p5551: add a script to test fetch pack-dir rescans
[gitweb.git] / rerere.c
index 587b7e2717b14748b92a5960f79947b5fba088f0..51376cf6da3b8ab8f8e0c4f20c307fef9dec8392 100644 (file)
--- a/rerere.c
+++ b/rerere.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "config.h"
 #include "lockfile.h"
 #include "string-list.h"
 #include "rerere.h"
@@ -8,6 +9,7 @@
 #include "ll-merge.h"
 #include "attr.h"
 #include "pathspec.h"
+#include "sha1-lookup.h"
 
 #define RESOLVED 0
 #define PUNTED 1
@@ -20,6 +22,28 @@ static int rerere_enabled = -1;
 /* automatically update cleanly resolved paths to the index */
 static int rerere_autoupdate;
 
+static int rerere_dir_nr;
+static int rerere_dir_alloc;
+
+#define RR_HAS_POSTIMAGE 1
+#define RR_HAS_PREIMAGE 2
+static struct rerere_dir {
+       unsigned char sha1[20];
+       int status_alloc, status_nr;
+       unsigned char *status;
+} **rerere_dir;
+
+static void free_rerere_dirs(void)
+{
+       int i;
+       for (i = 0; i < rerere_dir_nr; i++) {
+               free(rerere_dir[i]->status);
+               free(rerere_dir[i]);
+       }
+       FREE_AND_NULL(rerere_dir);
+       rerere_dir_nr = rerere_dir_alloc = 0;
+}
+
 static void free_rerere_id(struct string_list_item *item)
 {
        free(item->util);
@@ -27,7 +51,33 @@ static void free_rerere_id(struct string_list_item *item)
 
 static const char *rerere_id_hex(const struct rerere_id *id)
 {
-       return id->hex;
+       return sha1_to_hex(id->collection->sha1);
+}
+
+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)
@@ -35,20 +85,103 @@ const char *rerere_path(const struct rerere_id *id, const char *file)
        if (!file)
                return git_path("rr-cache/%s", rerere_id_hex(id));
 
-       return git_path("rr-cache/%s/%s", rerere_id_hex(id), file);
+       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", sha1_to_hex(rr_dir->sha1)));
+
+       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 const unsigned char *rerere_dir_sha1(size_t i, void *table)
+{
+       struct rerere_dir **rr_dir = table;
+       return rr_dir[i]->sha1;
+}
+
+static struct rerere_dir *find_rerere_dir(const char *hex)
+{
+       unsigned char sha1[20];
+       struct rerere_dir *rr_dir;
+       int pos;
+
+       if (get_sha1_hex(hex, sha1))
+               return NULL; /* BUG */
+       pos = sha1_pos(sha1, rerere_dir, rerere_dir_nr, rerere_dir_sha1);
+       if (pos < 0) {
+               rr_dir = xmalloc(sizeof(*rr_dir));
+               hashcpy(rr_dir->sha1, sha1);
+               rr_dir->status = NULL;
+               rr_dir->status_nr = 0;
+               rr_dir->status_alloc = 0;
+               pos = -1 - pos;
+
+               /* Make sure the array is big enough ... */
+               ALLOC_GROW(rerere_dir, rerere_dir_nr + 1, rerere_dir_alloc);
+               /* ... and add it in. */
+               rerere_dir_nr++;
+               memmove(rerere_dir + pos + 1, rerere_dir + pos,
+                       (rerere_dir_nr - pos - 1) * sizeof(*rerere_dir));
+               rerere_dir[pos] = rr_dir;
+               scan_rerere_dir(rr_dir);
+       }
+       return rerere_dir[pos];
 }
 
 static int has_rerere_resolution(const struct rerere_id *id)
 {
-       struct stat st;
+       const int both = RR_HAS_POSTIMAGE|RR_HAS_PREIMAGE;
+       int variant = id->variant;
 
-       return !stat(rerere_path(id, "postimage"), &st);
+       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));
-       xsnprintf(id->hex, sizeof(id->hex), "%s", hex);
+       id->collection = find_rerere_dir(hex);
+       id->variant = -1; /* not known yet */
        return id;
 }
 
