[PATCH/RFC 0/3] git rerere unresolve file

@@ -101,12 +101,13 @@ static int diff_two(const char *file1, const char *label1,
 int cmd_rerere(int argc, const char **argv, const char *prefix)
 {
 	struct string_list merge_rr = { NULL, 0, 0, 1 };
+	struct string_list merge_rr_done = { NULL, 0, 0, 1 };
 	int i, fd;
 
 	if (argc < 2)
 		return rerere();
 
-	fd = setup_rerere(&merge_rr);
+	fd = setup_rerere(&merge_rr, &merge_rr_done);
 	if (fd < 0)
 		return 0;
 

@@ -132,5 +133,6 @@ int cmd_rerere(int argc, const char **argv, const char *prefix)
 		usage(git_rerere_usage);
 
 	string_list_clear(&merge_rr, 1);
+	string_list_clear(&merge_rr_done, 1);
 	return 0;
 }

@@ -23,8 +23,20 @@ int has_rerere_resolution(const char *hex)
 	return !stat(rerere_path(hex, "postimage"), &st);
 }
 
-static void read_rr(struct string_list *rr)
+/*
+ * If MERGE_RR is read and rewritten by an old version, the section bound
+ * would not be preserved, and file names from both sections would be
+ * interleaved. We must make sure that the section marker does not end up
+ * in an arbitrary position. In particular, the safest result is that all
+ * paths are now in the first ("not done") section. Therefore, we choose
+ * a file name that sorts last (for all practical purposes).
+ */
+static const char section_mark[] =
+	"0000000000000000000000000000000000000000\t\377\377\377\377";
+
+static void read_rr(struct string_list *rr, struct string_list *rr_done)
 {
+	struct string_list *section = rr;
 	unsigned char sha1[20];
 	char buf[PATH_MAX];
 	FILE *in = fopen(merge_rr_path, "r");

@@ -43,14 +55,19 @@ static void read_rr(struct string_list *rr)
 			; /* do nothing */
 		if (i == sizeof(buf))
 			die("filename too long");
-		string_list_insert(buf, rr)->util = name;
+		if (prefixcmp(section_mark, name)) {
+			string_list_insert(buf, section)->util = name;
+		} else {
+			free(name);
+			section = rr_done;
+		}
 	}
 	fclose(in);
 }
 
 static struct lock_file write_lock;
 
-static int write_rr(struct string_list *rr, int out_fd)
+static void write_rr_section(struct string_list *rr, int out_fd)
 {
 	int i;
 	for (i = 0; i < rr->nr; i++) {

@@ -65,6 +82,17 @@ static int write_rr(struct string_list *rr, int out_fd)
 		    write_in_full(out_fd, path, length) != length)
 			die("unable to write rerere record");
 	}
+}
+
+static int write_rr(struct string_list *rr,
+		    struct string_list *rr_done, int out_fd)
+{
+	int length = strlen(section_mark)+1;
+
+	write_rr_section(rr, out_fd);
+	if (write_in_full(out_fd, section_mark, length) != length)
+		die("unable to write rerere record");
+	write_rr_section(rr_done, out_fd);
 	if (commit_lock_file(&write_lock) != 0)
 		die("unable to write rerere record");
 	return 0;

@@ -263,7 +291,8 @@ static int update_paths(struct string_list *update)
 	return status;
 }
 
-static int do_plain_rerere(struct string_list *rr, int fd)
+static int do_plain_rerere(struct string_list *rr,
+			   struct string_list *rr_done, int fd)
 {
 	struct string_list conflict = { NULL, 0, 0, 1 };
 	struct string_list update = { NULL, 0, 0, 1 };

@@ -328,13 +357,14 @@ static int do_plain_rerere(struct string_list *rr, int fd)
 		fprintf(stderr, "Recorded resolution for '%s'.\n", path);
 		copy_file(rerere_path(name, "postimage"), path, 0666);
 	mark_resolved:
+		string_list_insert(path, rr_done)->util = rr->items[i].util;
 		rr->items[i].util = NULL;
 	}
 
 	if (update.nr)
 		update_paths(&update);
 
-	return write_rr(rr, fd);
+	return write_rr(rr, rr_done, fd);
 }
 
 static int git_rerere_config(const char *var, const char *value, void *cb)

