Existing "tagname^0" notation means "dereference tag zero or more
times until you cannot dereference it anymore, and make sure it is a
commit -- otherwise barf".  But tags do not necessarily reference
commit objects.

This commit introduces a bit more generalized notation, "ref^{type}".
Existing "ref^0" is a shorthand for "ref^{commit}".  If the type
is empty, it just dereferences tags until it hits a non-tag object.

With this, "git-rev-parse --verify 'junio-gpg-pub^{}'" shows the blob
object name -- there is no need to manually read the tag object and
find out the object name anymore.

"git-rev-parse --verify 'HEAD^{tree}'" can be used to find out the
tree object name of the HEAD commit.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-show-branch acquires two new options. --sha1-name to name
commits using the unique prefix of their object names, and
--no-name to not to show names at all.

This was outlined in <7vk6gpyuyr.fsf@assigned-by-dhcp.cox.net>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

The earlier fix incorrectly dropped the code the original had to
ensure the found SHA1 is at least unique within the same pack.
Restore the check.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Unlike cases where "no such object exists", the case where specified
prefix is ambiguous would confuse the user if we say "no such commit"
or such.  Give an extra error message from the uniqueness check if
there are more than one objects that match the given prefix.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

The original code did not even check alternates, and was confused if
an unpacked object was uniquely found when there was another object
that shares the same prefix in the pack.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

This extends the ref reading to understand a "symbolic ref": a ref file
that starts with "ref: " and points to another ref file, and thus
introduces the notion of ref aliases.

This is in preparation of allowing HEAD to eventually not be a symlink,
but one of these symbolic refs instead.

[jc: Linus originally required the prefix to be "ref: " five bytes
 and nothing else, but I changed it to allow and strip any number of
 leading whitespaces to match what update-ref.c does.]
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

get_sha1() would not do sha1 completion of short SHA1's when they were
part of a more complex expression.  So doing

	git-rev-parse 72713283^

would work, and return 87c6aeb4. But using
the shorthand version

	git-rev-list 72713^

wouldn't work.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

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: NJunio C Hamano <junkio@cox.net>

I think Linus did a cut & paste from an early JIT code while
developing the current extended SHA1 notation, and left it there as a
courtesy, but the directory does not deserve to be treated any more
specially than, say, .git/refs/bisect.

If the subdirectories under .git/refs proliferate, we may want to
switch to scanning that hierarchy at runtime, instead of the current
hard-coded set, although I think that would be overkill.
Signed-off-by: NJunio C Hamano <junkio@cox.net>
From nobody Mon Sep 17 00:00:00 2001
Subject: [PATCH] Add a new extended SHA1 syntax <name>:<num>
From: Junio C Hamano <junkio@cox.net>
Date: 1124617434 -0700

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: NJunio C Hamano <junkio@cox.net>

---

 sha1_name.c |   41 +++++++++++++++++++++++++++++++++++++++++
 1 files changed, 41 insertions(+), 0 deletions(-)

d5098ce769da46df6d45dc8f41b06dd758fdaea7
diff --git a/sha1_name.c b/sha1_name.c
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -191,9 +191,29 @@ static int get_parent(const char *name, 
 	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, 
 	if (parent >= 0)
 		return get_parent(name, len, sha1, parent);
 
+	/* name:3 is name^^^,
+	 * name:12 is name^^^^^^^^^^^^, and
+	 * name: is name
+	 */
+	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;

The "get_sha1_hex()" function is designed to work with SHA1 hex strings
that may be followed by arbitrary crud. However, that's not acceptable for
"get_sha1()" which is used for command line arguments etc: we don't want
to silently allow random characters after the end of the SHA1.

So verify that the hex string is all we have.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

You can resolve a tag, and it does the right thing except that it might
end up writing the tag itself into the resulting HEAD, which will confuse
subsequent operations no end.

This makes sure that when we resolve two heads, we will have turned them
into proper commits before we start acting on them.

This also fixes the parsing of "treeish^0", which would incorrectly
resolve to "treeish" instead of causing an error.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-rev-parse HEAD^1 would fail, because of an off-by-one bug (but HEAD^
would yield the expected result). Also, when the parent does not exist, do
not silently return an incorrect SHA1. Of course, this no longer applies
to git-rev-parse alone, but every user of get_sha1().

While at it, add a test.
Signed-off-by: NJohannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Everybody envies rev-parse, who is the only one that can grok
the extended sha1 format.  Move the get_extended_sha1() out of
rev-parse, rename it to get_sha1() and make it available to
everybody else.

The one I posted earlier to the list had one bug where it did
not handle a name that ends with a digit correctly (it
incorrectly tried the "Nth parent" path).  This commit fixes it.
Signed-off-by: NJunio C Hamano <junkio@cox.net>