commit - 71641cee7c33b92d34395dd70335737fdf665d53
commit + 4434a15a4719fdf3ae54026f89dc2c9fc8692d16
blob - 8122fe9273cc37091dc13c83016ef03a2a436be5
blob + b6da5695eaab874ad02b4ba5ad0801b9748b60fb
--- got/got.1
+++ got/got.1
@@ -2837,7 +2837,10 @@ created with
 .Cm got import .
 .Pp
 Merge commits are commits based on multiple parent commits.
-The tip commit of the work tree's current branch, which must be set with
+The tip commit of the work tree's current branch, which must be
+must be in the
+.Dq refs/heads/
+reference namespace and must be set with
 .Cm got update -b
 before starting the
 .Cm merge
@@ -2882,6 +2885,13 @@ the work tree's current branch unmodified.
 .Pp
 .Cm got merge
 will refuse to run if certain preconditions are not met.
+If the work tree's current branch is not in the
+.Dq refs/heads/
+reference namespace then the work tree must first be switched to a
+branch in the
+.Dq refs/heads/
+namespace with
+.Cm got update -b .
 If the work tree is not yet fully updated to the tip commit of its
 branch, then the work tree must first be updated with
 .Cm got update .
blob - 2120baaa2759b6ec300835ada4b84aa2ef6cb37a
blob + 7ee57ef2c0cae82a5074cc265e15fd50297716f6
--- got/got.c
+++ got/got.c
@@ -13261,6 +13261,16 @@ cmd_merge(int argc, char *argv[])
 			goto done;
 		printf("Merge of %s aborted\n", branch_name);
 		goto done; /* nothing else to do */
+	}
+
+	if (strncmp(got_worktree_get_head_ref_name(worktree),
+	    "refs/heads/", 11) != 0) {
+		error = got_error_fmt(GOT_ERR_COMMIT_BRANCH,
+		    "work tree's current branch %s is outside the "
+		    "\"refs/heads/\" reference namespace; "
+		    "update -b required",
+		    got_worktree_get_head_ref_name(worktree));
+		goto done;
 	}
 
 	error = get_author(&author, repo, worktree);
blob - 92b590aa2ef2958738fb2d4e8419cb879fc9bf5c
blob + 0531f8b1f57c1f50521b6ec8c350bb9da1bebaf4
--- regress/cmdline/merge.sh
+++ regress/cmdline/merge.sh
@@ -1691,7 +1691,172 @@ test_merge_gitconfig_author() {
 	fi
 	test_done "$testroot" "$ret"
 }
+
+test_merge_fetched_branch() {
+	local testroot=`test_init merge_fetched_branch`
+	local testurl=ssh://127.0.0.1/$testroot
+	local commit_id=`git_show_head $testroot/repo`
+
+	got clone -q $testurl/repo $testroot/repo-clone
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got clone command failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
 
+	echo "modified alpha" > $testroot/repo/alpha
+	git_commit $testroot/repo -m "modified alpha"
+	local commit_id2=`git_show_head $testroot/repo`
+
+	got fetch -q -r $testroot/repo-clone > $testroot/stdout
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got fetch command failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	echo -n > $testroot/stdout.expected
+
+	cmp -s $testroot/stdout $testroot/stdout.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	got ref -l -r $testroot/repo-clone > $testroot/stdout
+
+	echo "HEAD: refs/heads/master" > $testroot/stdout.expected
+	echo "refs/heads/master: $commit_id" >> $testroot/stdout.expected
+	echo "refs/remotes/origin/HEAD: refs/remotes/origin/master" \
+		>> $testroot/stdout.expected
+	echo "refs/remotes/origin/master: $commit_id2" \
+		>> $testroot/stdout.expected
+
+	cmp -s $testroot/stdout $testroot/stdout.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	got checkout $testroot/repo-clone $testroot/wt > /dev/null
+
+	echo "modified beta" > $testroot/wt/beta
+	(cd $testroot/wt && got commit -m "modified beta" > /dev/null)
+	local commit_id3=`git_show_head $testroot/repo-clone`
+
+	(cd $testroot/wt && got update > /dev/null)
+	(cd $testroot/wt && got merge origin/master > $testroot/stdout)
+	local merge_commit_id=`git_show_head $testroot/repo-clone`
+
+	cat > $testroot/stdout.expected <<EOF
+G  alpha
+Merged refs/remotes/origin/master into refs/heads/master: $merge_commit_id
+EOF
+
+	cmp -s $testroot/stdout $testroot/stdout.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+	fi
+	test_done "$testroot" "$ret"
+}
+
+test_merge_fetched_branch_remote() {
+	local testroot=`test_init merge_fetched_branch_remote`
+	local testurl=ssh://127.0.0.1/$testroot
+	local commit_id=`git_show_head $testroot/repo`
+
+	got clone -q $testurl/repo $testroot/repo-clone
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got clone command failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	echo "modified alpha" > $testroot/repo/alpha
+	git_commit $testroot/repo -m "modified alpha"
+	local commit_id2=`git_show_head $testroot/repo`
+
+	got fetch -q -r $testroot/repo-clone > $testroot/stdout
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got fetch command failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	echo -n > $testroot/stdout.expected
+
+	cmp -s $testroot/stdout $testroot/stdout.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	got ref -l -r $testroot/repo-clone > $testroot/stdout
+
+	echo "HEAD: refs/heads/master" > $testroot/stdout.expected
+	echo "refs/heads/master: $commit_id" >> $testroot/stdout.expected
+	echo "refs/remotes/origin/HEAD: refs/remotes/origin/master" \
+		>> $testroot/stdout.expected
+	echo "refs/remotes/origin/master: $commit_id2" \
+		>> $testroot/stdout.expected
+
+	cmp -s $testroot/stdout $testroot/stdout.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	got checkout $testroot/repo-clone $testroot/wt > /dev/null
+
+	echo "modified beta" > $testroot/wt/beta
+	(cd $testroot/wt && got commit -m "modified beta" > /dev/null)
+	local commit_id3=`git_show_head $testroot/repo-clone`
+
+	(cd $testroot/wt && got update -b origin/master > /dev/null)
+	(cd $testroot/wt && got merge master > \
+		$testroot/stdout 2> $testroot/stderr)
+	local merge_commit_id=`git_show_head $testroot/repo-clone`
+
+	echo -n > $testroot/stdout.expected
+
+	cmp -s $testroot/stdout $testroot/stdout.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	echo -n "got: work tree's current branch refs/remotes/origin/master " \
+		> $testroot/stderr.expected
+	echo -n 'is outside the "refs/heads/" reference namespace; ' \
+		>> $testroot/stderr.expected
+	echo -n "update -b required: will not commit to a branch " \
+		>> $testroot/stderr.expected
+	echo 'outside the "refs/heads/" reference namespace' \
+		>> $testroot/stderr.expected
+
+	cmp -s $testroot/stderr $testroot/stderr.expected
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stderr.expected $testroot/stderr
+	fi
+	test_done "$testroot" "$ret"
+}
+
 test_parseargs "$@"
 run_test test_merge_basic
 run_test test_merge_forward
@@ -1707,3 +1872,5 @@ run_test test_merge_imported_branch
 run_test test_merge_interrupt
 run_test test_merge_umask
 run_test test_merge_gitconfig_author
+run_test test_merge_fetched_branch
+run_test test_merge_fetched_branch_remote