notes-merge.c

   1 #include "cache.h"
   2 #include "commit.h"
   3 #include "refs.h"
   4 #include "diff.h"
   5 #include "diffcore.h"
   6 #include "xdiff-interface.h"
   7 #include "ll-merge.h"
   8 #include "dir.h"
   9 #include "notes.h"
  10 #include "notes-merge.h"
  11
  12 struct notes_merge_pair {
  13         unsigned char obj[20], base[20], local[20], remote[20];
  14 };
  15
  16 void init_notes_merge_options(struct notes_merge_options *o)
  17 {
  18         memset(o, 0, sizeof(struct notes_merge_options));
  19         o->verbosity = NOTES_MERGE_VERBOSITY_DEFAULT;
  20 }
  21
  22 #define OUTPUT(o, v, ...) \
  23         do { \
  24                 if ((o)->verbosity >= (v)) { \
  25                         printf(__VA_ARGS__); \
  26                         puts(""); \
  27                 } \
  28         } while (0)
  29
  30 static int path_to_sha1(const char *path, unsigned char *sha1)
  31 {
  32         char hex_sha1[40];
  33         int i = 0;
  34         while (*path && i < 40) {
  35                 if (*path != '/')
  36                         hex_sha1[i++] = *path;
  37                 path++;
  38         }
  39         if (*path || i != 40)
  40                 return -1;
  41         return get_sha1_hex(hex_sha1, sha1);
  42 }
  43
  44 static int verify_notes_filepair(struct diff_filepair *p, unsigned char *sha1)
  45 {
  46         switch (p->status) {
  47         case DIFF_STATUS_MODIFIED:
  48                 assert(p->one->mode == p->two->mode);
  49                 assert(!is_null_sha1(p->one->sha1));
  50                 assert(!is_null_sha1(p->two->sha1));
  51                 break;
  52         case DIFF_STATUS_ADDED:
  53                 assert(is_null_sha1(p->one->sha1));
  54                 break;
  55         case DIFF_STATUS_DELETED:
  56                 assert(is_null_sha1(p->two->sha1));
  57                 break;
  58         default:
  59                 return -1;
  60         }
  61         assert(!strcmp(p->one->path, p->two->path));
  62         return path_to_sha1(p->one->path, sha1);
  63 }
  64
  65 static struct notes_merge_pair *find_notes_merge_pair_pos(
  66                 struct notes_merge_pair *list, int len, unsigned char *obj,
  67                 int insert_new, int *occupied)
  68 {
  69         /*
  70          * Both diff_tree_remote() and diff_tree_local() tend to process
  71          * merge_pairs in ascending order. Therefore, cache last returned
  72          * index, and search sequentially from there until the appropriate
  73          * position is found.
  74          *
  75          * Since inserts only happen from diff_tree_remote() (which mainly
  76          * _appends_), we don't care that inserting into the middle of the
  77          * list is expensive (using memmove()).
  78          */
  79         static int last_index;
  80         int i = last_index < len ? last_index : len - 1;
  81         int prev_cmp = 0, cmp = -1;
  82         while (i >= 0 && i < len) {
  83                 cmp = hashcmp(obj, list[i].obj);
  84                 if (!cmp) /* obj belongs @ i */
  85                         break;
  86                 else if (cmp < 0 && prev_cmp <= 0) /* obj belongs < i */
  87                         i--;
  88                 else if (cmp < 0) /* obj belongs between i-1 and i */
  89                         break;
  90                 else if (cmp > 0 && prev_cmp >= 0) /* obj belongs > i */
  91                         i++;
  92                 else /* if (cmp > 0) */ { /* obj belongs between i and i+1 */
  93                         i++;
  94                         break;
  95                 }
  96                 prev_cmp = cmp;
  97         }
  98         if (i < 0)
  99                 i = 0;
 100         /* obj belongs at, or immediately preceding, index i (0 <= i <= len) */
 101
 102         if (!cmp)
 103                 *occupied = 1;
 104         else {
 105                 *occupied = 0;
 106                 if (insert_new && i < len) {
 107                         memmove(list + i + 1, list + i,
 108                                 (len - i) * sizeof(struct notes_merge_pair));
 109                         memset(list + i, 0, sizeof(struct notes_merge_pair));
 110                 }
 111         }
 112         last_index = i;
 113         return list + i;
 114 }
 115
 116 static unsigned char uninitialized[20] =
 117         "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" \
 118         "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff";
 119
 120 static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
 121                                                  const unsigned char *base,
 122                                                  const unsigned char *remote,
 123                                                  int *num_changes)
 124 {
 125         struct diff_options opt;
 126         struct notes_merge_pair *changes;
 127         int i, len = 0;
 128
 129         trace_printf("\tdiff_tree_remote(base = %.7s, remote = %.7s)\n",
 130                sha1_to_hex(base), sha1_to_hex(remote));
 131
 132         diff_setup(&opt);
 133         DIFF_OPT_SET(&opt, RECURSIVE);
 134         opt.output_format = DIFF_FORMAT_NO_OUTPUT;
 135         if (diff_setup_done(&opt) < 0)
 136                 die("diff_setup_done failed");
 137         diff_tree_sha1(base, remote, "", &opt);
 138         diffcore_std(&opt);
 139
 140         changes = xcalloc(diff_queued_diff.nr, sizeof(struct notes_merge_pair));
 141
 142         for (i = 0; i < diff_queued_diff.nr; i++) {
 143                 struct diff_filepair *p = diff_queued_diff.queue[i];
 144                 struct notes_merge_pair *mp;
 145                 int occupied;
 146                 unsigned char obj[20];
