将 git 存储库转换为浅表存储库？

You can convert git repo to a shallow one in place along this lines:

git show-ref -s HEAD > .git/shallow
git reflog expire --expire=0
git prune
git prune-packed

Make sure to make backup since this is destructive operation, also keep in mind that cloning nor fetching from shallow repo is not supported! To really remove all the history you also need to remove all references to previous commits before pruning.

This worked for me:

git pull --depth 1
git gc --prune=all

This leaves the tags and reflog laying around, each of which reference additional commits that can use up space. Note that I would not erase the reflog unless severely needed: it contains local change history used for recovery from mistakes.

There are commands on how to erase the tags or even the reflog in the comments below, and a link to a similar question with a longer answer.

If you still have a lot of space used you may need to remove the tags, which you should try first before removing the reflog.

Create shallow clone of a local repo:

git clone --depth 1 file:///full/path/to/original/dir destination

Note that the first "address" should be a file://, that's important. Also, git will assume your original local file:// address to be the "remote" ("origin"), so you'll need to update the new repository specifying the correct git remote.

Note that a shallow repo (like one with git clone --depth 1 as a way to convert an existing repo to a shallow one) can fail on git repack.

See commit 5dcfbf5, commit 2588f6e, commit 328a435 (24 Oct 2018) by Johannes Schindelin (dscho).
^{(Merged by Junio C Hamano -- gitster -- in commit ea100b6, 06 Nov 2018)}

repack -ad: prune the list of shallow commits

git repack can drop unreachable commits without further warning, making the corresponding entries in .git/shallow invalid, which causes serious problems when deepening the branches.

One scenario where unreachable commits are dropped by git repack is when a git fetch --prune (or even a git fetch when a ref was force-pushed in the meantime) can make a commit unreachable that was reachable before.

Therefore it is not safe to assume that a git repack -adlf will keep unreachable commits alone (under the assumption that they had not been packed in the first place, which is an assumption at least some of Git's code seems to make).

This is particularly important to keep in mind when looking at the .git/shallow file: if any commits listed in that file become unreachable, it is not a problem, but if they go missing, it is a problem.
One symptom of this problem is that a deepening fetch may now fail with:

fatal: error in object: unshallow <commit-hash>

To avoid this problem, let's prune the shallow list in git repack when the -d option is passed, unless -A is passed, too (which would force the now-unreachable objects to be turned into loose objects instead of being deleted).
Additionally, we also need to take --keep-reachable and --unpack-unreachable=<date> into account.

Note: an alternative solution discussed during the review of this patch was to teach git fetch to simply ignore entries in .git/shallow if the corresponding commits do not exist locally.
A quick test, however, revealed that the .git/shallow file is written during a shallow clone, in which case the commits do not exist, either, but the "shallow" line does need to be sent.
Therefore, this approach would be a lot more finicky than the approach presented by the this patch.

Convert to shallow since a specific date:

git pull --shallow-since=YYYY-mm-dd
git gc --prune=all

Also works:

git fetch --shallow-since=YYYY-mm-dd
git gc --prune=all

Combining the answer from @fuzzyTew with what the comments on that answer:

git pull --depth 1
git tag -d $(git tag -l)
git reflog expire --expire=all --all
git gc --prune=all

Want to save space by running this across your entire disk? - Then run this fd command:

fd -HIFt d '.git' -x bash -c 'pushd "$0" && ( git pull --depth 1; git tag -d $(git tag -l); git reflog expire --expire=all --all; git gc --prune=all ) && popd' {//}

Or with just regular find:

find -type d -name '.git' -exec bash -c 'pushd "${0%/*}" && ( git pull --depth 1; git tag -d $(git tag -l); git reflog expire --expire=all --all; git gc --prune=all ) && popd' {} \;