| Message ID | 20220109045732.2497526-4-newren@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove the present-despite-SKIP_WORKTREE class of bugs | expand |
Elijah Newren wrote: > The fix is short (~30 lines), but the description is not. Sorry. > > There is a set of problems caused by files in what I'll refer to as the > "present-despite-SKIP_WORKTREE" state. This commit aims to not just fix > these problems, but remove the entire class as a possibility -- for > those using sparse checkouts. But first, we need to understand the > problems this class presents. A quick outline: > > * Problems > * User facing issues > * Problem space complexity > * Maintenance and code correctness challenges > * SKIP_WORKTREE expectations in Git > * Suggested solution > * Pros/Cons of suggested solution > * Notes on testcase modifications > > === User facing issues === > > There are various ways for users to get files to be present in the > working copy despite having the SKIP_WORKTREE bit set for that file in > the index. This may come from: > * various git commands not really supporting the SKIP_WORKTREE bit[1,2] > * users grabbing files from elsewhere and writing them to the worktree > (perhaps even cached in their editor) > * users attempting to "abort" a sparse-checkout operation with a > not-so-early Ctrl+C (updating $GIT_DIR/info/sparse-checkout and the > working tree is not atomic)[3]. > > Once users have present-despite-SKIP_WORKTREE files, any modifications > users make to these files will be ignored, possibly to users' confusion. > > Further: > * these files will not be updated by by standard commands > (switch/checkout/pull/merge/rebase will leave them alone unless > conflicts happen -- and even then, the conflicted file may be > written somewhere else to avoid overwriting the SKIP_WORKTREE file > that is present and in the way) > * there is nothing in Git that users can use to discover such > files (status, diff, grep, etc. all ignore it) > * there is no reasonable mechanism to "recover" from such a condition > (neither `git sparse-checkout reapply` nor `git reset --hard` will > correct it). > Just to add to this, files like these always force sparse index expansion in `git status` (and probably some other commands?), ruining a lot of the performance gains of using sparse index in the first place. > So, not only are users modifications ignored, but the files get > progressively more stale over time. At some point in the future, they > may change their sparseness specification or disable sparse-checkouts. > At that time, all present-despite-SKIP_WORKTREE files will show up as > having lots of modifications because they represent a version from a > different branch or commit. These might include user-made local changes > from days before, but the only way to tell is to have users look through > them all closely. > > If these users come to others for help, there will be no logs that > explain the issue; it's just a mysterious list of changes. Users might > adamantly claim (correctly, as it turns out) that they didn't modify > these files, while others presume they did. > > [1] https://lore.kernel.org/git/xmqqbmb1a7ga.fsf@gitster-ct.c.googlers.com/ > [2] https://lore.kernel.org/git/CABPp-BH9tju7WVm=QZDOvaMDdZbpNXrVWQdN-jmfN8wC6YVhmw@mail.gmail.com/ > [3] https://lore.kernel.org/git/CABPp-BFnFpzwGC11TLoLs8YK5yiisA5D5-fFjXnJsbESVDwZsA@mail.gmail.com/ > > === Problem space complexity === > > SKIP_WORKTREE has been part of Git for over a decade. Duy did lots of > work on it initially, and several others have since come along and put > lots of work into it. Stolee spent most of 2021 on the sparse-index, > with lots of bugfixes along the way including to non-sparse-index cases > as we are still trying to get sparse checkouts to behave reasonably. > Basically every codepath throughout the treat needs to be aware of an > additional type of file: tracked-but-not-present. The extra type > results in lots of extra testcases and lots of extra code everywhere. > > But, the sad thing is that we actually have more than one extra type. > We have tracked, tracked-but-not-present (SKIP_WORKTREE), and > tracked-but-promised-to-not-be-present-but-is-present-anyway > (present-despite-SKIP_WORKTREE). Two types is a monumental amount of > effort to support, and adding a third feels a bit like insanity[4]. > > [4] Some examples of which can be seen at > https://lore.kernel.org/git/CABPp-BGJ_Nvi5TmgriD9Bh6eNXE2EDq2f8e8QKXAeYG3BxZafA@mail.gmail.com/ > > === Maintenance and code correctness challenges === > > Matheus' patches to grep stalled for nearly a year, in part because of > complications of how to handle sparse-checkouts appropriately in all > cases[5][6] (with trying to sanely figure out how to sanely handle > present-despite-SKIP_WORKTREE files being one of the complications). > His rm/add follow-ups also took months because of those kinds of > issues[7]. The corner cases with things like submodules and > SKIP_WORKTREE with the addition of present-despite-SKIP_WORKTREE start > becoming really complex[8]. > > We've had to add ugly logic to merge-ort to attempt to handle > present-despite-SKIP_WORKTREE files[9], and basically just been forced > to give up in merge-recursive knowing full well that we'll sometimes > silently discard user modifications. Despite stash essentially being a > merge, it needed extra code (beyond what was in merge-ort and > merge-recursive) to manually tweak SKIP_WORKTREE bits in order to avoid > a few different bugs that'd result in an early abort with a partial > stash application[10]. > > [5] See https://lore.kernel.org/git/5f3f7ac77039d41d1692ceae4b0c5df3bb45b74a.1612901326.git.matheus.bernardino@usp.br/#t > and the dates on the thread; also Matheus and I had several > conversations off-list trying to resolve the issues over that time > [6] ...it finally kind of got unstuck after > https://lore.kernel.org/git/CABPp-BGJ_Nvi5TmgriD9Bh6eNXE2EDq2f8e8QKXAeYG3BxZafA@mail.gmail.com/ > [7] See for example > https://lore.kernel.org/git/CABPp-BHwNoVnooqDFPAsZxBT9aR5Dwk5D9sDRCvYSb8akxAJgA@mail.gmail.com/#t > and quotes like "The core functionality of sparse-checkout has always > been only partially implemented", a statement I still believe is true > today. > [8] https://lore.kernel.org/git/pull.809.git.git.1592356884310.gitgitgadget@gmail.com/ > [9] See commit 66b209b86a ("merge-ort: implement CE_SKIP_WORKTREE > handling with conflicted entries", 2021-03-20) > [10] See commit ba359fd507 ("stash: fix stash application in > sparse-checkouts", 2020-12-01) > > === SKIP_WORKTREE expectations in Git === > > A couple quotes: > > From [11] (before the "sparse-checkout" command existed): > If it needs too many special cases, hacks, and conditionals, then it > is not worth the complexity---if it is easier to write a correct code > by allowing Git to populate working tree files, it is perfectly fine > to do so. > > In a sense, the sparse checkout "feature" itself is a hack by itself, > and that is why I think this part should be "best effort" as well. > > From the git-sparse-checkout manual (still present today): > > THIS COMMAND IS EXPERIMENTAL. ITS BEHAVIOR, AND THE BEHAVIOR OF OTHER > COMMANDS IN THE PRESENCE OF SPARSE-CHECKOUTS, WILL LIKELY CHANGE IN > THE FUTURE. > > [11] https://lore.kernel.org/git/xmqqbmb1a7ga.fsf@gitster-ct.c.googlers.com/ > > === Suggested solution === > > SKIP_WORKTREE was written to allow sparse-checkouts, in particular, as > the name of the option implies, to allow the file to NOT be in the > worktree but consider it to be unchanged rather than deleted. > > The suggests a simple solution: present-despite-SKIP_WORKTREE files > should not exist, for those using sparse-checkouts. > > Enforce this at index loading time by checking if core.sparseCheckout is > true; if so, check files in the index with the SKIP_WORKTREE bit set to > verify that they are absent from the working tree. If they are present, > unset the bit (in memory, though any commands that write to the index > will record the update). > Since this solution is specific to a sparse-checkout, should this automatic unsetting only be done if the file is outside the sparse checkout definition? Otherwise, the `sparse-checkout reapply` cleanup suggested below doesn't return the original `skip-worktree` state. Admittedly, I imagine it's unlikely that someone is simultaneously using a sparse checkout and manually SKIP_WORKTREE-ing files *inside* the sparse checkout definition. But, given that you're not unsetting the flag for non-sparse-checkout SKIP_WORKTREE files, it seems like an additional constraint based on sparse checkout patterns would be consistent with other parts of this patch. > Users can, of course, can get the SKIP_WORKTREE bit back such as by > running `git sparse-checkout reapply` (if they have ensured the file is > unmodified and doesn't match the specified sparsity patterns). > There are some performance implications of this solution in a sparse index-enabled checkout. Any time an out-of-cone file is no longer SKIP_WORKTREE, its parent directory lineage will be