fetch: if not fetching from default remote, ignore default merge

When doing "git fetch <remote>" on a remote that does not have the
branch referenced in branch.<current-branch>.merge, git fetch failed.
It failed because it tried to add the "merge" ref to the refs to be
fetched.

Fix that.  And add a test case.

Incidentally, this unconvered a bug in our own test suite, where
"git pull <some-path>" was expected to merge the ref given in the
defaults, even if not pulling from the default remote.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

builtin-fetch.c

@@ -105,7 +105,13 @@ static struct ref *get_ref_map(struct transport *transport,
 				    !remote->fetch[0].pattern)
 					ref_map->merge = 1;
 			}
-			if (has_merge)
+			/*
+			 * if the remote we're fetching from is the same
+			 * as given in branch.<name>.remote, we add the
+			 * ref given in branch.<name>.merge, too.
+			 */
+			if (has_merge && !strcmp(branch->remote_name,
+						remote->name))
 				add_merge_config(&ref_map, remote_refs, branch, &tail);
 		} else {
 			ref_map = get_remote_ref(remote_refs, "HEAD");

t/t5510-fetch.sh

@@ -200,4 +200,12 @@ test_expect_success 'push via rsync' '
 '
 }
 
+test_expect_success 'fetch with a non-applying branch.<name>.merge' '
+	git config branch.master.remote yeti &&
+	git config branch.master.merge refs/heads/bigfoot &&
+	git config remote.blub.url one &&
+	git config remote.blub.fetch "refs/heads/*:refs/remotes/one/*" &&
+	git fetch blub
+'
+
 test_done

t/t5700-clone-reference.sh

@@ -38,7 +38,7 @@ cd "$base_dir"
 
 test_expect_success 'pulling from reference' \
 'cd C &&
-git pull ../B'
+git pull ../B master'
 
 cd "$base_dir"
 
@@ -61,7 +61,7 @@ test_expect_success 'existence of info/alternates' \
 cd "$base_dir"
 
 test_expect_success 'pulling from reference' \
-'cd D && git pull ../B'
+'cd D && git pull ../B master'
 
 cd "$base_dir"