分支改名与删除对对象的影响

  $ git config --get-regexp "^branch.old-name"; ls .git/refs/heads .git/logs/refs/heads | tr "\n" " "; echo
  branch.old-name.remote origin
  branch.old-name.merge refs/heads/old-name
  .git/logs/refs/heads: main old-name  .git/refs/heads: main old-name
  $ git branch -m old-name new-name; ls .git/refs/heads .git/logs/refs/heads | tr "\n" " "; echo; git config --get-regexp "^branch\.(old|new)-name"; cat .git/HEAD
  .git/logs/refs/heads: main new-name  .git/refs/heads: main new-name
  branch.new-name.remote origin
  branch.new-name.merge refs/heads/old-name
  ref: refs/heads/new-name
  对象数 5 → 5;分支指向的提交没变: True
  $ git reflog show new-name --format='%gd: %gs' | head -3
  new-name@{0}: Branch: renamed refs/heads/old-name to refs/heads/new-name
  new-name@{1}: commit: 分支上的提交
  new-name@{2}: branch: Created from HEAD
  upstream 仍是 origin/old-name(改名不会去改远程):
  $ git branch -vv | grep new-name | sed -E 's/[0-9a-f]{40}/<sha40>/g; s/\b[0-9a-f]{7}\b/<sha>/g'
  * new-name af81252 [origin/old-name] 分支上的提交

  $ git branch -m w victim 2>&1
  fatal: a branch named 'victim' already exists
  (退出码 128)
  $ git branch -M w victim 2>&1; git log -1 --format=%s victim
  只在w上
  被覆盖的 victim 原来指向的提交还在对象库里: True;有分支包含它吗: False(没有:它已不可达)

  $ git branch -d gone-soon 2>&1 | head -3
  error: the branch 'gone-soon' is not fully merged
  hint: If you are sure you want to delete it, run 'git branch -D gone-soon'
  hint: Disable this message with "git config set advice.forceDeleteBranch false"
  $ ls .git/logs/refs/heads | tr "\n" " "; echo; git branch -D gone-soon | sed -E "s/[0-9a-f]{7}/<sha>/"; ls .git/logs/refs/heads | tr "\n" " "; echo
  gone-soon main new-name victim
  Deleted branch gone-soon (was <sha>).
  main new-name victim
  对象数 13 → 13(分支删了,对象一个都没少);提交是否还在: True
  $ git reflog expire --expire=now --all; git gc -q --prune=now; echo "(清空 reflog 并 gc --prune=now 之后)"
  (清空 reflog 并 gc --prune=now 之后)
  对象数 8;提交是否还在: False

  $ git checkout -q -b feat1 && echo f > f1 && git add . && git commit -q -m feat1提交 && git push -q -u origin feat1 && git checkout -q main
  情形 A:feat1 已经推送(合并进了自己的 upstream origin/feat1),但没合并进 HEAD:
  $ git branch -d feat1 2>&1 | sed -E "s/[0-9a-f]{7}/<sha>/"; git branch --list feat1 | wc -l
  warning: deleting branch 'feat1' that has been merged to
           'refs/remotes/origin/feat1', but not yet merged to HEAD
  Deleted branch feat1 (was <sha>).
         0
  情形 B:feat2 合并进了 HEAD,但它的 upstream 是 origin/main,里面没有 feat2 的提交:
  $ git checkout -q -b feat2 && echo g > f2 && git add . && git commit -q -m feat2提交 && git checkout -q main && git merge -q --no-edit feat2 && git branch -u origin/main feat2 >/dev/null; git branch -d feat2 2>&1 | head -2; git branch --list feat2 | wc -l
  warning: not deleting branch 'feat2' that is not yet merged to
           'refs/remotes/origin/main', even though it is merged to HEAD
         1
  $ git branch -D feat2 | sed -E "s/[0-9a-f]{7}/<sha>/"
  Deleted branch feat2 (was <sha>).

  $ git branch -D main 2>&1 | head -2
  error: cannot delete branch 'main' used by worktree at '/work/l30'