push: also use "upstream" mapping when pushing a single ref

When the user is using the 'upstream' mode, these commands:

    $ git push
    $ git push origin

would find the 'upstream' branch for the current branch, and then
push the current branch to update it.  However, pushing a single
branch explicitly, i.e.

    $ git push origin $(git symbolic-ref --short HEAD)

would not go through the same ref mapping process, and ends up
updating the branch at 'origin' of the same name, which may not
necessarily be the upstream of the branch being pushed.

In the spirit similar to the previous one, map a colon-less refspec
using the upstream mapping logic.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/push.c

@@ -58,6 +58,17 @@ static const char *map_refspec(const char *ref,
 		}
 	}
 
+	if (push_default == PUSH_DEFAULT_UPSTREAM &&
+	    !prefixcmp(matched->name, "refs/heads/")) {
+		struct branch *branch = branch_get(matched->name + 11);
+		if (branch->merge_nr == 1 && branch->merge[0]->src) {
+			struct strbuf buf = STRBUF_INIT;
+			strbuf_addf(&buf, "%s:%s",
+				    ref, branch->merge[0]->src);
+			return strbuf_detach(&buf, NULL);
+		}
+	}
+
 	return ref;
 }
 

t/t5516-fetch-push.sh

@@ -1160,6 +1160,7 @@ test_expect_success 'with no remote.$name.push, it is not used as refmap' '
 		git pull ../testrepo master &&
 		git branch next &&
 		git config remote.dst.url ../dst &&
+		git config push.default matching &&
 		git push dst master &&
 		git show-ref refs/heads/master >../dst/expect
 	) &&
@@ -1171,6 +1172,35 @@ test_expect_success 'with no remote.$name.push, it is not used as refmap' '
 	test_cmp dst/expect dst/actual
 '
 
+test_expect_success 'with no remote.$name.push, upstream mapping is used' '
+	mk_test testrepo heads/master &&
+	rm -fr src dst &&
+	git init src &&
+	git init --bare dst &&
+	(
+		cd src &&
+		git pull ../testrepo master &&
+		git branch next &&
+		git config remote.dst.url ../dst &&
+		git config remote.dst.fetch "+refs/heads/*:refs/remotes/dst/*" &&
+		git config push.default upstream &&
+
+		git config branch.master.merge refs/heads/trunk &&
+		git config branch.master.remote dst &&
+
+		git push dst master &&
+		git show-ref refs/heads/master |
+		sed -e "s|refs/heads/master|refs/heads/trunk|" >../dst/expect
+	) &&
+	(
+		cd dst &&
+		test_must_fail git show-ref refs/heads/master &&
+		test_must_fail git show-ref refs/heads/next &&
+		git show-ref refs/heads/trunk >actual
+	) &&
+	test_cmp dst/expect dst/actual
+'
+
 test_expect_success 'push does not follow tags by default' '
 	mk_test testrepo heads/master &&
 	rm -fr src dst &&