@@ -67,7 +200,7 @@ static struct rerere_id *new_rerere_id(unsigned char *sha1)
 static void read_rr(struct string_list *rr)
 {
        struct strbuf buf = STRBUF_INIT;
-       FILE *in = fopen(git_path_merge_rr(), "r");
+       FILE *in = fopen_or_warn(git_path_merge_rr(), "r");
 
        if (!in)
                return;
@@ -75,16 +208,26 @@ static void read_rr(struct string_list *rr)
                char *path;
                unsigned char sha1[20];
                struct rerere_id *id;
+               int variant;
 
                /* There has to be the hash, tab, path and then NUL */
                if (buf.len < 42 || get_sha1_hex(buf.buf, sha1))
                        die("corrupt MERGE_RR");
 
-               if (buf.buf[40] != '\t')
+               if (buf.buf[40] != '.') {
+                       variant = 0;
+                       path = buf.buf + 40;
+               } else {
+                       errno = 0;
+                       variant = strtol(buf.buf + 41, &path, 10);
+                       if (errno)
+                               die("corrupt MERGE_RR");
+               }
+               if (*(path++) != '\t')
                        die("corrupt MERGE_RR");
                buf.buf[40] = '\0';
-               path = buf.buf + 41;
                id = new_rerere_id_hex(buf.buf);
+               id->variant = variant;
                string_list_insert(rr, path)->util = id;
        }
        strbuf_release(&buf);
@@ -105,10 +248,17 @@ static int write_rr(struct string_list *rr, int out_fd)
                id = rr->items[i].util;
                if (!id)
                        continue;
-               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) != buf.len)
+               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);
@@ -334,13 +484,14 @@ static int handle_file(const char *path, unsigned char *sha1, const char *output
        io.input = fopen(path, "r");
        io.io.wrerror = 0;
        if (!io.input)
-               return error("Could not open %s", path);
+               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 error("Could not write %s", output);
+                       return -1;
                }
        }
 
@@ -351,8 +502,7 @@ static int handle_file(const char *path, unsigned char *sha1, const char *output
                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("Failed to flush %s: %s",
-                                     path, strerror(errno));
+               io.io.wrerror = error_errno("Failed to flush %s", path);
 
        if (hunk_no < 0) {
                if (output)
@@ -364,103 +514,6 @@ static int handle_file(const char *path, unsigned char *sha1, const char *output
        return hunk_no;
 }
 
-/*
- * 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(const char *path, unsigned char *sha1, const char *output)
-{
-       mmfile_t mmfile[3] = {{NULL}};
-       mmbuffer_t result = {NULL, 0};
-       const struct cache_entry *ce;
-       int pos, len, i, hunk_no;
-       struct rerere_io_mem io;
-       int marker_size = ll_merge_marker_size(path);
-
-       /*
-        * Reproduce the conflicted merge in-core
-        */
-       len = strlen(path);
-       pos = cache_name_pos(path, len);
-       if (0 <= pos)
-               return -1;
-       pos = -pos - 1;
-
-       while (pos < active_nr) {
-               enum object_type type;
-               unsigned long size;
-
-               ce = active_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_sha1_file(ce->sha1, &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", 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.
-        */
-       hunk_no = handle_path(sha1, (struct rerere_io *)&io, marker_size);
-       strbuf_release(&io.input);
-       if (io.io.output)
-               fclose(io.io.output);
-       return hunk_no;
-}
-
 /*
  * Look at a cache entry at "i" and see if it is not conflicting,
  * conflicting and we are willing to handle, or conflicting and
@@ -568,6 +621,33 @@ int rerere_remaining(struct string_list *merge_rr)
        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(const struct rerere_id *id, const char *path,
+                    mmfile_t *cur, mmbuffer_t *result)
+{
+       int 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 = 1;
+       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, "", 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
@@ -582,30 +662,20 @@ static int merge(const struct rerere_id *id, const char *path)
 {
        FILE *f;
        int ret;
-       mmfile_t cur = {NULL, 0}, base = {NULL, 0}, other = {NULL, 0};
+       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(path, NULL, rerere_path(id, "thisimage")) < 0) {
-               ret = 1;
-               goto out;
-       }
-
-       if (read_mmfile(&cur, rerere_path(id, "thisimage")) ||
-           read_mmfile(&base, rerere_path(id, "preimage")) ||
-           read_mmfile(&other, rerere_path(id, "postimage"))) {
+       if ((handle_file(path, NULL, rerere_path(id, "thisimage")) < 0) ||
+           read_mmfile(&cur, rerere_path(id, "thisimage"))) {
                ret = 1;
                goto out;
        }
 