added to the sparse index, and performance would progressively (silently) degrade as more out-of-cone files were added. That said, a lot of my concern would be alleviated with some kind of warning indicating that a file just had SKIP_WORKTREE removed, including a mention of fixing it with `git sparse-checkout reapply`. It would be *extra* nice if `git status` could tell a user that they have non-SKIP_WORKTREE files outside the sparse definition, but I think that's less critical and probably better suited as a separate series. > === Pros/Cons of suggested solution === > > Pros: > > * Solves the user visible problems reported above, which I've been > complaining about for nearly a year but couldn't find a solution to. > * Much easier behavior in sparse-checkouts for users to reason about > * Very simple, ~30 lines of code. > * Significantly simplifies some ugly testcases, and obviates the need > to test an entire class of potential issues. > * Reduces code complexity, reasoning, and maintenance. Avoids > disagreements about weird corner cases[12]. > * It has been reported that some users might be (ab)using > SKIP_WORKTREE as a let-me-modify-but-keep-the-file-in-the-worktree > mechanism[13, and a few other similar references]. These users know > of multiple caveats and shortcomings in doing so; perhaps not > surprising given the "SKIP_WORKTREE expecations" section above. > However, these users use `git update-index --skip-worktree`, and not > `git sparse-checkout` or core.sparseCheckout=true. As such, these > users would be unaffected by this change and can continue abusing > the system as before. > > [12] https://lore.kernel.org/git/CABPp-BH9tju7WVm=QZDOvaMDdZbpNXrVWQdN-jmfN8wC6YVhmw@mail.gmail.com/ > [13] https://stackoverflow.com/questions/13630849/git-difference-between-assume-unchanged-and-skip-worktree > > Cons: > > * When core.sparseCheckout is enabled, this adds a performance cost to > reading the index. I'll defer discussion of this cost to a subsequent > patch, since I have some optimizations to add. > > === Notes on testcase modifications === > > The good: > * t1011: Compare to two cases above it ('read-tree will not throw away > dirty changes, non-sparse'); since the file is present, it should > match the non-sparse case now > * t1092: sparse-index & sparse-checkout now match full-worktree > behavior in more cases! Yaay for consistency! > * t6428, t7012: look at how much simpler the tests become! Merge and > stash can just fail early telling the user there's a file in the > way, instead of not noticing until it's about to write a file and > then have to implement sudden crash avoidance. Hurray for sanity! > * t7817: sparse behavior better matches full tree behavior. Hurray > for sanity! > > The confusing: > * t3705: These changes were ONLY needed on Windows, but they don't > hurt other platforms. Let's discuss each individually: > > * core.sparseCheckout should be false by default. Nothing in this > testcase toggles that until many, many tests later. However, > early tests (#5 in particular) were testing `update-index > --skip-worktree` behavior in a non-sparse-checkout, but the > Windows tests in CI were behaving as if core.sparseCheckout=true > had been specified somewhere. I do not have access to a Windows > machine. But I just manually did what should have been a no-op > and turned the config off. And it fixed the test. > * I have no idea why the leftover .gitattributes file from this > test was causing failures for test #18 on Windows, but only with > these changes of mine. Test #18 was checking for empty stderr, > and specifically wanted to know that some error completely > unrelated to file endings did not appear. The leftover > .gitattributes file thus caused some spurious stderr unrelated to > the thing being checked. Since other tests did not intend to > test normalization, just proactively remove the .gitattributes > file. I'm certain this is cleaner and better, I'm just unsure > why/how this didn't trigger problems before. > > Signed-off-by: Elijah Newren <newren@gmail.com> > --- > repository.c | 7 ++++ > sparse-index.c | 22 ++++++++++++ > sparse-index.h | 1 + > t/t1011-read-tree-sparse-checkout.sh | 2 +- > t/t1092-sparse-checkout-compatibility.sh | 16 ++++----- > t/t3705-add-sparse-checkout.sh | 2 ++ > t/t6428-merge-conflicts-sparse.sh | 23 +++---------- > t/t7012-skip-worktree-writing.sh | 44 ++++-------------------- > t/t7817-grep-sparse-checkout.sh | 11 ++++-- > 9 files changed, 62 insertions(+), 66 deletions(-) > > diff --git a/repository.c b/repository.c > index 34610c5a33..dfd1911902 100644 > --- a/repository.c > +++ b/repository.c > @@ -301,6 +301,13 @@ int repo_read_index(struct repository *repo) > if (repo->settings.command_requires_full_index) > ensure_full_index(repo->index); > > + /* > + * If sparse checkouts are in use, check whether paths with the > + * SKIP_WORKTREE attribute are missing from the worktree; if not, > + * clear that attribute for that path. > + */ > + ensure_skip_worktree_means_skip_worktree(repo->index); > + > return res; > } > > diff --git a/sparse-index.c b/sparse-index.c > index a1d505d50e..79d50e444c 100644 > --- a/sparse-index.c > +++ b/sparse-index.c > @@ -341,6 +341,28 @@ void ensure_correct_sparsity(struct index_state *istate) > ensure_full_index(istate); > } > > +void ensure_skip_worktree_means_skip_worktree(struct index_state *istate) I can feel the frustration behind this name. :) However, a more descriptive one would make the code easier to follow, e.g. 'clear_skip_worktree_from_present_files' (or something else indicating what it does to the index). > +{ > + int i; > + if (!core_apply_sparse_checkout) > + return; > + > +restart: > + for (i = 0; i < istate->cache_nr; i++) { > + struct cache_entry *ce = istate->cache[i]; > + struct stat st; > + > + if (ce_skip_worktree(ce) && !lstat(ce->name, &st)) { > + if (S_ISSPARSEDIR(ce->ce_mode)) { > + ensure_full_index(istate); > + goto restart; > + } > + ce->ce_flags &= ~CE_SKIP_WORKTREE; > + } > + } > +} > + > + > /* > * This static global helps avoid infinite recursion between > * expand_to_path() and index_file_exists(). > diff --git a/sparse-index.h b/sparse-index.h > index 656bd835b2..1007859ed4 100644 > --- a/sparse-index.h > +++ b/sparse-index.h > @@ -5,6 +5,7 @@ struct index_state; > #define SPARSE_INDEX_MEMORY_ONLY (1 << 0) > int convert_to_sparse(struct index_state *istate, int flags); > void ensure_correct_sparsity(struct index_state *istate); > +void ensure_skip_worktree_means_skip_worktree(struct index_state *istate); > > /* > * Some places in the codebase expect to search for a specific path. > diff --git a/t/t1011-read-tree-sparse-checkout.sh b/t/t1011-read-tree-sparse-checkout.sh > index 4ed0885bf2..dd957be1b7 100755 > --- a/t/t1011-read-tree-sparse-checkout.sh > +++ b/t/t1011-read-tree-sparse-checkout.sh > @@ -212,7 +212,7 @@ test_expect_success 'read-tree updates worktree, dirty case' ' > echo sub/added >.git/info/sparse-checkout && > git checkout -f top && > echo dirty >init.t && > - read_tree_u_must_succeed -m -u HEAD^ && > + read_tree_u_must_fail -m -u HEAD^ && > grep -q dirty init.t && > rm init.t > ' > diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh > index 0863c9747c..6f8538bb4c 100755 > --- a/t/t1092-sparse-checkout-compatibility.sh > +++ b/t/t1092-sparse-checkout-compatibility.sh > @@ -370,7 +370,7 @@ test_expect_success 'status/add: outside sparse cone' ' > write_script edit-contents <<-\EOF && > echo text >>$1 > EOF > - run_on_sparse ../edit-contents folder1/a && > + run_on_all ../edit-contents folder1/a && > run_on_all ../edit-contents folder1/new && > > test_sparse_match git status --porcelain=v2 && > @@ -379,8 +379,8 @@ test_expect_success 'status/add: outside sparse cone' ' > test_sparse_match test_must_fail git add folder1/a && > grep "Disable or modify the sparsity rules" sparse-checkout-err && > test_sparse_unstaged folder1/a && > - test_sparse_match test_must_fail git add --refresh folder1/a && > - grep "Disable or modify the sparsity rules" sparse-checkout-err && > + test_all_match git add --refresh folder1/a && > + test_must_be_empty sparse-checkout-err && > test_sparse_unstaged folder1/a && > test_sparse_match test_must_fail git add folder1/new && > grep "Disable or modify the sparsity rules" sparse-checkout-err && > @@ -642,11 +642,11 @@ test_expect_success 'update-index modify outside sparse definition' ' > run_on_sparse cp ../initial-repo/folder1/a folder1/a && > run_on_all ../edit-contents folder1/a && > > - # If file has skip-worktree enabled, update-index does not modify the > - # index entry > - test_sparse_match git update-index folder1/a && > - test_sparse_match git status --porcelain=v2 && > - test_must_be_empty sparse-checkout-out && > + # If file has skip-worktree enabled, but the file is present, it is > + # treated the same as if skip-worktree is disabled > + test_all_match git status --porcelain=v2 && > + test_all_match git update-index folder1/a && > + test_all_match git status --porcelain=v2 && > > # When skip-worktree is disabled (even on files outside sparse cone), file > # is updated in the index > diff --git a/t/t3705-add-sparse-checkout.sh b/t/t3705-add-sparse-checkout.sh > index f3143c9290..61506c1d7c 100755 > --- a/t/t3705-add-sparse-checkout.sh > +++ b/t/t3705-add-sparse-checkout.sh > @@ -19,6 +19,7 @@ setup_sparse_entry () { > fi && > git add sparse_entry && > git update-index --skip-worktree sparse_entry && > + git config core.sparseCheckout false && > git commit --allow-empty -m "ensure sparse_entry exists at HEAD" && > SPARSE_ENTRY_BLOB=$(git rev-parse :sparse_entry) > } > @@ -126,6 +127,7 @@ test_expect_success 'git add --chmod does not update sparse entries' ' > ' > > test_expect_success 'git add --renormalize does not update sparse entries' ' > + test_when_finished rm .gitattributes && > test_config core.autocrlf false && > setup_sparse_entry "LINEONE\r\nLINETWO\r\n" && > echo "sparse_entry text=auto" >.gitattributes && > diff --git a/t/t6428-merge-conflicts-sparse.sh b/t/t6428-merge-conflicts-sparse.sh > index 7e8bf497f8..142c9aaabc 100755 > --- a/t/t6428-merge-conflicts-sparse.sh > +++ b/t/t6428-merge-conflicts-sparse.sh > @@ -112,7 +112,7 @@ test_expect_success 'conflicting entries written to worktree even if sparse' ' > ) > ' > > -test_expect_merge_algorithm failure success 'present-despite-SKIP_WORKTREE handled reasonably' ' > +test_expect_success 'present-despite-SKIP_WORKTREE handled reasonably' ' > test_setup_numerals in_the_way && > ( > cd numerals_in_the_way && > @@ -132,26 +132,13 @@ test_expect_merge_algorithm failure success 'present-despite-SKIP_WORKTREE handl > > test_must_fail git merge -s recursive B^0 && > > - git ls-files -t >index_files && > - test_cmp expected-index index_files && > + test_path_is_missing .git/MERGE_HEAD && > > - test_path_is_file README && > test_path_is_file numerals && > > - test_cmp expected-merge numerals && > - > - # There should still be a file with "foobar" in it > - grep foobar * && > - > - # 5 other files: > - # * expected-merge > - # * expected-index > - # * index_files > - # * others > - # * whatever name was given to the numerals file that had > - # "foobar" in it > - git ls-files -o >others && > - test_line_count = 5 others > + # numerals should still have "foobar" in it > + echo foobar >expect && > + test_cmp expect numerals > ) > ' > > diff --git a/t/t7012-skip-worktree-writing.sh b/t/t7012-skip-worktree-writing.sh > index a1080b94e3..cb9f1a6981 100755 > --- a/t/t7012-skip-worktree-writing.sh > +++ b/t/t7012-skip-worktree-writing.sh > @@ -171,50 +171,20 @@ test_expect_success 'stash restore in sparse checkout' ' > > # Put a file in the working directory in the way > echo in the way >modified && > - git stash apply && > + test_must_fail git stash apply 2>error&& > > - # Ensure stash vivifies modifies paths... > - cat >expect <<-EOF && > - H addme > - H modified > - H removeme > - H subdir/A > - S untouched > - EOF > - git ls-files -t >actual && > - test_cmp expect actual && > + grep "changes.*would be overwritten by merge" error && > > - # ...and that the paths show up in status as changed... > - cat >expect <<-EOF && > - A addme > - M modified > - D removeme > - M subdir/A > - ?? actual > - ?? expect > - ?? modified.stash.XXXXXX > - EOF > - git status --porcelain | \ > - sed -e s/stash......./stash.XXXXXX/ >actual && > - test_cmp expect actual && > + echo in the way >expect && > + test_cmp expect modified && > + git diff --quiet HEAD ":!modified" && > > # ...and that working directory reflects the files correctly > - test_path_is_file addme && > + test_path_is_missing addme && > test_path_is_file modified && > test_path_is_missing removeme && > test_path_is_file subdir/A && > - test_path_is_missing untouched && > - > - # ...including that we have the expected "modified" file... > - cat >expect <<-EOF && > - modified > - tweaked > - EOF > - test_cmp expect modified && > - > - # ...and that the other "modified" file is still present... > - echo in the way >expect && > - test_cmp expect modified.stash.* > + test_path_is_missing untouched > ) > ' > > diff --git a/t/t7817-grep-sparse-checkout.sh b/t/t7817-grep-sparse-checkout.sh > index 590b99bbb6..eb59564565 100755 > --- a/t/t7817-grep-sparse-checkout.sh > +++ b/t/t7817-grep-sparse-checkout.sh > @@ -83,10 +83,13 @@ test_expect_success 'setup' ' > > # The test below covers a special case: the sparsity patterns exclude '/b' and > # sparse checkout is enabled, but the path exists in the working tree (e.g. > -# manually created after `git sparse-checkout init`). git grep should skip it. > +# manually created after `git sparse-checkout init`). Although b is marked > +# as SKIP_WORKTREE, git grep should notice it IS present in the worktree and > +# report it. > test_expect_success 'working tree grep honors sparse checkout' ' > cat >expect <<-EOF && > a:text > + b:new-text > EOF > test_when_finished "rm -f b" && > echo "new-text" >b && > @@ -126,12 +129,16 @@ test_expect_success 'grep --cached searches entries with the SKIP_WORKTREE bit' > ' > > # Note that sub2/ is present in the worktree but it is excluded by the sparsity > -# patterns, so grep should not recurse into it. > +# patterns. We also explicitly mark it as SKIP_WORKTREE in case it got cleared > +# by previous git commands. Thus sub2 starts as SKIP_WORKTREE but since it is > +# present in the working tree, grep should recurse into it. > test_expect_success 'grep --recurse-submodules honors sparse checkout in submodule' ' > cat >expect <<-EOF && > a:text > sub/B/b:text > + sub2/a:text > EOF > + git update-index --skip-worktree sub2 && > git grep --recurse-submodules "text" >actual && > test_cmp expect actual > '
On Mon, Jan 10, 2022 at 12:38 PM Victoria Dye <vdye@github.com> wrote: > > Elijah Newren wrote: ... > > === User facing issues === ... > > Further: > > * these files will not be updated by by standard commands > > (switch/checkout/pull/merge/rebase will leave them alone unless > > conflicts happen -- and even then, the conflicted file may be > > written somewhere else to avoid overwriting the SKIP_WORKTREE file > > that is present and in the way) > > * there is nothing in Git that users can use to discover such > > files (status, diff, grep, etc. all ignore it) > > * there is no reasonable mechanism to "recover" from such a condition > > (neither `git sparse-checkout reapply` nor `git reset --hard` will > > correct it). > > > > Just to add to this, files like these always force sparse index expansion in > `git status` (and probably some other commands?), ruining a lot of the > performance gains of using sparse index in the first place. Oh, good point. Another reason this state is just bad. ... > > === Suggested solution === > > > > SKIP_WORKTREE was written to allow sparse-checkouts, in particular, as > > the name of the option implies, to allow the file to NOT be in the > > worktree but consider it to be unchanged rather than deleted. > > > > The suggests a simple solution: present-despite-SKIP_WORKTREE files > > should not exist, for those using sparse-checkouts. > > > > Enforce this at index loading time by checking if core.sparseCheckout is > > true; if so, check files in the index with the SKIP_WORKTREE bit set to > > verify that they are absent from the working tree. If they are present, > > unset the bit (in memory, though any commands that write to the index > > will record the update). > > > > Since this solution is specific to a sparse-checkout, should this automatic > unsetting only be done if the file is outside the sparse checkout > definition? Otherwise, the `sparse-checkout reapply` cleanup suggested below > doesn't return the original `skip-worktree` state. That's an interesting distinction, but I think there are multiple problems with it: 1) I think you might be assuming this state would only be entered by a deliberate user choice, but that's far from the case 2) Allowing present-despite-SKIP_WORKTREE only for in-cone paths still allows the state to exist, which has multiple ramifications: 2A) while it solves user facing problems for out-of-cone present-despite-SKIP_WORKTREE files, it leaves user facing problems for in-cone ones 2B) it doesn't solve any of the complexity or need for special testing outlined in the commit message since the bad state is still possible for some paths 2C) Related to (2B), your series would need to do more work to make checkout-index sane 3) It's basically impossible to keep this kind of skip-worktree state in a sparse-checkout anyway. Let's look at (1), (2A), and (3) in more detail, since those may not be obvious: === (1) present-despite-SKIP_WORKTREE on in-cone can be triggered accidentally === Users can directly edit $GIT_DIR/info/sparse-checkout. We documented how for years. People wrote tools that did so. `git sparse-checkout` came much later. So, they could get into this state by having a sparse-checkout already, and then editing $GIT_DIR/info/sparse-checkout such that the files which used to be out-of-cone are now in-cone even though the working directory doesn't match. People could also get into this state without knowing about the $GIT_DIR/info/sparse-checkout file, with an in-opportune Ctrl-C during the middle of a `git sparse-checkout ...