templater: abstract away from joinfmt Future patches will add a wrapper for a list of template mappings, which will implement a custom join() something like {join(mappings % template)}. The original join() function is broken down as follows: if hasattr(joinset, 'joinfmt'): # hybrid.join() where values must be a list or a dict joinitems((joinfmt(x) for x in values), sep) elif isinstance(joinset, templateutil.wrapped): # mappable.join() show() else: # a plain list, a generator, or a byte string; joinfmt was identity() joinset = templateutil.unwrapvalue(context, joinset) joinitems(pycompat.maybebytestr(joinset), joiner)