Deprecate escaping closing delimiter in uppercase sigils

This aligns our uppercase sigils with Erlang/OTP 27.

Author: josevalim

lib/elixir/lib/kernel.ex

@@ -6054,8 +6054,7 @@ defmodule Kernel do
   Handles the sigil `~S` for strings.
 
   It returns a string without interpolations and without escape
-  characters, except for the escaping of the closing sigil character
-  itself.
+  characters.
 
   ## Examples
 
@@ -6066,12 +6065,6 @@ defmodule Kernel do
       iex> ~S(\o/)
       "\\o/"
 
-  However, if you want to reuse the sigil character itself on
-  the string, you need to escape it:
-
-      iex> ~S((\))
-      "()"
-
   """
   defmacro sigil_S(term, modifiers)
   defmacro sigil_S({:<<>>, _, [binary]}, []) when is_binary(binary), do: binary
@@ -6108,8 +6101,7 @@ defmodule Kernel do
   Handles the sigil `~C` for charlists.
 
   It returns a charlist without interpolations and without escape
-  characters, except for the escaping of the closing sigil character
-  itself.
+  characters.
 
   A charlist is a list of integers where all the integers are valid code points.
   The three expressions below are equivalent:
@@ -6519,8 +6511,7 @@ defmodule Kernel do
   Handles the sigil `~W` for list of words.
 
   It returns a list of "words" split by whitespace without interpolations
-  and without escape characters, except for the escaping of the closing
-  sigil character itself.
+  and without escape characters.
 
   ## Modifiers
 

lib/elixir/src/elixir_interpolation.erl

@@ -33,7 +33,17 @@ extract([$\n | Rest], Buffer, Output, Line, _Column, Scope, Interpol, Last) ->
   extract_nl(Rest, [$\n | Buffer], Output, Line, Scope, Interpol, Last);
 
 extract([$\\, Last | Rest], Buffer, Output, Line, Column, Scope, Interpol, Last) ->
-  extract(Rest, [Last | Buffer], Output, Line, Column+2, Scope, Interpol, Last);
+  NewScope =
+    %% TODO: Remove this on Elixir v2.0
+    case Interpol of
+      true ->
+        Scope;
+      false ->
+        Msg = "using \\~ts to escape the closing of an uppercase sigil is deprecated, please use another delimiter or a lowercase sigil instead",
+        prepend_warning(Line, Column, io_lib:format(Msg, [[Last]]), Scope)
+    end,
+
+  extract(Rest, [Last | Buffer], Output, Line, Column+2, NewScope, Interpol, Last);
 
 extract([$\\, Last, Last, Last | Rest], Buffer, Output, Line, Column, Scope, Interpol, [Last, Last, Last] = All) ->
   extract(Rest, [Last, Last, Last | Buffer], Output, Line, Column+4, Scope, Interpol, All);
@@ -279,3 +289,6 @@ build_string(Buffer, Output) -> [lists:reverse(Buffer) | Output].
 
 build_interpol(Line, Column, EndLine, EndColumn, Buffer, Output) ->
   [{{Line, Column, nil}, {EndLine, EndColumn, nil}, Buffer} | Output].
+
+prepend_warning(Line, Column, Msg, #elixir_tokenizer{warnings=Warnings} = Scope) ->
+  Scope#elixir_tokenizer{warnings = [{{Line, Column}, Msg} | Warnings]}.

lib/elixir/test/elixir/kernel/sigils_test.exs

@@ -27,8 +27,6 @@ defmodule Kernel.SigilsTest do
     assert ~S(f#{o}o) == "f\#{o}o"
     assert ~S(f\#{o}o) == "f\\\#{o}o"
     assert ~S(f\no) == "f\\no"
-    assert ~S(foo\)) == "foo)"
-    assert ~S[foo\]] == "foo]"
   end
 
   test "sigil S newline" do
@@ -42,14 +40,6 @@ bar) in ["foo\\\nbar", "foo\\\r\nbar"]
            """
   end
 
-  test "sigil S with escaping" do
-    assert "\"" == ~S"\""
-
-    assert "\"\"\"\n" == ~S"""
-           \"""
-           """
-  end
-
   test "sigil s/S expand to binary when possible" do
     assert Macro.expand(quote(do: ~s(foo)), __ENV__) == "foo"
     assert Macro.expand(quote(do: ~S(foo)), __ENV__) == "foo"

lib/elixir/test/elixir/kernel/warning_test.exs

@@ -1099,6 +1099,10 @@ defmodule Kernel.WarningTest do
     purge(UseSample)
   end
 
+  test "deprecated closing sigil delimiter" do
+    assert_warn_eval(["nofile:1:7", "deprecated"], "~S(foo\\))")
+  end
+
   test "deprecated not left in right" do
     assert_warn_eval(["nofile:1:7", "deprecated"], "not 1 in [1, 2, 3]")
   end