Adding upstream version 1:2.39.2.upstream/1%2.39.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1247 insertions, 0 deletions

diff --git a/rerere.c b/rerere.c
new file mode 100644
index 0000000..876ab43
--- /dev/null
+++ b/rerere.c
@@ -0,0 +1,1247 @@
+#include "cache.h"
+#include "config.h"
+#include "lockfile.h"
+#include "string-list.h"
+#include "rerere.h"
+#include "xdiff-interface.h"
+#include "dir.h"
+#include "resolve-undo.h"
+#include "ll-merge.h"
+#include "attr.h"
+#include "pathspec.h"
+#include "object-store.h"
+#include "hash-lookup.h"
+#include "strmap.h"
+
+#define RESOLVED 0
+#define PUNTED 1
+#define THREE_STAGED 2
+void *RERERE_RESOLVED = &RERERE_RESOLVED;
+
+/* 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;
+
+#define RR_HAS_POSTIMAGE 1
+#define RR_HAS_PREIMAGE 2
+struct rerere_dir {
+	int status_alloc, status_nr;
+	unsigned char *status;
+	char name[FLEX_ARRAY];
+};
+
+static struct strmap rerere_dirs = STRMAP_INIT;
+
+static void free_rerere_dirs(void)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *ent;
+
+	strmap_for_each_entry(&rerere_dirs, &iter, ent) {
+		struct rerere_dir *rr_dir = ent->value;
+		free(rr_dir->status);
+		free(rr_dir);
+	}
+	strmap_clear(&rerere_dirs, 0);
+}
+
+static void free_rerere_id(struct string_list_item *item)
+{
+	free(item->util);
+}
+
+static const char *rerere_id_hex(const struct rerere_id *id)
+{
+	return id->collection->name;
+}
+
+static void fit_variant(struct rerere_dir *rr_dir, int variant)
+{
+	variant++;
+	ALLOC_GROW(rr_dir->status, variant, rr_dir->status_alloc);
+	if (rr_dir->status_nr < variant) {
+		memset(rr_dir->status + rr_dir->status_nr,
+		       '\0', variant - rr_dir->status_nr);
+		rr_dir->status_nr = variant;
+	}
+}
+
+static void assign_variant(struct rerere_id *id)
+{
+	int variant;
+	struct rerere_dir *rr_dir = id->collection;
+
+	variant = id->variant;
+	if (variant < 0) {
+		for (variant = 0; variant < rr_dir->status_nr; variant++)
+			if (!rr_dir->status[variant])
+				break;
+	}
+	fit_variant(rr_dir, variant);
+	id->variant = variant;
+}
+
+const char *rerere_path(const struct rerere_id *id, const char *file)
+{
+	if (!file)
+		return git_path("rr-cache/%s", rerere_id_hex(id));
+
+	if (id->variant <= 0)
+		return git_path("rr-cache/%s/%s", rerere_id_hex(id), file);
+
+	return git_path("rr-cache/%s/%s.%d",
+			rerere_id_hex(id), file, id->variant);
+}
+
+static int is_rr_file(const char *name, const char *filename, int *variant)
+{
+	const char *suffix;
+	char *ep;
+
+	if (!strcmp(name, filename)) {
+		*variant = 0;
+		return 1;
+	}
+	if (!skip_prefix(name, filename, &suffix) || *suffix != '.')
+		return 0;
+
+	errno = 0;
+	*variant = strtol(suffix + 1, &ep, 10);
+	if (errno || *ep)
+		return 0;
+	return 1;
+}
+
+static void scan_rerere_dir(struct rerere_dir *rr_dir)
+{
+	struct dirent *de;
+	DIR *dir = opendir(git_path("rr-cache/%s", rr_dir->name));
+
+	if (!dir)
+		return;
+	while ((de = readdir(dir)) != NULL) {
+		int variant;
+
+		if (is_rr_file(de->d_name, "postimage", &variant)) {
+			fit_variant(rr_dir, variant);
+			rr_dir->status[variant] |= RR_HAS_POSTIMAGE;
+		} else if (is_rr_file(de->d_name, "preimage", &variant)) {
+			fit_variant(rr_dir, variant);
+			rr_dir->status[variant] |= RR_HAS_PREIMAGE;
+		}
+	}
+	closedir(dir);
+}
+
+static struct rerere_dir *find_rerere_dir(const char *hex)
+{
+	struct rerere_dir *rr_dir;
+
+	rr_dir = strmap_get(&rerere_dirs, hex);
+	if (!rr_dir) {
+		FLEX_ALLOC_STR(rr_dir, name, hex);
+		rr_dir->status = NULL;
+		rr_dir->status_nr = 0;
+		rr_dir->status_alloc = 0;
+		strmap_put(&rerere_dirs, hex, rr_dir);
+
+		scan_rerere_dir(rr_dir);
+	}
+	return rr_dir;
+}
+
+static int has_rerere_resolution(const struct rerere_id *id)
+{
+	const int both = RR_HAS_POSTIMAGE|RR_HAS_PREIMAGE;
+	int variant = id->variant;
+
+	if (variant < 0)
+		return 0;
+	return ((id->collection->status[variant] & both) == both);
+}
+
+static struct rerere_id *new_rerere_id_hex(char *hex)
+{
+	struct rerere_id *id = xmalloc(sizeof(*id));
+	id->collection = find_rerere_dir(hex);
+	id->variant = -1; /* not known yet */
+	return id;
+}
+
+static struct rerere_id *new_rerere_id(unsigned char *hash)
+{
+	return new_rerere_id_hex(hash_to_hex(hash));
+}
+
+/*
+ * $GIT_DIR/MERGE_RR file is a collection of records, each of which is
+ * "conflict ID", a HT and pathname, terminated with a NUL, and is
+ * used to keep track of the set of paths that "rerere" may need to
+ * work on (i.e. what is left by the previous invocation of "git
+ * rerere" during the current conflict resolution session).