-       /*
-        * A three-way merge. Note that this honors user-customizable
-        * low-level merge driver settings.
-        */
-       ret = ll_merge(&result, path, &base, NULL, &cur, "", &other, "", NULL);
+       ret = try_merge(id, path, &cur, &result);
        if (ret)
                goto out;
 
@@ -614,25 +684,20 @@ static int merge(const struct rerere_id *id, const char *path)
         * Mark that "postimage" was used to help gc.
         */
        if (utime(rerere_path(id, "postimage"), NULL) < 0)
-               warning("failed utime() on %s: %s",
-                       rerere_path(id, "postimage"),
-                       strerror(errno));
+               warning_errno("failed utime() on %s",
+                             rerere_path(id, "postimage"));
 
        /* Update "path" with the resolution */
        f = fopen(path, "w");
        if (!f)
-               return error("Could not open %s: %s", path,
-                            strerror(errno));
+               return error_errno("Could not open %s", path);
        if (fwrite(result.ptr, result.size, 1, f) != 1)
-               error("Could not write %s: %s", path, strerror(errno));
+               error_errno("Could not write %s", path);
        if (fclose(f))
-               return error("Writing %s failed: %s", path,
-                            strerror(errno));
+               return error_errno("Writing %s failed", path);
 
 out:
        free(cur.ptr);
-       free(base.ptr);
-       free(other.ptr);
        free(result.ptr);
 
        return ret;
@@ -644,7 +709,7 @@ static void update_paths(struct string_list *update)
 {
        int i;
 
-       hold_locked_index(&index_lock, 1);
+       hold_locked_index(&index_lock, LOCK_DIE_ON_ERROR);
 
        for (i = 0; i < update->nr; i++) {
                struct string_list_item *item = &update->items[i];
@@ -661,6 +726,13 @@ static void update_paths(struct string_list *update)
                rollback_lock_file(&index_lock);
 }
 
+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
@@ -672,12 +744,47 @@ static void do_rerere_one_path(struct string_list_item *rr_item,
                               struct string_list *update)
 {
        const char *path = rr_item->string;
-       const struct rerere_id *id = rr_item->util;
+       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(path, NULL, NULL)) {
+                       copy_file(rerere_path(id, "postimage"), path, 0666);
+                       id->collection->status[variant] |= RR_HAS_POSTIMAGE;
+                       fprintf(stderr, "Recorded resolution for '%s'.\n", 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(&vid, path))
+                       continue; /* failed to replay */
 
-       /* Is there a recorded resolution we could attempt to apply? */
-       if (has_rerere_resolution(id)) {
-               if (merge(id, path))
-                       return; /* 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);
@@ -685,15 +792,24 @@ static void do_rerere_one_path(struct string_list_item *rr_item,
                        fprintf(stderr,
                                "Resolved '%s' using previous resolution.\n",
                                path);
-       } else if (!handle_file(path, NULL, NULL)) {
-               /* The user has resolved it. */
-               copy_file(rerere_path(id, "postimage"), path, 0666);
-               fprintf(stderr, "Recorded resolution for '%s'.\n", path);
-       } else {
+               free_rerere_id(rr_item);
+               rr_item->util = NULL;
                return;
        }
-       free_rerere_id(rr_item);
-       rr_item->util = NULL;
+
+       /* None of the existing one applies; we need a new variant */
+       assign_variant(id);
+
+       variant = id->variant;
+       handle_file(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(stderr, "Recorded preimage for '%s'\n", path);
 }
 
 static int do_plain_rerere(struct string_list *rr, int fd)
@@ -731,24 +847,8 @@ static int do_plain_rerere(struct string_list *rr, int fd)
                id = new_rerere_id(sha1);
                string_list_insert(rr, path)->util = id;
 
