[PATCH] Add a new extended SHA1 syntax <name>~<num>

The new notation is a short-hand for <name> followed by <num>
caret ('^') characters.  E.g. "master~4" is the fourth
generation ancestor of the current "master" branch head,
following the first parents; same as "master^^^^" but a bit
more readable.

This will be used in the updated "git show-branch" command.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/sha1_name.c b/sha1_name.c
index 6744bbb..133af3b 100644 (file)
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -191,9 +191,29 @@ static int get_parent(const char *name, int len,
        return -1;
 }
 
+static int get_nth_ancestor(const char *name, int len,
+                           unsigned char *result, int generation)
+{
+       unsigned char sha1[20];
+       int ret = get_sha1_1(name, len, sha1);
+       if (ret)
+               return ret;
+
+       while (generation--) {
+               struct commit *commit = lookup_commit_reference(sha1);
+
+               if (!commit || parse_commit(commit) || !commit->parents)
+                       return -1;
+               memcpy(sha1, commit->parents->item->object.sha1, 20);
+       }
+       memcpy(result, sha1, 20);
+       return 0;
+}
+
 static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 {
        int parent, ret;
+       const char *cp;
 
        /* foo^[0-9] or foo^ (== foo^1); we do not do more than 9 parents. */
        if (len > 2 && name[len-2] == '^' &&
@@ -210,6 +230,27 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
        if (parent >= 0)
                return get_parent(name, len, sha1, parent);
 
+       /* "name~3" is "name^^^",
+        * "name~12" is "name^^^^^^^^^^^^", and
+        * "name~" and "name~0" are name -- not "name^0"!
+        */
+       parent = 0;
+       for (cp = name + len - 1; name <= cp; cp--) {
+               int ch = *cp;
+               if ('0' <= ch && ch <= '9')
+                       continue;
+               if (ch != '~')
+                       parent = -1;
+               break;
+       }
+       if (!parent && *cp == '~') {
+               int len1 = cp - name;
+               cp++;
+               while (cp < name + len)
+                       parent = parent * 10 + *cp++ - '0';
+               return get_nth_ancestor(name, len1, sha1, parent);
+       }
+
        ret = get_sha1_basic(name, len, sha1);
        if (!ret)
                return 0;