+ */
+static void read_rr(struct repository *r, struct string_list *rr)
+{
+	struct strbuf buf = STRBUF_INIT;
+	FILE *in = fopen_or_warn(git_path_merge_rr(r), "r");
+
+	if (!in)
+		return;
+	while (!strbuf_getwholeline(&buf, in, '\0')) {
+		char *path;
+		unsigned char hash[GIT_MAX_RAWSZ];
+		struct rerere_id *id;
+		int variant;
+		const unsigned hexsz = the_hash_algo->hexsz;
+
+		/* There has to be the hash, tab, path and then NUL */
+		if (buf.len < hexsz + 2 || get_sha1_hex(buf.buf, hash))
+			die(_("corrupt MERGE_RR"));
+
+		if (buf.buf[hexsz] != '.') {
+			variant = 0;
+			path = buf.buf + hexsz;
+		} else {
+			errno = 0;
+			variant = strtol(buf.buf + hexsz + 1, &path, 10);
+			if (errno)
+				die(_("corrupt MERGE_RR"));
+		}
+		if (*(path++) != '\t')
+			die(_("corrupt MERGE_RR"));
+		buf.buf[hexsz] = '\0';
+		id = new_rerere_id_hex(buf.buf);
+		id->variant = variant;
+		string_list_insert(rr, path)->util = id;
+	}
+	strbuf_release(&buf);
+	fclose(in);
+}
+
+static struct lock_file write_lock;
+
+static int write_rr(struct string_list *rr, int out_fd)
+{
+	int i;
+	for (i = 0; i < rr->nr; i++) {
+		struct strbuf buf = STRBUF_INIT;
+		struct rerere_id *id;
+
+		assert(rr->items[i].util != RERERE_RESOLVED);
+
+		id = rr->items[i].util;
+		if (!id)
+			continue;
+		assert(id->variant >= 0);
+		if (0 < id->variant)
+			strbuf_addf(&buf, "%s.%d\t%s%c",
+				    rerere_id_hex(id), id->variant,
+				    rr->items[i].string, 0);
+		else
+			strbuf_addf(&buf, "%s\t%s%c",
+				    rerere_id_hex(id),
+				    rr->items[i].string, 0);
+
+		if (write_in_full(out_fd, buf.buf, buf.len) < 0)
+			die(_("unable to write rerere record"));
+
+		strbuf_release(&buf);
+	}
+	if (commit_lock_file(&write_lock) != 0)
+		die(_("unable to write rerere record"));
+	return 0;
+}
+
+/*
+ * "rerere" interacts with conflicted file contents using this I/O
+ * abstraction.  It reads a conflicted contents from one place via
+ * "getline()" method, and optionally can write it out after
+ * normalizing the conflicted hunks to the "output".  Subclasses of
+ * rerere_io embed this structure at the beginning of their own
+ * rerere_io object.
+ */
+struct rerere_io {
+	int (*getline)(struct strbuf *, struct rerere_io *);
+	FILE *output;
+	int wrerror;
+	/* some more stuff */
+};
+
+static void ferr_write(const void *p, size_t count, FILE *fp, int *err)
+{
+	if (!count || *err)
+		return;
+	if (fwrite(p, count, 1, fp) != 1)
+		*err = errno;
+}
+
+static inline void ferr_puts(const char *s, FILE *fp, int *err)
+{
+	ferr_write(s, strlen(s), fp, err);
+}
+
+static void rerere_io_putstr(const char *str, struct rerere_io *io)
+{
+	if (io->output)
+		ferr_puts(str, io->output, &io->wrerror);
+}
+
+static void rerere_io_putmem(const char *mem, size_t sz, struct rerere_io *io)
+{
+	if (io->output)
+		ferr_write(mem, sz, io->output, &io->wrerror);
+}
+
+/*
+ * Subclass of rerere_io that reads from an on-disk file
+ */
+struct rerere_io_file {
+	struct rerere_io io;
+	FILE *input;
+};
+
+/*
+ * ... and its getline() method implementation
+ */
+static int rerere_file_getline(struct strbuf *sb, struct rerere_io *io_)
+{
+	struct rerere_io_file *io = (struct rerere_io_file *)io_;
+	return strbuf_getwholeline(sb, io->input, '\n');
+}
+
+/*
+ * Require the exact number of conflict marker letters, no more, no
+ * less, followed by SP or any whitespace
+ * (including LF).
+ */
+static int is_cmarker(char *buf, int marker_char, int marker_size)
+{
+	int want_sp;
+
+	/*
+	 * The beginning of our version and the end of their version
+	 * always are labeled like "<<<<< ours" or ">>>>> theirs",
+	 * hence we set want_sp for them.  Note that the version from
+	 * the common ancestor in diff3-style output is not always
+	 * labelled (e.g. "||||| common" is often seen but "|||||"
+	 * alone is also valid), so we do not set want_sp.
