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Re: [PATCH v4] sparse-checkout.txt: new document with sparse-checkout directions

From
Elijah Newren <newren@gmail.com>
Date
Nov 16, 2022, 05:49 UTC
Message-ID
<CABPp-BHaKH4sOPx2tx7CU+Uymvtu=mU1ZweGBDdWvhb-FgGA_Q@mail.gmail.com>
In-Reply-To
<CAOLTT8TzpfoH7pz7gxgFvNWOaUZUcg1q_Tap+2anwHfAUgDV8Q@mail.gmail.com>
On Mon, Nov 14, 2022 at 8:03 PM ZheNing Hu <adlternative@gmail.com> wrote:
> Elijah Newren via GitGitGadget <gitgitgadget@gmail.com> 于2022年11月6日周日 14:04写道：
[...]
Show 9 quoted lines
> > +sparsity patterns: patterns from $GIT_DIR/info/sparse-checkout used to
> > +       define the set of files of interest.  A warning: It is easy to
> > +       over-use this term (or the shortened "patterns" term), for two
> > +       reasons: (1) users in cone mode specify directories rather than
> > +       patterns (their directories are transformed into patterns, but
> > +       users may think you are talking about non-cone mode if you use the
> > +       word "patterns"), and (b) the sparse specification might
>
> nit: s/(b)/(2)/g
Thanks.
Show 17 quoted lines
> > +sparse specification: The set of paths in the user's area of focus.  This
> > +       is typically just the tracked files that match the sparsity
> > +       patterns, but the sparse specification can temporarily differ and
> > +       include additional files.  (See also "Sparse specification
> > +       vs. sparsity patterns")
> > +
> > +       * When working with history, the sparse specification is exactly
> > +         the set of files matching the sparsity patterns.
> > +       * When interacting with the working tree, the sparse specification
> > +         is the set of tracked files with a clear SKIP_WORKTREE bit or
> > +         tracked files present in the working copy.
>
> I'm guessing what you mean here is:
> Some files are stored with a flag bit of !SKIP_WORKTREE in its index entry.
> But files are "vivifying" (restore to worktree) or new files added to
> index (tracked files),
> they also belong to the sparse specification.
For this case, when interacting with the working tree, I mean the
union of the following two sets of files:
  * files with !SKIP_WORKTREE in the index entry
  * files present in the working copy whose index entry has the
SKIP_WORKTREE bit set.

The fact that files might be new index entries (i.e. newly tracked files) is irrelevant; it only matters whether such files fit into one of the two categories above or not.

The fact that files have been "vivified" is slightly ambiguous and thus a bad way to define this set. When git vivifies files, it'll clear the SKIP_WORKTREE bit. If an editor, or script external to git, or something else restores the file, it will likely overlook that detail. We want vivified files to be part of the sparse specification when interacting with the working tree regardless of whether the SKIP_WORKTREE bit was correctly updated, so I defined it the way I did to remove such ambiguity. (I guess I should note that as per af6a51875a ("repo_read_index: clear SKIP_WORKTREE bit from files present in worktree", 2022-01-14), git will clear the SKIP_WORKTREE bit for files present in the working copy as one of the first things it does, but that could leave people wondering whether I meant the SKIP_WORKTREE bit was set as of the time of git invocation. So, I explicitly call out files present in the working copy for which the index entry has the SKIP_WORKTREE bit set, so folks know these files are definitely included in the sparse specification.)

Show 30 quoted lines
> I think we can add some examples to describe these terms.
>
> #!/bin/sh
>
> set -x
>
> rm -rf mono-repo
> git init mono-repo -b main
> (
>   cd mono-repo &&
>   mkdir p1 p2 &&
>   echo a >p1/a &&
>   echo b >p1/b &&
>   echo a >p2/a &&
>   echo b >p2/b &&
>   git add . &&
>   git commit -m ok &&
>   git sparse-checkout set p1 &&
>   git ls-files -t &&
>   echo a >>p1/a &&
>   echo b >>p1/b &&
>   mkdir p2 p3 &&
>   echo next >>p2/a &&
>   echo next >>p3/c &&
>   git add p3/c &&
>   # p2/a and p3/c vivify
>   git ls-files -t &&
>   # compare wortree/commit
>   git --no-pager diff HEAD --name-only
> )

You've added a bunch of code with this example, but you have not said what the output should be, so how exactly does this help describe the terms?

