| Def.: Shallow commits do have parents, but not in the shallow | |
| repo, and therefore grafts are introduced pretending that | |
| these commits have no parents. | |
| The basic idea is to write the SHA1s of shallow commits into | |
| $GIT_DIR/shallow, and handle its contents like the contents | |
| of $GIT_DIR/info/grafts (with the difference that shallow | |
| cannot contain parent information). | |
| This information is stored in a new file instead of grafts, or | |
| even the config, since the user should not touch that file | |
| at all (even throughout development of the shallow clone, it | |
| was never manually edited!). | |
| Each line contains exactly one SHA1. When read, a commit_graft | |
| will be constructed, which has nr_parent < 0 to make it easier | |
| to discern from user provided grafts. | |
| Since fsck-objects relies on the library to read the objects, | |
| it honours shallow commits automatically. | |
| There are some unfinished ends of the whole shallow business: | |
| - maybe we have to force non-thin packs when fetching into a | |
| shallow repo (ATM they are forced non-thin). | |
| - A special handling of a shallow upstream is needed. At some | |
| stage, upload-pack has to check if it sends a shallow commit, | |
| and it should send that information early (or fail, if the | |
| client does not support shallow repositories). There is no | |
| support at all for this in this patch series. | |
| - Instead of locking $GIT_DIR/shallow at the start, just | |
| the timestamp of it is noted, and when it comes to writing it, | |
| a check is performed if the mtime is still the same, dying if | |
| it is not. | |
| - It is unclear how "push into/from a shallow repo" should behave. | |
| - If you deepen a history, you'd want to get the tags of the | |
| newly stored (but older!) commits. This does not work right now. | |
| To make a shallow clone, you can call "git-clone --depth 20 repo". | |
| The result contains only commit chains with a length of at most 20. | |
| It also writes an appropriate $GIT_DIR/shallow. | |
| You can deepen a shallow repository with "git-fetch --depth 20 | |
| repo branch", which will fetch branch from repo, but stop at depth | |
| 20, updating $GIT_DIR/shallow. |