Remove no_parens when using capture with arity (#14090)

Author: sabiwara

lib/elixir/src/elixir_fn.erl

@@ -112,6 +112,10 @@ capture_expr(Meta, Expr, S, E, Escaped, Sequential) ->
   case escape(Expr, E, Escaped) of
     {_, []} when not Sequential ->
       invalid_capture(Meta, Expr, E);
+    {{{'.', _, [_, _]} = Dot, _, Args}, []} ->
+      Meta2 = lists:keydelete(no_parens, 1, Meta),
+      Fn = {fn, Meta2, [{'->', Meta2, [[], {Dot, Meta2, Args}]}]},
+      {expand, Fn, S, E};
     {EExpr, EDict} ->
       EVars = validate(Meta, EDict, 1, E),
       Fn = {fn, Meta, [{'->', Meta, [EVars, EExpr]}]},

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -1203,6 +1203,11 @@ defmodule Kernel.ExpansionTest do
                 [{:->, [{:line, 1}], [[{:capture, [line: 1], nil}], {:capture, [line: 1], nil}]}]}
     end
 
+    test "removes no_parens when expanding 0-arity capture to fn" do
+      assert expand(quote(do: &foo().bar/0)) ==
+               quote(do: fn -> foo().bar() end)
+    end
+
     test "expands remotes" do
       assert expand(quote(do: &List.flatten/2)) ==
                quote(do: &:"Elixir.List".flatten/2)

lib/elixir/test/elixir/kernel/fn_test.exs

@@ -95,6 +95,12 @@ defmodule Kernel.FnTest do
     assert (&mod.flatten/1) == (&List.flatten/1)
   end
 
+  test "capture with module from local call" do
+    assert (&math_mod().pi/0).() == :math.pi()
+  end
+
+  defp math_mod, do: :math
+
   test "local partial application" do
     assert (&atb(&1, :utf8)).(:a) == "a"
     assert (&atb(List.to_atom(&1), :utf8)).(~c"a") == "a"