rerere: Separate libgit and builtin functions

This patch moves rerere()-related functions into a newly created
rerere.c file.
The setup_rerere() function is needed by both rerere() and cmd_rerere(),
so this function is moved to rerere.c and declared non-static (and "extern")
in newly created rerere.h file.

Signed-off-by: Stephan Beyer <s-beyer@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

6 files changed, 390 insertions, 355 deletions

diff --git a/Makefile b/Makefile
index 4796565ab3..de151638bb 100644
--- a/Makefile
+++ b/Makefile
@@ -363,6 +363,7 @@ LIB_H += quote.h
 LIB_H += reflog-walk.h
 LIB_H += refs.h
 LIB_H += remote.h
+LIB_H += rerere.h
 LIB_H += revision.h
 LIB_H += run-command.h
 LIB_H += sha1-lookup.h
@@ -447,6 +448,7 @@ LIB_OBJS += read-cache.o
 LIB_OBJS += reflog-walk.o
 LIB_OBJS += refs.o
 LIB_OBJS += remote.o
+LIB_OBJS += rerere.o
 LIB_OBJS += revision.o
 LIB_OBJS += run-command.o
 LIB_OBJS += server-info.o
diff --git a/builtin-commit.c b/builtin-commit.c
index 745c11e773..bdc83df55b 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -22,6 +22,7 @@
 #include "utf8.h"
 #include "parse-options.h"
 #include "path-list.h"
+#include "rerere.h"
 #include "unpack-trees.h"
 
 static const char * const builtin_commit_usage[] = {
diff --git a/builtin-rerere.c b/builtin-rerere.c
index 69c3a52d5e..5d40e16932 100644
--- a/builtin-rerere.c
+++ b/builtin-rerere.c
@@ -1,11 +1,10 @@
 #include "builtin.h"
 #include "cache.h"
 #include "path-list.h"
+#include "rerere.h"
 #include "xdiff/xdiff.h"
 #include "xdiff-interface.h"
 
-#include <time.h>
-
 static const char git_rerere_usage[] =
 "git-rerere [clear | status | diff | gc]";
 
@@ -13,14 +12,6 @@ static const char git_rerere_usage[] =
 static int cutoff_noresolve = 15;
 static int cutoff_resolve = 60;
 
-/* if rerere_enabled == -1, fall back to detection of .git/rr-cache */
-static int rerere_enabled = -1;
-
-/* automatically update cleanly resolved paths to the index */
-static int rerere_autoupdate;
-
-static char *merge_rr_path;
-
 static const char *rr_path(const char *name, const char *file)
 {
 	return git_path("rr-cache/%s/%s", name, file);
@@ -38,189 +29,6 @@ static int has_resolution(const char *name)
 	return !stat(rr_path(name, "postimage"), &st);
 }
 
