[PATCH v5 15/36] builtin: add rewrite helper

@@ -991,6 +991,7 @@ BUILTIN_OBJS += builtin/verify-tag.o
 BUILTIN_OBJS += builtin/write-tree.o
 
 BUILTIN_LIB_OBJS += builtin/sequencer.o
+BUILTIN_LIB_OBJS += builtin/rewrite.o
 BUILTIN_LIB_OBJS += $(BUILTIN_OBJS)
 
 GITLIBS = $(LIB_FILE) $(XDIFF_LIB)

@@ -0,0 +1,74 @@
+#include "cache.h"
+#include "rewrite.h"
+
+void add_rewritten(struct rewritten *list, unsigned char *from, unsigned char *to)
+{
+	struct rewritten_item *item;
+	if (list->nr + 1 >= list->alloc) {
+		list->alloc += 32;
+		list->items = xrealloc(list->items, list->alloc * sizeof(*list->items));
+	}
+	item = &list->items[list->nr];
+	hashcpy(item->from, from);
+	hashcpy(item->to, to);
+	list->nr++;
+}
+
+int store_rewritten(struct rewritten *list, const char *file)
+{
+	static struct lock_file lock;
+	struct strbuf buf = STRBUF_INIT;
+	int fd, i, ret = 0;
+
+	fd = hold_lock_file_for_update(&lock, file, LOCK_DIE_ON_ERROR);
+	for (i = 0; i < list->nr; i++) {
+		struct rewritten_item *item = &list->items[i];
+		strbuf_addf(&buf, "%s %s\n", sha1_to_hex(item->from), sha1_to_hex(item->to));
+	}
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
+		error(_("Could not write to %s"), file);
+		ret = 1;
+		goto leave;
+	}
+	if (commit_lock_file(&lock) < 0) {
+		error(_("Error wrapping up %s."), file);
+		ret = 1;
+		goto leave;
+	}
+leave:
+	strbuf_release(&buf);
+	return ret;
+}
+
+void load_rewritten(struct rewritten *list, const char *file)
+{
+	struct strbuf buf = STRBUF_INIT;
+	char *p;
+	int fd;
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return;
+	if (strbuf_read(&buf, fd, 0) < 0) {
+		close(fd);
+		strbuf_release(&buf);
+		return;
+	}
+	close(fd);
+
+	for (p = buf.buf; *p;) {
+		unsigned char from[20];
+		unsigned char to[20];
+		char *eol = strchrnul(p, '\n');
+		if (eol - p != 81)
+			/* wrong size */
+			break;
+		if (get_sha1_hex(p, from))
+			break;
+		if (get_sha1_hex(p + 41, to))
+			break;
+		add_rewritten(list, from, to);
+		p = *eol ? eol + 1 : eol;
+	}
+	strbuf_release(&buf);
+}

@@ -0,0 +1,18 @@
+#ifndef REWRITE_H
+#define REWRITE_H
+
+struct rewritten_item {
+	unsigned char from[20];
+	unsigned char to[20];
+};
+
+struct rewritten {
+	struct rewritten_item *items;
+	unsigned int nr, alloc;
+};
+
+void add_rewritten(struct rewritten *list, unsigned char *from, unsigned char *to);
+int store_rewritten(struct rewritten *list, const char *file);
+void load_rewritten(struct rewritten *list, const char *file);
+
+#endif