` command of some sort. I actually think it's more likely that people accidentally get into this state than deliberately. However, for sake of argument, let's presume people could only get into this state intentionally. I think we'd still want to make my changes for this class of files because of the other reasons, so let's move on to those... === (2A) present-despite-SKIP_WORKTREE on in-cone has user-facing problems too === So, we have a user who has some file(s) that are marked SKIP_WORKTREE despite being in-cone. Let's assume that the in-cone file has some dirty change(s). First, note that the in-cone file is already SKIP_WORKTREE: $ git ls-files -t S in-cone/foo.c S out-of-cone/tracked Now this user tries to switch to another branch which does differ in in-cone/foo.c (or try to do a rebase that involves in-cone/foo.c, or...): $ git checkout other-branch-modifying-in-cone error: Your local changes to the following files would be overwritten by checkout: in-cone/foo.c Please commit your changes or stash them before you switch branches. Aborting Oh, thinks the user, maybe I should check status before switching branches: $ git status --porcelain $ The user perhaps finds it odd that the file reported as having "local changes" doesn't show up in status, but decides to do what the error message reported anyway: $ git stash save foobar No local changes to save If neither status nor stash think there are any changes, why does checkout? Why can't I switch branches?? If they attempt to switch branches again anyway, they'll get the same local-changes error. Perhaps at this point they notice there were two possible solutions in the error message, so they decide to try committing the changes: $ git commit -am 'changes' On branch main You are in a sparse checkout with 0% of tracked files present. nothing to commit, working tree clean Three commands tell me my working tree is clean, but checkout says otherwise?!?!? Why can't I switch branches??? Stupid Git! (And if someone points them at `git add $FILENAME`, then they get another error message and are told to use `git add --sparse $FILENAME`...) In contrast, with my patch, none of this craziness happens and a locally modified file is detected and reported as locally modified by every command within a sparse checkout. It's so much saner for users. But, for sake of argument, let's ignore all of the reasons so far and instead pretend there are users who deliberately create skip-worktree files in-cone, and thus expect all these weirdnesses. Let's focus on the experience they might expect, and turn to item (3): === (3) present-despite-SKIP_WORKTREE on in-cone files will be aggressively cleared _anyway_, due to the fundamental design of sparse-checkout === Let's say I have a simple sparse-checkout with just a couple files: $ git ls-files -t H in-cone/foo.c S out-of-cone/tracked Now, I decide to make in-cone/foo.c skip-worktree, but keep it in the working tree and dirty its contents: $ git update-index --skip-worktree in-cone/foo.c $ echo dirty >in-cone/foo.c $ git ls-files -t S in-cone/foo.c S out-of-cone/tracked Now, status won't report our dirty modifications, commit won't include them, etc. Perhaps that's what the user wanted by marking it as skip-worktree. But as soon as they invoke any command that calls unpack_trees() in a way that might update the working copy (but which wouldn't need to touch the dirty files marked skip-worktree), the skip-worktree status is going to be dropped: $ git checkout -q HEAD^0 warning: The following paths were already present and thus not updated despite sparse patterns: in-cone/foo.c After fixing the above paths, you may want to run `git sparse-checkout reapply`. Switched to branch 'other-mod' $ git ls-files -t H in-cone/foo.c S out-of-cone/tracked This is not special to detaching HEAD; I could have switched to another branch and seen the same thing. Or rebased or cherry-picked or merge commits that didn't modify the skip-worktree file, and they'd all unset the skip-worktree bit for this file. This isn't a bug, either; it's by design. sparsity patterns have to be reapplied when switching branches in general (or rebasing or...), because that operation might bring in new files and so we need to know whether those new files should be SKIP_WORKTREE. You might say we could attempt to limit the SKIP_WORKTREE bit flipping to "just" new files, but due to the possibility of conflicts in earlier merges/rebases causing files to lose the SKIP_WORKTREE bit, we wanted future operations that were busy updating the bits anyway to update those files and clear the bit (and this pre-dated the work Stolee and I did on sparse-checkouts, btw). So, this means that checkout, merge, rebase, cherry-pick, etc. are going to be clearing SKIP_WORKTREE bits for in-cone files all the time. So, even if users did try to deliberately get into such a state, there's no point attempting to preserve the bit since so many commands are going to be aggressively clearing it anyway. > Admittedly, I imagine it's unlikely that someone is simultaneously using a > sparse checkout and manually SKIP_WORKTREE-ing files *inside* the sparse > checkout definition. But, given that you're not unsetting the flag for > non-sparse-checkout SKIP_WORKTREE files, it seems like an additional > constraint based on sparse checkout patterns would be consistent with > other parts of this patch. > > > Users can, of course, can get the SKIP_WORKTREE bit back such as by > > running `git sparse-checkout reapply` (if they have ensured the file is > > unmodified and doesn't match the specified sparsity patterns). > > > > There are some performance implications of this solution in a sparse > index-enabled checkout. Any time an out-of-cone file is no longer > SKIP_WORKTREE, its parent directory lineage will be added to the sparse index, > and performance would progressively (silently) degrade as more out-of-cone > files were added. Can I restate this a bit? """ The point of sparse-index is to allow operations to be faster due to needing to track fewer items in the index. Its performance is nearly linearly correlated with the number of paths it has to track, so fewer paths is better. If a user needs to work with more paths than they previously did, then their sparse-index will be correspondingly slower. And users who start modifying files, are obviously working with more paths than they previously did. """ Based on that restating, I think the only thing that could be considered a problem is your implication that the performance degradation would silently persist. If users don't undo or commit those local modifications, then they really are working with more files and I think it's fine for the sparse-index to remain expanded to include those files. In contrast, if users undo those local changes (or commit them so they are no longer dirty), then future checkout/rebase/merge/etc. operations will automatically (re-)set the SKIP_WORKTREE bit on those files, and the sparse-index can shrink again. These dirty files would be very similar to files that have conflicts during a merge: both have their SKIP_WORKTREE bit cleared despite being outside the sparsity paths. Continuing the comparison, after a user resolves a conflict and commits the changes, the previously conflicted file will automatically have its SKIP_WORKTREE bit set again by a future checkout/rebase/merge/etc. Or users can manually get it to be set earlier with a `git sparse-checkout reapply`. So the performance degradation from the additional paths the user is working with is only temporary, and only lasts roughly as long as the user is still working with these additional paths. To me, this feels like expected and wanted behavior. > That said, a lot of my concern would be alleviated with some kind of warning > indicating that a file just had SKIP_WORKTREE removed, including a mention > of fixing it with `git sparse-checkout reapply`. That might be interesting, but there's two problems here: * It'd affect more types of files and situations than intended. In particular, given [11], it could be quite noisy due to triggering on files other than those manually tweaked by users and even include files never involved in conflicts either. * It'd repeatedly trigger on the exact same files, possibly muddying other output unexpectedly. Given that we clear the bit in memory but not necessarily on disk, users would repeatedly see the same warning for the same files during sequences of read-only operations (like `git diff` or `git log`) and they warnings would only go away once the user ran a command that re-wrote the index (such as `git status`). I think the point of your suggestion was to help users recover from potentially persisting performance degradation; is that fair? If so, then as I highlighted above, I don't think we have any such persisting problem. [11] https://lore.kernel.org/git/xmqqbmb1a7ga.fsf@gitster-ct.c.googlers.com/ > It would be *extra* nice if `git status` could tell a user that they have > non-SKIP_WORKTREE files outside the sparse definition, but I think that's > less critical and probably better suited as a separate series. Oh, interesting idea. But I agree, it'd be better suited to a separate series. > > diff --git a/sparse-index.c b/sparse-index.c > > index a1d505d50e..79d50e444c 100644 > > --- a/sparse-index.c > > +++ b/sparse-index.c > > @@ -341,6 +341,28 @@ void ensure_correct_sparsity(struct index_state *istate) > > ensure_full_index(istate); > > } > > > > +void ensure_skip_worktree_means_skip_worktree(struct index_state *istate) > > I can feel the frustration behind this name. :) :-) > However, a more descriptive one would make the code easier to follow, e.g. > 'clear_skip_worktree_from_present_files' (or something else indicating what > it does to the index). Yeah, I did spend some time trying to come up with a better name (I realized it wasn't the best), but failed. Your suggestion seems obvious in hindsight. I like it; I'll make that change.
