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.

commit: move the addremove logic around to make the next changeset clearer Lets do the noise now, without changing any thing. So the new changeset can focus on the actual semantic changes.

largefiles: link the core dirstate._changing context to the lfdirstate one This will be much cleaner and safer to make sure the two dirstates are in sync. This way, the large-files dirstate will simply inherit the state of the main dirstate, so if the core code does the right thing, the large-files code should be right too.

dirstate: add a context for tracking files change Let us start to use it. We will enforce it later.

dirstate: invalidate the dirstate change on transaction failure If the change context lives inside a transaction, the change are not flushed to disk on exit as this is delegated to the transaction. As a result we should also delegate the part that do cleanup on failure. The issue was caught by tests with other change, but it seems useful to fix this as soon as possible.

dirstate: factor the "changing" context logic out This makes it reusable for other types of changes.

dirstate: introduce a `is_changing_any` property This will embrace other cases than changing parents.

dirstate: rename `pendingparentchange` to `is_changing_parents` This is clearer and more inline witht he other change we did.

dirstate: rename _parentwriters to _changing_level We will have context for changing more than parents, so lets be prepared.

largefiles: remove the `changing_parents` context in `openlfdirstate` This code might run in any kind of change context, we should rely on the higher level context instead of opening our own.

largefiles: remove the second `changing_parents` in `updatelfiles` Now that the `update_file` call have been migrated, we can drop the semantically-wrong `changing_parents` context.

largefiles: remove the first `changing_parents` in `updatelfiles` Now that the `update_file` call have been migrated, we can drop the semantically-wrong `changing_parents` context.

largefiles: use `hacky_extension_update_file` in `updatelfiles` This is what the function is meant for.

largefiles: use `hacky_extension_update_file` in `synclfdirstate` This is what the function is meant for.

largefiles: use `hacky_extension_update_file` in `openlfdirstate` This is what the function is meant for.

win32text: make the hacky call cover more cases Now that I understand what this is doing, It seems like the case for `p1_tracked` were covered by neither the code nor the test. Now the code cover it at least.

win32text: drop the `changing_parents` context in revert upgrade We are not changing parents here, so let us not pretend we do.

win32text: clean up and clarify the post-revert hack of dirstate The change is unrelated to changing parents and should not be a in a "changing_parents" context. This call is quite hacky, but now it is at least explicitly hacky. We will drop the `changing_parents` context in the next changesets, but we kept this change simple to help readability.

dirstate: introduce a `hacky_extension_update_file` method See inline documentation for details.

mq: properly take the wlock during the full qfold operation Otherwise the operation could be raced… for unknown result.

locking: hold the wlock for the full duration of the "keyword demo" The risk of racing the demo is low, since it seems to create its own repository on the fly. However it is clearer and more consistent.

locking: grab the wlock before touching the dirstate in `perfdirstatewrite` If we touch the dirstate, we should hold the `wlock`.

locking: take the `wlock` for the full `hg addremove` duration Otherwise, there is a race condition window between the time we resolve the file to addremove with the matcher and the time we lock the repo and modify the dirstate. For example, the working copy might have been updated away, or purged, and the matched files would no longer be correct.

locking: take the `wlock` for the full `hg forget` duration Otherwise, there is a race condition window between the time we resolve the file to forget with the matcher and the time we lock the repo and modify the dirstate. For example, the working copy might have been updated away, or purged, and the matched files would no longer be correct.

locking: take the `wlock` for the full `hg remove` duration Otherwise, there is a race condition window between the time we resolve the file to remove with the matcher and the time we lock the repo and modify the dirstate. For example, the working copy might have been updated away, or purged, and the matched files would no longer be correct.

locking: take the `wlock` for the full `hg add` duration Otherwise, there is a race condition window between the time we resolve the file to add with the matcher and the time we lock the repo and modify the dirstate. For example, the working copy might have been updated away, or purged, and the matched files would no longer be correct.

dirstate: drop some very fishy looking piece of code This piece of code is marking the **real** dirstate file as a temporary transaction file. This means it get deleted on transaction rollback. This this quite wrong, especially as the comment points out some `dirstate.pending` motivation and the `.pending` file should already be fully managed by the transaction. The only ready I can think of this behavior not having awful results right now is because other transaction logic restore backed up content above the one that got wrongfully deleted. Let us stop doing this anyway, All tests seems happy.