provide a nice @{...} syntax to always mean the current branch reflog

This is shorter than HEAD@{...} and being nameless it has no semantic
issues.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

sha1_name.c

@@ -279,7 +279,7 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	/* basic@{time or number} format to query ref-log */
 	reflog_len = at = 0;
 	if (str[len-1] == '}') {
-		for (at = 1; at < len - 1; at++) {
+		for (at = 0; at < len - 1; at++) {
 			if (str[at] == '@' && str[at+1] == '{') {
 				reflog_len = (len-1) - (at+2);
 				len = at;
@@ -289,10 +289,14 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	}
 
 	/* Accept only unambiguous ref paths. */
-	if (ambiguous_path(str, len))
+	if (len && ambiguous_path(str, len))
 		return -1;
 
-	refs_found = dwim_ref(str, len, sha1, &real_ref);
+	if (!len && reflog_len) {
+		/* allow "@{...}" to mean the current branch reflog */
+		refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
+	} else
+		refs_found = dwim_ref(str, len, sha1, &real_ref);
 
 	if (!refs_found)
 		return -1;
@@ -312,11 +316,12 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		 * In the mean time prevent people from getting used to
 		 * such a synonym until the work is completed.
 		 */
-		if (!strncmp("HEAD", str, len) &&
+		if (len && !strncmp("HEAD", str, len) &&
 		    !strncmp(real_ref, "refs/", 5)) {
 			error("reflog for HEAD has not been implemented yet\n"
-			      "Maybe you could try %s%s instead.",
-			      strchr(real_ref+5, '/')+1, str + len);
+			      "Maybe you could try %s%s instead, "
+			      "or just %s for current branch..",
+			      strchr(real_ref+5, '/')+1, str+len, str+len);
 			exit(-1);
 		}