absorb: preserve changesets which were already empty
Most commands in Mercurial (commit, rebase, absorb itself) don’t create empty
changesets or drop them if they become empty. If there’s a changeset that’s
empty, it must be a deliberate choice of the user. At least it shouldn’t be
absorb’s responsibility to prune them. The fact that changesets that became
empty during absorb are pruned, is unaffected by this.
This case was found while writing patches which make it possible to configure
absorb and rebase to not drop empty changesets. Even without having such config
set, I think it’s valuable to preserve changesets which were already empty.
$ cat <<EOF >> $HGRCPATH
> [extensions]
> purge =
> EOF
$ hg init test
$ cd test
$ echo a > changed
$ echo a > removed
$ echo a > source
$ hg ci -Am addfiles
adding changed
adding removed
adding source
$ echo a >> changed
$ echo a > added
$ hg add added
$ hg rm removed
$ hg cp source copied
$ hg diff --git > ../unknown.diff
Test adding on top of an unknown file
$ hg up -qC 0
$ hg purge
$ echo a > added
$ hg import --no-commit ../unknown.diff
applying ../unknown.diff
file added already exists
1 out of 1 hunks FAILED -- saving rejects to file added.rej
abort: patch failed to apply
[255]
Test modifying an unknown file
$ hg revert -aq
$ hg purge
$ hg rm changed
$ hg ci -m removechanged
$ echo a > changed
$ hg import --no-commit ../unknown.diff
applying ../unknown.diff
abort: cannot patch changed: file is not tracked
[255]
Test removing an unknown file
$ hg up -qC 0
$ hg purge
$ hg rm removed
$ hg ci -m removeremoved
created new head
$ echo a > removed
$ hg import --no-commit ../unknown.diff
applying ../unknown.diff
abort: cannot patch removed: file is not tracked
[255]
Test copying onto an unknown file
$ hg up -qC 0
$ hg purge
$ echo a > copied
$ hg import --no-commit ../unknown.diff
applying ../unknown.diff
abort: cannot create copied: destination already exists
[255]
$ cd ..