Elijah Newren wrote: > On Mon, Jan 10, 2022 at 12:38 PM Victoria Dye <vdye@github.com> wrote: >> >> Elijah Newren wrote: > ... >>> === User facing issues === > ... >>> Further: >>> * these files will not be updated by by standard commands >>> (switch/checkout/pull/merge/rebase will leave them alone unless >>> conflicts happen -- and even then, the conflicted file may be >>> written somewhere else to avoid overwriting the SKIP_WORKTREE file >>> that is present and in the way) >>> * there is nothing in Git that users can use to discover such >>> files (status, diff, grep, etc. all ignore it) >>> * there is no reasonable mechanism to "recover" from such a condition >>> (neither `git sparse-checkout reapply` nor `git reset --hard` will >>> correct it). >>> >> >> Just to add to this, files like these always force sparse index expansion in >> `git status` (and probably some other commands?), ruining a lot of the >> performance gains of using sparse index in the first place. > > Oh, good point. Another reason this state is just bad. > > ... >>> === Suggested solution === >>> >>> SKIP_WORKTREE was written to allow sparse-checkouts, in particular, as >>> the name of the option implies, to allow the file to NOT be in the >>> worktree but consider it to be unchanged rather than deleted. >>> >>> The suggests a simple solution: present-despite-SKIP_WORKTREE files >>> should not exist, for those using sparse-checkouts. >>> >>> Enforce this at index loading time by checking if core.sparseCheckout is >>> true; if so, check files in the index with the SKIP_WORKTREE bit set to >>> verify that they are absent from the working tree. If they are present, >>> unset the bit (in memory, though any commands that write to the index >>> will record the update). >>> >> >> Since this solution is specific to a sparse-checkout, should this automatic >> unsetting only be done if the file is outside the sparse checkout >> definition? Otherwise, the `sparse-checkout reapply` cleanup suggested below >> doesn't return the original `skip-worktree` state. > > That's an interesting distinction, but I think there are multiple > problems with it: > 1) I think you might be assuming this state would only be entered by > a deliberate user choice, but that's far from the case > 2) Allowing present-despite-SKIP_WORKTREE only for in-cone paths > still allows the state to exist, which has multiple ramifications: > 2A) while it solves user facing problems for out-of-cone > present-despite-SKIP_WORKTREE files, it leaves user facing problems > for in-cone ones > 2B) it doesn't solve any of the complexity or need for special > testing outlined in the commit message since the bad state is still > possible for some paths > 2C) Related to (2B), your series would need to do more work to > make checkout-index sane > 3) It's basically impossible to keep this kind of skip-worktree > state in a sparse-checkout anyway. > > Let's look at (1), (2A), and (3) in more detail, since those may not be obvious: > > === (1) present-despite-SKIP_WORKTREE on in-cone can be triggered > accidentally === > > Users can directly edit $GIT_DIR/info/sparse-checkout. We documented > how for years. People wrote tools that did so. `git sparse-checkout` > came much later. So, they could get into this state by having a > sparse-checkout already, and then editing > $GIT_DIR/info/sparse-checkout such that the files which used to be > out-of-cone are now in-cone even though the working directory doesn't > match. People could also get into this state without knowing about > the $GIT_DIR/info/sparse-checkout file, with an in-opportune Ctrl-C > during the middle of a `git sparse-checkout ...` command of some sort. > I actually think it's more likely that people accidentally get into > this state than deliberately. However, for sake of argument, let's > presume people could only get into this state intentionally. I think > we'd still want to make my changes for this class of files because of > the other reasons, so let's move on to those... > > === (2A) present-despite-SKIP_WORKTREE on in-cone has user-facing > problems too === > > So, we have a user who has some file(s) that are marked SKIP_WORKTREE > despite being in-cone. Let's assume that the in-cone file has some > dirty change(s). First, note that the in-cone file is already > SKIP_WORKTREE: > > $ git ls-files -t > S in-cone/foo.c > S out-of-cone/tracked > > Now this user tries to switch to another branch which does differ in > in-cone/foo.c (or try to do a rebase that involves in-cone/foo.c, > or...): > > $ git checkout other-branch-modifying-in-cone > error: Your local changes to the following files would be > overwritten by checkout: > in-cone/foo.c > Please commit your changes or stash them before you switch branches. > Aborting > > Oh, thinks the user, maybe I should check status before switching branches: > > $ git status --porcelain > $ > > The user perhaps finds it odd that the file reported as having "local > changes" doesn't show up in status, but decides to do what the error > message reported anyway: > > $ git stash save foobar > No local changes to save > > If neither status nor stash think there are any changes, why does > checkout? Why can't I switch branches?? If they attempt to switch > branches again anyway, they'll get the same local-changes error. > Perhaps at this point they notice there were two possible solutions in > the error message, so they decide to try committing the changes: > > $ git commit -am 'changes' > On branch main > You are in a sparse checkout with 0% of tracked files present. > > nothing to commit, working tree clean > > Three commands tell me my working tree is clean, but checkout says > otherwise?!?!? Why can't I switch branches??? Stupid Git! (And if > someone points them at `git add $FILENAME`, then they get another > error message and are told to use `git add --sparse $FILENAME`...) > > In contrast, with my patch, none of this craziness happens and a > locally modified file is detected and reported as locally modified by > every command within a sparse checkout. It's so much saner for users. > This particular issue also happens in non-sparse-checkout usage of SKIP_WORKTREE, but point (1) (+ a general desire to make sparse-checkout less "experimental") is a good reason to ensure the UX in a sparse-checkout isn't this frustrating. > But, for sake of argument, let's ignore all of the reasons so far and > instead pretend there are users who deliberately create skip-worktree > files in-cone, and thus expect all these weirdnesses. Let's focus on > the experience they might expect, and turn to item (3): > > === (3) present-despite-SKIP_WORKTREE on in-cone files will be > aggressively cleared _anyway_, due to the fundamental design of > sparse-checkout === > > Let's say I have a simple sparse-checkout with just a couple files: > > $ git ls-files -t > H in-cone/foo.c > S out-of-cone/tracked > > Now, I decide to make in-cone/foo.c skip-worktree, but keep it in the > working tree and dirty its contents: > > $ git update-index --skip-worktree in-cone/foo.c > $ echo dirty >in-cone/foo.c > $ git ls-files -t > S in-cone/foo.c > S out-of-cone/tracked > > Now, status won't report our dirty modifications, commit won't include > them, etc. Perhaps that's what the user wanted by marking it as > skip-worktree. But as soon as they invoke any command that calls > unpack_trees() in a way that might update the working copy (but which > wouldn't need to touch the dirty files marked skip-worktree), the > skip-worktree status is going to be dropped: > > $ git checkout -q HEAD^0 > warning: The following paths were already present and thus not > updated despite sparse patterns: > in-cone/foo.c > > After fixing the above paths, you may want to run `git > sparse-checkout reapply`. > Switched to branch 'other-mod' > $ git ls-files -t > H in-cone/foo.c > S out-of-cone/tracked > > This is not special to detaching HEAD; I could have switched to > another branch and seen the same thing. Or rebased or cherry-picked > or merge commits that didn't modify the skip-worktree file, and they'd > all unset the skip-worktree bit for this file. This