Improve none reporting

Author: josevalim

lib/elixir/lib/module/types.ex

@@ -27,7 +27,6 @@ defmodule Module.Types do
       # TODO: Reuse context from patterns and guards
       # TODO: Simplify pair types
       # TODO: Handle local calls
-      # TODO: Improve errors on bad apply if one of the arguments are empty
       {{fun, arity}, {:infer, pair_types}}
     end
   end

lib/elixir/lib/module/types/helpers.ex

@@ -202,6 +202,15 @@ defmodule Module.Types.Helpers do
     |> Macro.to_string()
   end
 
+  defp erl_to_ex(
+         :erlang,
+         :error,
+         [expr, :none, [error_info: {:%{}, _, [module: Exception]}]],
+         meta
+       ) do
+    {:raise, meta, [expr]}
+  end
+
   defp erl_to_ex(mod, fun, args, meta) do
     case :elixir_rewrite.erl_to_ex(mod, fun, args) do
       {Kernel, fun, args, _} -> {fun, meta, args}

lib/elixir/lib/module/types/of.ex

@@ -1076,6 +1076,21 @@ defmodule Module.Types.Of do
     {{:., _, [mod, fun]}, _, args} = expr
     {mod, fun, args, converter} = :elixir_rewrite.erl_to_ex(mod, fun, args)
 
+    explanation =
+      if i = Enum.find_index(args_types, &empty?/1) do
+        """
+        the #{integer_to_ordinal(i + 1)} argument is empty (often represented as none()), \
+        most likely because it is the result of an expression that always fails, such as \
+        a `raise` or a previous invalid call. This causes any subsequent function call with \
+        said value to always fail
+        """
+      else
+        """
+        but expected one of:
+        #{clauses_args_to_quoted_string(clauses, converter)}
+        """
+      end
+
     %{
       details: %{typing_traces: traces},
       message:
@@ -1089,9 +1104,8 @@ defmodule Module.Types.Of do
 
               #{args_to_quoted_string(args_types, domain, converter) |> indent(4)}
 
-          but expected one of:
-          #{clauses_args_to_quoted_string(clauses, converter)}
           """,
+          explanation,
           format_traces(traces)
         ])
     }
@@ -1278,4 +1292,13 @@ defmodule Module.Types.Of do
       single_line -> binary_slice(single_line, 1..-2//1)
     end
   end
+
+  defp integer_to_ordinal(i) do
+    case rem(i, 10) in [1, 2, 3] do
+      1 when rem(i, 100) != 11 -> "#{i}st"
+      2 when rem(i, 100) != 12 -> "#{i}nd"
+      3 when rem(i, 100) != 13 -> "#{i}rd"
+      _ -> "#{i}th"
+    end
+  end
 end

lib/elixir/test/elixir/module/types/expr_test.exs

@@ -165,6 +165,25 @@ defmodule Module.Types.ExprTest do
                {union(dynamic(), binary()), "GenServer.to_string/1 is undefined or private"}
     end
 
+    test "calling a function with none()" do
+      assert typeerror!(Integer.to_string(raise "oops")) |> strip_ansi() ==
+               ~l"""
+               incompatible types given to Integer.to_string/1:
+
+                   Integer.to_string(raise RuntimeError.exception("oops"))
+
+               given types:
+
+                   none()
+
+               the 1th argument is empty (often represented as none()), \
+               most likely because it is the result of an expression that \
+               always fails, such as a `raise` or a previous invalid call. \
+               This causes any subsequent function call with said value \
+               to always fail
+               """
+    end
+
     test "calling a nullary function on non atoms" do
       assert typeerror!([<<x::integer>>], x.foo_bar()) ==
                ~l"""