git: tag 和 branch 的关系

选自：

https://stackoverflow.com/questions/14613540/do-git-tags-only-apply-to-the-current-branch

 

 

• A tag is a pointer to a commit, and commits exist independently of branches.
  • It is important to understand that tags have no direct relationship with branches - they only ever identify a commit.
    • That commit can be pointed to from any number of branches - i.e., it can be part of the history of any number of branches - including none.
  • Therefore, running git show <tag> to see a tag's details contains no reference to any branches, only the ID of the commit that the tag points to.
    • (Commit IDs (a.k.a. object names or SHA-1 IDs) are 40-character strings composed of hex. digits that are hashes over the contents of a commit; e.g.: 6f6b5997506d48fc6267b0b60c3f0261b6afe7a2)

• Branches come into play only indirectly:
  • At the time of creating a tag, by implying the commit that the tag will point to:
    • Not specifying a target for a tag defaults to the current branch's most recent commit (a.k.a. HEAD); e.g.:
      • git tag v0.1.0 # tags HEAD of *current* branch
    • Specifying a branch name as the tag target defaults to that branch's most recent commit; e.g.:
      • git tag v0.1.0 develop # tags HEAD of 'develop' branch
    • (As others have noted, you can also specify a commit ID explicitly as the tag's target.)
  • When using git describe to describe the current branch:
    • git describe [--tags] describes the current branch in terms of the commits since the most recent [possibly lightweight] tag in this branch's history.
    • Thus, the tag referenced by git describe may NOT reflect the most recently created tag overall.