@@ -367,7 +397,7 @@ static int is_rerere_enabled(void)
 	return 1;
 }
 
-int setup_rerere(struct string_list *merge_rr)
+int setup_rerere(struct string_list *merge_rr, struct string_list *merge_rr_done)
 {
 	int fd;
 

@@ -378,17 +408,18 @@ int setup_rerere(struct string_list *merge_rr)
 	merge_rr_path = git_pathdup("MERGE_RR");
 	fd = hold_lock_file_for_update(&write_lock, merge_rr_path,
 				       LOCK_DIE_ON_ERROR);
-	read_rr(merge_rr);
+	read_rr(merge_rr, merge_rr_done);
 	return fd;
 }
 
 int rerere(void)
 {
 	struct string_list merge_rr = { NULL, 0, 0, 1 };
+	struct string_list merge_rr_done = { NULL, 0, 0, 1 };
 	int fd;
 
-	fd = setup_rerere(&merge_rr);
+	fd = setup_rerere(&merge_rr, &merge_rr_done);
 	if (fd < 0)
 		return 0;
-	return do_plain_rerere(&merge_rr, fd);
+	return do_plain_rerere(&merge_rr, &merge_rr_done, fd);
 }

@@ -3,7 +3,7 @@
 
 #include "string-list.h"
 
-extern int setup_rerere(struct string_list *);
+extern int setup_rerere(struct string_list *, struct string_list *);
 extern int rerere(void);
 extern const char *rerere_path(const char *hex, const char *file);
 extern int has_rerere_resolution(const char *hex);

@@ -229,6 +229,25 @@ static int find_conflict(struct string_list *conflict)
 	return 0;
 }
 
+static int record_preimage(struct string_list *rr, const char *path, int force)
+{
+	unsigned char sha1[20];
+	char *hex;
+	int ret;
+
+	ret = handle_file(path, sha1, NULL);
+	if (ret < 1)
+		return -1;
+
+	hex = xstrdup(sha1_to_hex(sha1));
+	string_list_insert(path, rr)->util = hex;
+	if (mkdir(git_path("rr-cache/%s", hex), 0755) && !force)
+		return -1;
+
+	handle_file(path, NULL, rerere_path(hex, "preimage"));
+	return 0;
+}
+
 static int merge(const char *name, const char *path)
 {
 	int ret;

@@ -310,17 +329,8 @@ static int do_plain_rerere(struct string_list *rr,
 	for (i = 0; i < conflict.nr; i++) {
 		const char *path = conflict.items[i].string;
 		if (!string_list_has_string(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));
-			string_list_insert(path, rr)->util = hex;
-			if (mkdir(git_path("rr-cache/%s", hex), 0755))
+			if (record_preimage(rr, path, 0))
 				continue;
-			handle_file(path, NULL, rerere_path(hex, "preimage"));
 			fprintf(stderr, "Recorded preimage for '%s'\n", path);
 		}
 	}

@@ -7,7 +7,7 @@ git-rerere - Reuse recorded resolution of conflicted merges
 
 SYNOPSIS
 --------
-'git rerere' ['clear'|'diff'|'status'|'gc']
+'git rerere' ['clear'|'diff'|'status'|'unresolve file...'|'gc']
 
 DESCRIPTION
 -----------

@@ -52,6 +52,14 @@ conflicts.  Additional arguments are passed directly to the system
 Like 'diff', but this only prints the filenames that will be tracked
 for resolutions.
 
+'unresolve'::
+
+Removes the resolution that was recorded for the specified files.
+The conflict sections are restored as well, although the direction of
+the "ours" and "theirs" sections may be inverted.
+You can use 'git checkout --conflict=merge file' to restore the
+original conflict markers in the correct direction.
+
 'gc'::
 
 This prunes records of conflicted merges that

@@ -7,7 +7,7 @@
 #include "xdiff-interface.h"
 
 static const char git_rerere_usage[] =
-"git rerere [clear | status | diff | gc]";
+"git rerere [clear | status | diff | unresolve file... | gc]";
 
 /* these values are days */
 static int cutoff_noresolve = 15;

@@ -102,7 +102,7 @@ int cmd_rerere(int argc, const char **argv, const char *prefix)
 {
 	struct string_list merge_rr = { NULL, 0, 0, 1 };
 	struct string_list merge_rr_done = { NULL, 0, 0, 1 };
-	int i, fd;
+	int i, fd, ret = 0;
 
 	if (argc < 2)
 		return rerere();

