Fix fetch/pull when run without --update-head-ok

Some confusing tutorials suggested that it would be a good idea to fetch
into the current branch with something like this:

	git fetch origin master:master

(or even worse: the same command line with "pull" instead of "fetch").
While it might make sense to store what you want to pull, it typically is
plain wrong when the current branch is "master".  This should only be
allowed when (an incorrect) "git pull origin master:master" tries to work
around by giving --update-head-ok to underlying "git fetch", and otherwise
we should refuse it, but somewhere along the lines we lost that behavior.

The check for the current branch is now _only_ performed in non-bare
repositories, which is an improvement from the original behaviour.

Some newer tests were depending on the broken behaviour of "git fetch"
this patch fixes, and have been adjusted.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Acked-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 30 insertions, 3 deletions

diff --git a/builtin-fetch.c b/builtin-fetch.c
index ee93d3a93..57c161d35 100644
--- a/builtin-fetch.c
+++ b/builtin-fetch.c
@@ -534,6 +534,19 @@ static void find_non_local_tags(struct transport *transport,
 	string_list_clear(&new_refs, 0);
 }
 
+static void check_not_current_branch(struct ref *ref_map)
+{
+	struct branch *current_branch = branch_get(NULL);
+
+	if (is_bare_repository() || !current_branch)
+		return;
+
+	for (; ref_map; ref_map = ref_map->next)
+		if (ref_map->peer_ref && !strcmp(current_branch->refname,
+					ref_map->peer_ref->name))
+			die("Refusing to fetch into current branch");
+}
+
 static int do_fetch(struct transport *transport,
 		    struct refspec *refs, int ref_count)
 {
@@ -558,6 +571,8 @@ static int do_fetch(struct transport *transport,
 	}
 
 	ref_map = get_ref_map(transport, refs, ref_count, tags, &autotags);
+	if (!update_head_ok)
+		check_not_current_branch(ref_map);
 
 	for (rm = ref_map; rm; rm = rm->next) {
 		if (rm->peer_ref)
diff --git a/t/t5405-send-pack-rewind.sh b/t/t5405-send-pack-rewind.sh
index 86abc6227..cb9aacc7b 100755
--- a/t/t5405-send-pack-rewind.sh
+++ b/t/t5405-send-pack-rewind.sh
@@ -12,7 +12,7 @@ test_expect_success setup '
 	mkdir another && (
 		cd another &&
 		git init &&
-		git fetch .. master:master
+		git fetch --update-head-ok .. master:master
 	) &&
 
 	>file2 && git add file2 && test_tick &&
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index c4496635d..0103e1a18 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -188,7 +188,7 @@ test_expect_success 'prune --dry-run' '
 test_expect_success 'add --mirror && prune' '
 	(mkdir mirror &&
 	 cd mirror &&
-	 git init &&
+	 git init --bare &&
 	 git remote add --mirror -f origin ../one) &&
 	(cd one &&
 	 git branch -m side2 side) &&
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index de26c2032..52094e78d 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -303,4 +303,16 @@ test_expect_success 'pushing nonexistent branch by mistake should not segv' '
 
 '
 
+test_expect_success 'refuse to fetch into the current branch' '
+
+	test_must_fail git fetch . side:master
+
+'
+
+test_expect_success 'fetch into the current branch with --update-head-ok' '
+
+	git fetch --update-head-ok . side:master
+
+'
+
 test_done
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index c6bc0a607..dba3a1b48 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -983,7 +983,7 @@ test_expect_success \
 	 git checkout subuse1 &&
 	 rm -rf sub && mkdir sub && cd sub &&
 	 git init &&
-	 git fetch .. refs/heads/sub:refs/heads/master &&
+	 git fetch --update-head-ok .. refs/heads/sub:refs/heads/master &&
 	 git checkout master &&
 	 cd .. &&
 	 git submodule init &&