From 10f2ef2305146e1ec40429b9e1c07c06ea3ae41b Mon Sep 17 00:00:00 2001
From: sabiwara <sabiwara@gmail.com>
Date: Fri, 20 Dec 2024 09:53:39 +0900
Subject: [PATCH 1/2] Remove no_parens when using capture with arity

Close #14089
---
 lib/elixir/src/elixir_fn.erl                     | 9 +++++++++
 lib/elixir/test/elixir/kernel/expansion_test.exs | 5 +++++
 lib/elixir/test/elixir/kernel/fn_test.exs        | 6 ++++++
 3 files changed, 20 insertions(+)

diff --git a/lib/elixir/src/elixir_fn.erl b/lib/elixir/src/elixir_fn.erl
index 668b201909d..89688ccae99 100644
--- a/lib/elixir/src/elixir_fn.erl
+++ b/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);
+    {EExpr, []} ->
+      Meta2 = lists:keydelete(no_parens, 1, Meta),
+      Fn = {fn, Meta2, [{'->', Meta2, [[], remove_no_parens(EExpr)]}]},
+      {expand, Fn, S, E};
     {EExpr, EDict} ->
       EVars = validate(Meta, EDict, 1, E),
       Fn = {fn, Meta, [{'->', Meta, [EVars, EExpr]}]},
@@ -121,6 +125,11 @@ capture_expr(Meta, Expr, S, E, Escaped, Sequential) ->
 invalid_capture(Meta, Arg, E) ->
   file_error(Meta, E, ?MODULE, {invalid_args_for_capture, Arg}).
 
+remove_no_parens({{'.', _, [_, _]} = Dot, Meta, Args}) when is_list(Args) ->
+  Meta2 = lists:keydelete(no_parens, 1, Meta),
+  {Dot, Meta2, Args};
+remove_no_parens(Other) -> Other.
+
 validate(Meta, [{Pos, Var} | T], Pos, E) ->
   [Var | validate(Meta, T, Pos + 1, E)];
 validate(Meta, [{Pos, _} | _], Expected, E) ->
diff --git a/lib/elixir/test/elixir/kernel/expansion_test.exs b/lib/elixir/test/elixir/kernel/expansion_test.exs
index 81b0a65a70b..4e08384a5b0 100644
--- a/lib/elixir/test/elixir/kernel/expansion_test.exs
+++ b/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)
diff --git a/lib/elixir/test/elixir/kernel/fn_test.exs b/lib/elixir/test/elixir/kernel/fn_test.exs
index 1304d753577..0d0e8471994 100644
--- a/lib/elixir/test/elixir/kernel/fn_test.exs
+++ b/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"

From 129b5880c324ca77ae834e50865e872871591ee9 Mon Sep 17 00:00:00 2001
From: sabiwara <sabiwara@gmail.com>
Date: Fri, 20 Dec 2024 10:43:42 +0900
Subject: [PATCH 2/2] More concise implementation

---
 lib/elixir/src/elixir_fn.erl | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/lib/elixir/src/elixir_fn.erl b/lib/elixir/src/elixir_fn.erl
index 89688ccae99..fafdbd8207a 100644
--- a/lib/elixir/src/elixir_fn.erl
+++ b/lib/elixir/src/elixir_fn.erl
@@ -112,9 +112,9 @@ capture_expr(Meta, Expr, S, E, Escaped, Sequential) ->
   case escape(Expr, E, Escaped) of
     {_, []} when not Sequential ->
       invalid_capture(Meta, Expr, E);
-    {EExpr, []} ->
+    {{{'.', _, [_, _]} = Dot, _, Args}, []} ->
       Meta2 = lists:keydelete(no_parens, 1, Meta),
-      Fn = {fn, Meta2, [{'->', Meta2, [[], remove_no_parens(EExpr)]}]},
+      Fn = {fn, Meta2, [{'->', Meta2, [[], {Dot, Meta2, Args}]}]},
       {expand, Fn, S, E};
     {EExpr, EDict} ->
       EVars = validate(Meta, EDict, 1, E),
@@ -125,11 +125,6 @@ capture_expr(Meta, Expr, S, E, Escaped, Sequential) ->
 invalid_capture(Meta, Arg, E) ->
   file_error(Meta, E, ?MODULE, {invalid_args_for_capture, Arg}).
 
-remove_no_parens({{'.', _, [_, _]} = Dot, Meta, Args}) when is_list(Args) ->
-  Meta2 = lists:keydelete(no_parens, 1, Meta),
-  {Dot, Meta2, Args};
-remove_no_parens(Other) -> Other.
-
 validate(Meta, [{Pos, Var} | T], Pos, E) ->
   [Var | validate(Meta, T, Pos + 1, E)];
 validate(Meta, [{Pos, _} | _], Expected, E) ->