String.slice(str, 0, -1) raises FunctionClauseError

重現 String.slice(str, 0, -1) 的情況，並從 lib/elixir_script/passes/translate/form.ex:28 開始，接著檢查 lib/elixir_script/passes/translate/forms/map.ex 中的 map 處理，以及 lib/elixir_script/passes/translate/function.ex 中的編譯路徑。完成的條件是：該表達式能在不出現所回報的 FunctionClauseError 的情況下編譯，且產生的 JavaScript 行為已被涵蓋或驗證。

This snippet of Elixir:

String.slice(str, 0, -1)

Started with slice/2 form of this call, but swapped to slice/3 to confirm the error wasn't being generated by the Elixir range.

Raises the following exception

** (EXIT from #PID<0.95.0>) an exception was raised:
** (FunctionClauseError) no function clause matching in ElixirScript.Translate.Form.compile/2
lib/elixir_script/passes/translate/form.ex:28: ElixirScript.Translate.Form.compile(&Inspect.inspect/2, %{anonymous_fn: false, function: {:struct, nil}, in_guard: false, module: Inspect.Opts, pid: #PID<0.200.0>, vars: %{}})
lib/elixir_script/passes/translate/form.ex:16: ElixirScript.Translate.Form.compile!/2
lib/elixir_script/passes/translate/forms/map.ex:37: anonymous fn/2 in ElixirScript.Translate.Forms.Map.compile/2
(elixir 1.10.4) lib/enum.ex:1396: Enum."-map/2-lists^map/1-0-"/2
(elixir 1.10.4) lib/enum.ex:1396: Enum."-map/2-lists^map/1-0-"/2
lib/elixir_script/passes/translate/forms/map.ex:32: ElixirScript.Translate.Forms.Map.compile/2
lib/elixir_script/passes/translate/form.ex:16: ElixirScript.Translate.Form.compile!/2
lib/elixir_script/passes/translate/function.ex:170: ElixirScript.Translate.Function.compile_block/2

Modified Transcript.Form.compile! as follows:

  @spec compile!(any, map) :: ESTree.Node.t()
  def compile!(ast, state) do
    {js_ast, _} = compile(ast, state)
    js_ast
  rescue
    e -> Logger.debug inspect({:compile!, ast, state})
         raise RuntimeError, message: inspect({"compile!/2", e})
  end

Which revealed the following debugging info:

03:45:21.580 [debug] {:compile!, &Inspect.inspect/2, %{anonymous_fn: false, function: {:struct, nil}, in_guard: false, module: Inspect.Opts, pid: #PID<0.200.0>, vars: %{}}}

03:45:21.696 [debug] {:compile!, {:%{}, [line: 74], [struct: Inspect.Opts, base: :decimal, binaries: :infer, char_lists: :infer, charlists: :infer, custom_options: [], inspect_fun: &Inspect.inspect/2, limit: 50, pretty: false, printable_limit: 4096, safe: true, structs: true, syntax_colors: [], width: 80]}, %{anonymous_fn: false, function: {:struct, nil}, in_guard: false, module: Inspect.Opts, pid: #PID<0.200.0>, vars: %{}}}

Thoughts

Not too familiar with this codebase, but I'm working from the premise that inspect_fun: &Inspect.inspect/2 might be malformed, for it to be promoted into the ast parameter of compile!.