push: support pushing HEAD to real branch name

This teaches "push <remote> HEAD" to resolve HEAD on the local
side to its real branch name, e.g. master, and then act as if
the real branch name was specified. So we have a shorthand for
pushing the current branch. Besides HEAD, no other symbolic ref
is resolved.

Thanks to Daniel Barkalow <barkalow@iabervon.org> for suggesting
this implementation, which is much simpler than the
implementation proposed before.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-push.c

@@ -44,6 +44,15 @@ static void set_refspecs(const char **refs, int nr)
 			strcat(tag, refs[i]);
 			ref = tag;
 		}
+		if (!strcmp("HEAD", ref)) {
+			unsigned char sha1_dummy[20];
+			ref = resolve_ref(ref, sha1_dummy, 1, NULL);
+			if (!ref)
+				die("HEAD cannot be resolved.");
+			if (prefixcmp(ref, "refs/heads/"))
+				die("HEAD cannot be resolved to branch.");
+			ref = xstrdup(ref + 11);
+		}
 		add_refspec(ref);
 	}
 }

t/t5516-fetch-push.sh

@@ -244,6 +244,23 @@ test_expect_success 'push with colon-less refspec (4)' '
 
 '
 
+test_expect_success 'push with HEAD' '
+
+	mk_test heads/master &&
+	git checkout master &&
+	git push testrepo HEAD &&
+	check_push_result $the_commit heads/master
+
+'
+
+test_expect_success 'push with HEAD nonexisting at remote' '
+
+	mk_test heads/master &&
+	git checkout -b local master &&
+	git push testrepo HEAD &&
+	check_push_result $the_commit heads/local
+'
+
 test_expect_success 'push with dry-run' '
 
 	mk_test heads/master &&