-               /*
-                * If the directory does not exist, create
-                * it.  mkdir_in_gitdir() will fail with
-                * EEXIST if there already is one.
-                *
-                * NEEDSWORK: make sure "gc" does not remove
-                * preimage without removing the directory.
-                */
-               if (mkdir_in_gitdir(rerere_path(id, NULL)))
-                       continue;
-
-               /*
-                * We are the first to encounter this
-                * conflict.  Ask handle_file() to write the
-                * normalized contents to the "preimage" file.
-                */
-               handle_file(path, NULL, rerere_path(id, "preimage"));
-               fprintf(stderr, "Recorded preimage for '%s'\n", path);
+               /* Ensure that the directory exists. */
+               mkdir_in_gitdir(rerere_path(id, NULL));
        }
 
        for (i = 0; i < rr->nr; i++)
@@ -812,12 +912,112 @@ int setup_rerere(struct string_list *merge_rr, int flags)
 int rerere(int flags)
 {
        struct string_list merge_rr = STRING_LIST_INIT_DUP;
-       int fd;
+       int fd, status;
 
        fd = setup_rerere(&merge_rr, flags);
        if (fd < 0)
                return 0;
-       return do_plain_rerere(&merge_rr, fd);
+       status = do_plain_rerere(&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(const char *path, unsigned char *sha1, const char *output)
+{
+       mmfile_t mmfile[3] = {{NULL}};
+       mmbuffer_t result = {NULL, 0};
+       const struct cache_entry *ce;
+       int pos, len, i, hunk_no;
+       struct rerere_io_mem io;
+       int marker_size = ll_merge_marker_size(path);
+
+       /*
+        * Reproduce the conflicted merge in-core
+        */
+       len = strlen(path);
+       pos = cache_name_pos(path, len);
+       if (0 <= pos)
+               return -1;
+       pos = -pos - 1;
+
+       while (pos < active_nr) {
+               enum object_type type;
+               unsigned long size;
+
+               ce = active_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_sha1_file(ce->oid.hash, &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", 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.
+        */
+       hunk_no = handle_path(sha1, (struct rerere_io *)&io, marker_size);
+       strbuf_release(&io.input);
+       if (io.io.output)
+               fclose(io.io.output);
+       return hunk_no;
 }
 
 static int rerere_forget_one_path(const char *path, struct string_list *rr)
@@ -838,11 +1038,43 @@ static int rerere_forget_one_path(const char *path, struct string_list *rr)
 
        /* Nuke the recorded resolution for the conflict */
        id = new_rerere_id(sha1);
+
+       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(path, sha1, 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(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))
-               return (errno == ENOENT
-                       ? error("no remembered resolution for %s", path)
-                       : error("cannot unlink %s: %s", filename, strerror(errno)));
+       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
@@ -861,6 +1093,10 @@ static int rerere_forget_one_path(const char *path, struct string_list *rr)
        item->util = id;
        fprintf(stderr, "Forgot resolution for %s\n", path);
        return 0;
+
+fail_exit:
+       free(id);
+       return -1;
 }
 
 int rerere_forget(struct pathspec *pathspec)
@@ -897,29 +1133,16 @@ int rerere_forget(struct pathspec *pathspec)
  * Garbage collection support
  */
 
