Make HEAD lookups work with reftable #2389
Conversation
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Executing an external process every time the status line is updated (basically every keystroke) will severely impact UI responsiveness, albeit a lot more for some users than others. Is there anything we can cache on? |
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We could cache on I can add that functionality, but it may take me a day or two to get it done. |
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I would encourage you to use the command conditionally once |
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Okay, I've updated this to keep the regular implemntation and only use the reftable implementation only when |
Git has a new ref storage backend called reftable that stores all refs, including HEAD, as well as all reflogs, in a binary format under .git/reftable. Because the HEAD file is important in determining whether a directory is a Git repository, Git retains this file, but it always contains "ref: refs/heads/.invalid", thus pointing to an invalid ref, since ref components may not start with a dot. In such a configuration, the only practical possibility is to invoke a Git command to resolve HEAD for us, so use git rev-parse to do so if we find this invalid ref in the HEAD file. Look up the object ID and the value for HEAD at the same time to avoid the overhead of two calls and use the former if the latter is HEAD (that is, we're not on a branch). Unfortunately, this doesn't work when we have an unborn branch without any commits, such as when a repository is newly initialized. Fall back to git symbolic-ref in such a case. Use the regular head cache, as well as a new reftable head cache that tracks .git/reftable/tables.list. The reftable format uses several binary files plus a list of tables and the table list will change whenever a regular ref or symref (including HEAD) changes, which is what we want to know.
Git has a new ref storage backend called reftable that stores all refs, including HEAD, as well as all reflogs, in a binary format under .git/reftable. Because the HEAD file is important in determining whether a directory is a Git repository, Git retains this file, but it always contains "ref: refs/heads/.invalid", thus pointing to an invalid ref, since ref components may not start with a dot.
In such a configuration, the only practical possibility is to invoke a Git command to resolve HEAD for us, so use git rev-parse to do so. Look up the object ID and the value for HEAD at the same time to avoid the overhead of two calls and use the former if the latter is HEAD (that is, we're not on a branch).
Unfortunately, this doesn't work when we have an unborn branch without any commits, such as when a repository is newly initialized. Fall back to git symbolic-ref in such a case.
Note that the head cache cannot be preserved here because the .git/HEAD file does not have to change when the branch changes with reftable (in fact, it will not), so remove that code here.
Fixes #2371