-static void read_rr(struct path_list *rr)
-{
-	unsigned char sha1[20];
-	char buf[PATH_MAX];
-	FILE *in = fopen(merge_rr_path, "r");
-	if (!in)
-		return;
-	while (fread(buf, 40, 1, in) == 1) {
-		int i;
-		char *name;
-		if (get_sha1_hex(buf, sha1))
-			die("corrupt MERGE_RR");
-		buf[40] = '\0';
-		name = xstrdup(buf);
-		if (fgetc(in) != '\t')
-			die("corrupt MERGE_RR");
-		for (i = 0; i < sizeof(buf) && (buf[i] = fgetc(in)); i++)
-			; /* do nothing */
-		if (i == sizeof(buf))
-			die("filename too long");
-		path_list_insert(buf, rr)->util = name;
-	}
-	fclose(in);
-}
-
-static struct lock_file write_lock;
-
-static int write_rr(struct path_list *rr, int out_fd)
-{
-	int i;
-	for (i = 0; i < rr->nr; i++) {
-		const char *path;
-		int length;
-		if (!rr->items[i].util)
-			continue;
-		path = rr->items[i].path;
-		length = strlen(path) + 1;
-		if (write_in_full(out_fd, rr->items[i].util, 40) != 40 ||
-		    write_in_full(out_fd, "\t", 1) != 1 ||
-		    write_in_full(out_fd, path, length) != length)
-			die("unable to write rerere record");
-	}
-	if (commit_lock_file(&write_lock) != 0)
-		die("unable to write rerere record");
-	return 0;
-}
-
-static int handle_file(const char *path,
-	 unsigned char *sha1, const char *output)
-{
-	SHA_CTX ctx;
-	char buf[1024];
-	int hunk = 0, hunk_no = 0;
-	struct strbuf one, two;
-	FILE *f = fopen(path, "r");
-	FILE *out = NULL;
-
-	if (!f)
-		return error("Could not open %s", path);
-
-	if (output) {
-		out = fopen(output, "w");
-		if (!out) {
-			fclose(f);
-			return error("Could not write %s", output);
-		}
-	}
-
-	if (sha1)
-		SHA1_Init(&ctx);
-
-	strbuf_init(&one, 0);
-	strbuf_init(&two,  0);
-	while (fgets(buf, sizeof(buf), f)) {
-		if (!prefixcmp(buf, "<<<<<<< ")) {
-			if (hunk)
-				goto bad;
-			hunk = 1;
-		} else if (!prefixcmp(buf, "=======") && isspace(buf[7])) {
-			if (hunk != 1)
-				goto bad;
-			hunk = 2;
-		} else if (!prefixcmp(buf, ">>>>>>> ")) {
-			if (hunk != 2)
-				goto bad;
-			if (strbuf_cmp(&one, &two) > 0)
-				strbuf_swap(&one, &two);
-			hunk_no++;
-			hunk = 0;
-			if (out) {
-				fputs("<<<<<<<\n", out);
-				fwrite(one.buf, one.len, 1, out);
-				fputs("=======\n", out);
-				fwrite(two.buf, two.len, 1, out);
-				fputs(">>>>>>>\n", out);
-			}
-			if (sha1) {
-				SHA1_Update(&ctx, one.buf ? one.buf : "",
-					    one.len + 1);
-				SHA1_Update(&ctx, two.buf ? two.buf : "",
-					    two.len + 1);
-			}
-			strbuf_reset(&one);
-			strbuf_reset(&two);
-		} else if (hunk == 1)
-			strbuf_addstr(&one, buf);
-		else if (hunk == 2)
-			strbuf_addstr(&two, buf);
-		else if (out)
-			fputs(buf, out);
-		continue;
-	bad:
-		hunk = 99; /* force error exit */
-		break;
-	}
-	strbuf_release(&one);
-	strbuf_release(&two);
-
-	fclose(f);
-	if (out)
-		fclose(out);
-	if (sha1)
-		SHA1_Final(sha1, &ctx);
-	if (hunk) {
-		if (output)
-			unlink(output);
-		return error("Could not parse conflict hunks in %s", path);
-	}
-	return hunk_no;
-}
-
-static int find_conflict(struct path_list *conflict)
-{
-	int i;
-	if (read_cache() < 0)
-		return error("Could not read index");
-	for (i = 0; i+1 < active_nr; i++) {
-		struct cache_entry *e2 = active_cache[i];
-		struct cache_entry *e3 = active_cache[i+1];
-		if (ce_stage(e2) == 2 &&
-		    ce_stage(e3) == 3 &&
-		    ce_same_name(e2, e3) &&
-		    S_ISREG(e2->ce_mode) &&
-		    S_ISREG(e3->ce_mode)) {
-			path_list_insert((const char *)e2->name, conflict);
-			i++; /* skip over both #2 and #3 */
-		}
-	}
-	return 0;
-}
-
-static int merge(const char *name, const char *path)
-{
-	int ret;
-	mmfile_t cur, base, other;
-	mmbuffer_t result = {NULL, 0};
-	xpparam_t xpp = {XDF_NEED_MINIMAL};
-
-	if (handle_file(path, NULL, rr_path(name, "thisimage")) < 0)
-		return 1;
-
-	if (read_mmfile(&cur, rr_path(name, "thisimage")) ||
-			read_mmfile(&base, rr_path(name, "preimage")) ||
-			read_mmfile(&other, rr_path(name, "postimage")))
-		return 1;
-	ret = xdl_merge(&base, &cur, "", &other, "",
-			&xpp, XDL_MERGE_ZEALOUS, &result);
-	if (!ret) {
-		FILE *f = fopen(path, "w");
-		if (!f)
-			return error("Could not write to %s", path);
-		fwrite(result.ptr, result.size, 1, f);
-		fclose(f);
-	}
-
-	free(cur.ptr);
-	free(base.ptr);
-	free(other.ptr);
-	free(result.ptr);
-
-	return ret;
-}
-
 static void unlink_rr_item(const char *name)
 {
 	unlink(rr_path(name, "thisimage"));
@@ -229,6 +37,17 @@ static void unlink_rr_item(const char *name)
 	rmdir(git_path("rr-cache/%s", name));
 }
 