Show 24 quoted lines
> > +       * When modifying or showing results from the index, the sparse
> > +         specification is the set of files with a clear SKIP_WORKTREE bit
> > +         or that differ in the index from HEAD.
>
> #!/bin/sh
>
> set -x
>
> rm -rf mono-repo
> git init mono-repo -b main
> (
>   cd mono-repo &&
>   mkdir p1 p2 &&
>   echo a >p1/a &&
>   echo b >p1/b &&
>   echo a >p2/a &&
>   echo b >p2/b &&
>   git add . &&
>   git commit -m ok &&
>   git sparse-checkout set p1 &&
>   git update-index --chmod=+x p2/a &&
>   # compare commit/index
>   git --no-pager diff --cached --name-only
> )

Same issue here; you haven't stated the expected output of these commands, so I don't see how they help with the description at all.

Perhaps it's worth noting why I think the sparse specification should be extended when dealing with the index:

  * "mergy" commands (merge, rebase, cherry-pick, am, revert) can
modify the index outside the sparsity patterns, without creating a
commit.
  * `git commit` (or `rebase --continue`, or whatever) will create a
commit from whatever staged versions of files there are
  => `git status` should show what is about to be committed
  => `git diff --cached --name-only` ought to be usable to show what
is to be committed
  => `git grep --cached ...` ought to be usable to search through what
is about to be committed

See also https://lore.kernel.org/git/CABPp-BESkb=04vVnqTvZyeCa+7cymX7rosUW3rhtA02khMJKHA@mail.gmail.com/ (starting with the paragraph with "leery" in it), and the thread starting there. If the sparse specification is not expanded, users will get some nasty surprises, and the only other alternative I can think of to avoid such surprises would be making several commands always run full tree. Running full-tree with a non-default option to run sparse forces behavior A folks into a "pick your poison" situation, which is not nice. Extending the sparse specification to include files whose index entries do not match HEAD for index-related operations provides the nice middle ground that avoids such usability problems while also allowing users to avoid operating on a full tree.

[...]
Show 6 quoted lines
>  I think A's users might need a little more refinement.
>
> A: Some users are _only_ interested in the sparse portion of the repo,
> but they don't want to download all the blobs, they can accept to download
> other data later using partial-clone, which can reduce the local storage size.
> (Current default behavior)

Behavior A is definitely not the current default behavior. Also, behavior A is not tied to partial clones; some users may well want it even with a dense clone, so we need to avoid suggesting it is only for users with partial clones. (Though, if users are using partial clones with behavior A, then I agree with the part you wrote other than your parenthetical comment.)

> A** : Some users are _only_ interested in the sparse portion of the repo,
> but they want to download all the blobs in it to avoid some unnecessary
> network connections afterwards.

Here you just repeated `A*` but relabelled it as `A**`. Yes, this one is explicitly tied to partial clone behavior.

[...]
Show 15 quoted lines
> > +    The fact that files can move between the 'tracked' and 'untracked'
> > +    categories means some commands will have to treat untracked files
> > +    differently.  But if we have to treat untracked files differently,
> > +    then additional commands may also need changes:
> > +
> > +      * status
> > +      * clean
> > +
>
> I'm a bit worried about git status, because it's used in many shells
> (e.g. zsh) i
> in the git prompt function. Its default behavior is restricted, otherwise users
> may get blocked when they use zsh to cd to that directory. I don't know how
> to reproduce this problem (since the scenario is built on checkout to a local
> unborn branch).

