Merge branch 'fc/at-head'

Instead of typing four capital letters "HEAD", you can say "@" now,
e.g. "git log @".

* fc/at-head:
  Add new @ shortcut for HEAD
  sha1-name: pass len argument to interpret_branch_name()

Documentation/git-check-ref-format.txt

@@ -54,6 +54,8 @@ Git imposes the following rules on how references are named:
 
 . They cannot contain a sequence `@{`.
 
+. They cannot be the single character `@`.
+
 . They cannot contain a `\`.
 
 These rules make it easy for shell script based tools to parse

Documentation/revisions.txt

@@ -58,6 +58,9 @@ the '$GIT_DIR/refs' directory or from the '$GIT_DIR/packed-refs' file.
 While the ref name encoding is unspecified, UTF-8 is preferred as
 some output processing may assume ref names in UTF-8.
 
+'@'::
+  '@' alone is a shortcut for 'HEAD'.
+
 '<refname>@\{<date>\}', e.g. 'master@\{yesterday\}', 'HEAD@\{5 minutes ago\}'::
   A ref followed by the suffix '@' with a date specification
   enclosed in a brace

cache.h

@@ -880,7 +880,7 @@ extern char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, i
 
 extern int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref);
 extern int dwim_log(const char *str, int len, unsigned char *sha1, char **ref);
-extern int interpret_branch_name(const char *str, struct strbuf *);
+extern int interpret_branch_name(const char *str, int len, struct strbuf *);
 extern int get_sha1_mb(const char *str, unsigned char *sha1);
 
 extern int refname_match(const char *abbrev_name, const char *full_name, const char **rules);

refs.c

@@ -72,6 +72,10 @@ int check_refname_format(const char *refname, int flags)
 {
 	int component_len, component_count = 0;
 
+	if (!strcmp(refname, "@"))
+		/* Refname is a single character '@'. */
+		return -1;
+
 	while (1) {
 		/* We are at the start of a path component. */
 		component_len = check_refname_component(refname, flags);
@@ -1951,7 +1955,7 @@ static int remove_empty_directories(const char *file)
 static char *substitute_branch_name(const char **string, int *len)
 {
 	struct strbuf buf = STRBUF_INIT;
-	int ret = interpret_branch_name(*string, &buf);
+	int ret = interpret_branch_name(*string, *len, &buf);
 
 	if (ret == *len) {
 		size_t size;

revision.c

@@ -200,7 +200,7 @@ static void add_pending_object_with_mode(struct rev_info *revs,
 		revs->no_walk = 0;
 	if (revs->reflog_info && obj->type == OBJ_COMMIT) {
 		struct strbuf buf = STRBUF_INIT;
-		int len = interpret_branch_name(name, &buf);
+		int len = interpret_branch_name(name, 0, &buf);
 		int st;
 
 		if (0 < len && name[len] && buf.len)

sha1_name.c

@@ -1006,6 +1006,28 @@ int get_sha1_mb(const char *name, unsigned char *sha1)
 	return st;
 }
 
+/* parse @something syntax, when 'something' is not {.*} */
+static int interpret_empty_at(const char *name, int namelen, int len, struct strbuf *buf)
+{
+	const char *next;
+
+	if (len || name[1] == '{')
+		return -1;
+
+	/* make sure it's a single @, or @@{.*}, not @foo */
+	next = strchr(name + len + 1, '@');
+	if (next && next[1] != '{')
+		return -1;
+	if (!next)
+		next = name + namelen;
+	if (next != name + 1)
+		return -1;
+
+	strbuf_reset(buf);
+	strbuf_add(buf, "HEAD", 4);
+	return 1;
+}
+
 static int reinterpret(const char *name, int namelen, int len, struct strbuf *buf)
 {
 	/* we have extra data, which might need further processing */
@@ -1014,7 +1036,7 @@ static int reinterpret(const char *name, int namelen, int len, struct strbuf *bu
 	int ret;
 
 	strbuf_add(buf, name + len, namelen - len);
-	ret = interpret_branch_name(buf->buf, &tmp);
+	ret = interpret_branch_name(buf->buf, buf->len, &tmp);
 	/* that data was not interpreted, remove our cruft */
 	if (ret < 0) {
 		strbuf_setlen(buf, used);
@@ -1048,14 +1070,16 @@ static int reinterpret(const char *name, int namelen, int len, struct strbuf *bu
  * If the input was ok but there are not N branch switches in the
  * reflog, it returns 0.
  */
-int interpret_branch_name(const char *name, struct strbuf *buf)
+int interpret_branch_name(const char *name, int namelen, struct strbuf *buf)
 {
 	char *cp;
 	struct branch *upstream;
-	int namelen = strlen(name);
 	int len = interpret_nth_prior_checkout(name, buf);
 	int tmp_len;
 
+	if (!namelen)
+		namelen = strlen(name);
+
 	if (!len) {
 		return len; /* syntax Ok, not enough switches */
 	} else if (len > 0) {
@@ -1068,9 +1092,15 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 	cp = strchr(name, '@');
 	if (!cp)
 		return -1;
+
+	len = interpret_empty_at(name, namelen, cp - name, buf);
+	if (len > 0)
+		return reinterpret(name, namelen, len, buf);
+
 	tmp_len = upstream_mark(cp, namelen - (cp - name));
 	if (!tmp_len)
 		return -1;
+
 	len = cp + tmp_len - name;
 	cp = xstrndup(name, cp - name);
 	upstream = branch_get(*cp ? cp : NULL);
@@ -1102,7 +1132,7 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 int strbuf_branchname(struct strbuf *sb, const char *name)
 {
 	int len = strlen(name);
-	int used = interpret_branch_name(name, sb);
+	int used = interpret_branch_name(name, len, sb);
 
 	if (used == len)
 		return 0;

t/t1508-at-combinations.sh

@@ -32,6 +32,9 @@ test_expect_success 'setup' '
 	git checkout -b upstream-branch &&
 	test_commit upstream-one &&
 	test_commit upstream-two &&
+	git checkout -b @/at-test &&
+	git checkout -b @@/at-test &&
+	git checkout -b @at-test &&
 	git checkout -b old-branch &&
 	test_commit old-one &&
 	test_commit old-two &&
@@ -55,6 +58,11 @@ check "HEAD@{u}" ref refs/heads/upstream-branch
 check "@{u}@{1}" commit upstream-one
 check "@{-1}@{u}" ref refs/heads/master
 check "@{-1}@{u}@{1}" commit master-one
+check "@" commit new-two
+check "@@{u}" ref refs/heads/upstream-branch
+check "@@/at-test" ref refs/heads/@@/at-test
+check "@/at-test" ref refs/heads/@/at-test
+check "@at-test" ref refs/heads/@at-test
 nonsense "@{u}@{-1}"
 nonsense "@{0}@{0}"
 nonsense "@{1}@{u}"