fix: improve handling of matched/unmatched expressions

lib/spitfire.ex

@@ -788,14 +788,33 @@ defmodule Spitfire do
         end
 
       parser = parser |> next_token() |> eat_eoe()
+      rhs_parser = parser
       {rhs, parser} = parse_expression(parser, precedence, false, false, false)
 
+      {rhs, parser} =
+        if unparenthesized_do_end_block?(rhs) do
+          parse_expression(rhs_parser, @lowest, false, false, false)
+        else
+          {rhs, parser}
+        end
+
       ast = {token, meta, [rhs]}
 
       {ast, parser}
     end
   end
 
+  defp unparenthesized_do_end_block?(ast) do
+    case ast do
+      {_, meta, _} when is_list(meta) ->
+        Keyword.has_key?(meta, :do) && Keyword.has_key?(meta, :end) &&
+          not Keyword.has_key?(meta, :parens)
+
+      _ ->
+        false
+    end
+  end
+
   defp parse_prefix_lone_identifer(parser) do
     trace "parse_prefix_lone_identifer", trace_meta(parser) do
       token = current_token(parser)

test/spitfire_test.exs

@@ -2163,6 +2163,16 @@ defmodule SpitfireTest do
         assert Spitfire.parse(code) == s2q(code)
       end
     end
+
+    test "operators on unmatched expression" do
+      code = ~S'''
+      +case a do
+        _ -> b
+      end |> c ** d >>> e
+      '''
+
+      assert Spitfire.parse(code) == s2q(code)
+    end
   end
 
   describe "code with errors" do