isn't a bug, > either; it's by design. sparsity patterns have to be reapplied when > switching branches in general (or rebasing or...), because that > operation might bring in new files and so we need to know whether > those new files should be SKIP_WORKTREE. You might say we could > attempt to limit the SKIP_WORKTREE bit flipping to "just" new files, > but due to the possibility of conflicts in earlier merges/rebases > causing files to lose the SKIP_WORKTREE bit, we wanted future > operations that were busy updating the bits anyway to update those > files and clear the bit (and this pre-dated the work Stolee and I did > on sparse-checkouts, btw). > > So, this means that checkout, merge, rebase, cherry-pick, etc. are > going to be clearing SKIP_WORKTREE bits for in-cone files all the > time. > > So, even if users did try to deliberately get into such a state, > there's no point attempting to preserve the bit since so many commands > are going to be aggressively clearing it anyway. > Ahh, I should have remembered that - it's also really helpful context for understanding why you can/should aggressively unset SKIP_WORKTREE (because git will aggressively re-set it if a file is up-to-date). >> Admittedly, I imagine it's unlikely that someone is simultaneously using a >> sparse checkout and manually SKIP_WORKTREE-ing files *inside* the sparse >> checkout definition. But, given that you're not unsetting the flag for >> non-sparse-checkout SKIP_WORKTREE files, it seems like an additional >> constraint based on sparse checkout patterns would be consistent with >> other parts of this patch. >> >>> Users can, of course, can get the SKIP_WORKTREE bit back such as by >>> running `git sparse-checkout reapply` (if they have ensured the file is >>> unmodified and doesn't match the specified sparsity patterns). >>> >> >> There are some performance implications of this solution in a sparse >> index-enabled checkout. Any time an out-of-cone file is no longer >> SKIP_WORKTREE, its parent directory lineage will be added to the sparse index, >> and performance would progressively (silently) degrade as more out-of-cone >> files were added. > > Can I restate this a bit? > > """ > The point of sparse-index is to allow operations to be faster due to > needing to track fewer items in the index. Its performance is nearly > linearly correlated with the number of paths it has to track, so fewer > paths is better. If a user needs to work with more paths than they > previously did, then their sparse-index will be correspondingly > slower. > > And users who start modifying files, are obviously working with more > paths than they previously did. > """ > > Based on that restating, I think the only thing that could be > considered a problem is your implication that the performance > degradation would silently persist. If users don't undo or commit > those local modifications, then they really are working with more > files and I think it's fine for the sparse-index to remain expanded to > include those files. In contrast, if users undo those local changes > (or commit them so they are no longer dirty), then future > checkout/rebase/merge/etc. operations will automatically (re-)set the > SKIP_WORKTREE bit on those files, and the sparse-index can shrink > again. These dirty files would be very similar to files that have > conflicts during a merge: both have their SKIP_WORKTREE bit cleared > despite being outside the sparsity paths. Continuing the comparison, > after a user resolves a conflict and commits the changes, the > previously conflicted file will automatically have its SKIP_WORKTREE > bit set again by a future checkout/rebase/merge/etc. Or users can > manually get it to be set earlier with a `git sparse-checkout > reapply`. So the performance degradation from the additional paths > the user is working with is only temporary, and only lasts roughly as > long as the user is still working with these additional paths. To me, > this feels like expected and wanted behavior. > >> That said, a lot of my concern would be alleviated with some kind of warning >> indicating that a file just had SKIP_WORKTREE removed, including a mention >> of fixing it with `git sparse-checkout reapply`. > > That might be interesting, but there's two problems here: > * It'd affect more types of files and situations than intended. In > particular, given [11], it could be quite noisy due to triggering on > files other than those manually tweaked by users and even include > files never involved in conflicts either. > * It'd repeatedly trigger on the exact same files, possibly muddying > other output unexpectedly. Given that we clear the bit in memory but > not necessarily on disk, users would repeatedly see the same warning > for the same files during sequences of read-only operations (like `git > diff` or `git log`) and they warnings would only go away once the user > ran a command that re-wrote the index (such as `git status`). > > I think the point of your suggestion was to help users recover from > potentially persisting performance degradation; is that fair? If so, > then as I highlighted above, I don't think we have any such persisting > problem. > Yes, the performance degradation was my main concern, but I agree that it wouldn't be a persistent problem based on your explanation. Thanks for the clarification! > [11] https://lore.kernel.org/git/xmqqbmb1a7ga.fsf@gitster-ct.c.googlers.com/ > >> It would be *extra* nice if `git status` could tell a user that they have >> non-SKIP_WORKTREE files outside the sparse definition, but I think that's >> less critical and probably better suited as a separate series. > > Oh, interesting idea. But I agree, it'd be better suited to a separate series. > >>> diff --git a/sparse-index.c b/sparse-index.c >>> index a1d505d50e..79d50e444c 100644 >>> --- a/sparse-index.c >>> +++ b/sparse-index.c >>> @@ -341,6 +341,28 @@ void ensure_correct_sparsity(struct index_state *istate) >>> ensure_full_index(istate); >>> } >>> >>> +void ensure_skip_worktree_means_skip_worktree(struct index_state *istate) >> >> I can feel the frustration behind this name. :) > > :-) > >> However, a more descriptive one would make the code easier to follow, e.g. >> 'clear_skip_worktree_from_present_files' (or something else indicating what >> it does to the index). > > Yeah, I did spend some time trying to come up with a better name (I > realized it wasn't the best), but failed. Your suggestion seems > obvious in hindsight. I like it; I'll make that change.
diff --git a/repository.c b/repository.c index 34610c5a33..dfd1911902 100644 --- a/repository.c +++ b/repository.c @@ -301,6 +301,13 @@ int repo_read_index(struct repository *repo) if (repo->settings.command_requires_full_index) ensure_full_index(repo->index); + /* + * If sparse checkouts are in use, check whether paths with the + * SKIP_WORKTREE attribute are missing from the worktree; if not, + * clear that attribute for that path. + */ + ensure_skip_worktree_means_skip_worktree(repo->index); + return res; } diff --git a/sparse-index.c b/sparse-index.c index a1d505d50e..79d50e444c 100644 --- a/sparse-index.c +++ b/sparse-index.c @@ -341,6 +341,28 @@ void ensure_correct_sparsity(struct index_state *istate) ensure_full_index(istate); } +void ensure_skip_worktree_means_skip_worktree(struct index_state *istate) +{ + int i; + if (!core_apply_sparse_checkout) + return; + +restart: + for (i = 0; i < istate->cache_nr; i++) { + struct cache_entry *ce = istate->cache[i]; + struct stat st; + + if (ce_skip_worktree(ce) && !lstat(ce->name, &st)) { + if (S_ISSPARSEDIR(ce->ce_mode)) { + ensure_full_index(istate); + goto restart; + } + ce->ce_flags &= ~CE_SKIP_WORKTREE; + } + } +} + + /* * This static global helps avoid infinite recursion between * expand_to_path() and index_file_exists(). diff --git a/sparse-index.h b/sparse-index.h index 656bd835b2..1007859ed4 100644 --- a/sparse-index.h +++ b/sparse-index.h @@ -5,6 +5,7 @@ struct index_state; #define SPARSE_INDEX_MEMORY_ONLY (1 << 0) int convert_to_sparse(struct index_state *istate, int flags); void ensure_correct_sparsity(struct index_state *istate); +void ensure_skip_worktree_means_skip_worktree(struct index_state *istate); /* * Some places in the codebase expect to search for a specific path. diff --git a/t/t1011-read-tree-sparse-checkout.sh b/t/t1011-read-tree-sparse-checkout.sh index 4ed0885bf2..dd957be1b7 100755 --- a/t/t1011-read-tree-sparse-checkout.sh +++ b/t/t1011-read-tree-sparse-checkout.sh @@ -212,7 +212,7 @@ test_expect_success 'read-tree updates worktree, dirty case' ' echo sub/added >.git/info/sparse-checkout && git checkout -f top && echo dirty >init.t && - read_tree_u_must_succeed -m -u HEAD^ && + read_tree_u_must_fail -m -u HEAD^ && grep -q dirty init.t && rm init.t ' diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh index 0863c9747c..6f8538bb4c 100755 --- a/t/t1092-sparse-checkout-compatibility.sh +++ b/t/t1092-sparse-checkout-compatibility.sh @@ -370,7 +370,7 @@ test_expect_success 'status/add: outside sparse cone' ' write_script edit-contents <<-\EOF && echo text >>$1 EOF - run_on_sparse ../edit-contents folder1/a && + run_on_all ../edit-contents folder1/a && run_on_all ../edit-contents folder1/new && test_sparse_match git status --porcelain=v2 && @@ -379,8 +379,8 @@ test_expect_success 'status/add: outside sparse cone' ' test_sparse_match test_must_fail git add folder1/a && grep "Disable or modify the sparsity rules" sparse-checkout-err && test_sparse_unstaged folder1/a && - test_sparse_match test_must_fail git add --refresh folder1/a && - grep "Disable or modify the sparsity rules" sparse-checkout-err && + test_all_match git add --refresh folder1/a && + test_must_be_empty sparse-checkout-err && test_sparse_unstaged folder1/a && test_sparse_match test_must_fail git add folder1/new && grep "Disable or modify the sparsity rules" sparse-checkout-err && @@ -642,11 +642,11 @@ test_expect_success 'update-index modify outside sparse definition' ' run_on_sparse cp ../initial-repo/folder1/a folder1/a && run_on_all ../edit-contents folder1/a && - # If file has skip-worktree enabled, update-index does not modify the - # index entry - test_sparse_match git update-index folder1/a && - test_sparse_match git status --porcelain=v2 && - test_must_be_empty sparse-checkout-out && + # If file has skip-worktree enabled, but the file is present, it is + # treated the same as if skip-worktree is disabled + test_all_match git status --porcelain=v2 && + test_all_match git update-index folder1/a && + test_all_match git status --porcelain=v2 && # When skip-worktree is disabled (even on files outside sparse cone), file # is updated in the index diff --git a/t/t3705-add-sparse-checkout.sh b/t/t3705-add-sparse-checkout.sh index f3143c9290..61506c1d7c 100755 --- a/t/t3705-add-sparse-checkout.sh +++ b/t/t3705-add-sparse-checkout.sh @@ -19,6 +19,7 @@ setup_sparse_entry () { fi && git add sparse_entry && git update-index --skip-worktree sparse_entry && + git config core.sparseCheckout false && git commit --allow-empty -m "ensure sparse_entry exists at HEAD" && SPARSE_ENTRY_BLOB=$(git rev-parse :sparse_entry) } @@ -126,6 +127,7 @@ test_expect_success 'git add --chmod does not update sparse entries' ' ' test_expect_success 'git add --renormalize does not update sparse entries' ' + test_when_finished rm .gitattributes && test_config core.autocrlf false && setup_sparse_entry "LINEONE\r\nLINETWO\r\n" && echo "sparse_entry text=auto" >.gitattributes && diff --git a/t/t6428-merge-conflicts-sparse.sh b/t/t6428-merge-conflicts-sparse.sh index 7e8bf497f8..142c9aaabc 100755 --- a/t/t6428-merge-conflicts-sparse.sh +++ b/t/t6428-merge-conflicts-sparse.sh @@ -112,7 +112,7 @@ test_expect_success 'conflicting entries written to worktree even if sparse' ' ) ' -test_expect_merge_algorithm failure success 'present-despite-SKIP_WORKTREE handled reasonably' ' +test_expect_success 'present-despite-SKIP_WORKTREE handled reasonably' ' test_setup_numerals in_the_way && ( cd numerals_in_the_way && @@ -132,26 +132,13 @@ test_expect_merge_algorithm failure success 'present-despite-SKIP_WORKTREE handl test_must_fail git merge -s recursive B^0 && - git ls-files -t >index_files && - test_cmp expected-index index_files && + test_path_is_missing .git/MERGE_HEAD && - test_path_is_file README && test_path_is_file numerals && - test_cmp expected-merge numerals && - - # There should still be a file with "foobar" in it - grep foobar * && - - # 5 other files: - # * expected-merge - # * expected-index - # * index_files - # * others - # * whatever name was given to the numerals file that had - # "foobar" in it - git ls-files -o >others && - test_line_count = 5 others + # numerals should still have "foobar" in it + echo foobar >expect && + test_cmp expect numerals ) ' diff --git a/t/t7012-skip-worktree-writing.sh b/t/t7012-skip-worktree-writing.sh index a1080b94e3..cb9f1a6981 100755 --- a/t/t7012-skip-worktree-writing.sh +++ b/t/t7012-skip-worktree-writing.sh @@ -171,50 +171,20 @@ test_expect_success 'stash restore in sparse checkout' ' # Put a file in the working directory in the way echo in the way >modified && - git stash apply && + test_must_fail git stash apply 2>error&& - # Ensure stash vivifies modifies paths... - cat >expect <<-EOF && - H addme - H modified - H removeme - H subdir/A - S untouched - EOF - git ls-files -t >actual && - test_cmp expect actual && + grep "changes.*would be overwritten by merge" error && - # ...and that the paths show up in status as changed... - cat >expect <<-EOF && - A addme - M modified - D removeme - M subdir/A - ?? actual - ?? expect - ?? modified.stash.XXXXXX - EOF - git status --porcelain | \ - sed -e s/stash......./stash.XXXXXX/ >actual && - test_cmp expect actual && + echo in the way >expect && + test_cmp expect modified && + git diff --quiet HEAD ":!modified" && # ...and that working directory reflects the files correctly - test_path_is_file addme && + test_path_is_missing addme && test_path_is_file modified && test_path_is_missing removeme && test_path_is_file subdir/A && - test_path_is_missing untouched && - - # ...including that we have the expected "modified" file... - cat >expect <<-EOF && - modified - tweaked - EOF - test_cmp expect modified && - - # ...and that the other "modified" file is still present... - echo in the way >expect && - test_cmp expect modified.stash.* + test_path_is_missing untouched ) ' diff --git a/t/t7817-grep-sparse-checkout.sh b/t/t7817-grep-sparse-checkout.sh index 590b99bbb6..eb59564565 100755 --- a/t/t7817-grep-sparse-checkout.sh +++ b/t/t7817-grep-sparse-checkout.sh @@ -83,10 +83,13 @@ test_expect_success 'setup' ' # The test below covers a special case: the sparsity patterns exclude '/b' and # sparse checkout is enabled, but the path exists in the working tree (e.g. -# manually created after `git sparse-checkout init`). git grep should skip it. +# manually created after `git sparse-checkout init`). Although b is marked +# as SKIP_WORKTREE, git grep should notice it IS present in the worktree and +# report it. test_expect_success 'working tree grep honors sparse checkout' ' cat >expect <<-EOF && a:text + b:new-text EOF test_when_finished "rm -f b" && echo "new-text" >b && @@ -126,12 +129,16 @@ test_expect_success 'grep --cached searches entries with the SKIP_WORKTREE bit' ' # Note that sub2/ is present in the worktree but it is excluded by the sparsity -# patterns, so grep should not recurse into it. +# patterns. We also explicitly mark it as SKIP_WORKTREE in case it got cleared +# by previous git commands. Thus sub2 starts as SKIP_WORKTREE but since it is +# present in the working tree, grep should recurse into it. test_expect_success 'grep --recurse-submodules honors sparse checkout in submodule' ' cat >expect <<-EOF && a:text sub/B/b:text + sub2/a:text EOF + git update-index --skip-worktree sub2 && git grep --recurse-submodules "text" >actual && test_cmp expect actual '
The fix is short (~30 lines), but the description is not. Sorry. There is a set of problems caused by files in what I'll refer to as the "present-despite-SKIP_WORKTREE" state. This commit aims to not just fix these problems, but remove the entire class as a possibility -- for those using sparse checkouts. But first, we need to understand the problems this class presents. A quick outline: * Problems * User facing issues * Problem space complexity * Maintenance and code correctness challenges * SKIP_WORKTREE expectations in Git * Suggested solution * Pros/Cons of suggested solution * Notes on testcase modifications === User facing issues === There are various ways for users to get files to be present in the working copy despite having the SKIP_WORKTREE bit set for that file in the index. This may come from: * various git commands not really supporting the SKIP_WORKTREE bit[1,2] * users grabbing files from elsewhere and writing them to the worktree (perhaps even cached in their editor) * users attempting to "abort" a sparse-checkout operation with a not-so-early Ctrl+C (updating $GIT_DIR/info/sparse-checkout and the working tree is not atomic)[3]. Once users have present-despite-SKIP_WORKTREE files, any modifications users make to these files will be ignored, possibly to users' confusion. Further: * these files will not be updated by by standard commands (switch/checkout/pull/merge/rebase will leave them alone unless conflicts happen -- and even then, the conflicted file may be written somewhere else to avoid overwriting the SKIP_WORKTREE file that is present and in the way) * there is nothing in Git that users can use to discover such files (status, diff, grep, etc. all ignore it) * there is no reasonable mechanism to "recover" from such a condition (neither `git sparse-checkout reapply` nor `git reset --hard` will correct it). So, not only are users modifications ignored, but the files get progressively more stale over time. At some point in the future, they may change their sparseness specification or disable sparse-checkouts. At that time, all present-despite-SKIP_WORKTREE files will show up as having lots of modifications because they represent a version from a different branch or commit. These might include user-made local changes