Fix fun_fetch

Author: josevalim

lib/elixir/lib/module/types/descr.ex

@@ -365,15 +365,6 @@ defmodule Module.Types.Descr do
 
   ## Bitmaps
 
-  @doc """
-  Optimized version of `not empty?(intersection(fun(), type))`.
-  """
-  def fun_type?(:term), do: true
-  def fun_type?(%{dynamic: :term}), do: true
-  def fun_type?(%{dynamic: %{bitmap: bitmap}}) when (bitmap &&& @bit_fun) != 0, do: true
-  def fun_type?(%{bitmap: bitmap}) when (bitmap &&& @bit_fun) != 0, do: true
-  def fun_type?(_), do: false
-
   @doc """
   Optimized version of `not empty?(intersection(binary(), type))`.
   """
@@ -434,6 +425,29 @@ defmodule Module.Types.Descr do
         do: {type, [], []}
   end
 
+  ## Funs
+
+  @doc """
+  Checks there is precisely one function with said arity.
+  """
+  def fun_fetch(:term, _arity), do: :error
+
+  def fun_fetch(%{} = descr, _arity) do
+    {static_or_dynamic, static} = Map.pop(descr, :dynamic, descr)
+
+    if fun_only?(static) do
+      case static_or_dynamic do
+        :term -> :ok
+        %{bitmap: bitmap} when (bitmap &&& @bit_fun) != 0 -> :ok
+        %{} -> :error
+      end
+    else
+      :error
+    end
+  end
+
+  defp fun_only?(descr), do: empty?(difference(descr, fun()))
+
   ## Atoms
 
   # The atom component of a type consists of pairs `{tag, set}` where `set` is a

lib/elixir/lib/module/types/expr.ex

@@ -305,10 +305,9 @@ defmodule Module.Types.Expr do
          {:ok, _args_types, context} <-
            map_reduce_ok(args, context, &of_expr(&1, stack, &2)) do
       context =
-        if fun_type?(fun_type) do
-          context
-        else
-          Of.incompatible_warn(fun, fun(), fun_type, stack, context)
+        case fun_fetch(fun_type, length(args)) do
+          :ok -> context
+          :error -> Of.incompatible_warn(fun, fun(), fun_type, stack, context)
         end
 
       {:ok, dynamic(), context}

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

@@ -271,6 +271,13 @@ defmodule Module.Types.DescrTest do
   end
 
   describe "projections" do
+    test "fun_fetch" do
+      assert fun_fetch(term(), 1) == :error
+      assert fun_fetch(union(term(), dynamic(fun())), 1) == :error
+      assert fun_fetch(fun(), 1) == :ok
+      assert fun_fetch(dynamic(), 1) == :ok
+    end
+
     test "atom_fetch" do
       assert atom_fetch(term()) == :error
       assert atom_fetch(union(term(), dynamic(atom([:foo, :bar])))) == :error