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-rw-r--r--Documentation/git-push.txt86
-rw-r--r--builtin-push.c9
-rw-r--r--transport.c10
-rw-r--r--transport.h3
4 files changed, 103 insertions, 5 deletions
diff --git a/Documentation/git-push.txt b/Documentation/git-push.txt
index 2653388..58d2bd5 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
--------
diff --git a/builtin-push.c b/builtin-push.c
index 1d92e22..50328f4 100644
--- a/builtin-push.c
+++ b/builtin-push.c
@@ -140,6 +140,7 @@ static int do_push(const char *repo, int flags)
struct transport *transport =
transport_get(remote, url[i]);
int err;
+ int nonfastforward;
if (receivepack)
transport_set_option(transport,
TRANS_OPT_RECEIVEPACK, receivepack);
@@ -148,13 +149,19 @@ static int do_push(const char *repo, int flags)
if (flags & TRANSPORT_PUSH_VERBOSE)
fprintf(stderr, "Pushing to %s\n", url[i]);
- err = transport_push(transport, refspec_nr, refspec, flags);
+ err = transport_push(transport, refspec_nr, refspec, flags,
+ &nonfastforward);
err |= transport_disconnect(transport);
if (!err)
continue;
error("failed to push some refs to '%s'", url[i]);
+ if (nonfastforward) {
+ printf("To prevent you from losing history, non-fast-forward updates were rejected.\n"
+ "Merge the remote changes before pushing again.\n"
+ "See 'non-fast forward' section of 'git push --help' for details.\n");
+ }
errs++;
}
return !!errs;
diff --git a/transport.c b/transport.c
index de0d587..f231b35 100644
--- a/transport.c
+++ b/transport.c
@@ -820,7 +820,7 @@ static int print_one_push_status(struct ref *ref, const char *dest, int count, i
}
static void print_push_status(const char *dest, struct ref *refs,
- int verbose, int porcelain)
+ int verbose, int porcelain, int * nonfastforward)
{
struct ref *ref;
int n = 0;
@@ -835,11 +835,14 @@ static void print_push_status(const char *dest, struct ref *refs,
if (ref->status == REF_STATUS_OK)
n += print_one_push_status(ref, dest, n, porcelain);
+ *nonfastforward = 0;
for (ref = refs; ref; ref = ref->next) {
if (ref->status != REF_STATUS_NONE &&
ref->status != REF_STATUS_UPTODATE &&
ref->status != REF_STATUS_OK)
n += print_one_push_status(ref, dest, n, porcelain);
+ if (ref->status == REF_STATUS_REJECT_NONFASTFORWARD)
+ *nonfastforward = 1;
}
}
@@ -997,7 +1000,8 @@ int transport_set_option(struct transport *transport,
}
int transport_push(struct transport *transport,
- int refspec_nr, const char **refspec, int flags)
+ int refspec_nr, const char **refspec, int flags,
+ int * nonfastforward)
{
verify_remote_names(refspec_nr, refspec);
@@ -1024,7 +1028,7 @@ int transport_push(struct transport *transport,
ret = transport->push_refs(transport, remote_refs, flags);
- print_push_status(transport->url, remote_refs, verbose | porcelain, porcelain);
+ print_push_status(transport->url, remote_refs, verbose | porcelain, porcelain, nonfastforward);
if (!(flags & TRANSPORT_PUSH_DRY_RUN)) {
struct ref *ref;
diff --git a/transport.h b/transport.h
index 51b5397..639f13d 100644
--- a/transport.h
+++ b/transport.h
@@ -68,7 +68,8 @@ int transport_set_option(struct transport *transport, const char *name,
const char *value);
int transport_push(struct transport *connection,
- int refspec_nr, const char **refspec, int flags);
+ int refspec_nr, const char **refspec, int flags,
+ int * nonfastforward);
const struct ref *transport_get_remote_refs(struct transport *transport);