Checks what recipes are being built to see which of the alternative
        and optional dependencies are being used,
        and returns a list of these.

def check_recipe_choices(self):
        '''Checks what recipes are being built to see which of the alternative
        and optional dependencies are being used,
        and returns a list of these.'''
        recipes = []
        built_recipes = self.ctx.recipe_build_order
        for recipe in self.depends:
            if isinstance(recipe, (tuple, list)):
                for alternative in recipe:
                    if alternative in built_recipes:
                        recipes.append(alternative)
                        break
        for recipe in self.opt_depends:
            if recipe in built_recipes:
                recipes.append(recipe)
        return sorted(recipes)