Type check the function type on fun.()

Author: josevalim

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

@@ -318,6 +318,13 @@ defmodule Module.Types.Descr do
 
   ## Bitmaps
 
+  @doc """
+  Optimized version of `not empty?(intersection(fun(), type))`.
+  """
+  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))`.
   """

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

@@ -301,9 +301,16 @@ defmodule Module.Types.Expr do
 
   # TODO: fun.(args)
   def of_expr({{:., _meta1, [fun]}, _meta2, args}, stack, context) do
-    with {:ok, _fun_type, context} <- of_expr(fun, stack, context),
-         {:ok, _arg_types, context} <-
+    with {:ok, fun_type, context} <- of_expr(fun, stack, context),
+         {: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)
+        end
+
       {:ok, dynamic(), context}
     end
   end

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

@@ -21,6 +21,34 @@ defmodule Module.Types.ExprTest do
     assert typecheck!(fn -> :ok end) == fun()
   end
 
+  describe "funs" do
+    test "incompatible" do
+      assert typewarn!([%x{}], x.(1, 2)) ==
+               {dynamic(),
+                ~l"""
+                incompatible types in expression:
+
+                    x
+
+                expected type:
+
+                    fun()
+
+                but got type:
+
+                    dynamic(atom())
+
+                where "x" was given the type:
+
+                    # type: dynamic(atom())
+                    # from: types_test.ex:LINE-2
+                    %x{}
+
+                typing violation found at:\
+                """}
+    end
+  end
+
   describe "remotes" do
     test "dynamic calls" do
       assert typecheck!([%x{}], x.foo_bar()) == dynamic()