+static int git_rerere_gc_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "gc.rerereresolved"))
+		cutoff_resolve = git_config_int(var, value);
+	else if (!strcmp(var, "gc.rerereunresolved"))
+		cutoff_noresolve = git_config_int(var, value);
+	else
+		return git_default_config(var, value, cb);
+	return 0;
+}
+
 static void garbage_collect(struct path_list *rr)
 {
 	struct path_list to_remove = { NULL, 0, 0, 1 };
@@ -237,6 +56,7 @@ static void garbage_collect(struct path_list *rr)
 	int i, cutoff;
 	time_t now = time(NULL), then;
 
+	git_config(git_rerere_gc_config, NULL);
 	dir = opendir(git_path("rr-cache"));
 	while ((e = readdir(dir))) {
 		const char *name = e->d_name;
@@ -289,181 +109,25 @@ static int diff_two(const char *file1, const char *label1,
 	return 0;
 }
 
-static struct lock_file index_lock;
-
-static int update_paths(struct path_list *update)
-{
-	int i;
-	int fd = hold_locked_index(&index_lock, 0);
-	int status = 0;
-
-	if (fd < 0)
-		return -1;
-
-	for (i = 0; i < update->nr; i++) {
-		struct path_list_item *item = &update->items[i];
-		if (add_file_to_cache(item->path, ADD_CACHE_IGNORE_ERRORS))
-			status = -1;
-	}
-
-	if (!status && active_cache_changed) {
-		if (write_cache(fd, active_cache, active_nr) ||
-		    commit_locked_index(&index_lock))
-			die("Unable to write new index file");
-	} else if (fd >= 0)
-		rollback_lock_file(&index_lock);
-	return status;
-}
-
-static int do_plain_rerere(struct path_list *rr, int fd)
-{
-	struct path_list conflict = { NULL, 0, 0, 1 };
-	struct path_list update = { NULL, 0, 0, 1 };
-	int i;
-
-	find_conflict(&conflict);
-
-	/*
-	 * MERGE_RR records paths with conflicts immediately after merge
-	 * failed.  Some of the conflicted paths might have been hand resolved
-	 * in the working tree since then, but the initial run would catch all
-	 * and register their preimages.
-	 */
-
-	for (i = 0; i < conflict.nr; i++) {
-		const char *path = conflict.items[i].path;
-		if (!path_list_has_path(rr, path)) {
-			unsigned char sha1[20];
-			char *hex;
-			int ret;
-			ret = handle_file(path, sha1, NULL);
-			if (ret < 1)
-				continue;
-			hex = xstrdup(sha1_to_hex(sha1));
-			path_list_insert(path, rr)->util = hex;
-			if (mkdir(git_path("rr-cache/%s", hex), 0755))
-				continue;;
-			handle_file(path, NULL, rr_path(hex, "preimage"));
-			fprintf(stderr, "Recorded preimage for '%s'\n", path);
-		}
-	}
-
-	/*
-	 * Now some of the paths that had conflicts earlier might have been
-	 * hand resolved.  Others may be similar to a conflict already that
-	 * was resolved before.
-	 */
-
-	for (i = 0; i < rr->nr; i++) {
-		int ret;
-		const char *path = rr->items[i].path;
-		const char *name = (const char *)rr->items[i].util;
-
-		if (has_resolution(name)) {
-			if (!merge(name, path)) {
-				fprintf(stderr, "Resolved '%s' using "
-						"previous resolution.\n", path);
-				if (rerere_autoupdate)
