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Re: [PATCH v6 0/5] teach submodules to know they're submodules

From
Emily Shaffer <emilyshaffer@google.com>
Date
Nov 23, 2021, 20:28 UTC
Message-ID
<YZ1PA3YBdOfg0/cf@google.com>
In-Reply-To
<20211117232846.2596110-1-jonathantanmy@google.com>
On Wed, Nov 17, 2021 at 03:28:46PM -0800, Jonathan Tan wrote:
Show 36 quoted lines
> 
> Emily Shaffer <emilyshaffer@google.com> writes:
> > For the original cover letter, see
> > https://lore.kernel.org/git/20210611225428.1208973-1-emilyshaffer%40google.com.
> 
> Also for reference, v4 and v5 (as a reply to v4) can be found here:
> https://lore.kernel.org/git/20211014203416.2802639-1-emilyshaffer@google.com/
> 
> > Since v5:
> > 
> > A couple things. Firstly, a semantics change *back* to the semantics of
> > v3 - we map from gitdir to gitdir, *not* from common dir to common dir,
> > so that theoretically a submodule with multiple worktrees in multiple
> > superproject worktrees will be able to figure out which worktree of the
> > superproject it's in. (Realistically, that's not really possible right
> > now, but I'd like to change that soon.)
> 
> Makes sense. Also, thanks for the tests covering what happens when this
> is run from worktrees.
> 
> > Secondly, a rewording of comments and commit messages to indicate that
> > this isn't a cache of some expensive operation, but rather intended to
> > be the source of truth for all submodules. I also added a fifth commit
> > rewriting `git rev-parse --show-superproject-working-tree` to
> > demonstrate what that means in practice - but from a practical
> > standpoint, I'm a little worried about that fifth patch. More details in
> > the patch 5 description.
> 
> OK - this is not the "this variable being missing is OK" idea that I had
> [1], but we want to be able to depend on it to some extent. (And it is
> not a cache either - we are not planning to perform an operation to
> obtain the superproject gitdir if the cache is missing, but we are just
> going to assume that there is no superproject.)
> 
> To that end, the 5th patch is misleading - it is behaving exactly like a
> cache. I think it's better to drop it.
Yeah, I think you are right.
Show 8 quoted lines
> 
> What would make sense to me (and seems to be in the spirit of this patch
> set) is to describe this as something that Git commands can rely on to
> determine if the current repo is a submodule, for performance reasons.
> So maybe Git commands/parameters that directly reference the submodule
> concept like "--show-superproject-working-tree" will work hard to find
> the superproject (by searching the filesystem), but those that do not
> (e.g. "git status") can make assumptions.

Oh interesting, I like the idea of that distinction. Thanks for the suggestion.

I wonder, though, how best to delineate. I'd almost rather say like I suggested to Ævar (https://lore.kernel.org/git/YZ1KLNwsxx7IR1%2B5%40google.com), that we can treat "--show-superproject-working-tree" as a "legacy" option people are already using, and treat anything added from now on as "if it doesn't think it is a submodule, you should 'git submodule update' in the superproject". That relies on us being able to reliably keep the value of submodule.superprojectGitDir correct, but I think the gitdir->gitdir linking helps with that (as opposed to earlier iterations).

> 
> Making this variable a source of truth wouldn't work, I think, because
> the source of truth is whether this repo appears in a .gitmodules file
> (and that hasn't changed).

Interestingly, '--show-superproject-working-tree' doesn't check the .gitmodules file at all. It checks whether the project found in the filesystem above it knows about an object named path/to/superproject/ which is a gitlink - that is, it asks the index, not .gitmodules, as far as I understand it. So if the only existing alternative to submodule.superprojectGitDir isn't treating .gitmodules as source of truth, then what does that mean?

