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2020-12-21worktree: teach `repair` to fix multi-directional breakageLibravatar Eric Sunshine1-0/+26
`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>
2020-08-31worktree: teach "repair" to fix outgoing links to worktreesLibravatar Eric Sunshine1-0/+86
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>
2020-08-31worktree: teach "repair" to fix worktree back-links to main worktreeLibravatar Eric Sunshine1-0/+82
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>
2020-08-27worktree: add skeleton "repair" commandLibravatar Eric Sunshine1-0/+11
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>