I feel the original -------/+++++++ pair is slightly confusing because
each half can be a separator by itself. I don't know what character other
than '-'/'+' is preferred, but let's pick '%' (for "mod") per @martinvonz
suggestion.
In 8ae9540f2c, I made `jj move/squash/unsquash` not abandon the
working copy if it became empty because that would lose any
description associated with it. It turned out that the new behavior
was also confusing because it made it unclear if the working-copy
commit was actually abandoned. Let's roll back that change and instead
ask the user for a combined description when both the source and
destination commits have non-empty descriptions. Not discarding a
non-empty description seems like a good improvement regardless of the
behavior related to working-copy commits. It's also how `hg fold`
behaves (though hg doesn't allow the description to be empty).
This patch adds `jj obslog -p` for including the diff compared to the
predecessor (the first predecessor if there are several). If the
predecessor's parents are different, then we create a temporary tree
by rebasing the predecessor to have the same parents and we use the
result as base for the diff. That way, we avoid polluting the diff
with the changes caused by the rebase. (I don't think we currently
have any commands that can change both parents and content, so the
diff should always be empty for rewrites caused by a rebase.)
Working on this also reminded me that it'll be really nice when we
replace `jj obslog` by something based on the operation log - I really
miss seeing information about the operation in the output (like `hg
obslog` gets from its obsmarkers).