+	 */
+	want_sp = (marker_char == '<') || (marker_char == '>');
+
+	while (marker_size--)
+		if (*buf++ != marker_char)
+			return 0;
+	if (want_sp && *buf != ' ')
+		return 0;
+	return isspace(*buf);
+}
+
+static void rerere_strbuf_putconflict(struct strbuf *buf, int ch, size_t size)
+{
+	strbuf_addchars(buf, ch, size);
+	strbuf_addch(buf, '\n');
+}
+
+static int handle_conflict(struct strbuf *out, struct rerere_io *io,
+			   int marker_size, git_hash_ctx *ctx)
+{
+	enum {
+		RR_SIDE_1 = 0, RR_SIDE_2, RR_ORIGINAL
+	} hunk = RR_SIDE_1;
+	struct strbuf one = STRBUF_INIT, two = STRBUF_INIT;
+	struct strbuf buf = STRBUF_INIT, conflict = STRBUF_INIT;
+	int has_conflicts = -1;
+
+	while (!io->getline(&buf, io)) {
+		if (is_cmarker(buf.buf, '<', marker_size)) {
+			if (handle_conflict(&conflict, io, marker_size, NULL) < 0)
+				break;
+			if (hunk == RR_SIDE_1)
+				strbuf_addbuf(&one, &conflict);
+			else
+				strbuf_addbuf(&two, &conflict);
+			strbuf_release(&conflict);
+		} else if (is_cmarker(buf.buf, '|', marker_size)) {
+			if (hunk != RR_SIDE_1)
+				break;
+			hunk = RR_ORIGINAL;
+		} else if (is_cmarker(buf.buf, '=', marker_size)) {
+			if (hunk != RR_SIDE_1 && hunk != RR_ORIGINAL)
+				break;
+			hunk = RR_SIDE_2;
+		} else if (is_cmarker(buf.buf, '>', marker_size)) {
+			if (hunk != RR_SIDE_2)
+				break;
+			if (strbuf_cmp(&one, &two) > 0)
+				strbuf_swap(&one, &two);
+			has_conflicts = 1;
+			rerere_strbuf_putconflict(out, '<', marker_size);
+			strbuf_addbuf(out, &one);
+			rerere_strbuf_putconflict(out, '=', marker_size);
+			strbuf_addbuf(out, &two);
+			rerere_strbuf_putconflict(out, '>', marker_size);
+			if (ctx) {
+				the_hash_algo->update_fn(ctx, one.buf ?
+							 one.buf : "",
+							 one.len + 1);
+				the_hash_algo->update_fn(ctx, two.buf ?
+							 two.buf : "",
+							 two.len + 1);
+			}
+			break;
+		} else if (hunk == RR_SIDE_1)
+			strbuf_addbuf(&one, &buf);
+		else if (hunk == RR_ORIGINAL)
+			; /* discard */
+		else if (hunk == RR_SIDE_2)
+			strbuf_addbuf(&two, &buf);
+	}
+	strbuf_release(&one);
+	strbuf_release(&two);
+	strbuf_release(&buf);
+
+	return has_conflicts;
+}
+
+/*
+ * Read contents a file with conflicts, normalize the conflicts
+ * by (1) discarding the common ancestor version in diff3-style,
+ * (2) reordering our side and their side so that whichever sorts
+ * alphabetically earlier comes before the other one, while
+ * computing the "conflict ID", which is just an SHA-1 hash of
+ * one side of the conflict, NUL, the other side of the conflict,
+ * and NUL concatenated together.
+ *
+ * Return 1 if conflict hunks are found, 0 if there are no conflict
+ * hunks and -1 if an error occurred.
+ */
+static int handle_path(unsigned char *hash, struct rerere_io *io, int marker_size)
+{
+	git_hash_ctx ctx;
+	struct strbuf buf = STRBUF_INIT, out = STRBUF_INIT;
+	int has_conflicts = 0;
+	if (hash)
+		the_hash_algo->init_fn(&ctx);
+
+	while (!io->getline(&buf, io)) {
+		if (is_cmarker(buf.buf, '<', marker_size)) {
+			has_conflicts = handle_conflict(&out, io, marker_size,
+							hash ? &ctx : NULL);
+			if (has_conflicts < 0)
+				break;
+			rerere_io_putmem(out.buf, out.len, io);
+			strbuf_reset(&out);
+		} else
+			rerere_io_putstr(buf.buf, io);
+	}
+	strbuf_release(&buf);
+	strbuf_release(&out);
+
+	if (hash)
+		the_hash_algo->final_fn(hash, &ctx);
+
+	return has_conflicts;
+}
+
+/*
+ * Scan the path for conflicts, do the "handle_path()" thing above, and
+ * return the number of conflict hunks found.
