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My prior version of git-describe ran very slowly on even reasonably sized projects like git.git and linux.git as it tended to identify a large number of possible tags and then needed to generate the revision list for each of those tags to sort them and select the best tag to describe the input commit. All we really need is the number of commits in the input revision which are not in the tag. We can generate these counts during the revision walking and tag matching loop by assigning a color to each tag and coloring the commits as we walk them. This limits us to identifying no more than 26 possible tags, as there is limited space available within the flags field of struct commit. The limitation of 26 possible tags is hopefully not going to be a problem in real usage, as most projects won't create 26 maintenance releases and merge them back into a development trunk after the development trunk was tagged with a release candidate tag. If that does occur git-describe will start to revert to its old behavior of using the newer maintenance release tag to describe the development trunk, rather than the development trunk's own tag. The suggested workaround would be to retag the development trunk's tip. However since even 26 possible tags can take a while to generate a description for on some projects I'm defaulting the limit to 10 but offering the user --candidates to increase the number of possible matches if they need a more accurate result. I specifically chose 10 for the default as it seems unlikely projects will have more than 10 maintenance releases merged into a development trunk before retagging the development trunk, and it seems to perform about the same on linux.git as v1.4.4.4 git-describe. A large amount of debugging information was also added during the development of this change, so I've left it in to be toggled on with --debug. It may be useful to the end user to help them understand why git-describe took one particular tag over another. Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
110 lines
3.1 KiB
Plaintext
110 lines
3.1 KiB
Plaintext
git-describe(1)
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===============
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NAME
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----
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git-describe - Show the most recent tag that is reachable from a commit
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SYNOPSIS
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--------
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'git-describe' [--all] [--tags] [--abbrev=<n>] <committish>...
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DESCRIPTION
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-----------
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The command finds the most recent tag that is reachable from a
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commit, and if the commit itself is pointed at by the tag, shows
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the tag. Otherwise, it suffixes the tag name with abbreviated
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object name of the commit.
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OPTIONS
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-------
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<committish>::
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The object name of the committish.
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--all::
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Instead of using only the annotated tags, use any ref
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found in `.git/refs/`.
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--tags::
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Instead of using only the annotated tags, use any tag
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found in `.git/refs/tags`.
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--abbrev=<n>::
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Instead of using the default 8 hexadecimal digits as the
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abbreviated object name, use <n> digits.
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--candidates=<n>::
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Instead of considering only the 10 most recent tags as
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candidates to describe the input committish consider
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up to <n> candidates. Increasing <n> above 10 will take
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slightly longer but may produce a more accurate result.
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--debug::
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Verbosely display information about the searching strategy
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being employed to standard error. The tag name will still
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be printed to standard out.
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EXAMPLES
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--------
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With something like git.git current tree, I get:
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[torvalds@g5 git]$ git-describe parent
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v1.0.4-g2414721b
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i.e. the current head of my "parent" branch is based on v1.0.4,
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but since it has a few commits on top of that, it has added the
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git hash of the thing to the end: "-g" + 8-char shorthand for
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the commit `2414721b194453f058079d897d13c4e377f92dc6`.
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Doing a "git-describe" on a tag-name will just show the tag name:
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[torvalds@g5 git]$ git-describe v1.0.4
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v1.0.4
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With --all, the command can use branch heads as references, so
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the output shows the reference path as well:
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[torvalds@g5 git]$ git describe --all --abbrev=4 v1.0.5^2
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tags/v1.0.0-g975b
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[torvalds@g5 git]$ git describe --all HEAD^
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heads/lt/describe-g975b
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SEARCH STRATEGY
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---------------
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For each committish supplied "git describe" will first look for
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a tag which tags exactly that commit. Annotated tags will always
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be preferred over lightweight tags, and tags with newer dates will
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always be preferred over tags with older dates. If an exact match
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is found, its name will be output and searching will stop.
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If an exact match was not found "git describe" will walk back
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through the commit history to locate an ancestor commit which
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has been tagged. The ancestor's tag will be output along with an
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abbreviation of the input committish's SHA1.
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If multiple tags were found during the walk then the tag which
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has the fewest commits different from the input committish will be
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selected and output. Here fewest commits different is defined as
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the number of commits which would be shown by "git log tag..input"
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will be the smallest number of commits possible.
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Author
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------
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Written by Linus Torvalds <torvalds@osdl.org>, but somewhat
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butchered by Junio C Hamano <junkio@cox.net>
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Documentation
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--------------
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Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
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GIT
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---
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Part of the gitlink:git[7] suite
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