Could you elaborate? I'm not sure if you are talking about an existing problem that you are worried about being exacerbated, or a hypothetical problem that could occur with changes. Further, your wording is so vague about the problem, that I have no idea what its nature is or whether any changes to status would even possibly have any bearing on it. But the suggested changes to git status are simply:

> > +    In particular, `status` may need to report any untracked files outside
> > +    the sparsity specification as an erroneous condition (especially to
> > +    avoid the user trying to `git add` them, forcing `git add` to display
> > +    an error).
[...]
Show 7 quoted lines
> > +    ls-files may be slightly special in that e.g. `git ls-files -t` is
> > +    often used to see what is sparse and what is not.  Perhaps -t should
> > +    always work on the full tree?
> > +
>
> Recently git ls-files added a --format option, perhaps this can be modified to
> show if a file is SKIP_WORKTREE in the future.

If so, then you've made my question also applicable for `--format`; much like -t, should --format always work on the full tree? (Or maybe just when the format specifies the skip worktree bit?)

[...]
Show 11 quoted lines
> > +  * If a config option is added (sparse.scope?) what should the values and
> > +    description be?  "sparse" (behavior A), "worktree-sparse-history-dense"
> > +    (behavior B), "dense" (behavior C)?  There's a risk of confusion,
> > +    because even for Behaviors A and B we want some commands to be
> > +    full-tree and others to operate sparsely, so the wording may need to be
> > +    more tied to the usecases and somehow explain that.  Also, right now,
> > +    the primary difference we are focusing is just the history-querying
> > +    commands (log/diff/grep).  Previous config suggestion here: [13]
> > +
>
> Maybe sparse.scope={sparse, all}?

I guess that's people's common first guess. However, when you dig in, I think this would be badly broken -- see my response to Stolee I just sent out.

Previous: Elijah NewrenNext: ZheNing Hu
Message 36 of 46 in “sparse-checkout.txt: new document with sparse-checkout directions”
  1. sparse-checkout.txt: new document with sparse-checkout directionsElijah Newren via GitGitGadget, Sep 25, 2022
  2. Junio C HamanoSep 26, 2022
  3. Junio C HamanoSep 26, 2022
  4. Elijah NewrenSep 27, 2022
  5. Junio C HamanoSep 27, 2022
  6. Victoria DyeSep 26, 2022
  7. Junio C HamanoSep 26, 2022
  8. Elijah NewrenSep 27, 2022
  9. Junio C HamanoSep 27, 2022
  10. Elijah NewrenSep 28, 2022
  11. Elijah NewrenSep 27, 2022
  12. Derrick StoleeSep 27, 2022
  13. Elijah NewrenSep 28, 2022
  14. Junio C HamanoSep 27, 2022
  15. Elijah NewrenSep 28, 2022
  16. Derrick StoleeSep 27, 2022
  17. Elijah NewrenSep 28, 2022
  18. Derrick StoleeSep 28, 2022
  19. Elijah NewrenOct 6, 2022
  20. Derrick StoleeOct 6, 2022
  21. Elijah NewrenOct 7, 2022
  22. ZheNing HuSep 30, 2022
  23. Elijah NewrenOct 6, 2022
  24. ZheNing HuOct 15, 2022
  25. Elijah NewrenOct 15, 2022
  26. ZheNing HuOct 15, 2022
  27. ZheNing HuSep 30, 2022
  28. sparse-checkout.txt: new document with sparse-checkout directionsElijah Newren via GitGitGadget, Sep 28, 2022
  29. sparse-checkout.txt: new document with sparse-checkout directionsElijah Newren via GitGitGadget, Oct 8, 2022
  30. sparse-checkout.txt: new document with sparse-checkout directionsElijah Newren via GitGitGadget, Nov 6, 2022
  31. Derrick StoleeNov 7, 2022
  32. Elijah NewrenNov 16, 2022
  33. ZheNing HuNov 15, 2022
  34. ZheNing HuNov 16, 2022
  35. Elijah NewrenNov 16, 2022
  36. Elijah NewrenNov 16, 2022
  37. ZheNing HuNov 16, 2022
  38. ZheNing HuNov 16, 2022
  39. ZheNing HuNov 16, 2022
  40. Elijah NewrenNov 19, 2022
  41. Elijah NewrenNov 19, 2022
  42. ZheNing HuNov 23, 2022
  43. ZheNing HuJan 14, 2023
  44. Elijah NewrenJan 20, 2023
  45. ZheNing HuJan 23, 2023
  46. Elijah NewrenJan 24, 2023

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