+ */
+static int handle_file(struct index_state *istate,
+		       const char *path, unsigned char *hash, const char *output)
+{
+	int has_conflicts = 0;
+	struct rerere_io_file io;
+	int marker_size = ll_merge_marker_size(istate, path);
+
+	memset(&io, 0, sizeof(io));
+	io.io.getline = rerere_file_getline;
+	io.input = fopen(path, "r");
+	io.io.wrerror = 0;
+	if (!io.input)
+		return error_errno(_("could not open '%s'"), path);
+
+	if (output) {
+		io.io.output = fopen(output, "w");
+		if (!io.io.output) {
+			error_errno(_("could not write '%s'"), output);
+			fclose(io.input);
+			return -1;
+		}
+	}
+
+	has_conflicts = handle_path(hash, (struct rerere_io *)&io, marker_size);
+
+	fclose(io.input);
+	if (io.io.wrerror)
+		error(_("there were errors while writing '%s' (%s)"),
+		      path, strerror(io.io.wrerror));
+	if (io.io.output && fclose(io.io.output))
+		io.io.wrerror = error_errno(_("failed to flush '%s'"), path);
+
+	if (has_conflicts < 0) {
+		if (output)
+			unlink_or_warn(output);
+		return error(_("could not parse conflict hunks in '%s'"), path);
+	}
+	if (io.io.wrerror)
+		return -1;
+	return has_conflicts;
+}
+
+/*
+ * Look at a cache entry at "i" and see if it is not conflicting,
+ * conflicting and we are willing to handle, or conflicting and
+ * we are unable to handle, and return the determination in *type.
+ * Return the cache index to be looked at next, by skipping the
+ * stages we have already looked at in this invocation of this
+ * function.
+ */
+static int check_one_conflict(struct index_state *istate, int i, int *type)
+{
+	const struct cache_entry *e = istate->cache[i];
+
+	if (!ce_stage(e)) {
+		*type = RESOLVED;
+		return i + 1;
+	}
+
+	*type = PUNTED;
+	while (i < istate->cache_nr && ce_stage(istate->cache[i]) == 1)
+		i++;
+
+	/* Only handle regular files with both stages #2 and #3 */
+	if (i + 1 < istate->cache_nr) {
+		const struct cache_entry *e2 = istate->cache[i];
+		const struct cache_entry *e3 = istate->cache[i + 1];
+		if (ce_stage(e2) == 2 &&
+		    ce_stage(e3) == 3 &&
+		    ce_same_name(e, e3) &&
+		    S_ISREG(e2->ce_mode) &&
+		    S_ISREG(e3->ce_mode))
+			*type = THREE_STAGED;
+	}
+
+	/* Skip the entries with the same name */
+	while (i < istate->cache_nr && ce_same_name(e, istate->cache[i]))
+		i++;
+	return i;
+}
+
+/*
+ * Scan the index and find paths that have conflicts that rerere can
+ * handle, i.e. the ones that has both stages #2 and #3.
+ *
+ * NEEDSWORK: we do not record or replay a previous "resolve by
+ * deletion" for a delete-modify conflict, as that is inherently risky
+ * without knowing what modification is being discarded.  The only
+ * safe case, i.e. both side doing the deletion and modification that
+ * are identical to the previous round, might want to be handled,
+ * though.
+ */
+static int find_conflict(struct repository *r, struct string_list *conflict)
+{
+	int i;
+
+	if (repo_read_index(r) < 0)
+		return error(_("index file corrupt"));
+
+	for (i = 0; i < r->index->cache_nr;) {
+		int conflict_type;
+		const struct cache_entry *e = r->index->cache[i];
+		i = check_one_conflict(r->index, i, &conflict_type);
+		if (conflict_type == THREE_STAGED)
+			string_list_insert(conflict, (const char *)e->name);
+	}
+	return 0;
+}
+
+/*
+ * The merge_rr list is meant to hold outstanding conflicted paths
+ * that rerere could handle.  Abuse the list by adding other types of
+ * entries to allow the caller to show "rerere remaining".
+ *
+ * - Conflicted paths that rerere does not handle are added
+ * - Conflicted paths that have been resolved are marked as such
+ *   by storing RERERE_RESOLVED to .util field (where conflict ID
+ *   is expected to be stored).
+ *
+ * Do *not* write MERGE_RR file out after calling this function.
+ *
+ * NEEDSWORK: we may want to fix the caller that implements "rerere
+ * remaining" to do this without abusing merge_rr.
+ */
+int rerere_remaining(struct repository *r, struct string_list *merge_rr)
+{
+	int i;
+
+	if (setup_rerere(r, merge_rr, RERERE_READONLY))
+		return 0;
+	if (repo_read_index(r) < 0)
+		return error(_("index file corrupt"));
+
+	for (i = 0; i < r->index->cache_nr;) {
+		int conflict_type;
+		const struct cache_entry *e = r->index->cache[i];
+		i = check_one_conflict(r->index, i, &conflict_type);
+		if (conflict_type == PUNTED)
+			string_list_insert(merge_rr, (const char *)e->name);
+		else if (conflict_type == RESOLVED) {
+			struct string_list_item *it;
+			it = string_list_lookup(merge_rr, (const char *)e->name);
+			if (it) {
+				free_rerere_id(it);
+				it->util = RERERE_RESOLVED;
+			}
+		}
+	}
+	return 0;
+}
+
+/*
+ * Try using the given conflict resolution "ID" to see
+ * if that recorded conflict resolves cleanly what we
+ * got in the "cur".
