Standard methods missing in Ruby C API

For a few years now, I’ve been using my Ruby-enhanced MicroEMACS to write editor extensions. I implemented this feature using the Ruby C API, which allows Ruby code to manipulate the edit buffer. But when I tried to build the editor on Linux Mint 22 (Ubuntu 24.04), I discovered that the Time.now class method is no longer available in editor extensions. A similar issue occurred on Fedora 42: the Symbol#to_s instance method doesn’t produce the expected result.

Time.now

The Time.now problem affected an extension I’d written that used Time.new in several places, and now I was getting an error that Time didn’t have a now method. This seemed weird, because outside of the editor, Time.now still worked. After a long slog through Ruby documentation, source code, and header files, I came across this commit in the Ruby source code with this comment: “Moved Time.now to builtin”.

Somehow the Ruby interpreter, when run outside of the editor, is able to patch up the Time class to use the built-in definition, but I wasn’t able to figure out how to do that using only the Ruby C API. However, I did find a way to do that in a mix of C and Ruby.

First, in the editor’s C code, define a Ruby-callable function that uses rb_time_timespec_new to fetch the current local time:

static VALUE
my_now (VALUE self)
{
  struct timespec ts;
  VALUE now;

  rb_timespec_now (&ts);
  now = rb_time_timespec_new (&ts, INT_MAX);
  return now;
}

Then tell Ruby about this function and give it the name timenow:

  rb_define_global_function("timenow", my_now, 0);

Finally, in the Ruby helper script that the editor loads at startup, add some code that dynamically creates the Time.now class method if it’s not available:

class Time
  unless Time.respond_to?(:now)
    class << self
      define_method(:now) { timenow }
    end
  end
end

This works on Linux Mint 21 (which does provide Time.now via the API) and Linux Mint 22 (which does not provide Time.now via the API).

Symbol#to_s

I installed Fedora 42 on a spare laptop, and discovered a similar problem: calling to_s on a symbol didn’t produce the expected string, but instead seemed to do nothing, i.e. returned the symbol unchanged. This caused the editor’s helper file pe.rb to fail when attempting to call a MicroEMACS command. Also, the method Symbol#name, which works outside the editor, was undefined, so I couldn’t use that.

The solution was very similar to the Time.now solution: implement a helper function in C to fetch the string representation of a symbol, and define a Symbol#to_s method to use that helper function.

First, in the editor’s C code, define a Ruby-callable function that uses rb_sym_to_s to get the string name of a symbol:

static VALUE
my_sym2str (VALUE self, VALUE sym)
{
  VALUE ret;

  ret = rb_sym_to_s (sym);
  return ret;
}

Then tell Ruby about this function and give it the name sym2str:

  rb_define_global_function("sym2str", my_sym2str, 1);

Finally, in the Ruby helper script that the editor loads at startup, add some code that dynamically creates the Symbol#to_s instance method if Symbol#name is not available:

class Symbol
  unless :name.respond_to?(:name)
    define_method(:to_s) { sym2str(self) }
  end
end