2009-08-20 13:46:59 +00:00
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#!/bin/sh
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#
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# Copyright (c) 2008 Nguyễn Thái Ngọc Duy
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#
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test_description='test worktree writing operations when skip-worktree is used'
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2024-06-11 09:19:59 +00:00
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TEST_PASSES_SANITIZE_LEAK=true
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2009-08-20 13:46:59 +00:00
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. ./test-lib.sh
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test_expect_success 'setup' '
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test_commit init &&
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echo modified >> init.t &&
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touch added &&
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git add init.t added &&
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git commit -m "modified and added" &&
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git tag top
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'
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test_expect_success 'read-tree updates worktree, absent case' '
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git checkout -f top &&
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git update-index --skip-worktree init.t &&
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rm init.t &&
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git read-tree -m -u HEAD^ &&
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echo init > expected &&
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test_cmp expected init.t
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'
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test_expect_success 'read-tree updates worktree, dirty case' '
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git checkout -f top &&
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git update-index --skip-worktree init.t &&
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echo dirty >> init.t &&
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test_must_fail git read-tree -m -u HEAD^ &&
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grep -q dirty init.t &&
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test "$(git ls-files -t init.t)" = "S init.t" &&
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git update-index --no-skip-worktree init.t
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'
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test_expect_success 'read-tree removes worktree, absent case' '
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git checkout -f top &&
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git update-index --skip-worktree added &&
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rm added &&
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git read-tree -m -u HEAD^ &&
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test ! -f added
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'
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test_expect_success 'read-tree removes worktree, dirty case' '
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git checkout -f top &&
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git update-index --skip-worktree added &&
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echo dirty >> added &&
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test_must_fail git read-tree -m -u HEAD^ &&
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grep -q dirty added &&
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test "$(git ls-files -t added)" = "S added" &&
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git update-index --no-skip-worktree added
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'
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setup_absent() {
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test -f 1 && rm 1
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git update-index --remove 1 &&
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2016-07-16 05:06:25 +00:00
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git update-index --add --cacheinfo 100644 $EMPTY_BLOB 1 &&
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2009-08-20 13:46:59 +00:00
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git update-index --skip-worktree 1
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}
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setup_dirty() {
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git update-index --force-remove 1 &&
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echo dirty > 1 &&
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2016-07-16 05:06:25 +00:00
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git update-index --add --cacheinfo 100644 $EMPTY_BLOB 1 &&
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2009-08-20 13:46:59 +00:00
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git update-index --skip-worktree 1
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}
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test_dirty() {
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2016-07-16 05:06:25 +00:00
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echo "100644 $EMPTY_BLOB 0 1" > expected &&
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2009-08-20 13:46:59 +00:00
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git ls-files --stage 1 > result &&
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test_cmp expected result &&
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echo dirty > expected
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test_cmp expected 1
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}
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cat >expected <<EOF
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S 1
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H 2
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H init.t
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S sub/1
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H sub/2
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EOF
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test_expect_success 'index setup' '
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git checkout -f init &&
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mkdir sub &&
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touch ./1 ./2 sub/1 sub/2 &&
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git add 1 2 sub/1 sub/2 &&
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git update-index --skip-worktree 1 sub/1 &&
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git ls-files -t > result &&
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test_cmp expected result
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'
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test_expect_success 'git-rm fails if worktree is dirty' '
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setup_dirty &&
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test_must_fail git rm 1 &&