from days before, but the only way to tell is to have users look through them all closely. If these users come to others for help, there will be no logs that explain the issue; it's just a mysterious list of changes. Users might adamantly claim (correctly, as it turns out) that they didn't modify these files, while others presume they did. [1] https://lore.kernel.org/git/xmqqbmb1a7ga.fsf@gitster-ct.c.googlers.com/ [2] https://lore.kernel.org/git/CABPp-BH9tju7WVm=QZDOvaMDdZbpNXrVWQdN-jmfN8wC6YVhmw@mail.gmail.com/ [3] https://lore.kernel.org/git/CABPp-BFnFpzwGC11TLoLs8YK5yiisA5D5-fFjXnJsbESVDwZsA@mail.gmail.com/ === Problem space complexity === SKIP_WORKTREE has been part of Git for over a decade. Duy did lots of work on it initially, and several others have since come along and put lots of work into it. Stolee spent most of 2021 on the sparse-index, with lots of bugfixes along the way including to non-sparse-index cases as we are still trying to get sparse checkouts to behave reasonably. Basically every codepath throughout the treat needs to be aware of an additional type of file: tracked-but-not-present. The extra type results in lots of extra testcases and lots of extra code everywhere. But, the sad thing is that we actually have more than one extra type. We have tracked, tracked-but-not-present (SKIP_WORKTREE), and tracked-but-promised-to-not-be-present-but-is-present-anyway (present-despite-SKIP_WORKTREE). Two types is a monumental amount of effort to support, and adding a third feels a bit like insanity[4]. [4] Some examples of which can be seen at https://lore.kernel.org/git/CABPp-BGJ_Nvi5TmgriD9Bh6eNXE2EDq2f8e8QKXAeYG3BxZafA@mail.gmail.com/ === Maintenance and code correctness challenges === Matheus' patches to grep stalled for nearly a year, in part because of complications of how to handle sparse-checkouts appropriately in all cases[5][6] (with trying to sanely figure out how to sanely handle present-despite-SKIP_WORKTREE files being one of the complications). His rm/add follow-ups also took months because of those kinds of issues[7]. The corner cases with things like submodules and SKIP_WORKTREE with the addition of present-despite-SKIP_WORKTREE start becoming really complex[8]. We've had to add ugly logic to merge-ort to attempt to handle present-despite-SKIP_WORKTREE files[9], and basically just been forced to give up in merge-recursive knowing full well that we'll sometimes silently discard user modifications. Despite stash essentially being a merge, it needed extra code (beyond what was in merge-ort and merge-recursive) to manually tweak SKIP_WORKTREE bits in order to avoid a few different bugs that'd result in an early abort with a partial stash application[10]. [5] See https://lore.kernel.org/git/5f3f7ac77039d41d1692ceae4b0c5df3bb45b74a.1612901326.git.matheus.bernardino@usp.br/#t and the dates on the thread; also Matheus and I had several conversations off-list trying to resolve the issues over that time [6] ...it finally kind of got unstuck after https://lore.kernel.org/git/CABPp-BGJ_Nvi5TmgriD9Bh6eNXE2EDq2f8e8QKXAeYG3BxZafA@mail.gmail.com/ [7] See for example https://lore.kernel.org/git/CABPp-BHwNoVnooqDFPAsZxBT9aR5Dwk5D9sDRCvYSb8akxAJgA@mail.gmail.com/#t and quotes like "The core functionality of sparse-checkout has always been only partially implemented", a statement I still believe is true today. [8] https://lore.kernel.org/git/pull.809.git.git.1592356884310.gitgitgadget@gmail.com/ [9] See commit 66b209b86a ("merge-ort: implement CE_SKIP_WORKTREE handling with conflicted entries", 2021-03-20) [10] See commit ba359fd507 ("stash: fix stash application in sparse-checkouts", 2020-12-01) === SKIP_WORKTREE expectations in Git === A couple quotes: From [11] (before the "sparse-checkout" command existed): If it needs too many special cases, hacks, and conditionals, then it is not worth the complexity---if it is easier to write a correct code by allowing Git to populate working tree files, it is perfectly fine to do so. In a sense, the sparse checkout "feature" itself is a hack by itself, and that is why I think this part should be "best effort" as well. From the git-sparse-checkout manual (still present today): THIS COMMAND IS EXPERIMENTAL. ITS BEHAVIOR, AND THE BEHAVIOR OF OTHER COMMANDS IN THE PRESENCE OF SPARSE-CHECKOUTS, WILL LIKELY CHANGE IN THE FUTURE. [11] https://lore.kernel.org/git/xmqqbmb1a7ga.fsf@gitster-ct.c.googlers.com/ === Suggested solution === SKIP_WORKTREE was written to allow sparse-checkouts, in particular, as the name of the option implies, to allow the file to NOT be in the worktree but consider it to be unchanged rather than deleted. The suggests a simple solution: present-despite-SKIP_WORKTREE files should not exist, for those using sparse-checkouts. Enforce this at index loading time by checking if core.sparseCheckout is true; if so, check files in the index with the SKIP_WORKTREE bit set to verify that they are absent from the working tree. If they are present, unset the bit (in memory, though any commands that write to the index will record the update). Users can, of course, can get the SKIP_WORKTREE bit back such as by running `git sparse-checkout reapply` (if they have ensured the file is unmodified and doesn't match the specified sparsity patterns). === Pros/Cons of suggested solution === Pros: * Solves the user visible problems reported above, which I've been complaining about for nearly a year but couldn't find a solution to. * Much easier behavior in sparse-checkouts for users to reason about * Very simple, ~30 lines of code. * Significantly simplifies some ugly testcases, and obviates the need to test an entire class of potential issues. * Reduces code complexity, reasoning, and maintenance. Avoids disagreements about weird corner cases[12]. * It has been reported that some users might be (ab)using SKIP_WORKTREE as a let-me-modify-but-keep-the-file-in-the-worktree mechanism[13, and a few other similar references]. These users know of multiple caveats and shortcomings in doing so; perhaps not surprising given the "SKIP_WORKTREE expecations" section above. However, these users use `git update-index --skip-worktree`, and not `git sparse-checkout` or core.sparseCheckout=true. As such, these users would be unaffected by this change and can continue abusing the system as before. [12] https://lore.kernel.org/git/CABPp-BH9tju7WVm=QZDOvaMDdZbpNXrVWQdN-jmfN8wC6YVhmw@mail.gmail.com/ [13] https://stackoverflow.com/questions/13630849/git-difference-between-assume-unchanged-and-skip-worktree Cons: * When core.sparseCheckout is enabled, this adds a performance cost to reading the index. I'll defer discussion of this cost to a subsequent patch, since I have some optimizations to add. === Notes on testcase modifications === The good: * t1011: Compare to two cases above it ('read-tree will not throw away dirty changes, non-sparse'); since the file is present, it should match the non-sparse case now * t1092: sparse-index & sparse-checkout now match full-worktree behavior in more cases! Yaay for consistency! * t6428, t7012: look at how much simpler the tests become! Merge and stash can just fail early telling the user there's a file in the way, instead of not noticing until it's about to write a file and then have to implement sudden crash avoidance. Hurray for sanity! * t7817: sparse behavior better matches full tree behavior. Hurray for sanity! The confusing: * t3705: These changes were ONLY needed on Windows, but they don't hurt other platforms. Let's discuss each individually: * core.sparseCheckout should be false by default. Nothing in this testcase toggles that until many, many tests later. However, early tests (#5 in particular) were testing `update-index --skip-worktree` behavior in a non-sparse-checkout, but the Windows tests in CI were behaving as if core.sparseCheckout=true had been specified somewhere. I do not have access to a Windows machine. But I just manually did what should have been a no-op and turned the config off. And it fixed the test. * I have no idea why the leftover .gitattributes file from this test was causing failures for test #18 on Windows, but only with these changes of mine. Test #18 was checking for empty stderr, and specifically wanted to know that some error completely unrelated to file endings did not appear. The leftover .gitattributes file thus caused some spurious stderr unrelated to the thing being checked. Since other tests did not intend to test normalization, just proactively remove the .gitattributes file. I'm certain this is cleaner and better, I'm just unsure why/how this didn't trigger problems before. Signed-off-by: Elijah Newren <newren@gmail.com> --- repository.c | 7 ++++ sparse-index.c | 22 ++++++++++++ sparse-index.h | 1 + t/t1011-read-tree-sparse-checkout.sh | 2 +- t/t1092-sparse-checkout-compatibility.sh | 16 ++++----- t/t3705-add-sparse-checkout.sh | 2 ++ t/t6428-merge-conflicts-sparse.sh | 23 +++---------- t/t7012-skip-worktree-writing.sh | 44 ++++-------------------- t/t7817-grep-sparse-checkout.sh | 11 ++++-- 9 files changed, 62 insertions(+), 66 deletions(-)