[PATCH] push: point to 'git pull' and 'git push --force' in case of non-fast forward

[Matthieu Moy <Matthieu.Moy@imag.fr>]

'git push' failing because of non-fast forward is a very common situation,
and a beginner does not necessarily understand "fast forward" immediately.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
---
That may be a bit verbose, but I think it's worth it.

Ideally, there should be a core.expertUser config variable to disable
these kind of messages, but that's another story.

 builtin-push.c |    9 ++++++++-
 transport.c    |   10 +++++++---
 transport.h    |    3 ++-
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/builtin-push.c b/builtin-push.c
index 1d92e22..214ca77 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("Some branch push were rejected due to non-fast forward:\n");
+			printf("Merge the remote changes (git pull) before pushing your's\n");
+			printf("or use git push --force to discard the remote changes.\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);
 
-- 
1.6.4.57.g116738.dirty