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author | Matthieu Moy <Matthieu.Moy@imag.fr> | 2009-08-08 09:51:08 +0200 |
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committer | Junio C Hamano <gitster@pobox.com> | 2009-08-12 16:15:47 -0700 |
commit | 07436e43daf1a97d3d702090d6289f745bd5ad90 (patch) | |
tree | e8f0cbf00412a6028e5b1f12a8f9f55383bfc1d2 /Documentation/git-push.txt | |
parent | e89df7dcda9836518a68cce27231625f90d94749 (diff) | |
download | git-07436e43daf1a97d3d702090d6289f745bd5ad90.tar.gz git-07436e43daf1a97d3d702090d6289f745bd5ad90.tar.xz |
push: point to 'git pull' and 'git push --force' in case of non-fast forward
'git push' failing because of non-fast forward is a very common situation,
and a beginner does not necessarily understand "fast forward" immediately.
Add a new section to the git-push documentation and refer them to it.
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Nanako Shiraishi <nanako3@lavabit.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'Documentation/git-push.txt')
-rw-r--r-- | Documentation/git-push.txt | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/Documentation/git-push.txt b/Documentation/git-push.txt index 2653388fd..58d2bd5d4 100644 --- a/Documentation/git-push.txt +++ b/Documentation/git-push.txt @@ -195,6 +195,92 @@ reason:: refs, no explanation is needed. For a failed ref, the reason for failure is described. +Note about fast-forwards +------------------------ + +When an update changes a branch (or more in general, a ref) that used to +point at commit A to point at another commit B, it is called a +fast-forward update if and only if B is a descendant of A. + +In a fast-forward update from A to B, the set of commits that the original +commit A built on top of is a subset of the commits the new commit B +builds on top of. Hence, it does not lose any history. + +In contrast, a non-fast-forward update will lose history. For example, +suppose you and somebody else started at the same commit X, and you built +a history leading to commit B while the other person built a history +leading to commit A. The history looks like this: + +---------------- + + B + / + ---X---A + +---------------- + +Further suppose that the other person already pushed changes leading to A +back to the original repository you two obtained the original commit X. + +The push done by the other person updated the branch that used to point at +commit X to point at commit A. It is a fast-forward. + +But if you try to push, you will attempt to update the branch (that +now points at A) with commit B. This does _not_ fast-forward. If you did +so, the changes introduced by commit A will be lost, because everybody +will now start building on top of B. + +The command by default does not allow an update that is not a fast-forward +to prevent such loss of history. + +If you do not want to lose your work (history from X to B) nor the work by +the other person (history from X to A), you would need to first fetch the +history from the repository, create a history that contains changes done +by both parties, and push the result back. + +You can perform "git pull", resolve potential conflicts, and "git push" +the result. A "git pull" will create a merge commit C between commits A +and B. + +---------------- + + B---C + / / + ---X---A + +---------------- + +Updating A with the resulting merge commit will fast-forward and your +push will be accepted. + +Alternatively, you can rebase your change between X and B on top of A, +with "git pull --rebase", and push the result back. The rebase will +create a new commit D that builds the change between X and B on top of +A. + +---------------- + + B D + / / + ---X---A + +---------------- + +Again, updating A with this commit will fast-forward and your push will be +accepted. + +There is another common situation where you may encounter non-fast-forward +rejection when you try to push, and it is possible even when you are +pushing into a repository nobody else pushes into. After you push commit +A yourself (in the first picture in this section), replace it with "git +commit --amend" to produce commit B, and you try to push it out, because +forgot that you have pushed A out already. In such a case, and only if +you are certain that nobody in the meantime fetched your earlier commit A +(and started building on top of it), you can run "git push --force" to +overwrite it. In other words, "git push --force" is a method reserved for +a case where you do mean to lose history. + + Examples -------- |