merge: indicate remote tracking branches in merge message

Previously when merging directly from a local tracking
branch like:

  git merge origin/master

The merge message said:

   Merge commit 'origin/master'

     * commit 'origin/master':
       ...

Instead, let's be more explicit about what we are merging:

   Merge remote branch 'origin/master'

     * origin/master:
       ...

We accomplish this by recognizing remote tracking branches
in git-merge when we build the simulated FETCH_HEAD output
that we feed to fmt-merge-msg.

In addition to a new test in t7608, we have to tweak the
expected output of t3409, which does such a merge.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-merge.c

@@ -375,6 +375,11 @@ static void merge_name(const char *remote, struct strbuf *msg)
 				    sha1_to_hex(branch_head), remote);
 			goto cleanup;
 		}
+		if (!prefixcmp(found_ref, "refs/remotes/")) {
+			strbuf_addf(msg, "%s\t\tremote branch '%s' of .\n",
+				    sha1_to_hex(branch_head), remote);
+			goto cleanup;
+		}
 	}
 
 	/* See if remote matches <name>^^^.. or <name>~<number> */

t/t3409-rebase-preserve-merges.sh

@@ -71,7 +71,7 @@ test_expect_success 'rebase -p fakes interactive rebase' '
 	git fetch &&
 	git rebase -p origin/topic &&
 	test 1 = $(git rev-list --all --pretty=oneline | grep "Modify A" | wc -l) &&
-	test 1 = $(git rev-list --all --pretty=oneline | grep "Merge commit" | wc -l)
+	test 1 = $(git rev-list --all --pretty=oneline | grep "Merge remote branch " | wc -l)
 	)
 '
 

t/t7608-merge-messages.sh

@@ -47,4 +47,14 @@ test_expect_success 'ambiguous tag' '
 	check_oneline "Merge commit QambiguousQ"
 '
 
+test_expect_success 'remote branch' '
+	git checkout -b remote master &&
+	test_commit remote-1 &&
+	git update-ref refs/remotes/origin/master remote &&
+	git checkout master &&
+	test_commit master-5 &&
+	git merge origin/master &&
+	check_oneline "Merge remote branch Qorigin/masterQ"
+'
+
 test_done