexical.erl", line: 15]},
       {:elixir_compiler, :quoted, 3,
        [file: ~c"src/elixir_compiler.erl", line: 17]}
     ]
   }

Expected behavior

position and file properties populated

[josevalim]

Yes, this is intentional, and you can look into the stacktrace in said cases. The issue is that, when a stacktrace is given, we can't guarantee it is precise, and showing the snippet could be misleading.

[sabiwara]

Yes, this is intentional, and you can look into the stacktrace in said cases. The issue is that, when a stacktrace is given, we can't guarantee it is precise, and showing the snippet could be misleading.

Maybe we should document the Code.diagnostic type accordingly, or provide a function to fetch the file & position from a diagnostic?

[josevalim]

I think we should document IO.warn instead.

[josevalim]

But i think the point is that we don't want to conflate the file and position with the one in the stacktrace. maybe it is fine for IDEs, but not generally.

[lukaszsamson]

@josevalim I fail to see how 2c1ca00 improves the situation. When emitting diagnostics I need to map the diagnostic to document URI (see https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#publishDiagnosticsParams). There is no such thing as diagnostic with null URI. Even if I emit something fake as file:///nofile or unknown:abcd the editor will try to open that file and navigate to diagnostic range. If I substitute mix.exs then the diagnostic is invalid, misplaced and confusing.

[josevalim]

Please read my previous comment. This is not an issue, I have only improved the docs. Elixir's definition of a diagnostic does not have to match the language server one. It is up to you to convert our diagnostic to something that makes sense to LSP. What Elixir is saying is that: if there is a file+position, then the diagnostic is precise. If there is only a stacktrace, then you can decide if you want to infer the file+position from the stacktrace or not. It is up to you. Elixir chooses to not emit a snippet in such cases. You may choose to traverse the stacktrace (perhaps trying to match against one of the project modules/files) or not show the diagnostic in editor (because, once again, it is not precise).

[josevalim]

I have pushed more docs, this time to Code.diagnostic and Mix.Tasks.Compiler.Diagnostic.

[lukaszsamson]

Thanks for explaining that

You may choose to traverse the stacktrace (perhaps trying to match against one of the project modules/files)

Thats what I need to do. Is there an API for that?

[josevalim]

No, but I think it is specific to your use case. But the stacktrace is a publically documented data structure, so you can traverse it as you prefer.