-					path_list_insert(path, &update);
-				goto mark_resolved;
-			}
-		}
-
-		/* Let's see if we have resolved it. */
-		ret = handle_file(path, NULL, NULL);
-		if (ret)
-			continue;
-
-		fprintf(stderr, "Recorded resolution for '%s'.\n", path);
-		copy_file(rr_path(name, "postimage"), path, 0666);
-	mark_resolved:
-		rr->items[i].util = NULL;
-	}
-
-	if (update.nr)
-		update_paths(&update);
-
-	return write_rr(rr, fd);
-}
-
-static int git_rerere_config(const char *var, const char *value, void *cb)
-{
-	if (!strcmp(var, "gc.rerereresolved"))
-		cutoff_resolve = git_config_int(var, value);
-	else if (!strcmp(var, "gc.rerereunresolved"))
-		cutoff_noresolve = git_config_int(var, value);
-	else if (!strcmp(var, "rerere.enabled"))
-		rerere_enabled = git_config_bool(var, value);
-	else if (!strcmp(var, "rerere.autoupdate"))
-		rerere_autoupdate = git_config_bool(var, value);
-	else
-		return git_default_config(var, value, cb);
-	return 0;
-}
-
-static int is_rerere_enabled(void)
-{
-	struct stat st;
-	const char *rr_cache;
-	int rr_cache_exists;
-
-	if (!rerere_enabled)
-		return 0;
-
-	rr_cache = git_path("rr-cache");
-	rr_cache_exists = !stat(rr_cache, &st) && S_ISDIR(st.st_mode);
-	if (rerere_enabled < 0)
-		return rr_cache_exists;
-
-	if (!rr_cache_exists &&
-	    (mkdir(rr_cache, 0777) || adjust_shared_perm(rr_cache)))
-		die("Could not create directory %s", rr_cache);
-	return 1;
-}
-
-static int setup_rerere(struct path_list *merge_rr)
-{
-	int fd;
-
-	git_config(git_rerere_config, NULL);
-	if (!is_rerere_enabled())
-		return -1;
-
-	merge_rr_path = xstrdup(git_path("rr-cache/MERGE_RR"));
-	fd = hold_lock_file_for_update(&write_lock, merge_rr_path, 1);
-	read_rr(merge_rr);
-	return fd;
-}
-
-int rerere(void)
-{
-	struct path_list merge_rr = { NULL, 0, 0, 1 };
-	int fd;
-
-	fd = setup_rerere(&merge_rr);
-	if (fd < 0)
-		return 0;
-	return do_plain_rerere(&merge_rr, fd);
-}
-
 int cmd_rerere(int argc, const char **argv, const char *prefix)
 {
 	struct path_list merge_rr = { NULL, 0, 0, 1 };
 	int i, fd;
 
+	if (argc < 2)
+		return rerere();
+
 	fd = setup_rerere(&merge_rr);
 	if (fd < 0)
 		return 0;
 
-	if (argc < 2)
-		return do_plain_rerere(&merge_rr, fd);
-	else if (!strcmp(argv[1], "clear")) {
+	if (!strcmp(argv[1], "clear")) {
 		for (i = 0; i < merge_rr.nr; i++) {
 			const char *name = (const char *)merge_rr.items[i].util;
 			if (!has_resolution(name))
 				unlink_rr_item(name);
 		}
-		unlink(merge_rr_path);
+		unlink(git_path("rr-cache/MERGE_RR"));
 	} else if (!strcmp(argv[1], "gc"))
 		garbage_collect(&merge_rr);
 	else if (!strcmp(argv[1], "status"))
diff --git a/commit.h b/commit.h
index 2d94d4148e..fda7ad03c0 100644
--- a/commit.h
+++ b/commit.h
@@ -131,7 +131,6 @@ extern struct commit_list *get_shallow_commits(struct object_array *heads,
 int in_merge_bases(struct commit *, struct commit **, int);
 