-/*
- * Note that this is not reentrant but is used only one-at-a-time
- * so it does not matter right now.
- */
-static struct rerere_id *dirname_to_id(const char *name)
-{
-       static struct rerere_id id;
-       xsnprintf(id.hex, sizeof(id.hex), "%s", name);
-       return &id;
-}
-
-static time_t rerere_created_at(const char *dir_name)
+static time_t rerere_created_at(struct rerere_id *id)
 {
        struct stat st;
-       struct rerere_id *id = dirname_to_id(dir_name);
 
        return stat(rerere_path(id, "preimage"), &st) ? (time_t) 0 : st.st_mtime;
 }
 
-static time_t rerere_last_used_at(const char *dir_name)
+static time_t rerere_last_used_at(struct rerere_id *id)
 {
        struct stat st;
-       struct rerere_id *id = dirname_to_id(dir_name);
 
        return stat(rerere_path(id, "postimage"), &st) ? (time_t) 0 : st.st_mtime;
 }
@@ -929,15 +1152,28 @@ static time_t rerere_last_used_at(const char *dir_name)
  */
 static void unlink_rr_item(struct rerere_id *id)
 {
-       unlink(rerere_path(id, "thisimage"));
-       unlink(rerere_path(id, "preimage"));
-       unlink(rerere_path(id, "postimage"));
-       /*
-        * NEEDSWORK: what if this rmdir() fails?  Wouldn't we then
-        * assume that we already have preimage recorded in
-        * do_plain_rerere()?
-        */
-       rmdir(rerere_path(id, NULL));
+       unlink_or_warn(rerere_path(id, "thisimage"));
+       remove_variant(id);
+       id->collection->status[id->variant] = 0;
+}
+
+static void prune_one(struct rerere_id *id, time_t now,
+                     int cutoff_resolve, int cutoff_noresolve)
+{
+       time_t then;
+       int 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 < now - cutoff * 86400)
+               unlink_rr_item(id);
 }
 
 void rerere_gc(struct string_list *rr)
@@ -945,8 +1181,8 @@ void rerere_gc(struct string_list *rr)
        struct string_list to_remove = STRING_LIST_INIT_DUP;
        DIR *dir;
        struct dirent *e;
-       int i, cutoff;
-       time_t now = time(NULL), then;
+       int i;
+       time_t now = time(NULL);
        int cutoff_noresolve = 15;
        int cutoff_resolve = 60;
 
@@ -961,25 +1197,32 @@ void rerere_gc(struct string_list *rr)
                die_errno("unable to open rr-cache directory");
        /* Collect stale conflict IDs ... */
        while ((e = readdir(dir))) {
+               struct rerere_dir *rr_dir;
+               struct rerere_id id;
+               int now_empty;
+
                if (is_dot_or_dotdot(e->d_name))
                        continue;
-
-               then = rerere_last_used_at(e->d_name);
-               if (then) {
-                       cutoff = cutoff_resolve;
-               } else {
-                       then = rerere_created_at(e->d_name);
-                       if (!then)
-                               continue;
-                       cutoff = cutoff_noresolve;
+               rr_dir = find_rerere_dir(e->d_name);
+               if (!rr_dir)
+                       continue; /* or should we remove 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, now, cutoff_resolve, cutoff_noresolve);
+                       if (id.collection->status[id.variant])
+                               now_empty = 0;
                }
-               if (then < now - cutoff * 86400)
+               if (now_empty)
                        string_list_append(&to_remove, e->d_name);
        }
        closedir(dir);
-       /* ... and then remove them one-by-one */
+
+       /* ... and then remove the empty directories */
        for (i = 0; i < to_remove.nr; i++)
-               unlink_rr_item(dirname_to_id(to_remove.items[i].string));
+               rmdir(git_path("rr-cache/%s", to_remove.items[i].string));
        string_list_clear(&to_remove, 0);
        rollback_lock_file(&write_lock);
 }
@@ -1000,8 +1243,10 @@ void rerere_clear(struct string_list *merge_rr)
 
        for (i = 0; i < merge_rr->nr; i++) {
                struct rerere_id *id = merge_rr->items[i].util;
-               if (!has_rerere_resolution(id))
+               if (!has_rerere_resolution(id)) {
                        unlink_rr_item(id);
+                       rmdir(rerere_path(id, NULL));
+               }
        }
        unlink_or_warn(git_path_merge_rr());
        rollback_lock_file(&write_lock);