@@ -129,10 +129,13 @@ int cmd_rerere(int argc, const char **argv, const char *prefix)
 			const char *name = (const char *)merge_rr.items[i].util;
 			diff_two(rerere_path(name, "preimage"), path, path, path);
 		}
+	else if (!strcmp(argv[1], "unresolve"))
+		ret = unresolve_rerere(&merge_rr, &merge_rr_done,
+				       get_pathspec(prefix, &argv[2]), fd);
 	else
 		usage(git_rerere_usage);
 
 	string_list_clear(&merge_rr, 1);
 	string_list_clear(&merge_rr_done, 1);
-	return 0;
+	return ret;
 }

@@ -140,7 +140,7 @@ static int handle_file(const char *path,
 		git_SHA1_Init(&ctx);
 
 	while (fgets(buf, sizeof(buf), f)) {
-		if (!prefixcmp(buf, "<<<<<<< ")) {
+		if (!prefixcmp(buf, "<<<<<<<") && isspace(buf[7])) {
 			if (hunk != RR_CONTEXT)
 				goto bad;
 			hunk = RR_SIDE_1;

@@ -152,7 +152,7 @@ static int handle_file(const char *path,
 			if (hunk != RR_SIDE_1 && hunk != RR_ORIGINAL)
 				goto bad;
 			hunk = RR_SIDE_2;
-		} else if (!prefixcmp(buf, ">>>>>>> ")) {
+		} else if (!prefixcmp(buf, ">>>>>>>") && isspace(buf[7])) {
 			if (hunk != RR_SIDE_2)
 				goto bad;
 			if (strbuf_cmp(&one, &two) > 0)

@@ -248,23 +248,29 @@ static int record_preimage(struct string_list *rr, const char *path, int 

@@ -347,7 +353,7 @@ static int do_plain_rerere(struct string_list *rr,
 		const char *name = (const char *)rr->items[i].util;
 
 		if (has_rerere_resolution(name)) {
-			if (!merge(name, path)) {
+			if (!merge(name, path, RESOLVE)) {
 				if (rerere_autoupdate)
 					string_list_insert(path, &update);
 				fprintf(stderr,

@@ -433,3 +439,57 @@ int rerere(void)
 		return 0;
 	return do_plain_rerere(&merge_rr, &merge_rr_done, fd);
 }
+
+static int unresolve_check(struct string_list *rr_done, const char *path)
+{
+	struct string_list_item *item = string_list_lookup(path, rr_done);
+
+	if (!item) {
+		warning("not resolved using a previous resolution: %s", path);
+		return 0;
+	}
+	if (!has_rerere_resolution(item->util))
+		return error("no resolution found for %s", path);
+	if (merge(item->util, path, UNRESOLVE_CHECK))
+		return error("cannot revert resolution of %s", path);
+	return 0;
+}
+
+int unresolve_rerere_1(struct string_list *rr, struct string_list *rr_done,
+		       const char *path)
+{
+	struct string_list_item *item = string_list_lookup(path, rr_done);
+
+	if (!item)
+		return 0;
+	if (merge(item->util, path, UNRESOLVE))
+		return -1;
+
+	if (record_preimage(rr, path, 1))
+		return error("no conflict markers found: %s", path);
+
+	item->util = NULL;
+	unlink_or_warn(rerere_path(item->util, "postimage"));
+	return 0;
+}
+
+int unresolve_rerere(struct string_list *rr, struct string_list *rr_done,
+		     const char **pathspec, int fd)
+{
+	int i, ret = 0;
+
+	if (!pathspec)
+		return error("unresolve what?");
+
+	for (i = 0; pathspec[i]; i++) {
+		ret |= unresolve_check(rr_done, pathspec[i]);
+	}
+	if (ret)
+		return ret;
+
+	for (i = 0; !ret && pathspec[i]; i++) {
+		ret = unresolve_rerere_1(rr, rr_done, pathspec[i]);
+	}
+	ret |= write_rr(rr, rr_done, fd);
+	return ret;
+}

@@ -7,5 +7,7 @@ extern int setup_rerere(struct string_list *, struct string_list *);
 extern int rerere(void);
 extern const char *rerere_path(const char *hex, const char *file);
 extern int has_rerere_resolution(const char *hex);
+extern int unresolve_rerere(struct string_list *, struct string_list *,
+	const char **, int);
 
 #endif