Thanks Ævar for the feedback! I've incorporated all of the suggestions,
except breaking up the tests in 1/6 into their own patch - I wasn't
convinced of the value of having prescriptive tests (with
test_expect_failure), and I found it difficult to discuss descriptive tests
(with test_expect_success) without also having the code in the same diff.
FWIW, this version (and the previous one) "git rebase -x 'make test'"
cleanly :)

Note for Junio: this version is based on ab/submodule-cleanup (and so will
future versions).

= Description

This series is a refactor of "git submodule--helper update" that replaces
"--recursive-prefix" with "--super-prefix" (see Background). This was
initially motivated by:

 * Junio's suggestion to simplify the code [1] (in response to a memory leak
   found by Johannes Schindelin [2]).
 * A desire to use the module_list API + get_submodule_displaypath() outside
   of builtin/submodule--helper.c (I expect to use this to check out
   branches in each submodule).

But it also happens to remove some overly complicated/duplicated code that
was literally converted from shell :)

= Background

When recursing into nested submodules, Git commands keep track of the path
from the superproject to the submodule in order to print a "display path" to
the user, e.g.

Submodule path '../super/sub/nested-sub': checked out 'abcdef'

For historical reasons, "git submodule--helper update" uses
"--recursive-prefix" for this purpose, but it should use "--super-prefix"
instead because:

 * That's what every other command uses (not just submodule--helper
   subcommands).
 * Using the "--super-prefix" helper functions makes the "git
   submodule--helper update" code simpler

= Patch organization

 * Patch 1/6 makes sure that display paths are only computed using display
   path helper functions ([do_]get_submodule_displaypath()) and fixes some
   display paths that we never realized were broken.
 * Patches 2-3/6 simplify and deduplicate some display path computations.
 * Patch 4/6 (authored by Ævar) removes SUPPORT_SUPER_PREFIX where it's not
   needed.
   * This doesn't affect correctness, but we want to do this eventually, so
     do it now to make 5/6 a bit cleaner.
 * Patch 5/6 replaces "--recursive-prefix" with "--super-prefix", making
   do_get_submodule_displaypath() obsolete.
   * GGG outputs an odd diff; I recommend viewing it with "--histogram"
 * Patch 6/6 removes do_get_submodule_displaypath().

= Series history

Changes in v2:

 * Rebase onto ab/submodule-cleanup (previously master)
 * Cherry pick https://github.com/avar/git/commit/f445c57490d into 4/6
 * Style fixes in .c and tests

= Future work

At the end of this series, get_submodule_displaypath() can be moved to
submodule.h, which would make submodule.c:get_super_prefix_or_empty()
obsolete. I have a patch that demonstrates this (CI run: [4]), but I decided
to keep this series more focused on "git submodule--helper update" so that
it's easier to review.

[1] https://lore.kernel.org/git/xmqq35g5xmmv.fsf@gitster.g [2]
https://lore.kernel.org/git/877a45867ae368bf9e053caedcb6cf421e02344d.1655336146.git.gitgitgadget@gmail.com
[3]
https://lore.kernel.org/git/patch-v3-02.12-082e015781e-20220622T142012Z-avarab@gmail.com
[4] https://github.com/chooglen/git/actions/runs/2572557584

Glen Choo (6):
  submodule--helper: eliminate internal "--update" option
  submodule--helper update: use display path helper
  submodule--helper: don't recreate recursive prefix
  submodule--helper: use correct display path helper
  submodule--helper update: use --super-prefix
  submodule--helper: remove display path helper

Ævar Arnfjörð Bjarmason (12):
  git-submodule.sh: remove unused sanitize_submodule_env()
  git-submodule.sh: remove unused $prefix variable
  git-submodule.sh: make the "$cached" variable a boolean
  git-submodule.sh: remove unused top-level "--branch" argument
  submodule--helper: have --require-init imply --init
  submodule update: remove "-v" option
  submodule--helper: rename "absorb-git-dirs" to "absorbgitdirs"
  submodule--helper: report "submodule" as our name in some "-h" output
  submodule--helper: understand --checkout, --merge and --rebase
    synonyms
  git-submodule.sh: use "$quiet", not "$GIT_QUIET"
  git-sh-setup.sh: remove "say" function, change last users
  submodule--helper: remove unused SUPPORT_SUPER_PREFIX flags

 builtin/submodule--helper.c    | 161 +++++++++++++++------------------
 contrib/subtree/git-subtree.sh |  15 ++-
 git-instaweb.sh                |   2 +-
 git-sh-setup.sh                |  16 ----
 git-submodule.sh               |  88 +++++++-----------
 submodule.c                    |   2 +-
 t/t7406-submodule-update.sh    |  58 +++++++++++-
 7 files changed, 175 insertions(+), 167 deletions(-)

base-commit: 8168d5e9c23ed44ae3d604f392320d66556453c9

Submitted-As: https://lore.kernel.org/git/pull.1282.v2.git.git.1656623978.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1282.git.git.1656372017.gitgitgadget@gmail.com