[PATCH 12/16] subtree: rewriting outgoing commits

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Which is exactly the opposite of rewriting incoming commits.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 subtree.c |  173 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 subtree.h |    1 +
 2 files changed, 174 insertions(+), 0 deletions(-)

diff --git a/subtree.c b/subtree.c
index 8c075be..739ff5f 100644
--- a/subtree.c
+++ b/subtree.c
@@ -359,3 +359,176 @@ void subtree_import()
 	if (revs.pending.nr)
 		free(revs.pending.objects);
 }
+
+/*
+ * The opposite of narrow_tree(). Put the subtree back to the original tree.
+ */
+static int widen_tree(const unsigned char *sha1,
+		      unsigned char *newsha1,
+		      const unsigned char *subtree_sha1,
+		      const char *prefix)
+{
+	struct tree_desc desc;
+	struct name_entry entry;
+	struct strbuf buffer;
+	const char *slash;
+	int subtree_len;
+	enum object_type type;
+	unsigned long size;
+	char *tree;
+
+	slash = strchr(prefix, '/');
+	subtree_len = slash ? slash - prefix : strlen(prefix);
+
+	tree = read_sha1_file(sha1, &type, &size);
+	if (type != OBJ_TREE)
+		die("%s is not a tree", sha1_to_hex(sha1));
+
+	init_tree_desc(&desc, tree, size);
+	strbuf_init(&buffer, 8192);
+	while (tree_entry(&desc, &entry)) {
+		strbuf_addf(&buffer, "%o %.*s%c", entry.mode, strlen(entry.path), entry.path, '\0');
+
+		if (S_ISDIR(entry.mode) &&
+		    subtree_len == strlen(entry.path) &&
+		    !strncmp(entry.path, prefix, subtree_len)) {
+			unsigned char newtree_sha1[20];
+
+			if (slash && slash[1]) /* trailing slash does not count */
+				widen_tree(entry.sha1, newtree_sha1, subtree_sha1,
+					   prefix+subtree_len+1);
+			else
+				/* replace the tree */
+				memcpy(newtree_sha1, subtree_sha1, 20);
+
+			strbuf_add(&buffer, newtree_sha1, 20);
+		}
+		else
+			strbuf_add(&buffer, entry.sha1, 20);
+	}
+	free(tree);
+
+	if (write_sha1_file(buffer.buf, buffer.len, tree_type, newsha1)) {
+		error("Could not write replaced tree for %s", sha1_to_hex(sha1));
+		strbuf_release(&buffer);
+		return 1;
+	}
+	strbuf_release(&buffer);
+	return 0;
+}
+
+static int find_subtree(const unsigned char *sha1, unsigned char *newsha1, const char *prefix)
+{
+	struct tree_desc desc;
+	struct name_entry entry;
+	const char *slash;
+	enum object_type type;
+	unsigned long size;
+	int subtree_len;
+	char *tree;
+
+	slash = strchr(prefix, '/');
+	subtree_len = slash ? slash - prefix : strlen(prefix);
+
+	tree = read_sha1_file(sha1, &type, &size);
+	if (type != OBJ_TREE)
+		die("%s is not a tree", sha1_to_hex(sha1));
+
+	init_tree_desc(&desc, tree, size);
+	while (tree_entry(&desc, &entry)) {
+		if (!S_ISDIR(entry.mode))
+			continue;
+
+		if (subtree_len == strlen(entry.path) &&
+		    !strncmp(entry.path, prefix, subtree_len)) {
+
+			if (slash && slash[1]) { /* trailing slash does not count */
+				if (find_subtree(entry.sha1, newsha1, prefix+subtree_len+1))
+					return 1;
+			}
+			else
+				memcpy(newsha1, entry.sha1, 20);
+			free(tree);
+			return 0;
+		}
+	}
+	free(tree);
+
+	return 1;
+}
+
+/* The opposite of shadow_commit() */
+static int expose_commit(const unsigned char *sha1, unsigned char *newsha1,
+			 const unsigned char *basesha1,
+			 const char *prefix, FILE *fp)
+{
+	unsigned char treesha1[20], subtree_sha1[20];
+	enum object_type type;
+	unsigned long size, base_size;
+	void *base_buffer, *buffer;
+	int saved_read_replace_refs = read_replace_refs;
+
+	/* Get subtree from the new commit, sha1 */
+	read_replace_refs = 0;
+	buffer = read_sha1_file(sha1, &type, &size);
+	read_replace_refs = saved_read_replace_refs;
+	get_sha1_hex(buffer+5, treesha1);
+
+	if (!buffer || type != OBJ_COMMIT ||
+	    find_subtree(treesha1, subtree_sha1, prefix)) {
+		free(buffer);
+		error("Failed to find subtree tree in base commit %s", sha1_to_hex(sha1));
+		return 1;
+	}
+
+	/* Get the old base tree from basesha1 */
+	read_replace_refs = 0;
+	base_buffer = read_sha1_file(basesha1, &type, &base_size);
+	read_replace_refs = saved_read_replace_refs;
+	get_sha1_hex(base_buffer+5, treesha1);
+
+	if (!buffer || type != OBJ_COMMIT ||
+	    widen_tree(treesha1, newsha1, subtree_sha1, prefix)) {
+		free(buffer);
+		error("Failed to widen tree for commit %s", sha1_to_hex(sha1));
+		return 1;
+	}
+	free(base_buffer);
+
+	/* replace new tree in */
+	memcpy((char*)buffer+5, sha1_to_hex(newsha1), 40);
+
+	if (write_sha1_file(buffer, size, commit_type, newsha1)) {
+		free(buffer);
+		error("Could not write replaced commit for %s", sha1_to_hex(sha1));
+		return 1;
+	}
+
+	if (fp) {
+		char buf[82];
+		memcpy(buf, sha1_to_hex(newsha1), 40);
+		buf[40] = ' ';
+		memcpy(buf+41, sha1_to_hex(sha1), 40);
+		buf[81] = '\n';
+		fwrite(buf, 82, 1, fp);
+	}
+	free(buffer);
+
+	return 0;
+}
+
+int subtree_export(unsigned char *sha1, unsigned char *basesha1, unsigned char *newsha1)
+{
+	FILE *fp;
+
+	fp = fopen(git_path("subtree"), "a+");
+	if (expose_commit(sha1, newsha1, basesha1, core_subtree, fp))
+		die("Failed to rewrite commit %s", sha1_to_hex(sha1));
+	fclose(fp);
+
+	if (subtree_commit)
+		free(subtree_commit);
+	prepare_subtree_commit();
+
+	return 0;
+}
diff --git a/subtree.h b/subtree.h
index 3512e2a..081838f 100644
--- a/subtree.h
+++ b/subtree.h
@@ -1,3 +1,4 @@
 void prepare_subtree_commit();
 const unsigned char *subtree_lookup_object(const unsigned char *sha1);
 void subtree_import();
+int subtree_export(unsigned char *sha1, unsigned char *basesha1, unsigned char *newsha1);
-- 
1.7.1.rc1.69.g24c2f7