Comment 33 for bug 349914

(In reply to comment #24)

> However, the PangoFcFontMap API docs say that a PangoFcFontMap should provide
> these functions. We create a PangoFcFontMap and pass it to Pango, so it would
> be reasonable for any future version of Pango or any shaper modules to expect
> these methods to be present.

If your concern future pango versions, then I suggest adding a compile-time version check on pango and setting the new methods instead of the deprecated new_font() and default_substitute().