Fix a bug where unquote_splicing did not work on the left side of a stab op

Author: José Valim

CHANGELOG.md

@@ -4,8 +4,9 @@
 
 * bug fix
   * [Dict] `Enum.to_list` and `Dict.to_list` now return the same results for dicts
-  * [Record] Fix a bug where nested records cannot be defined
+  * [Kernel] Fix a bug where `unquote_splicing` did not work on the left side of a stab op
   * [Mix] Fix a bug where `mix deps.get` was not retrieving nested dependencies
+  * [Record] Fix a bug where nested records cannot be defined
 
 * deprecations
 

lib/elixir/src/elixir_parser.yrl

@@ -215,8 +215,8 @@ stab_eol -> stab eol : '$1'.
 
 stab_expr -> expr : '$1'.
 stab_expr -> stab_op stab_maybe_expr : build_op('$1', [], '$2').
-stab_expr -> call_args_no_parens stab_op stab_maybe_expr : build_op('$2', '$1', '$3').
-stab_expr -> call_args_parens_not_one stab_op stab_maybe_expr : build_op('$2', '$1', '$3').
+stab_expr -> call_args_no_parens stab_op stab_maybe_expr : build_op('$2', unwrap_splice('$1'), '$3').
+stab_expr -> call_args_parens_not_one stab_op stab_maybe_expr : build_op('$2', unwrap_splice('$1'), '$3').
 
 stab_maybe_expr -> 'expr' : '$1'.
 stab_maybe_expr -> '$empty' : nil.
@@ -591,6 +591,18 @@ build_stab([], Marker, Temp, Acc) ->
   H = { Marker, build_block(lists:reverse(Temp)) },
   lists:reverse([H|Acc]).
 
+%% Every time the parser sees a (unquote_splicing())
+%% it assumes that a block is being spliced, wrapping
+%% the splicing in a __block__. But in the stab cause,
+%% we can have (unquote_splicing(1,2,3)) -> :ok, in such
+%% case, we don't actually want the block, since it is
+%% an arg style call. unwrap_splice unwraps the splice
+%% from such blocks.
+unwrap_splice([{ '__block__', [], [{ unquote_splicing, _, _ }] = Splice }]) ->
+  Splice;
+
+unwrap_splice(Other) -> Other.
+
 %% Errors
 
 throw(Line, Error, Token) ->

lib/elixir/test/elixir/kernel/quote_test.exs

@@ -102,6 +102,16 @@ defmodule Kernel.QuoteTest do
     assert quote(do: [unquote_splicing(contents)|[1,2,3]]) == [1,2,3,1,2,3]
   end
 
+  test :splice_on_stab do
+    { fun, [] } =
+      Code.eval_quoted(quote(do: fn(unquote_splicing([1,2,3])) -> :ok end), [])
+    assert fun.(1,2,3) == :ok
+
+    { fun, [] } =
+      Code.eval_quoted(quote(do: fn(1, unquote_splicing([2,3])) -> :ok end), [])
+    assert fun.(1,2,3) == :ok
+  end
+
   test :stab do
     assert { :->, _, [{[],_}] } = (quote do -> end)
     assert { :->, _, [{[],_}] } = (quote do: (->))