view .hg-format-source @ 5680:18a70ae9fb0b

topic: add a basic in-memory cache for topic information

Right now reading topic information twice means we uncompress a full revision
twice. On a simple `hg topic --age` in my mercurial clone, the total runtime
goes from 40s to 10s. Still too slow, but significantly less.

{"pattern": "glob:hgext3rd/**/*.py", "tool": "byteify-strings"}