tag: move the prohibition of tagging the `null` rev up to the `wdir()` check It makes sense to do these together, and avoid another revision lookup.

branching: merge with default the first part of the fix is there

tests: remove unnecessary --traceback argument

dirstate: remove the dedicated backup logic When alone, the dirstate can now take care of its commit/rollback pattern itself. When in a transaction, the transaction deal with commit/rollback pattern quite fine. Why did you have a dedicated backup logic?

localrepo: stop doing special dirstate backup at transaction open Since the dirstate writes are already managed by the transaction, we already do a backup of the dirstate when necessary (and even trigger one to keep `hg rollback` happy). We needs some special code to deal with the initial empty checkout, but it is not too complicated. Managing variable filename (as dirstate-v2 uses) at the "journalfile" level, is complex and fragile (which is consistent with the fact these files are not journal…). If we no longer do it, our life is significantly simpler. In some sense, we apply the xkcd-1134¹ solution to our savebackup/restorebackup problem. [1] https://xkcd.com/1134/ (the change to test-hardlink are expect as decreasing the number of duplicated backup drive the hardlink count down)

localrepo: "blindly" do a dirstate backup at the end of the transaction Having the file backup mechanism dealing with file backup as benefit. So lets move closer to that. The fact `hg rollback` even needs this is sad. I hope to have the time to implement one of the alternative soon.

test-hardlink: stop explicitly listing `undo.dirstate` The files is on its way out.

localrepo: enforce a clean dirstate when the transaction open This is important to simplify the backup process. This also seems like a quite reasonable expectation. See inline documentation for details.

dirstate: explicitly backup the datafile Since the transaction does not know about this file, we need to explicitly mark it for backup before touching it.

mq: write the dirstate before stripping I am not certain why it is dirty (probably the `repo.setparent` call a right before. However I know we need it flushed before the repository starts to be stripped.

dirstate: simplify the shelve hack to not go through the disk We already have the data in memory, so why not simply keep the data in memory? This avoid abusing the `savebackup/restorebackup` logic and will make our life easier.

dirstate: detect potential fishy transaction patterns while changing If we rely on the transaction more, we should be more careful about the transaction. Adding extra security seems reasonable.

dirstate: generalize the dirstate's invalidation on transaction abort The previous code was too specific, we should add the invalidation at next to the `addfilegenerator` in the `write` call.

dirstate: simplify some methods' decorator Since `changing_parents` and `changing_files` are mutually exclusive, having both `@requires_changing_files` and `@requires_not_changing_parents` on a method is redundant.

dirstate: document the functions that need consolidation They are more functions that make the dirstate dirty but does not currently enforce a clean change scoping, we add comments in front of each of them so clarify this. There is no urgency to it, but the world will be a better place when all of them have proper scoping in place.

dirstate: make `restorebackup` more robust when it is a noop If there are no data_file, we might not be able to determine its filename. Which can be safely ignored. (all this code is on the way out anyway)

dirstate-guard: remove the feature The dirstate guard duplicated some of the logic already implemented in the transaction (and now the changing_* context). However the feature was incomplete, for example, living only in memory meant we could not recover from the hardest crash. In addition this duplicated with the transaction logic meant things could go out of sync or step on each other. Removing the feature now that we no longer needs it seems the safest.

rollback: remove the dirstateguard usage Thanks to the previous changeset, we no longer needs it. begone !

rollback: explicitly skip dirstate rollback when applicable instead of letting the transaction logic overwrite the dirstate and then overwrite that overwrite with a backup. We simply do not restore the dirstate related file during the _playback call. This open the way to removing the last dirstate guard usage.

rollback: detect "parentgone" case earlier Detecting this earlier will help us to affect the rollback process sooner, which will help the next changesets. To keep things simple, we degrade the behavior a bit when the `undo.desc` is missing. However since `hg rollback` is not supposed to be used and the `undo.desc` file have been introduced in mercurial 1.6 (2010). I think this is an acceptable evil.

rollback: avoid a `hg commit --addremove` at a critical point The rollback behavior around `hg commit --addremove` has changed slightly. It does not really matters here but keeping that variant out of the way cannot hurt.

rollback: display some graphlog before/after a test piece This make the situation clearer.

