Do not open nesting for character literals

lib/irb/nesting_parser.rb

@@ -222,6 +222,7 @@ def heredoc_string_like(node, type)
           # Heredoc closing contains trailing newline. We need to exclude it
           close_location_start(node.closing_loc) if node.closing_loc && !node.closing.empty?
         elsif node.opening
+          return if node.opening == '?' && node.closing.nil? # Character literal has no closing
           open_location(node.location, type, node.opening)
           if node.closing && node.closing != ''
             # Closing of `"#{\n` is "\n". We need to treat it as not-closed.

test/irb/test_nesting_parser.rb

@@ -347,5 +347,15 @@ def test_case_in
         assert_equal(['in'], next_opens.map(&:tok))
       end
     end
+
+    def test_char_literal
+      code = <<~EOS
+        ?a
+      EOS
+      prev_opens, next_opens, min_depth = parse_by_line(code).last
+      assert_equal([], prev_opens)
+      assert_equal([], next_opens)
+      assert_equal(0, min_depth)
+    end
   end
 end