pull: add t5572 for submodule updates

Test that the pull command updates the work tree as expected (for
submodule changes which don't result in conflicts) when used without
arguments or with the '--ff', '--ff-only' and '--no-ff' flag each. Add
helper functions to reset the branch to be updated to to the current
HEAD so that pull is doing the transition from HEAD to the given branch.

Set KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES
and KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR to
document that pull has the same --no-ff known failures merge has.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
cherry-pick: add t3512 for submodule updates

Test that the cherry-pick command updates the work tree as expected (for
submodule changes which don't result in conflicts).

Set KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES
and KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR to
document that cherry-pick has the same --no-ff known failures merge has.

Implement the KNOWN_FAILURE_CHERRY_PICK_SEES_EMPTY_COMMIT switch to expect
the known failure that while cherry picking just a SHA-1 update for an
ignored submodule the commit incorrectly fails with "The previous
cherry-pick is now empty, possibly due to conflict resolution.".

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
am: add t4255 for submodule updates

Test that the am command updates the work tree as expected (for submodule
changes which don't result in conflicts). To make that work add two
helper functions that use format-patch to create the input for am.

Add the KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES
switch to expect the known failure that --no-ff merges attempt to merge
the new files in the former submodule directory with those of the removed
submodule.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
stash: add t3906 for submodule updates

Test that the stash apply command updates the work tree as expected for
changes which don't result in conflicts. To make that work add a helper
function that uses read-tree to apply the changes of the target commit
to the work tree, then stashes these changes and at last applies that
stash.

Implement the KNOWN_FAILURE_STASH_DOES_IGNORE_SUBMODULE_CHANGES switch
and reuse two other already present switches to expect the known
failure that stash does ignore submodule changes.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
revert: add t3513 for submodule updates

Test that the revert command updates the work tree as expected (for
submodule changes which don't result in conflicts). Add a helper function
to first revert the checked out target commit to make the last revert
produce the to-be-tested work tree.

Set the KNOWN_FAILURE_CHERRY_PICK_SEES_EMPTY_COMMIT and
KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR switches to
document that revert has the similar failures.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
!!! WIP !!! checkout-index: add t2025 for submodule updates

TODO: fix or expect failing tests

Test that the checkout-index command updates the work tree as expected
(for submodule changes which don't result in conflicts) with or without
the '-f' flag.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
!!! WIP !!! reminder of what is still left to do ...