+ */
+static int try_merge(struct index_state *istate,
+		     const struct rerere_id *id, const char *path,
+		     mmfile_t *cur, mmbuffer_t *result)
+{
+	enum ll_merge_result ret;
+	mmfile_t base = {NULL, 0}, other = {NULL, 0};
+
+	if (read_mmfile(&base, rerere_path(id, "preimage")) ||
+	    read_mmfile(&other, rerere_path(id, "postimage"))) {
+		ret = LL_MERGE_CONFLICT;
+	} else {
+		/*
+		 * A three-way merge. Note that this honors user-customizable
+		 * low-level merge driver settings.
+		 */
+		ret = ll_merge(result, path, &base, NULL, cur, "", &other, "",
+			       istate, NULL);
+	}
+
+	free(base.ptr);
+	free(other.ptr);
+
+	return ret;
+}
+
+/*
+ * Find the conflict identified by "id"; the change between its
+ * "preimage" (i.e. a previous contents with conflict markers) and its
+ * "postimage" (i.e. the corresponding contents with conflicts
+ * resolved) may apply cleanly to the contents stored in "path", i.e.
+ * the conflict this time around.
+ *
+ * Returns 0 for successful replay of recorded resolution, or non-zero
+ * for failure.
+ */
+static int merge(struct index_state *istate, const struct rerere_id *id, const char *path)
+{
+	FILE *f;
+	int ret;
+	mmfile_t cur = {NULL, 0};
+	mmbuffer_t result = {NULL, 0};
+
+	/*
+	 * Normalize the conflicts in path and write it out to
+	 * "thisimage" temporary file.
+	 */
+	if ((handle_file(istate, path, NULL, rerere_path(id, "thisimage")) < 0) ||
+	    read_mmfile(&cur, rerere_path(id, "thisimage"))) {
+		ret = 1;
+		goto out;
+	}
+
+	ret = try_merge(istate, id, path, &cur, &result);
+	if (ret)
+		goto out;
+
+	/*
+	 * A successful replay of recorded resolution.
+	 * Mark that "postimage" was used to help gc.
+	 */
+	if (utime(rerere_path(id, "postimage"), NULL) < 0)
+		warning_errno(_("failed utime() on '%s'"),
+			      rerere_path(id, "postimage"));
+
+	/* Update "path" with the resolution */
+	f = fopen(path, "w");
+	if (!f)
+		return error_errno(_("could not open '%s'"), path);
+	if (fwrite(result.ptr, result.size, 1, f) != 1)
+		error_errno(_("could not write '%s'"), path);
+	if (fclose(f))
+		return error_errno(_("writing '%s' failed"), path);
+
+out:
+	free(cur.ptr);
+	free(result.ptr);
+
+	return ret;
+}
+
+static void update_paths(struct repository *r, struct string_list *update)
+{
+	struct lock_file index_lock = LOCK_INIT;
+	int i;
+
+	repo_hold_locked_index(r, &index_lock, LOCK_DIE_ON_ERROR);
+
+	for (i = 0; i < update->nr; i++) {
+		struct string_list_item *item = &update->items[i];
+		if (add_file_to_index(r->index, item->string, 0))
+			exit(128);
+		fprintf_ln(stderr, _("Staged '%s' using previous resolution."),
+			item->string);
+	}
+
+	if (write_locked_index(r->index, &index_lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		die(_("unable to write new index file"));
+}
+
+static void remove_variant(struct rerere_id *id)
+{
+	unlink_or_warn(rerere_path(id, "postimage"));
+	unlink_or_warn(rerere_path(id, "preimage"));
+	id->collection->status[id->variant] = 0;
+}
+
+/*
+ * The path indicated by rr_item may still have conflict for which we
+ * have a recorded resolution, in which case replay it and optionally
+ * update it.  Or it may have been resolved by the user and we may
+ * only have the preimage for that conflict, in which case the result
+ * needs to be recorded as a resolution in a postimage file.
+ */
+static void do_rerere_one_path(struct index_state *istate,
+			       struct string_list_item *rr_item,
+			       struct string_list *update)
+{
+	const char *path = rr_item->string;
+	struct rerere_id *id = rr_item->util;
+	struct rerere_dir *rr_dir = id->collection;
+	int variant;
+
+	variant = id->variant;
+
+	/* Has the user resolved it already? */
+	if (variant >= 0) {
+		if (!handle_file(istate, path, NULL, NULL)) {
+			copy_file(rerere_path(id, "postimage"), path, 0666);
+			id->collection->status[variant] |= RR_HAS_POSTIMAGE;
+			fprintf_ln(stderr, _("Recorded resolution for '%s'."), path);
+			free_rerere_id(rr_item);
+			rr_item->util = NULL;
+			return;
+		}
+		/*
+		 * There may be other variants that can cleanly
+		 * replay.  Try them and update the variant number for
+		 * this one.
+		 */
+	}
+
+	/* Does any existing resolution apply cleanly? */
+	for (variant = 0; variant < rr_dir->status_nr; variant++) {
+		const int both = RR_HAS_PREIMAGE | RR_HAS_POSTIMAGE;
+		struct rerere_id vid = *id;
+
+		if ((rr_dir->status[variant] & both) != both)
+			continue;
+
+		vid.variant = variant;
+		if (merge(istate, &vid, path))
+			continue; /* failed to replay */
+
+		/*
+		 * If there already is a different variant that applies
+		 * cleanly, there is no point maintaining our own variant.