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test_dirty
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'
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cat >expected <<EOF
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Would remove expected
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Would remove result
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EOF
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2011-04-12 23:33:39 +00:00
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test_expect_success 'git-clean, absent case' '
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2009-08-20 13:46:59 +00:00
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setup_absent &&
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git clean -n > result &&
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2021-02-11 01:53:53 +00:00
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test_cmp expected result
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2009-08-20 13:46:59 +00:00
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'
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2011-04-12 23:33:39 +00:00
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test_expect_success 'git-clean, dirty case' '
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2009-08-20 13:46:59 +00:00
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setup_dirty &&
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git clean -n > result &&
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2021-02-11 01:53:53 +00:00
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test_cmp expected result
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2009-08-20 13:46:59 +00:00
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'
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2019-10-30 10:49:37 +00:00
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test_expect_success '--ignore-skip-worktree-entries leaves worktree alone' '
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test_commit keep-me &&
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git update-index --skip-worktree keep-me.t &&
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rm keep-me.t &&
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: ignoring the worktree &&
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git update-index --remove --ignore-skip-worktree-entries keep-me.t &&
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git diff-index --cached --exit-code HEAD &&
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: not ignoring the worktree, a deletion is staged &&
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git update-index --remove keep-me.t &&
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test_must_fail git diff-index --cached --exit-code HEAD \
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--diff-filter=D -- keep-me.t
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'
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stash: fix stash application in sparse-checkouts
sparse-checkouts are built on the patterns in the
$GIT_DIR/info/sparse-checkout file, where commands have modified
behavior for paths that do not match those patterns. The differences in
behavior, as far as the bugs concerned here, fall into three different
categories (with git subcommands that fall into each category listed):
* commands that only look at files matching the patterns:
* status
* diff
* clean
* update-index
* commands that remove files from the working tree that do not match
the patterns, and restore files that do match them:
* read-tree
* switch
* checkout
* reset (--hard)
* commands that omit writing files to the working tree that do not
match the patterns, unless those files are not clean:
* merge
* rebase
* cherry-pick
* revert
There are some caveats above, e.g. a plain `git diff` ignores files
outside the sparsity patterns but will show diffs for paths outside the
sparsity patterns when revision arguments are passed. (Technically,
diff is treating the sparse paths as matching HEAD.) So, there is some
internal inconsistency among these commands. There are also additional
commands that should behave differently in the face of sparse-checkouts,
as the sparse-checkout documentation alludes to, but the above is
sufficient for me to explain how `git stash` is affected.
What is relevant here is that logically 'stash' should behave like a
merge; it three-way merges the changes the user had in progress at stash
creation time, the HEAD at the time the stash was created, and the
current HEAD, in order to get the stashed changes applied to the current
branch. However, this simplistic view doesn't quite work in practice,
because stash tweaks it a bit due to two factors: (1) flags like
--keep-index and --include-untracked (why we used two different verbs,
'keep' and 'include', is a rant for another day) modify what should be
staged at the end and include more things that should be quasi-merged,
(2) stash generally wants changes to NOT be staged. It only provides
exceptions when (a) some of the changes had conflicts and thus we want
to use stages to denote the clean merges and higher order stages to
mark the conflicts, or (b) if there is a brand new file we don't want
it to become untracked.
stash has traditionally gotten this special behavior by first doing a
merge, and then when it's clean, applying a pipeline of commands to
modify the result. This series of commands for
unstaging-non-newly-added-files came from the following commands:
git diff-index --cached --name-only --diff-filter=A $CTREE >"$a"
git read-tree --reset $CTREE
git update-index --add --stdin <"$a"
rm -f "$a"
Looking back at the different types of special sparsity handling listed
at the beginning of this message, you may note that we have at least one
of each type covered here: merge, diff-index, and read-tree. The weird
mix-and-match led to 3 different bugs:
(1) If a path merged cleanly and it didn't match the sparsity patterns,
the merge backend would know to avoid writing it to the working tree and
keep the SKIP_WORKTREE bit, simply only updating it in the index.
Unfortunately, the subsequent commands would essentially undo the
changes in the index and thus simply toss the changes altogether since
there was nothing left in the working tree. This means the stash is
only partially applied.
(2) If a path existed in the worktree before `git stash apply` despite
having the SKIP_WORKTREE bit set, then the `git read-tree --reset` would
print an error message of the form
error: Entry 'modified' not uptodate. Cannot merge.
and cause stash to abort early.
(3) If there was a brand new file added by the stash, then the
diff-index command would save that pathname to the temporary file, the
read-tree --reset would remove it from the index, and the update-index
command would barf due to no such file being present in the working
copy; it would print a message of the form:
error: NEWFILE: does not exist and --remove not passed
fatal: Unable to process path NEWFILE
and then cause stash to abort early.
Basically, the whole idea of unstage-unless-brand-new requires special
care when you are dealing with a sparse-checkout. Fix these problems
by applying the following simple rule:
When we unstage files, if they have the SKIP_WORKTREE bit set,
clear that bit and write the file out to the working directory.
(*) If there's already a file present in the way, rename it first.
