[PATCH v2 0/4] cache parent project's gitdir in submodules

The reception for this series seemed pretty good in v1, so I'm dropping the RFC.

Tested: https://github.com/nasamuffin/git/actions/runs/941100646

Sinec v1, mostly platform-friendliness fixes. Also added documentation for the new config option - wordsmithing help is always welcome.

 - Emily

Emily Shaffer (4):
  t7400-submodule-basic: modernize inspect() helper
  introduce submodule.superprojectGitDir cache
  submodule: cache superproject gitdir during absorbgitdirs
  submodule: cache superproject gitdir during 'update'

 Documentation/config/submodule.txt | 12 ++++++++
 builtin/submodule--helper.c        |  4 +++
 git-submodule.sh                   | 10 ++++++
 submodule.c                        | 10 ++++++
 t/t7400-submodule-basic.sh         | 49 ++++++++++++++----------------
 t/t7406-submodule-update.sh        | 10 ++++++
 t/t7412-submodule-absorbgitdirs.sh |  9 +++++-
 7 files changed, 77 insertions(+), 27 deletions(-)

Range-diff against v1:
1:  d6284438fb = 1:  a6718eea80 t7400-submodule-basic: modernize inspect() helper
2:  56470e2eab ! 2:  4cebe7bcb5 introduce submodule.superprojectGitDir cache
    @@ Commit message
     
         Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
     
    + ## Documentation/config/submodule.txt ##
    +@@ Documentation/config/submodule.txt: submodule.alternateErrorStrategy::
    + 	`ignore`, `info`, `die`. Default is `die`. Note that if set to `ignore`
    + 	or `info`, and if there is an error with the computed alternate, the
    + 	clone proceeds as if no alternate was specified.
    ++
    ++submodule.superprojectGitDir::
    ++	The relative path from the submodule's worktree  to the superproject's
    ++	gitdir. This config should only be present in projects which are
    ++	submodules, but is not guaranteed to be present in every submodule. It
    ++	is set automatically during submodule creation.
    +++
    ++	In situations where more than one superproject references the same
    ++	submodule worktree, the value of this config and the behavior of
    ++	operations which use it are undefined. To reference a single project
    ++	from multiple superprojects, it is better to create a worktree of the
    ++	submodule for each superproject.
    +
      ## builtin/submodule--helper.c ##
     @@ builtin/submodule--helper.c: static int module_clone(int argc, const char **argv, const char *prefix)
      		git_config_set_in_file(p, "submodule.alternateErrorStrategy",
3:  42f954f523 ! 3:  df97a9c2bb submodule: cache superproject gitdir during absorbgitdirs
    @@ submodule.c: static void relocate_single_git_dir_into_superproject(const char *p
     
      ## t/t7412-submodule-absorbgitdirs.sh ##
     @@ t/t7412-submodule-absorbgitdirs.sh: test_expect_success 'absorb the git dir' '
    - 	test -d .git/modules/sub1 &&
      	git status >actual.1 &&
      	git -C sub1 rev-parse HEAD >actual.2 &&
    -+	test . -ef "$(git -C sub1 config submodule.superprojectGitDir)" &&
      	test_cmp expect.1 actual.1 &&
    - 	test_cmp expect.2 actual.2
    +-	test_cmp expect.2 actual.2
    ++	test_cmp expect.2 actual.2 &&
    ++
    ++	# make sure the submodule cached the superproject gitdir correctly
    ++	test-tool path-utils real_path . >expect &&
    ++	test-tool path-utils real_path \
    ++		"$(git -C sub1 config submodule.superprojectGitDir)" >actual &&
    ++
    ++	test_cmp expect actual
      '
    + 
    + test_expect_success 'absorbing does not fail for deinitialized submodules' '
4:  4f55ab42c7 ! 4:  a3f3be58ad submodule: cache superproject gitdir during 'update'
    @@ git-submodule.sh: cmd_update()
     +		# Cache a pointer to the superproject's gitdir. This may have
     +		# changed, so rewrite it unconditionally. Writes it to worktree
     +		# if applicable, otherwise to local.
    ++		relative_gitdir="$(git rev-parse --path-format=relative \
    ++						 --prefix "${sm_path}" \
    ++						 --git-dir)"
     +
    -+		sp_gitdir="$(git rev-parse --absolute-git-dir)"
    -+		relative_gitdir="$(realpath --relative-to "$sm_path" "$sp_gitdir")"
     +		git -C "$sm_path" config --worktree \
     +			submodule.superprojectgitdir "$relative_gitdir"
     +
    @@ git-submodule.sh: cmd_update()
      			(
     
      ## t/t7406-submodule-update.sh ##
    -@@ t/t7406-submodule-update.sh: test_expect_success 'submodule update --quiet passes quietness to merge/rebase'
    +@@ t/t7406-submodule-update.sh: test_expect_success 'submodule update --quiet passes quietness to fetch with a s
      	)
      '