rollback: show that the safety works in a associated test That test section is checking that --force is overcoming the safety check, however we did not check that the safety properly detect the situation. We now do for clarity.

dirstate-guard: remove its usage in `backout` We can simply replace it with a transaction.

dirstate-guard: remove the usage in `import` It is now redundant with the transaction spawning the same scope.

dirstate-guard: replace a usage in `rebase` with a transaction Opening the transaction sooner will provide us with the same benefit.

dirstate-guard: remove usage in `rebase` Now that the dirstate change and write are clearer, it does not seems we need to use a dirstate-guard here anymore. The transaction already wrap the full operation.

dirstate-guard: remove it usage in `mq` The code it covered is also covered by a `changing_parents` context.

dirstate: enforce the use of `changing_files` context to change tracking Now that everything is using the new context, we can start enforcing its usage.

dirstate: warn if we write to the dirstate without holding the wlock Writing the dirstate without holding the wlock can race with other update and overwrite important change. The comment questionning the current state of things was right, we should the `wlock` should always cover the dirstate. (Yes, this is me, agreeing with myself, half a decade later).

dirstate: avoid transaction backup/restore if we do not hold the lock Doing overwriting the dirstate content without holding the lock is a recipe for disaster.

dirstate: issue a developer warning on implicit write on wlock release Our goal is to get rid of all these to clarify the writing pattern, so it is time to warn about this (and later, forbid it).

status: fix post status invalidation If the dirstate changed under us, we should throw away what we have a reload it, should we not ?

status: fix post status writing With dirstate-v2, the status process itself might update internal states. So we make sure this get written on disk

dirstate: use `dirstate.change_files` to scope the change in `shelve` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `unshelve` This is the way.

shelve: adjust what happens in some `changing_parents` context It seems like the rest is more about changing tracked_files, so we let start with moving them out of the `changing_parents` contexts.

dirstate: use `dirstate.change_files` to scope the change in `lfconvert` This is the way.

largefiles: rely on main scoping for writing dirstate in `markcommitted` Yeah, cleaner code.

largefiles: rely on main scoping for writing dirstate in `mergeupdate` Yeah, cleaner code.

largefiles: rely on the higher level `changing_giles` in `mergerecordupdates` Now that context open on the main dirstate also affect the underlying one, we can skip opening our own in `mergerecordupdates`

dirstate: use wlock and `dirstate.change_files` to scope the change in `mq` This is the way.

subrepo: use `changing_files` context in subrepository code This is better, not ideal, but better.

subrepo: let black expand some call on multiple lines early newer version of black are righfully doing this, so I apply it before more semantic change to reduce noise in the next changeset.

dirstate: use `dirstate.change_files` to scope the change in `import` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `automv` This is... mostly... the way.

dirstate: use `dirstate.change_files` to scope the change in `amend` This is the way.

dirstate: use the `changing_files` context in the `keyword` demo This is the way.

dirstate: wrap repository change in appropriate context in `test-context` We need the `wlock` (to add files), the `lock` (to commit), a `transaction` (to commit) and a `changing_files` context (to add files). Strictly speaking, we could let the commit take the `lock` and create a `transaction`, but it seems more consistent that way.

dirstate: use wlock and changing_files context in `test-revlog-ancestry` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `revert` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `gpg` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `tag` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `rename` This is the way, unless we are not actually touching the working copy. In such cases we don't need to do something.

dirstate: use `dirstate.change_files` to scope the change in `copy` This is the way, unless we are not actually touching the working copy. In such cases we don't need to do something.

dirstate: use `dirstate.change_files` to scope the change in `remove` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `forget` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `addremove` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `add` This is the way.

commit: use `dirstate.change_files` to scope the associated `addremove` This was significantly more complicated than I expected, because multiple extensions get in the way. I introduced a context that lazily open the transaction and associated context to work around these complication. See the inline documentation for details. Introducing the wrapping transaction remove the need for dirstate-guard (one of the ultimate goal of all this), and slightly affect the result of a `hg rollback` after a `hg commit --addremove`. That last part is deemed fine. It aligns the behavior with what happens after a failed `hg commit --addremove` and nobody should be using `hg rollback` anyway. The small output change in the test come from the different transaction timing and fact the transaction now backup the dirstate before the addremove, which might mean "no file to backup" when the repository starts from an empty state.