 extern int interactive_add(int argc, const char **argv, const char *prefix);
-extern int rerere(void);
 
 static inline int single_parent(struct commit *commit)
 {
diff --git a/rerere.c b/rerere.c
new file mode 100644
index 0000000000..eec2b50107
--- /dev/null
+++ b/rerere.c
@@ -0,0 +1,360 @@
+#include "cache.h"
+#include "path-list.h"
+#include "rerere.h"
+#include "xdiff/xdiff.h"
+#include "xdiff-interface.h"
+
+/* if rerere_enabled == -1, fall back to detection of .git/rr-cache */
+static int rerere_enabled = -1;
+
+/* automatically update cleanly resolved paths to the index */
+static int rerere_autoupdate;
+
+static char *merge_rr_path;
+
+static const char *rr_path(const char *name, const char *file)
+{
+	return git_path("rr-cache/%s/%s", name, file);
+}
+
+static int has_resolution(const char *name)
+{
+	struct stat st;
+	return !stat(rr_path(name, "postimage"), &st);
+}
+
+static void read_rr(struct path_list *rr)
+{
+	unsigned char sha1[20];
+	char buf[PATH_MAX];
+	FILE *in = fopen(merge_rr_path, "r");
+	if (!in)
+		return;
+	while (fread(buf, 40, 1, in) == 1) {
+		int i;
+		char *name;
+		if (get_sha1_hex(buf, sha1))
+			die("corrupt MERGE_RR");
+		buf[40] = '\0';
+		name = xstrdup(buf);
+		if (fgetc(in) != '\t')
+			die("corrupt MERGE_RR");
+		for (i = 0; i < sizeof(buf) && (buf[i] = fgetc(in)); i++)
+			; /* do nothing */
+		if (i == sizeof(buf))
+			die("filename too long");
+		path_list_insert(buf, rr)->util = name;
+	}
+	fclose(in);
+}
+
+static struct lock_file write_lock;
+
+static int write_rr(struct path_list *rr, int out_fd)
+{
+	int i;
+	for (i = 0; i < rr->nr; i++) {
+		const char *path;
+		int length;
+		if (!rr->items[i].util)
+			continue;
+		path = rr->items[i].path;
+		length = strlen(path) + 1;
+		if (write_in_full(out_fd, rr->items[i].util, 40) != 40 ||
+		    write_in_full(out_fd, "\t", 1) != 1 ||
+		    write_in_full(out_fd, path, length) != length)
+			die("unable to write rerere record");
+	}
+	if (commit_lock_file(&write_lock) != 0)
+		die("unable to write rerere record");
+	return 0;
+}
+
+static int handle_file(const char *path,
+	 unsigned char *sha1, const char *output)
+{
+	SHA_CTX ctx;
+	char buf[1024];
+	int hunk = 0, hunk_no = 0;
+	struct strbuf one, two;
+	FILE *f = fopen(path, "r");
+	FILE *out = NULL;
+
+	if (!f)
+		return error("Could not open %s", path);
+
+	if (output) {
+		out = fopen(output, "w");
+		if (!out) {
+			fclose(f);
+			return error("Could not write %s", output);
+		}
+	}
+
+	if (sha1)
+		SHA1_Init(&ctx);
+
+	strbuf_init(&one, 0);
+	strbuf_init(&two,  0);
+	while (fgets(buf, sizeof(buf), f)) {
+		if (!prefixcmp(buf, "<<<<<<< ")) {
+			if (hunk)
+				goto bad;
+			hunk = 1;
+		} else if (!prefixcmp(buf, "=======") && isspace(buf[7])) {
+			if (hunk != 1)
+				goto bad;
+			hunk = 2;
+		} else if (!prefixcmp(buf, ">>>>>>> ")) {
+			if (hunk != 2)
+				goto bad;
+			if (strbuf_cmp(&one, &two) > 0)
+				strbuf_swap(&one, &two);
+			hunk_no++;
+			hunk = 0;
+			if (out) {
+				fputs("<<<<<<<\n", out);
+				fwrite(one.buf, one.len, 1, out);
+				fputs("=======\n", out);
