Jonathan Tan 33f3a420a1 workspace: recover from missing operation ... If the operation corresponding to a workspace is missing for some reason (the specific situation in the test in this commit is that an operation was abandoned and garbage-collected from another workspace), currently, jj fails with a 255 error code. Teach jj a way to recover from this situation. When jj detects such a situation, it prints a message and stops operation, similar to when a workspace is stale. The message tells the user what command to run. When that command is run, jj loads the repo at the @ operation (instead of the operation of the workspace), creates a new commit on the @ commit with an empty tree, and then proceeds as usual - in particular, including the auto-snapshotting of the working tree, which creates another commit that obsoletes the newly created commit. There are several design points I considered. 1) Whether the recovery should be automatic, or (as in this commit) manual in that the user should be prompted to run a command. The user might prefer to recover in another way (e.g. by simply deleting the workspace) and this situation is (hopefully) rare enough that I think it's better to prompt the user. 2) Which command the user should be prompted to run (and thus, which command should be taught to perform the recovery). I chose "workspace update-stale" because the circumstances are very similar to it: it's symptom is that the regular jj operation is blocked somewhere at the beginning, and "workspace update-stale" already does some special work before the blockage (this commit adds more of such special work). But it might be better for something more explicitly named, or even a sequence of commands (e.g. "create a new operation that becomes @ that no workspace points to", "low-level command that makes a workspace point to the operation @") but I can see how this can be unnecessarily confusing for the user. 3) How we recover. I can think of several ways: a) Always create a commit, and allow the automatic snapshotting to create another commit that obsoletes this commit. b) Create a commit but somehow teach the automatic snapshotting to replace the created commit in-place (so it has no predecessor, as viewed in "obslog"). c) Do either a) or b), with the added improvement that if there is no diff between the newly created commit and the former @, to behave as if no new commit was created (@ remains as the former @). I chose a) since it was the simplest and most easily reasoned about, which I think is the best way to go when recovering from a rare situation.		2024-02-09 00:38:47 -08:00
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custom-backend
custom-command
custom-global-flag
custom-working-copy	workspace: recover from missing operation	2024-02-09 00:38:47 -08:00