Unclear exception raised without reference to program text when `raise :symbol` appears in source

[slondr]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.1.3] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit:ns]

Elixir 1.17.3 (compiled with Erlang/OTP 27)

Operating system

Arch Linux

Current behavior

When compiling the following file with elixirc a.ex:

defmodule A do
  def foo do
    raise :todo
  end
end

A rather unhelpful error message appears indicating a problem in elixir's Module.ParallelChecker, which doesn't indicate what if anything in the program text is wrong:

** (EXIT from #PID<0.95.0>) an exception was raised:
    ** (FunctionClauseError) no function clause matching in :lists.duplicate/2
        (stdlib 6.1.2) lists.erl:510: :lists.duplicate(-3, 126)
        (elixir 1.17.3) src/elixir_errors.erl:223: :elixir_errors.highlight_below_line/2
        (elixir 1.17.3) src/elixir_errors.erl:156: :elixir_errors.format_snippet/6
        (elixir 1.17.3) src/elixir_errors.erl:74: :elixir_errors.print_diagnostic/2
        (elixir 1.17.3) lib/module/parallel_checker.ex:323: anonymous fn/2 in Module.ParallelChecker.emit_warnings/2
        (elixir 1.17.3) lib/enum.ex:4353: Enum.flat_map_list/2
        (elixir 1.17.3) lib/module/parallel_checker.ex:267: Module.ParallelChecker.check_module/3
        (elixir 1.17.3) lib/module/parallel_checker.ex:82: anonymous fn/6 in Module.ParallelChecker.spawn/4

Expected behavior

elixirc tells me about the problem with my source code.

At the suggestion of some kind folks in the elixir irc chat, I used break! to hop into parallel_checker.ex:323, which did seem to have error information about the unacceptable argument to raise at the time of the error.

[josevalim]

Unfortunately I cannot reproduce this:

~/OSS/phoenix[main %]$ elixirc a.ex
    warning: redefining module A (current version loaded from Elixir.A.beam)
    │
  1 │ defmodule A do
    │ ~~~~~~~~~~~~~~
    │
    └─ a.ex:1: A (module)

    warning: :todo.exception/1 is undefined (module :todo is not available or is yet to be defined)
    │
  3 │     raise :todo
    │     ~~~~~~~~~~~
    │
    └─ a.ex:3: A.foo/0

I will try to look at the stacktrace though and understand what is going wrong.

[josevalim]

I got this! The error only happens if you use tabs for indentation.

[slondr]

That'll do it :D