+				fwrite(two.buf, two.len, 1, out);
+				fputs(">>>>>>>\n", out);
+			}
+			if (sha1) {
+				SHA1_Update(&ctx, one.buf ? one.buf : "",
+					    one.len + 1);
+				SHA1_Update(&ctx, two.buf ? two.buf : "",
+					    two.len + 1);
+			}
+			strbuf_reset(&one);
+			strbuf_reset(&two);
+		} else if (hunk == 1)
+			strbuf_addstr(&one, buf);
+		else if (hunk == 2)
+			strbuf_addstr(&two, buf);
+		else if (out)
+			fputs(buf, out);
+		continue;
+	bad:
+		hunk = 99; /* force error exit */
+		break;
+	}
+	strbuf_release(&one);
+	strbuf_release(&two);
+
+	fclose(f);
+	if (out)
+		fclose(out);
+	if (sha1)
+		SHA1_Final(sha1, &ctx);
+	if (hunk) {
+		if (output)
+			unlink(output);
+		return error("Could not parse conflict hunks in %s", path);
+	}
+	return hunk_no;
+}
+
+static int find_conflict(struct path_list *conflict)
+{
+	int i;
+	if (read_cache() < 0)
+		return error("Could not read index");
+	for (i = 0; i+1 < active_nr; i++) {
+		struct cache_entry *e2 = active_cache[i];
+		struct cache_entry *e3 = active_cache[i+1];
+		if (ce_stage(e2) == 2 &&
+		    ce_stage(e3) == 3 &&
+		    ce_same_name(e2, e3) &&
+		    S_ISREG(e2->ce_mode) &&
+		    S_ISREG(e3->ce_mode)) {
+			path_list_insert((const char *)e2->name, conflict);
+			i++; /* skip over both #2 and #3 */
+		}
+	}
+	return 0;
+}
+
+static int merge(const char *name, const char *path)
+{
+	int ret;
+	mmfile_t cur, base, other;
+	mmbuffer_t result = {NULL, 0};
+	xpparam_t xpp = {XDF_NEED_MINIMAL};
+
+	if (handle_file(path, NULL, rr_path(name, "thisimage")) < 0)
+		return 1;
+
+	if (read_mmfile(&cur, rr_path(name, "thisimage")) ||
+			read_mmfile(&base, rr_path(name, "preimage")) ||
+			read_mmfile(&other, rr_path(name, "postimage")))
+		return 1;
+	ret = xdl_merge(&base, &cur, "", &other, "",
+			&xpp, XDL_MERGE_ZEALOUS, &result);
+	if (!ret) {
+		FILE *f = fopen(path, "w");
+		if (!f)
+			return error("Could not write to %s", path);
+		fwrite(result.ptr, result.size, 1, f);
+		fclose(f);
+	}
+
+	free(cur.ptr);
+	free(base.ptr);
+	free(other.ptr);
+	free(result.ptr);
+
+	return ret;
+}
+
+static struct lock_file index_lock;
+
+static int update_paths(struct path_list *update)
+{
+	int i;
+	int fd = hold_locked_index(&index_lock, 0);
+	int status = 0;
+
+	if (fd < 0)
+		return -1;
+
+	for (i = 0; i < update->nr; i++) {
+		struct path_list_item *item = &update->items[i];
+		if (add_file_to_cache(item->path, ADD_CACHE_IGNORE_ERRORS))
+			status = -1;
+	}
+
+	if (!status && active_cache_changed) {
+		if (write_cache(fd, active_cache, active_nr) ||
+		    commit_locked_index(&index_lock))
+			die("Unable to write new index file");
+	} else if (fd >= 0)
+		rollback_lock_file(&index_lock);
+	return status;
+}
+
+static int do_plain_rerere(struct path_list *rr, int fd)
+{
+	struct path_list conflict = { NULL, 0, 0, 1 };
+	struct path_list update = { NULL, 0, 0, 1 };
+	int i;
+
+	find_conflict(&conflict);
+
+	/*
+	 * MERGE_RR records paths with conflicts immediately after merge
+	 * failed.  Some of the conflicted paths might have been hand resolved