+		 */
+		if (0 <= id->variant && id->variant != variant)
+			remove_variant(id);
+
+		if (rerere_autoupdate)
+			string_list_insert(update, path);
+		else
+			fprintf_ln(stderr,
+				   _("Resolved '%s' using previous resolution."),
+				   path);
+		free_rerere_id(rr_item);
+		rr_item->util = NULL;
+		return;
+	}
+
+	/* None of the existing one applies; we need a new variant */
+	assign_variant(id);
+
+	variant = id->variant;
+	handle_file(istate, path, NULL, rerere_path(id, "preimage"));
+	if (id->collection->status[variant] & RR_HAS_POSTIMAGE) {
+		const char *path = rerere_path(id, "postimage");
+		if (unlink(path))
+			die_errno(_("cannot unlink stray '%s'"), path);
+		id->collection->status[variant] &= ~RR_HAS_POSTIMAGE;
+	}
+	id->collection->status[variant] |= RR_HAS_PREIMAGE;
+	fprintf_ln(stderr, _("Recorded preimage for '%s'"), path);
+}
+
+static int do_plain_rerere(struct repository *r,
+			   struct string_list *rr, int fd)
+{
+	struct string_list conflict = STRING_LIST_INIT_DUP;
+	struct string_list update = STRING_LIST_INIT_DUP;
+	int i;
+
+	find_conflict(r, &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++) {
+		struct rerere_id *id;
+		unsigned char hash[GIT_MAX_RAWSZ];
+		const char *path = conflict.items[i].string;
+		int ret;
+
+		/*
+		 * Ask handle_file() to scan and assign a
+		 * conflict ID.  No need to write anything out
+		 * yet.
+		 */
+		ret = handle_file(r->index, path, hash, NULL);
+		if (ret != 0 && string_list_has_string(rr, path)) {
+			remove_variant(string_list_lookup(rr, path)->util);
+			string_list_remove(rr, path, 1);
+		}
+		if (ret < 1)
+			continue;
+
+		id = new_rerere_id(hash);
+		string_list_insert(rr, path)->util = id;
+
+		/* Ensure that the directory exists. */
+		mkdir_in_gitdir(rerere_path(id, NULL));
+	}
+
+	for (i = 0; i < rr->nr; i++)
+		do_rerere_one_path(r->index, &rr->items[i], &update);
+
+	if (update.nr)
+		update_paths(r, &update);
+
+	return write_rr(rr, fd);
+}
+
+static void git_rerere_config(void)
+{
+	git_config_get_bool("rerere.enabled", &rerere_enabled);
+	git_config_get_bool("rerere.autoupdate", &rerere_autoupdate);
+	git_config(git_default_config, NULL);
+}
+
+static GIT_PATH_FUNC(git_path_rr_cache, "rr-cache")
+
+static int is_rerere_enabled(void)
+{
+	int rr_cache_exists;
+
+	if (!rerere_enabled)
+		return 0;
+
+	rr_cache_exists = is_directory(git_path_rr_cache());
+	if (rerere_enabled < 0)
+		return rr_cache_exists;
+
+	if (!rr_cache_exists && mkdir_in_gitdir(git_path_rr_cache()))
+		die(_("could not create directory '%s'"), git_path_rr_cache());
+	return 1;
+}
+
+int setup_rerere(struct repository *r, struct string_list *merge_rr, int flags)
+{
+	int fd;
+
+	git_rerere_config();
+	if (!is_rerere_enabled())
+		return -1;
+
+	if (flags & (RERERE_AUTOUPDATE|RERERE_NOAUTOUPDATE))
+		rerere_autoupdate = !!(flags & RERERE_AUTOUPDATE);
+	if (flags & RERERE_READONLY)
+		fd = 0;
+	else
+		fd = hold_lock_file_for_update(&write_lock,
+					       git_path_merge_rr(r),
+					       LOCK_DIE_ON_ERROR);
+	read_rr(r, merge_rr);
+	return fd;
+}
+
+/*
+ * The main entry point that is called internally from codepaths that
+ * perform mergy operations, possibly leaving conflicted index entries
+ * and working tree files.