 147
 148                 if (verify_notes_filepair(p, obj)) {
 149                         trace_printf("\t\tCannot merge entry '%s' (%c): "
 150                                "%.7s -> %.7s. Skipping!\n", p->one->path,
 151                                p->status, sha1_to_hex(p->one->sha1),
 152                                sha1_to_hex(p->two->sha1));
 153                         continue;
 154                 }
 155                 mp = find_notes_merge_pair_pos(changes, len, obj, 1, &occupied);
 156                 if (occupied) {
 157                         /* We've found an addition/deletion pair */
 158                         assert(!hashcmp(mp->obj, obj));
 159                         if (is_null_sha1(p->one->sha1)) { /* addition */
 160                                 assert(is_null_sha1(mp->remote));
 161                                 hashcpy(mp->remote, p->two->sha1);
 162                         } else if (is_null_sha1(p->two->sha1)) { /* deletion */
 163                                 assert(is_null_sha1(mp->base));
 164                                 hashcpy(mp->base, p->one->sha1);
 165                         } else
 166                                 assert(!"Invalid existing change recorded");
 167                 } else {
 168                         hashcpy(mp->obj, obj);
 169                         hashcpy(mp->base, p->one->sha1);
 170                         hashcpy(mp->local, uninitialized);
 171                         hashcpy(mp->remote, p->two->sha1);
 172                         len++;
 173                 }
 174                 trace_printf("\t\tStored remote change for %s: %.7s -> %.7s\n",
 175                        sha1_to_hex(mp->obj), sha1_to_hex(mp->base),
 176                        sha1_to_hex(mp->remote));
 177         }
 178         diff_flush(&opt);
 179         diff_tree_release_paths(&opt);
 180
 181         *num_changes = len;
 182         return changes;
 183 }
 184
 185 static void diff_tree_local(struct notes_merge_options *o,
 186                             struct notes_merge_pair *changes, int len,
 187                             const unsigned char *base,
 188                             const unsigned char *local)
 189 {
 190         struct diff_options opt;
 191         int i;
 192
 193         trace_printf("\tdiff_tree_local(len = %i, base = %.7s, local = %.7s)\n",
 194                len, sha1_to_hex(base), sha1_to_hex(local));
 195
 196         diff_setup(&opt);
 197         DIFF_OPT_SET(&opt, RECURSIVE);
 198         opt.output_format = DIFF_FORMAT_NO_OUTPUT;
 199         if (diff_setup_done(&opt) < 0)
 200                 die("diff_setup_done failed");
 201         diff_tree_sha1(base, local, "", &opt);
 202         diffcore_std(&opt);
 203
 204         for (i = 0; i < diff_queued_diff.nr; i++) {
 205                 struct diff_filepair *p = diff_queued_diff.queue[i];
 206                 struct notes_merge_pair *mp;
 207                 int match;
 208                 unsigned char obj[20];
 209
 210                 if (verify_notes_filepair(p, obj)) {
 211                         trace_printf("\t\tCannot merge entry '%s' (%c): "
 212                                "%.7s -> %.7s. Skipping!\n", p->one->path,
 213                                p->status, sha1_to_hex(p->one->sha1),
 214                                sha1_to_hex(p->two->sha1));
 215                         continue;
 216                 }
 217                 mp = find_notes_merge_pair_pos(changes, len, obj, 0, &match);
 218                 if (!match) {
 219                         trace_printf("\t\tIgnoring local-only change for %s: "
 220                                "%.7s -> %.7s\n", sha1_to_hex(obj),
 221                                sha1_to_hex(p->one->sha1),
 222                                sha1_to_hex(p->two->sha1));
 223                         continue;
 224                 }
 225
 226                 assert(!hashcmp(mp->obj, obj));
 227                 if (is_null_sha1(p->two->sha1)) { /* deletion */
 228                         /*
 229                          * Either this is a true deletion (1), or it is part
 230                          * of an A/D pair (2), or D/A pair (3):
 231                          *
 232                          * (1) mp->local is uninitialized; set it to null_sha1
 233                          * (2) mp->local is not uninitialized; don't touch it
 234                          * (3) mp->local is uninitialized; set it to null_sha1
 235                          *     (will be overwritten by following addition)
 236                          */
 237                         if (!hashcmp(mp->local, uninitialized))
 238                                 hashclr(mp->local);
 239                 } else if (is_null_sha1(p->one->sha1)) { /* addition */
 240                         /*
 241                          * Either this is a true addition (1), or it is part
 242                          * of an A/D pair (2), or D/A pair (3):
 243                          *
 244                          * (1) mp->local is uninitialized; set to p->two->sha1
 245                          * (2) mp->local is uninitialized; set to p->two->sha1
 246                          * (3) mp->local is null_sha1;     set to p->two->sha1
 247                          */
 248                         assert(is_null_sha1(mp->local) ||
 249                                !hashcmp(mp->local, uninitialized));
 250                         hashcpy(mp->local, p->two->sha1);
 251                 } else { /* modification */
 252                         /*
 253                          * This is a true modification. p->one->sha1 shall
 254                          * match mp->base, and mp->local shall be uninitialized.
