Re: How to fix (and find) many git-* --check errors?

[Jeff King <peff@peff.net>]

On Fri, Aug 08, 2008 at 02:49:00PM +0200, "Peter Valdemar Mørch (Lists)" wrote:

> (The diff between "the empty commit" and HEAD - well between the first
> commit and HEAD anyway. Is there a ref for "totally empty" or the
> revision before the first commit? Or a more elegant way to get this
> list?)

It is not advertised, but we always recognize the empty sha1 of the
empty tree:

  git diff --check 4b825dc642cb6eb9a060e54bf8d69288fbee4904

In fact, just the other day I was using this for the Nth time and got
tired of looking it up in the code, so I wrote the patch below. I don't
know if it is too crazy to be included in mainline git (it was discussed
a long time ago, but I think the general response was "what would it be
good for?").

---
 cache.h     |    4 ++++
 refs.c      |    4 ++++
 sha1_file.c |    3 +--
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/cache.h b/cache.h
index 30f1d62..4aa02ae 100644
--- a/cache.h
+++ b/cache.h
@@ -567,6 +567,10 @@ static inline unsigned int hexval(unsigned char c)
 #define MINIMUM_ABBREV 4
 #define DEFAULT_ABBREV 7
 
+#define EMPTY_TREE_SHA1 \
+	"\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60" \
+	"\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04"
+
 extern int get_sha1(const char *str, unsigned char *sha1);
 extern int get_sha1_with_mode(const char *str, unsigned char *sha1, unsigned *mode);
 extern int get_sha1_hex(const char *hex, unsigned char *sha1);
diff --git a/refs.c b/refs.c
index 39a3b23..0acbcbc 100644
--- a/refs.c
+++ b/refs.c
@@ -427,6 +427,10 @@ const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *
 				}
 				list = list->next;
 			}
+			if (!strcmp(ref, "EMPTY")) {
+				hashcpy(sha1, (unsigned char *)EMPTY_TREE_SHA1);
+				return ref;
+			}
 			if (reading || errno != ENOENT)
 				return NULL;
 			hashclr(sha1);
diff --git a/sha1_file.c b/sha1_file.c
index 2aff59b..38aad13 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1985,8 +1985,7 @@ static int cached_object_nr, cached_object_alloc;
 
 static struct cached_object empty_tree = {
 	/* empty tree sha1: 4b825dc642cb6eb9a060e54bf8d69288fbee4904 */
-	"\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60"
-	"\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04",
+	EMPTY_TREE_SHA1,
 	OBJ_TREE,
 	"",
 	0
-- 
1.6.0.rc1.260.g4782