+ */
+int repo_rerere(struct repository *r, int flags)
+{
+	struct string_list merge_rr = STRING_LIST_INIT_DUP;
+	int fd, status;
+
+	fd = setup_rerere(r, &merge_rr, flags);
+	if (fd < 0)
+		return 0;
+	status = do_plain_rerere(r, &merge_rr, fd);
+	free_rerere_dirs();
+	return status;
+}
+
+/*
+ * Subclass of rerere_io that reads from an in-core buffer that is a
+ * strbuf
+ */
+struct rerere_io_mem {
+	struct rerere_io io;
+	struct strbuf input;
+};
+
+/*
+ * ... and its getline() method implementation
+ */
+static int rerere_mem_getline(struct strbuf *sb, struct rerere_io *io_)
+{
+	struct rerere_io_mem *io = (struct rerere_io_mem *)io_;
+	char *ep;
+	size_t len;
+
+	strbuf_release(sb);
+	if (!io->input.len)
+		return -1;
+	ep = memchr(io->input.buf, '\n', io->input.len);
+	if (!ep)
+		ep = io->input.buf + io->input.len;
+	else if (*ep == '\n')
+		ep++;
+	len = ep - io->input.buf;
+	strbuf_add(sb, io->input.buf, len);
+	strbuf_remove(&io->input, 0, len);
+	return 0;
+}
+
+static int handle_cache(struct index_state *istate,
+			const char *path, unsigned char *hash, const char *output)
+{
+	mmfile_t mmfile[3] = {{NULL}};
+	mmbuffer_t result = {NULL, 0};
+	const struct cache_entry *ce;
+	int pos, len, i, has_conflicts;
+	struct rerere_io_mem io;
+	int marker_size = ll_merge_marker_size(istate, path);
+
+	/*
+	 * Reproduce the conflicted merge in-core
+	 */
+	len = strlen(path);
+	pos = index_name_pos(istate, path, len);
+	if (0 <= pos)
+		return -1;
+	pos = -pos - 1;
+
+	while (pos < istate->cache_nr) {
+		enum object_type type;
+		unsigned long size;
+
+		ce = istate->cache[pos++];
+		if (ce_namelen(ce) != len || memcmp(ce->name, path, len))
+			break;
+		i = ce_stage(ce) - 1;
+		if (!mmfile[i].ptr) {
+			mmfile[i].ptr = read_object_file(&ce->oid, &type,
+							 &size);
+			mmfile[i].size = size;
+		}
+	}
+	for (i = 0; i < 3; i++)
+		if (!mmfile[i].ptr && !mmfile[i].size)
+			mmfile[i].ptr = xstrdup("");
+
+	/*
+	 * NEEDSWORK: handle conflicts from merges with
+	 * merge.renormalize set, too?
+	 */
+	ll_merge(&result, path, &mmfile[0], NULL,
+		 &mmfile[1], "ours",
+		 &mmfile[2], "theirs",
+		 istate, NULL);
+	for (i = 0; i < 3; i++)
+		free(mmfile[i].ptr);
+
+	memset(&io, 0, sizeof(io));
+	io.io.getline = rerere_mem_getline;
+	if (output)
+		io.io.output = fopen(output, "w");
+	else
+		io.io.output = NULL;
+	strbuf_init(&io.input, 0);
+	strbuf_attach(&io.input, result.ptr, result.size, result.size);
+
+	/*
+	 * Grab the conflict ID and optionally write the original
+	 * contents with conflict markers out.
+	 */
+	has_conflicts = handle_path(hash, (struct rerere_io *)&io, marker_size);
+	strbuf_release(&io.input);
+	if (io.io.output)
+		fclose(io.io.output);
+	return has_conflicts;
+}
+
+static int rerere_forget_one_path(struct index_state *istate,
+				  const char *path,
+				  struct string_list *rr)
+{
+	const char *filename;
+	struct rerere_id *id;
+	unsigned char hash[GIT_MAX_RAWSZ];
+	int ret;
+	struct string_list_item *item;
+
+	/*
+	 * Recreate the original conflict from the stages in the
+	 * index and compute the conflict ID
+	 */
+	ret = handle_cache(istate, path, hash, NULL);
+	if (ret < 1)
+		return error(_("could not parse conflict hunks in '%s'"), path);
+
+	/* Nuke the recorded resolution for the conflict */
+	id = new_rerere_id(hash);
+
+	for (id->variant = 0;
+	     id->variant < id->collection->status_nr;
+	     id->variant++) {
+		mmfile_t cur = { NULL, 0 };
+		mmbuffer_t result = {NULL, 0};
+		int cleanly_resolved;
+
+		if (!has_rerere_resolution(id))
+			continue;
+
+		handle_cache(istate, path, hash, rerere_path(id, "thisimage"));
+		if (read_mmfile(&cur, rerere_path(id, "thisimage"))) {
+			free(cur.ptr);
+			error(_("failed to update conflicted state in '%s'"), path);
+			goto fail_exit;
+		}
+		cleanly_resolved = !try_merge(istate, id, path, &cur, &result);
+		free(result.ptr);
+		free(cur.ptr);
+		if (cleanly_resolved)
+			break;
+	}
+
+	if (id->collection->status_nr <= id->variant) {
+		error(_("no remembered resolution for '%s'"), path);
+		goto fail_exit;
+	}
+
+	filename = rerere_path(id, "postimage");
+	if (unlink(filename)) {
+		if (errno == ENOENT)
+			error(_("no remembered resolution for '%s'"), path);
+		else
+			error_errno(_("cannot unlink '%s'"), filename);
+		goto fail_exit;
+	}
+
+	/*
+	 * Update the preimage so that the user can resolve the
+	 * conflict in the working tree, run us again to record
+	 * the postimage.
+	 */
+	handle_cache(istate, path, hash, rerere_path(id, "preimage"));
+	fprintf_ln(stderr, _("Updated preimage for '%s'"), path);
+
+	/*
+	 * And remember that we can record resolution for this
+	 * conflict when the user is done.
+	 */
+	item = string_list_insert(rr, path);
+	free_rerere_id(item);
+	item->util = id;
+	fprintf(stderr, _("Forgot resolution for '%s'\n"), path);
+	return 0;
+
+fail_exit:
+	free(id);
+	return -1;
+}
+
+int rerere_forget(struct repository *r, struct pathspec *pathspec)
+{
+	int i, fd;
+	struct string_list conflict = STRING_LIST_INIT_DUP;
+	struct string_list merge_rr = STRING_LIST_INIT_DUP;
+
+	if (repo_read_index(r) < 0)
+		return error(_("index file corrupt"));
+
+	fd = setup_rerere(r, &merge_rr, RERERE_NOAUTOUPDATE);
+	if (fd < 0)
+		return 0;
+
+	/*
+	 * The paths may have been resolved (incorrectly);
+	 * recover the original conflicted state and then
+	 * find the conflicted paths.
