[PATCH 0/4] submodules: unset core.worktree when no working tree present

v2: I reworded the commit messages to explain the patches from the ground up instead of only linking to the old commits, that got reverted.

I disagree with that first stance (I can freely admit those commits happened), but agree on the second point, so I explained why the code is the best for the code base now. So I kept those pointers in there, too, to make it easier for future code archeologists.

v1:

A couple days before the 2.19 release we had a bug report about broken submodules[1] and reverted[2] the commits leading up to them.

The behavior of said bug fixed itself by taking a different approach[3], specifically by a weaker enforcement of having `core.worktree` set in a submodule [4].

The revert [2] was overly broad as we neared the release, such that we wanted to rather keep the known buggy behavior of always having `core.worktree` set, rather than figuring out how to fix the new bug of having 'git submodule update' not working in old style repository setups.

This series re-introduces those reverted patches, with no changes in code, but with drastically changed commit messages, as those focus on why it is safe to re-introduce them instead of explaining the desire for the change.

[1] https://public-inbox.org/git/2659750.rG6xLiZASK@twilight
[2] f178c13fda (Revert "Merge branch 'sb/submodule-core-worktree'", 2018-09-07)
[3] 4d6d6ef1fc (Merge branch 'sb/submodule-update-in-c', 2018-09-17)
[4] 74d4731da1 (submodule--helper: replace connect-gitdir-workingtree by ensure-core-worktree, 2018-08-13)
Stefan Beller (4):
  submodule update: add regression test with old style setups
  submodule: unset core.worktree if no working tree is present
  submodule--helper: fix BUG message in ensure_core_worktree
  submodule deinit: unset core.worktree

 builtin/submodule--helper.c        |  4 +++-
 submodule.c                        | 14 ++++++++++++++
 submodule.h                        |  2 ++
 t/lib-submodule-update.sh          |  5 +++--
 t/t7400-submodule-basic.sh         |  5 +++++
 t/t7412-submodule-absorbgitdirs.sh |  7 ++++++-
 6 files changed, 33 insertions(+), 4 deletions(-)