Show 5 quoted lines
> 
> To this end, I'll comment on the changes I'd like to see on the
> individual patches too.
> 
> [1] https://lore.kernel.org/git/20210727174650.2462099-1-jonathantanmy@google.com/
Previous: Jonathan TanNext: Emily Shaffer
Message 14 of 64 in “teach submodules to know they're submodules”
  1. 0/5 teach submodules to know they're submodulesEmily Shaffer, Nov 17, 2021
  2. 1/5 t7400-submodule-basic: modernize inspect() helperEmily Shaffer, Nov 17, 2021
  3. 2/5 introduce submodule.superprojectGitDir recordEmily Shaffer, Nov 17, 2021
  4. Jonathan TanNov 17, 2021
  5. 3/5 submodule: record superproject gitdir during absorbgitdirsEmily Shaffer, Nov 17, 2021
  6. 4/5 submodule: record superproject gitdir during 'update'Emily Shaffer, Nov 17, 2021
  7. 5/5 submodule: use config to find superproject worktreeEmily Shaffer, Nov 17, 2021
  8. 0/2 submodule: test what happens if submodule.superprojectGitDir isn't aroundÆvar Arnfjörð Bjarmason, Nov 17, 2021
  9. 1/2 submodule tests: fix potentially broken "config .. --unset"Ævar Arnfjörð Bjarmason, Nov 17, 2021
  10. 2/2 submodule: add test mode for checking absence of "superProjectGitDir"Ævar Arnfjörð Bjarmason, Nov 17, 2021
  11. Emily ShafferNov 23, 2021
  12. Ævar Arnfjörð BjarmasonNov 24, 2021
  13. Jonathan TanNov 17, 2021
  14. Emily ShafferNov 23, 2021
  15. 0/5 teach submodules to know they're submodulesEmily Shaffer, Feb 3, 2022
  16. 1/4 t7400-submodule-basic: modernize inspect() helperEmily Shaffer, Feb 3, 2022
  17. 2/4 introduce submodule.superprojectGitDir recordEmily Shaffer, Feb 3, 2022
  18. 3/4 submodule: record superproject gitdir during absorbgitdirsEmily Shaffer, Feb 3, 2022
  19. 4/4 submodule: record superproject gitdir during 'update'Emily Shaffer, Feb 3, 2022
  20. Junio C HamanoFeb 3, 2022
  21. Ævar Arnfjörð BjarmasonFeb 4, 2022
  22. Junio C HamanoFeb 4, 2022
  23. Jonathan NiederFeb 7, 2022
  24. Junio C HamanoFeb 7, 2022
  25. Jonathan NiederFeb 8, 2022
  26. Junio C HamanoFeb 8, 2022
  27. Emily ShafferFeb 10, 2022
  28. Jonathan NiederFeb 10, 2022
  29. Ævar Arnfjörð BjarmasonFeb 12, 2022
  30. Junio C HamanoFeb 13, 2022
  31. 0/3 teach submodules to know they're submodulesEmily Shaffer, Mar 1, 2022
  32. 1/3 t7400-submodule-basic: modernize inspect() helperEmily Shaffer, Mar 1, 2022
  33. 2/3 introduce submodule.hasSuperproject recordEmily Shaffer, Mar 1, 2022
  34. Junio C HamanoMar 1, 2022
  35. Emily ShafferMar 8, 2022
  36. Glen ChooMar 8, 2022
  37. Glen ChooMar 8, 2022
  38. 3/3 rev-parse: short-circuit superproject worktree when config unsetEmily Shaffer, Mar 1, 2022
  39. Junio C HamanoMar 1, 2022
  40. Emily ShafferMar 9, 2022
  41. Junio C HamanoMar 1, 2022
  42. Emily ShafferMar 8, 2022
  43. 0/3 teach submodules to know they're submodulesEmily Shaffer, Mar 10, 2022
  44. 1/3 t7400-submodule-basic: modernize inspect() helperEmily Shaffer, Mar 10, 2022
  45. 2/3 introduce submodule.hasSuperproject recordEmily Shaffer, Mar 10, 2022
  46. Junio C HamanoMar 10, 2022
  47. Glen ChooMar 10, 2022
  48. Glen ChooMar 10, 2022
  49. Junio C HamanoMar 10, 2022
  50. Glen ChooMar 10, 2022
  51. Glen ChooMar 10, 2022
  52. Emily ShafferMar 15, 2022
  53. Emily ShafferMar 15, 2022
  54. Glen ChooMar 15, 2022
  55. Emily ShafferMar 15, 2022
  56. Junio C HamanoMar 15, 2022
  57. Junio C HamanoMar 10, 2022
  58. Glen ChooMar 10, 2022
  59. Emily ShafferMar 15, 2022
  60. 3/3 rev-parse: short-circuit superproject worktree when config unsetEmily Shaffer, Mar 10, 2022
  61. Junio C HamanoMar 10, 2022
  62. Eric SunshineMar 10, 2022
  63. Ævar Arnfjörð BjarmasonMar 11, 2022
  64. Junio C HamanoMar 13, 2022

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