+	 */
+	unmerge_index(r->index, pathspec);
+	find_conflict(r, &conflict);
+	for (i = 0; i < conflict.nr; i++) {
+		struct string_list_item *it = &conflict.items[i];
+		if (!match_pathspec(r->index, pathspec, it->string,
+				    strlen(it->string), 0, NULL, 0))
+			continue;
+		rerere_forget_one_path(r->index, it->string, &merge_rr);
+	}
+	return write_rr(&merge_rr, fd);
+}
+
+/*
+ * Garbage collection support
+ */
+
+static timestamp_t rerere_created_at(struct rerere_id *id)
+{
+	struct stat st;
+
+	return stat(rerere_path(id, "preimage"), &st) ? (time_t) 0 : st.st_mtime;
+}
+
+static timestamp_t rerere_last_used_at(struct rerere_id *id)
+{
+	struct stat st;
+
+	return stat(rerere_path(id, "postimage"), &st) ? (time_t) 0 : st.st_mtime;
+}
+
+/*
+ * Remove the recorded resolution for a given conflict ID
+ */
+static void unlink_rr_item(struct rerere_id *id)
+{
+	unlink_or_warn(rerere_path(id, "thisimage"));
+	remove_variant(id);
+	id->collection->status[id->variant] = 0;
+}
+
+static void prune_one(struct rerere_id *id,
+		      timestamp_t cutoff_resolve, timestamp_t cutoff_noresolve)
+{
+	timestamp_t then;
+	timestamp_t cutoff;
+
+	then = rerere_last_used_at(id);
+	if (then)
+		cutoff = cutoff_resolve;
+	else {
+		then = rerere_created_at(id);
+		if (!then)
+			return;
+		cutoff = cutoff_noresolve;
+	}
+	if (then < cutoff)
+		unlink_rr_item(id);
+}
+
+/* Does the basename in "path" look plausibly like an rr-cache entry? */
+static int is_rr_cache_dirname(const char *path)
+{
+	struct object_id oid;
+	const char *end;
+	return !parse_oid_hex(path, &oid, &end) && !*end;
+}
+
+void rerere_gc(struct repository *r, struct string_list *rr)
+{
+	struct string_list to_remove = STRING_LIST_INIT_DUP;
+	DIR *dir;
+	struct dirent *e;
+	int i;
+	timestamp_t now = time(NULL);
+	timestamp_t cutoff_noresolve = now - 15 * 86400;
+	timestamp_t cutoff_resolve = now - 60 * 86400;
+
+	if (setup_rerere(r, rr, 0) < 0)
+		return;
+
+	git_config_get_expiry_in_days("gc.rerereresolved", &cutoff_resolve, now);
+	git_config_get_expiry_in_days("gc.rerereunresolved", &cutoff_noresolve, now);
+	git_config(git_default_config, NULL);
+	dir = opendir(git_path("rr-cache"));
+	if (!dir)
+		die_errno(_("unable to open rr-cache directory"));
+	/* Collect stale conflict IDs ... */
+	while ((e = readdir_skip_dot_and_dotdot(dir))) {
+		struct rerere_dir *rr_dir;
+		struct rerere_id id;
+		int now_empty;
+
+		if (!is_rr_cache_dirname(e->d_name))
+			continue; /* or should we remove e->d_name? */
+
+		rr_dir = find_rerere_dir(e->d_name);
+
+		now_empty = 1;
+		for (id.variant = 0, id.collection = rr_dir;
+		     id.variant < id.collection->status_nr;
+		     id.variant++) {
+			prune_one(&id, cutoff_resolve, cutoff_noresolve);
+			if (id.collection->status[id.variant])
+				now_empty = 0;
+		}
+		if (now_empty)
+			string_list_append(&to_remove, e->d_name);
+	}
+	closedir(dir);
+
+	/* ... and then remove the empty directories */
+	for (i = 0; i < to_remove.nr; i++)
+		rmdir(git_path("rr-cache/%s", to_remove.items[i].string));
+	string_list_clear(&to_remove, 0);
+	rollback_lock_file(&write_lock);
+}
+
+/*
+ * During a conflict resolution, after "rerere" recorded the
+ * preimages, abandon them if the user did not resolve them or
+ * record their resolutions.  And drop $GIT_DIR/MERGE_RR.
+ *
+ * NEEDSWORK: shouldn't we be calling this from "reset --hard"?
+ */
+void rerere_clear(struct repository *r, struct string_list *merge_rr)
+{
+	int i;
+
+	if (setup_rerere(r, merge_rr, 0) < 0)
+		return;
+
+	for (i = 0; i < merge_rr->nr; i++) {
+		struct rerere_id *id = merge_rr->items[i].util;
+		if (!has_rerere_resolution(id)) {
+			unlink_rr_item(id);
+			rmdir(rerere_path(id, NULL));
+		}
+	}
+	unlink_or_warn(git_path_merge_rr(r));
+	rollback_lock_file(&write_lock);
+}