1 files changed, 122 insertions, 0 deletions
diff --git a/replace_object.c b/replace_object.c
new file mode 100644
index 0000000000..0ab2dc1374
--- /dev/null
+++ b/replace_object.c
@@ -0,0 +1,122 @@
+#include "cache.h"
+#include "sha1-lookup.h"
+#include "refs.h"
+#include "commit.h"
+
+/*
+ * An array of replacements.  The array is kept sorted by the original
+ * sha1.
+ */
+static struct replace_object {
+	unsigned char original[20];
+	unsigned char replacement[20];
+} **replace_object;
+
+static int replace_object_alloc, replace_object_nr;
+
+static const unsigned char *replace_sha1_access(size_t index, void *table)
+{
+	struct replace_object **replace = table;
+	return replace[index]->original;
+}
+
+static int replace_object_pos(const unsigned char *sha1)
+{
+	return sha1_pos(sha1, replace_object, replace_object_nr,
+			replace_sha1_access);
+}
+
+static int register_replace_object(struct replace_object *replace,
+				   int ignore_dups)
+{
+	int pos = replace_object_pos(replace->original);
+
+	if (0 <= pos) {
+		if (ignore_dups)
+			free(replace);
+		else {
+			free(replace_object[pos]);
+			replace_object[pos] = replace;
+		}
+		return 1;
+	}
+	pos = -pos - 1;
+	ALLOC_GROW(replace_object, replace_object_nr + 1, replace_object_alloc);
+	replace_object_nr++;
+	if (pos < replace_object_nr)
+		memmove(replace_object + pos + 1,
+			replace_object + pos,
+			(replace_object_nr - pos - 1) *
+			sizeof(*replace_object));
+	replace_object[pos] = replace;
+	return 0;
+}
+
+static int register_replace_ref(const char *refname,
+				const unsigned char *sha1,
+				int flag, void *cb_data)
+{
+	/* Get sha1 from refname */
+	const char *slash = strrchr(refname, '/');
+	const char *hash = slash ? slash + 1 : refname;
+	struct replace_object *repl_obj = xmalloc(sizeof(*repl_obj));
+
+	if (strlen(hash) != 40 || get_sha1_hex(hash, repl_obj->original)) {
+		free(repl_obj);
+		warning("bad replace ref name: %s", refname);
+		return 0;
+	}
+
+	/* Copy sha1 from the read ref */
+	hashcpy(repl_obj->replacement, sha1);
+
+	/* Register new object */
+	if (register_replace_object(repl_obj, 1))
+		die("duplicate replace ref: %s", refname);
+
+	return 0;
+}
+
+static void prepare_replace_object(void)
+{
+	static int replace_object_prepared;
+
+	if (replace_object_prepared)
+		return;
+
+	for_each_replace_ref(register_replace_ref, NULL);
+	replace_object_prepared = 1;
+	if (!replace_object_nr)
+		check_replace_refs = 0;
+}
+
+/* We allow "recursive" replacement. Only within reason, though */
+#define MAXREPLACEDEPTH 5
+
+/*
+ * If a replacement for object sha1 has been set up, return the
+ * replacement object's name (replaced recursively, if necessary).
+ * The return value is either sha1 or a pointer to a
+ * permanently-allocated value.  This function always respects replace
+ * references, regardless of the value of check_replace_refs.
+ */
+const unsigned char *do_lookup_replace_object(const unsigned char *sha1)
+{
+	int pos, depth = MAXREPLACEDEPTH;
+	const unsigned char *cur = sha1;
+
+	prepare_replace_object();
+
+	/* Try to recursively replace the object */
+	do {
+		if (--depth < 0)
+			die("replace depth too high for object %s",
+			    sha1_to_hex(sha1));
+
+		pos = replace_object_pos(cur);
+		if (0 <= pos)
+			cur = replace_object[pos]->replacement;
+	} while (0 <= pos);
+
+	return cur;
+}