It's common to create empty working-copy commits while using jj, and
currently the author timestamp for a commit is only set when it is first
created. If you create an empty commit, then don't work on a repo for a
few days, and then start working on a new feature without abandoning the
working-copy commit, the author timestamp will remain as the time the
commit was created rather than being updated to the time that work began
or finished.
This commit changes the behavior so that discardable commits (empty
commits with no description) by the current user have their author
timestamps reset when they are rewritten, meaning that the author
timestamp will become finalized whenever a commit is given a description
or becomes non-empty.
I'm going to make some `jj parallelize` cases that currently error out
instead be successful. Some of the will result in ancestor merges with
the root commit. This patch updates those tests to avoid that.
`jj parallelize` was a good example of a command that can be
simplified by the new API, so I decided to rewrite it as an example.
The rewritten version is more flexible and doesn't actually need the
restrictions from the old version (such as checking that the commits
are connected). I still left the check for now to keep this patch
somewhat small. A subsequent commit will remove the restrictions.
Parallelize revisions by making them siblings
Running `jj parallelize 1::2` will transform the history like this:
```text
3
| 3
2 / \
| -> 1 2
1 \ /
| 0
0
```
Each of the target revisions is rebased onto the parents of the root(s) of
the target revset (not to be confused with the repo root). The children of
the head(s) of the target revset are rebased onto the target revisions.
The target revset is the union of the REVISIONS arguments.
The target revset being parallelized must satisfy several conditions,
otherwise the command will fail.
1. The heads of the target revset must not have different children.
2. The roots of the target revset must not have different parents.
3. The parents of all target revisions except the roots must also be
parallelized. This means that the target revisions must be connected.
