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`git worktree repair` knows how to repair the two-way links between the
repository and a worktree as long as a link in one or the other
direction is sound. For instance, if a linked worktree is moved (without
using `git worktree move`), repair is possible because the worktree
still knows the location of the repository even though the repository no
longer knows where the worktree is. Similarly, if the repository is
moved, repair is possible since the repository still knows the locations
of the worktrees even though the worktrees no longer know where the
repository is.
However, if both the repository and the worktrees are moved, then links
are severed in both directions, and no repair is possible. This is the
case even when the new worktree locations are specified as arguments to
`git worktree repair`. The reason for this limitation is twofold. First,
when `repair` consults the worktree's gitfile (/path/to/worktree/.git)
to determine the corresponding <repo>/worktrees/<id>/gitdir file to fix,
<repo> is the old path to the repository, thus it is unable to fix the
`gitdir` file at its new location since it doesn't know where it is.
Second, when `repair` consults <repo>/worktrees/<id>/gitdir to find the
location of the worktree's gitfile (/path/to/worktree/.git), the path
recorded in `gitdir` is the old location of the worktree's gitfile, thus
it is unable to repair the gitfile since it doesn't know where it is.
Fix these shortcomings by teaching `repair` to attempt to infer the new
location of the <repo>/worktrees/<id>/gitdir file when the location
recorded in the worktree's gitfile has become stale but the file is
otherwise well-formed. The inference is intentionally simple-minded.
For each worktree path specified as an argument, `git worktree repair`
manually reads the ".git" gitfile at that location and, if it is
well-formed, extracts the <id>. It then searches for a corresponding
<id> in <repo>/worktrees/ and, if found, concludes that there is a
reasonable match and updates <repo>/worktrees/<id>/gitdir to point at
the specified worktree path. In order for <repo> to be known, `git
worktree repair` must be run in the main worktree or bare repository.
`git worktree repair` first attempts to repair each incoming
/path/to/worktree/.git gitfile to point at the repository, and then
attempts to repair outgoing <repo>/worktrees/<id>/gitdir files to point
at the worktrees. This sequence was chosen arbitrarily when originally
implemented since the order of fixes is immaterial as long as one side
of the two-way link between the repository and a worktree is sound.
However, for this new repair technique to work, the order must be
reversed. This is because the new inference mechanism, when it is
successful, allows the outgoing <repo>/worktrees/<id>/gitdir file to be
repaired, thus fixing one side of the two-way link. Once that side is
fixed, the other side can be fixed by the existing repair mechanism,
hence the order of repairs is now significant.
Two safeguards are employed to avoid hijacking a worktree from a
different repository if the user accidentally specifies a foreign
worktree as an argument. The first, as described above, is that it
requires an <id> match between the repository and the worktree. That
itself is not foolproof for preventing hijack, so the second safeguard
is that the inference will only kick in if the worktree's
/path/to/worktree/.git gitfile does not point at a repository.
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The .git/worktrees/<id>/gitdir file points at the location of a linked
worktree's .git file. Its content must be of the form
/path/to/worktree/.git (from which the location of the worktree itself
can be derived by stripping the "/.git" suffix). If the gitdir file is
deleted or becomes corrupted or outdated, then Git will be unable to
find the linked worktree. An easy way for the gitdir file to become
outdated is for the user to move the worktree manually (without using
"git worktree move"). Although it is possible to manually update the
gitdir file to reflect the new linked worktree location, doing so
requires a level of knowledge about worktree internals beyond what a
user should be expected to know offhand.
Therefore, teach "git worktree repair" how to repair broken or outdated
.git/worktrees/<id>/gitdir files automatically. (For this to work, the
command must either be invoked from within the worktree whose gitdir
file requires repair, or from within the main or any linked worktree by
providing the path of the broken worktree as an argument to "git
worktree repair".)
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The .git file in a linked worktree is a "gitfile" which points back to
the .git/worktrees/<id> entry in the main worktree or bare repository.
If a worktree's .git file is deleted or becomes corrupted or outdated,
then the linked worktree won't know how to find the repository or any of
its own administrative files (such as 'index', 'HEAD', etc.). An easy
way for the .git file to become outdated is for the user to move the
main worktree or bare repository. Although it is possible to manually
update each linked worktree's .git file to reflect the new repository
location, doing so requires a level of knowledge about worktree
internals beyond what a user should be expected to know offhand.
Therefore, teach "git worktree repair" how to repair broken or outdated
worktree .git files automatically. (For this to work, the command must
be invoked from within the main worktree or bare repository, or from
within a worktree which has not become disconnected from the repository
-- such as one which was created after the repository was moved.)
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Worktree administrative files can become corrupted or outdated due to
external factors. Although, it is often possible to recover from such
situations by hand-tweaking these files, doing so requires intimate
knowledge of worktree internals. While information necessary to make
such repairs manually can be obtained from git-worktree.txt and
gitrepository-layout.txt, we can assist users more directly by teaching
git-worktree how to repair its administrative files itself (at least to
some extent). Therefore, add a "git worktree repair" command which
attempts to correct common problems which may arise due to factors
beyond Git's control.
At this stage, the "repair" command is a mere skeleton; subsequent
commits will flesh out the functionality.
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Eric Sunshine