search for: xsubstitutions

...ons (e.g. %s) to absolute paths, and I'd like to be able to introduce substitutions for the source path relative to the source root. This seems generally useful -- if there was a way in lit.cfg to register a function for substitution instead of a simple pair, we could do stuff like: config.xsubstitutions.append(('%r', lambda s: os.path.relpath(s, some_root))) Most of the simple builtin substitutions are variations on this theme, so I guess they could be implemented similarly. Is this a useful direction? Would you accept lit patches to that end? Thanks, - Kim