+	 * in the working tree since then, but the initial run would catch all
+	 * and register their preimages.
+	 */
+
+	for (i = 0; i < conflict.nr; i++) {
+		const char *path = conflict.items[i].path;
+		if (!path_list_has_path(rr, path)) {
+			unsigned char sha1[20];
+			char *hex;
+			int ret;
+			ret = handle_file(path, sha1, NULL);
+			if (ret < 1)
+				continue;
+			hex = xstrdup(sha1_to_hex(sha1));
+			path_list_insert(path, rr)->util = hex;
+			if (mkdir(git_path("rr-cache/%s", hex), 0755))
+				continue;;
+			handle_file(path, NULL, rr_path(hex, "preimage"));
+			fprintf(stderr, "Recorded preimage for '%s'\n", path);
+		}
+	}
+
+	/*
+	 * Now some of the paths that had conflicts earlier might have been
+	 * hand resolved.  Others may be similar to a conflict already that
+	 * was resolved before.
+	 */
+
+	for (i = 0; i < rr->nr; i++) {
+		int ret;
+		const char *path = rr->items[i].path;
+		const char *name = (const char *)rr->items[i].util;
+
+		if (has_resolution(name)) {
+			if (!merge(name, path)) {
+				fprintf(stderr, "Resolved '%s' using "
+						"previous resolution.\n", path);
+				if (rerere_autoupdate)
+					path_list_insert(path, &update);
+				goto mark_resolved;
+			}
+		}
+
+		/* Let's see if we have resolved it. */
+		ret = handle_file(path, NULL, NULL);
+		if (ret)
+			continue;
+
+		fprintf(stderr, "Recorded resolution for '%s'.\n", path);
+		copy_file(rr_path(name, "postimage"), path, 0666);
+	mark_resolved:
+		rr->items[i].util = NULL;
+	}
+
+	if (update.nr)
+		update_paths(&update);
+
+	return write_rr(rr, fd);
+}
+
+static int git_rerere_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "rerere.enabled"))
+		rerere_enabled = git_config_bool(var, value);
+	else if (!strcmp(var, "rerere.autoupdate"))
+		rerere_autoupdate = git_config_bool(var, value);
+	else
+		return git_default_config(var, value, cb);
+	return 0;
+}
+
+static int is_rerere_enabled(void)
+{
+	struct stat st;
+	const char *rr_cache;
+	int rr_cache_exists;
+
+	if (!rerere_enabled)
+		return 0;
+
+	rr_cache = git_path("rr-cache");
+	rr_cache_exists = !stat(rr_cache, &st) && S_ISDIR(st.st_mode);
+	if (rerere_enabled < 0)
+		return rr_cache_exists;
+
+	if (!rr_cache_exists &&
+	    (mkdir(rr_cache, 0777) || adjust_shared_perm(rr_cache)))
+		die("Could not create directory %s", rr_cache);
+	return 1;
+}
+
+int setup_rerere(struct path_list *merge_rr)
+{
+	int fd;
+
+	git_config(git_rerere_config, NULL);
+	if (!is_rerere_enabled())
+		return -1;
+
+	merge_rr_path = xstrdup(git_path("rr-cache/MERGE_RR"));
+	fd = hold_lock_file_for_update(&write_lock, merge_rr_path, 1);
+	read_rr(merge_rr);
+	return fd;
+}
+
+int rerere(void)
+{
+	struct path_list merge_rr = { NULL, 0, 0, 1 };
+	int fd;
+
+	fd = setup_rerere(&merge_rr);
+	if (fd < 0)
+		return 0;
+	return do_plain_rerere(&merge_rr, fd);
+}
diff --git a/rerere.h b/rerere.h
new file mode 100644
index 0000000000..35b0fa86a3
--- /dev/null
+++ b/rerere.h
@@ -0,0 +1,9 @@
+#ifndef RERERE_H
+#define RERERE_H
+
+#include "path-list.h"
+
+extern int setup_rerere(struct path_list *);
+extern int rerere(void);
+
+#endif