lfs: add a TODO file This is a cleaned up and reorganized list of items I sent out about a year ago. But tracking this in the repo (like the narrow extension) gives more visibility in case anyone wants to help out.

copies: make "limit" argument to _tracefile() mandatory We always pass a limit. I think the fact that it was optional was also the reason we checked ">=limit" before we used it. So now we can remove that condition too. Differential Revision: https://phab.mercurial-scm.org/D6335

localrepo: don't use defaults arguments that will never be overridden The commithook() callback will be called when the lock is released. lock.release() calls the callback without arguments, so it was quite confusing to me that this function declared extra arguments. We can just close on the variables in the outer scope instead. Differential Revision: https://phab.mercurial-scm.org/D6336

tags: avoid double-reversing a list Differential Revision: https://phab.mercurial-scm.org/D6337

updatecaches: also warm hgtagsfnodescache Now that a full update of this cache run in a reasonable amount of time, we can warm everything when during a full update.

hgtagsfnodescache: inherit fnode from parent when possible If a changeset does not update the content of `.hgtags`, it means it will use the same file-node (for `.hgtags`) as its parents. In this case we can directly reuse the parent's file-node. We use this property when updating the `hgtagsfnodescache` taking a faster path if we already have a cached value for the parents of the node we are looking at. Doing so provides a large performance boost when looking at a lot of fnodes, especially on repository with very large manifest: timing for `tagsmod.fnoderevs(ui, repo, repo.changelog.revs())` mercurial: (41907 revisions, 1923 files) before: 6.9 seconds after: 2.7 seconds (-54%) pypy: (96266 revisions, 5198 files) before: 80 seconds after: 20 seconds (-75%) mozilla-central: (463411 revisions, 272080 files) before: 7166.4 seconds after: 47.8 seconds (-99%, x150 speedup) On a copy of mozilla-try with about 35K heads ans 1.7M changesets, this moves the computation from many hours to a couple of minutes, making it more interesting to do a full warm up of this cache before computing tags (from a cold cache). There seems to be other performance low hanging fruits, like avoiding the use of changectx or a more revision centric logic. However, the new code is fast enough for my needs right now.

hgtagsfnodescache: handle nullid lookup The null revision is empty, so it `.hgtags` content is `nullid` in regards with the `hgtagsfnodescache`. Dealing with `nullid` will help with the next changeset. Before this change, feeding `nullid` to `hgtagsfnodescache.getfnode` would return a wrong result (fnode for tip).