[PATCH] Rename and extend read_tree_with_tree_or_commit_sha1

This patch renames read_tree_with_tree_or_commit_sha1() to
read_object_with_reference() and extends it to automatically
dereference not just "commit" objects but "tag" objects.  With
this patch, you can say e.g.:

    ls-tree $tag
    read-tree -m $(merge-base $tag $HEAD) $tag $HEAD
    diff-cache $tag
    diff-tree $tag $HEAD

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

cache.h

@@ -143,9 +143,10 @@ extern int error(const char *err, ...);
 
 extern int cache_name_compare(const char *name1, int len1, const char *name2, int len2);
 
-extern void *read_tree_with_tree_or_commit_sha1(const unsigned char *sha1,
-						unsigned long *size,
-						unsigned char *tree_sha1_ret);
+extern void *read_object_with_reference(const unsigned char *sha1,
+					const unsigned char *required_type,
+					unsigned long *size,
+					unsigned char *sha1_ret);
 
 static inline void *xmalloc(int size)
 {

diff-cache.c

@@ -180,7 +180,7 @@ int main(int argc, char **argv)
 
 	mark_merge_entries();
 
-	tree = read_tree_with_tree_or_commit_sha1(tree_sha1, &size, 0);
+	tree = read_object_with_reference(tree_sha1, "tree", &size, 0);
 	if (!tree)
 		die("bad tree object %s", argv[1]);
 	if (read_tree(tree, size, 1))

diff-tree.c

@@ -238,10 +238,10 @@ static int diff_tree_sha1(const unsigned char *old, const unsigned char *new, co
 	unsigned long size1, size2;
 	int retval;
 
-	tree1 = read_tree_with_tree_or_commit_sha1(old, &size1, 0);
+	tree1 = read_object_with_reference(old, "tree", &size1, 0);
 	if (!tree1)
 		die("unable to read source tree (%s)", sha1_to_hex(old));
-	tree2 = read_tree_with_tree_or_commit_sha1(new, &size2, 0);
+	tree2 = read_object_with_reference(new, "tree", &size2, 0);
 	if (!tree2)
 		die("unable to read destination tree (%s)", sha1_to_hex(new));
 	retval = diff_tree(tree1, size1, tree2, size2, base);

git-mktag.c

@@ -114,7 +114,7 @@ int main(int argc, char **argv)
 	// Read the signature
 	size = read(0, buffer, MAXSIZE);
 
-	// Verify it for some basic sanity: it needs to start with "object <sha1>\ntag "
+	// Verify it for some basic sanity: it needs to start with "object <sha1>\ntype "
 	if (verify_tag(buffer, size) < 0)
 		die("invalid tag signature file");
 

ls-tree.c

@@ -73,7 +73,7 @@ static int list(unsigned char *sha1)
 	void *buffer;
 	unsigned long size;
 
-	buffer = read_tree_with_tree_or_commit_sha1(sha1, &size, 0);
+	buffer = read_object_with_reference(sha1, "tree", &size, 0);
 	if (!buffer)
 		die("unable to read sha1 file");
 	list_recursive(buffer, "tree", size, NULL);

read-tree.c

@@ -12,7 +12,7 @@ static int unpack_tree(unsigned char *sha1)
 	void *buffer;
 	unsigned long size;
 
-	buffer = read_tree_with_tree_or_commit_sha1(sha1, &size, 0);
+	buffer = read_object_with_reference(sha1, "tree", &size, 0);
 	if (!buffer)
 		return -1;
 	return read_tree(buffer, size, stage);

sha1_file.c

@@ -189,44 +189,49 @@ void * read_sha1_file(const unsigned char *sha1, char *type, unsigned long *size
 	return NULL;
 }
 
-void *read_tree_with_tree_or_commit_sha1(const unsigned char *sha1,
-					 unsigned long *size,
-					 unsigned char *tree_sha1_return)
+void *read_object_with_reference(const unsigned char *sha1,
+				 const unsigned char *required_type,
+				 unsigned long *size,
+				 unsigned char *actual_sha1_return)
 {
 	char type[20];
 	void *buffer;
 	unsigned long isize;
-	int was_commit = 0;
-	unsigned char tree_sha1[20];
+	unsigned char actual_sha1[20];
 
-	buffer = read_sha1_file(sha1, type, &isize);
+	memcpy(actual_sha1, sha1, 20);
+	while (1) {
+		int ref_length = -1;
+		const char *ref_type = NULL;
 
-	/* 
-	 * We might have read a commit instead of a tree, in which case
-	 * we parse out the tree_sha1 and attempt to read from there.
-	 * (buffer + 5) is because the tree sha1 is always at offset 5
-	 * in a commit record ("tree ").
-	 */
-	if (buffer &&
-	    !strcmp(type, "commit") &&
-	    !get_sha1_hex(buffer + 5, tree_sha1)) {
-		free(buffer);
-		buffer = read_sha1_file(tree_sha1, type, &isize);
-		was_commit = 1;
+		buffer = read_sha1_file(actual_sha1, type, &isize);
+		if (!buffer)
+			return NULL;
+		if (!strcmp(type, required_type)) {
+			*size = isize;
+			if (actual_sha1_return)
+				memcpy(actual_sha1_return, actual_sha1, 20);
+			return buffer;
+		}
+		/* Handle references */
+		else if (!strcmp(type, "commit"))
+			ref_type = "tree ";
+		else if (!strcmp(type, "tag"))
+			ref_type = "object ";
+		else {
+			free(buffer);
+			return NULL;
+		}
+		ref_length = strlen(ref_type);
+
+		if (memcmp(buffer, ref_type, ref_length) ||
+		    get_sha1_hex(buffer + ref_length, actual_sha1)) {
+			free(buffer);
+			return NULL;
+		}
+		/* Now we have the ID of the referred-to object in
+		 * actual_sha1.  Check again. */
 	}
-
-	/*
-	 * Now do we have something and if so is it a tree?
-	 */
-	if (!buffer || strcmp(type, "tree")) {
-		free(buffer);
-		return NULL;
-	}
-
-	*size = isize;
-	if (tree_sha1_return)
-		memcpy(tree_sha1_return, was_commit ? tree_sha1 : sha1, 20);
-	return buffer;
 }
 
 int write_sha1_file(char *buf, unsigned long len, const char *type, unsigned char *returnsha1)