f4609b896f
This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because there is some breakage in the git build related to the netrc credentials helper which someone has taken care of in nixpkgs. The stable channel is not used for anything other than git, so this should be fine. Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb
60 lines
2.5 KiB
Text
60 lines
2.5 KiB
Text
Shallow commits
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===============
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.Definition
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*********************************************************
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Shallow commits do have parents, but not in the shallow
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repo, and therefore grafts are introduced pretending that
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these commits have no parents.
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*********************************************************
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$GIT_DIR/shallow lists commit object names and tells Git to
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pretend as if they are root commits (e.g. "git log" traversal
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stops after showing them; "git fsck" does not complain saying
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the commits listed on their "parent" lines do not exist).
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Each line contains exactly one object name. When read, a commit_graft
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will be constructed, which has nr_parent < 0 to make it easier
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to discern from user provided grafts.
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Note that the shallow feature could not be changed easily to
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use replace refs: a commit containing a `mergetag` is not allowed
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to be replaced, not even by a root commit. Such a commit can be
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made shallow, though. Also, having a `shallow` file explicitly
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listing all the commits made shallow makes it a *lot* easier to
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do shallow-specific things such as to deepen the history.
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Since fsck-objects relies on the library to read the objects,
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it honours shallow commits automatically.
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There are some unfinished ends of the whole shallow business:
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- maybe we have to force non-thin packs when fetching into a
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shallow repo (ATM they are forced non-thin).
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- A special handling of a shallow upstream is needed. At some
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stage, upload-pack has to check if it sends a shallow commit,
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and it should send that information early (or fail, if the
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client does not support shallow repositories). There is no
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support at all for this in this patch series.
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- Instead of locking $GIT_DIR/shallow at the start, just
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the timestamp of it is noted, and when it comes to writing it,
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a check is performed if the mtime is still the same, dying if
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it is not.
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- It is unclear how "push into/from a shallow repo" should behave.
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- If you deepen a history, you'd want to get the tags of the
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newly stored (but older!) commits. This does not work right now.
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To make a shallow clone, you can call "git-clone --depth 20 repo".
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The result contains only commit chains with a length of at most 20.
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It also writes an appropriate $GIT_DIR/shallow.
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You can deepen a shallow repository with "git-fetch --depth 20
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repo branch", which will fetch branch from repo, but stop at depth
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20, updating $GIT_DIR/shallow.
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The special depth 2147483647 (or 0x7fffffff, the largest positive
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number a signed 32-bit integer can contain) means infinite depth.
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