Through the years the functionality to handle @{-N} and @{u} has moved
around the code, and as a result, code that once made sense, doesn't any
more.

There is no need to call this function recursively with the branch of
@{-N} substituted because dwim_{ref,log} already replaces it.

However, there's one corner-case where @{-N} resolves to a detached
HEAD, in which case we wouldn't get any ref back.

So we parse the nth-prior manually, and deal with it depending on
weather it's a SHA-1, or a ref.

Signed-off-by: Felipe Contreras <felipe.contre...@gmail.com>
---
 sha1_name.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/sha1_name.c b/sha1_name.c
index 3820f28..6428001 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -431,13 +431,14 @@ static inline int upstream_mark(const char *string, int 
len)
 }
 
 static int get_sha1_1(const char *name, int len, unsigned char *sha1, unsigned 
lookup_flags);
+static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf);
 
 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 {
        static const char *warn_msg = "refname '%.*s' is ambiguous.";
        char *real_ref = NULL;
        int refs_found = 0;
-       int at, reflog_len;
+       int at, reflog_len, nth_prior = 0;
 
        if (len == 40 && !get_sha1_hex(str, sha1))
                return 0;
@@ -447,6 +448,10 @@ static int get_sha1_basic(const char *str, int len, 
unsigned char *sha1)
        if (len && str[len-1] == '}') {
                for (at = len-2; at >= 0; at--) {
                        if (str[at] == '@' && str[at+1] == '{') {
+                               if (at == 0 && str[2] == '-') {
+                                       nth_prior = 1;
+                                       continue;
+                               }
                                if (!upstream_mark(str + at, len - at)) {
                                        reflog_len = (len-1) - (at+2);
                                        len = at;
@@ -460,20 +465,22 @@ static int get_sha1_basic(const char *str, int len, 
unsigned char *sha1)
        if (len && ambiguous_path(str, len))
                return -1;
 
-       if (!len && reflog_len) {
+       if (nth_prior) {
                struct strbuf buf = STRBUF_INIT;
-               int ret;
-               /* try the @{-N} syntax for n-th checkout */
-               ret = interpret_branch_name(str+at, &buf);
-               if (ret > 0) {
-                       /* substitute this branch name and restart */
-                       return get_sha1_1(buf.buf, buf.len, sha1, 0);
-               } else if (ret == 0) {
-                       return -1;
+               int detached;
+
+               if (interpret_nth_prior_checkout(str, &buf) > 0) {
+                       detached = (buf.len == 40 && !get_sha1_hex(buf.buf, 
sha1));
+                       strbuf_release(&buf);
+                       if (detached)
+                               return 0;
                }
+       }
+
+       if (!len && reflog_len)
                /* allow "@{...}" to mean the current branch reflog */
                refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
-       } else if (reflog_len)
+       else if (reflog_len)
                refs_found = dwim_log(str, len, sha1, &real_ref);
        else
                refs_found = dwim_ref(str, len, sha1, &real_ref);
-- 
1.8.3.rc0.401.g45bba44

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