Fix crash in Macro.to_string

lib/elixir/lib/code/normalizer.ex

@@ -174,16 +174,17 @@ defmodule Code.Normalizer do
 
   # Sigils
   defp do_normalize({sigil, meta, [{:<<>>, _, args} = string, modifiers]} = quoted, state)
-       when is_list(args) and is_atom(sigil) do
-    case Atom.to_string(sigil) do
-      "sigil_" <> _ ->
-        meta =
-          meta
-          |> patch_meta_line(state.parent_meta)
-          |> Keyword.put_new(:delimiter, "\"")
-
-        {sigil, meta, [do_normalize(string, %{state | parent_meta: meta}), modifiers]}
+       when is_atom(sigil) and is_list(args) and is_list(modifiers) do
+    with "sigil_" <> _ <- Atom.to_string(sigil),
+         true <- binary_interpolated?(args),
+         true <- List.ascii_printable?(modifiers) do
+      meta =
+        meta
+        |> patch_meta_line(state.parent_meta)
+        |> Keyword.put_new(:delimiter, "\"")
 
+      {sigil, meta, [do_normalize(string, %{state | parent_meta: meta}), modifiers]}
+    else
       _ ->
         normalize_call(quoted, state)
     end

lib/elixir/test/elixir/code_normalizer/quoted_ast_test.exs

@@ -172,6 +172,20 @@ defmodule Code.Normalizer.QuotedASTTest do
              ) == ~s[~S"""\n"123"\n"""]
     end
 
+    test "regression: invalid sigil calls" do
+      assert quoted_to_string(quote do: sigil_r(<<"foo", 123>>, [])) ==
+               "sigil_r(<<\"foo\", 123>>, [])"
+
+      assert quoted_to_string(quote do: sigil_r(<<"foo">>, :invalid_modifiers)) ==
+               "sigil_r(\"foo\", :invalid_modifiers)"
+
+      assert quoted_to_string(quote do: sigil_r(<<"foo">>, [:invalid_modifier])) ==
+               "sigil_r(\"foo\", [:invalid_modifier])"
+
+      assert quoted_to_string(quote do: sigil_r(<<"foo">>, [])) == "~r\"foo\""
+      assert quoted_to_string(quote do: sigil_r(<<"foo">>, [?a, ?b, ?c])) == "~r\"foo\"abc"
+    end
+
     test "tuple" do
       assert quoted_to_string(quote do: {1, 2}) == "{1, 2}"
       assert quoted_to_string(quote do: {1}) == "{1}"