On Sat, Mar 17, 2018 at 01:17:12PM +0100, Michal Novotny wrote: > let's say I have made an annotated tag on a certain treeish: > > $ git tag -a -m msg tagname HEAD: > > Now, I can try to see the content of the tag: > > $ git tag -v tagname > object 42a1c36553a50ceae2f75ffc4b1446c6c393eae7 > type tree > tag tagname > tagger clime <cl...@redhat.com> 1521288727 +0100 > > msg > error: no signature found > > > Can I use that object ID 42a1c36553a50ceae2f75ffc4b1446c6c393eae7 to > get back to a particular commit from which the tag was created? The > reason is that I would eventually like to checkout that commit.
In general, you can't, and that's because there can be any number of commits referencing that tree. A typical case is a tree object representing a subdirectory of your project which changes rarily, if ever - in this case, each commit which includes the same state of this subdirectory will refer the same tree object. Another point to consider is that the commit itself only refers to a single tree object -- that one which records the state of the top-level project directory, and it usually refers to other three objects which may, in turn, refer to others and so on - all the way down. So actually a generic approach to what you need is a full scan of all the commits in the repository with recursive traversing of the hierarchy of trees of each of them (via `git ls-tree`) and looking for the SHA-1 name of the reference tree object. As you can see, this is not going to be fast on repos of realistic size.
