[PATCH 7/7 (v2)] checkout -: make "-" to mean "previous branch" everywhere

[Junio C Hamano <gitster@pobox.com>]

This is iffy, in that it teaches the very low level machinery to interpret
it as "the tip of the previous branch" when "-" is fed to it, and has a
high risk of unintended side effects.

This makes "git log ..-" to work as expected, which is marginally useful
because the revision parameter parser misinterprets the other direction
"git log -..".  It also makes "git check-ref-format --branch -" to work,
which is not very useful because Porcelains can always ask for @{-1}.

It also makes a refname whose last component is "-" forbidden.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin-checkout.c |    8 +++++---
 refs.c             |    3 +++
 sha1_name.c        |   21 +++++++++++++--------
 3 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/builtin-checkout.c b/builtin-checkout.c
index 66df0c0..6b3b450 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -666,9 +666,11 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		arg = argv[0];
 		has_dash_dash = (argc > 1) && !strcmp(argv[1], "--");
 
-		if (!strcmp(arg, "-"))
-			arg = "@{-1}";
-
+		{
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_branchname(&sb, arg);
+			arg = strbuf_detach(&sb, NULL);
+		}
 		if (get_sha1(arg, rev)) {
 			if (has_dash_dash)          /* case (1) */
 				die("invalid reference: %s", arg);
diff --git a/refs.c b/refs.c
index e355489..7e27537 100644
--- a/refs.c
+++ b/refs.c
@@ -735,6 +735,9 @@ int check_ref_format(const char *ref)
 		if (!ch) {
 			if (ref <= cp - 2 && cp[-2] == '.')
 				return CHECK_REF_FORMAT_ERROR;
+			if (ref <= cp - 2 && cp[-2] == '-' &&
+			    (cp - 3 < ref || cp[-3] == '/'))
+				return CHECK_REF_FORMAT_ERROR;
 			if (level < 2)
 				return CHECK_REF_FORMAT_ONELEVEL;
 			return ret;
diff --git a/sha1_name.c b/sha1_name.c
index 904bcd9..3972f4c 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -758,14 +758,19 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 	const char *brace;
 	char *num_end;
 
-	if (name[0] != '@' || name[1] != '{' || name[2] != '-')
-		return -1;
-	brace = strchr(name, '}');
-	if (!brace)
-		return -1;
-	nth = strtol(name+3, &num_end, 10);
-	if (num_end != brace)
-		return -1;
+	if (name[0] == '-' && !name[1]) {
+		nth = 1;
+		brace = name; /* "end of branch name expression" */
+	} else {
+		if (name[0] != '@' || name[1] != '{' || name[2] != '-')
+			return -1;
+		brace = strchr(name, '}');
+		if (!brace)
+			return -1;
+		nth = strtol(name+3, &num_end, 10);
+		if (num_end != brace)
+			return -1;
+	}
 	if (nth <= 0)
 		return -1;
 	cb.alloc = nth;
-- 
1.6.2.1.299.gda643a