This fixes all three problems in t7012.13 and allows us to mark it as
passing.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-12-01 22:25:18 +00:00
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test_expect_success 'stash restore in sparse checkout' '
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2020-12-01 22:25:16 +00:00
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test_create_repo stash-restore &&
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(
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cd stash-restore &&
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mkdir subdir &&
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echo A >subdir/A &&
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echo untouched >untouched &&
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echo removeme >removeme &&
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echo modified >modified &&
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git add . &&
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git commit -m Initial &&
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echo AA >>subdir/A &&
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echo addme >addme &&
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echo tweaked >>modified &&
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rm removeme &&
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git add addme &&
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git stash push &&
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2022-04-22 02:32:18 +00:00
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git sparse-checkout set --no-cone subdir &&
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2020-12-01 22:25:16 +00:00
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# Ensure after sparse-checkout we only have expected files
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cat >expect <<-EOF &&
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S modified
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S removeme
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H subdir/A
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S untouched
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EOF
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git ls-files -t >actual &&
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test_cmp expect actual &&
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test_path_is_missing addme &&
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test_path_is_missing modified &&
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test_path_is_missing removeme &&
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test_path_is_file subdir/A &&
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test_path_is_missing untouched &&
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# Put a file in the working directory in the way
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echo in the way >modified &&
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repo_read_index: clear SKIP_WORKTREE bit from files present in worktree
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 degrade performance for the sparse-index case due
to requiring the index to be expanded (see commit 55dfcf9591
("sparse-checkout: clear tracked sparse dirs", 2021-09-08) for why
we try to delete entire directories outside the sparse cone).
* 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.
* Helps prevent slow performance degradation with a sparse-index.
* 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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-01-14 15:59:41 +00:00
|
|
|
test_must_fail git stash apply 2>error&&
|
2020-12-01 22:25:16 +00:00
|
|
|
|
repo_read_index: clear SKIP_WORKTREE bit from files present in worktree
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 degrade performance for the sparse-index case due
to requiring the index to be expanded (see commit 55dfcf9591
("sparse-checkout: clear tracked sparse dirs", 2021-09-08) for why
we try to delete entire directories outside the sparse cone).
* 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.
* Helps prevent slow performance degradation with a sparse-index.
* 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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-01-14 15:59:41 +00:00
|
|
|
grep "changes.*would be overwritten by merge" error &&
|
2020-12-01 22:25:16 +00:00
|
|
|
|
repo_read_index: clear SKIP_WORKTREE bit from files present in worktree
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 degrade performance for the sparse-index case due
to requiring the index to be expanded (see commit 55dfcf9591
("sparse-checkout: clear tracked sparse dirs", 2021-09-08) for why
we try to delete entire directories outside the sparse cone).
* 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.
* Helps prevent slow performance degradation with a sparse-index.
* 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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-01-14 15:59:41 +00:00
|
|
|
echo in the way >expect &&
|
|
|
|
|
test_cmp expect modified &&
|
|
|
|
|
git diff --quiet HEAD ":!modified" &&
|
2020-12-01 22:25:16 +00:00
|
|
|
|
|
|
|
|
# ...and that working directory reflects the files correctly
|
repo_read_index: clear SKIP_WORKTREE bit from files present in worktree
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 degrade performance for the sparse-index case due
to requiring the index to be expanded (see commit 55dfcf9591
("sparse-checkout: clear tracked sparse dirs", 2021-09-08) for why
we try to delete entire directories outside the sparse cone).
* 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.
* Helps prevent slow performance degradation with a sparse-index.
* 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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-01-14 15:59:41 +00:00
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test_path_is_missing addme &&
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2020-12-01 22:25:16 +00:00
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test_path_is_file modified &&
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test_path_is_missing removeme &&
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test_path_is_file subdir/A &&
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repo_read_index: clear SKIP_WORKTREE bit from files present in worktree
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 degrade performance for the sparse-index case due
to requiring the index to be expanded (see commit 55dfcf9591
("sparse-checkout: clear tracked sparse dirs", 2021-09-08) for why
we try to delete entire directories outside the sparse cone).
* 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.
* Helps prevent slow performance degradation with a sparse-index.
* 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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-01-14 15:59:41 +00:00
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test_path_is_missing untouched
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2020-12-01 22:25:16 +00:00
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)
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'
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2010-04-19 08:14:32 +00:00
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#TODO test_expect_failure 'git-apply adds file' false
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#TODO test_expect_failure 'git-apply updates file' false
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#TODO test_expect_failure 'git-apply removes file' false
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#TODO test_expect_failure 'git-mv to skip-worktree' false
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#TODO test_expect_failure 'git-mv from skip-worktree' false
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#TODO test_expect_failure 'git-checkout' false
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2009-08-20 13:46:59 +00:00
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test_done
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