 255                          * Set mp->local to p->two->sha1.
 256                          */
 257                         assert(!hashcmp(p->one->sha1, mp->base));
 258                         assert(!hashcmp(mp->local, uninitialized));
 259                         hashcpy(mp->local, p->two->sha1);
 260                 }
 261                 trace_printf("\t\tStored local change for %s: %.7s -> %.7s\n",
 262                        sha1_to_hex(mp->obj), sha1_to_hex(mp->base),
 263                        sha1_to_hex(mp->local));
 264         }
 265         diff_flush(&opt);
 266         diff_tree_release_paths(&opt);
 267 }
 268
 269 static void check_notes_merge_worktree(struct notes_merge_options *o)
 270 {
 271         if (!o->has_worktree) {
 272                 /*
 273                  * Must establish NOTES_MERGE_WORKTREE.
 274                  * Abort if NOTES_MERGE_WORKTREE already exists
 275                  */
 276                 if (file_exists(git_path(NOTES_MERGE_WORKTREE))) {
 277                         if (advice_resolve_conflict)
 278                                 die("You have not concluded your previous "
 279                                     "notes merge (%s exists).\nPlease, use "
 280                                     "'git notes merge --commit' or 'git notes "
 281                                     "merge --reset' to commit/abort the "
 282                                     "previous merge before you start a new "
 283                                     "notes merge.", git_path("NOTES_MERGE_*"));
 284                         else
 285                                 die("You have not concluded your notes merge "
 286                                     "(%s exists).", git_path("NOTES_MERGE_*"));
 287                 }
 288
 289                 if (safe_create_leading_directories(git_path(
 290                                 NOTES_MERGE_WORKTREE "/.test")))
 291                         die_errno("unable to create directory %s",
 292                                   git_path(NOTES_MERGE_WORKTREE));
 293                 o->has_worktree = 1;
 294         } else if (!file_exists(git_path(NOTES_MERGE_WORKTREE)))
 295                 /* NOTES_MERGE_WORKTREE should already be established */
 296                 die("missing '%s'. This should not happen",
 297                     git_path(NOTES_MERGE_WORKTREE));
 298 }
 299
 300 static void write_buf_to_worktree(const unsigned char *obj,
 301                                   const char *buf, unsigned long size)
 302 {
 303         int fd;
 304         char *path = git_path(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
 305         if (safe_create_leading_directories(path))
 306                 die_errno("unable to create directory for '%s'", path);
 307         if (file_exists(path))
 308                 die("found existing file at '%s'", path);
 309
 310         fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, 0666);
 311         if (fd < 0)
 312                 die_errno("failed to open '%s'", path);
 313
 314         while (size > 0) {
 315                 long ret = write_in_full(fd, buf, size);
 316                 if (ret < 0) {
 317                         /* Ignore epipe */
 318                         if (errno == EPIPE)
 319                                 break;
 320                         die_errno("notes-merge");
 321                 } else if (!ret) {
 322                         die("notes-merge: disk full?");
 323                 }
 324                 size -= ret;
 325                 buf += ret;
 326         }
 327
 328         close(fd);
 329 }
 330
 331 static void write_note_to_worktree(const unsigned char *obj,
 332                                    const unsigned char *note)
 333 {
 334         enum object_type type;
 335         unsigned long size;
 336         void *buf = read_sha1_file(note, &type, &size);
 337
 338         if (!buf)
 339                 die("cannot read note %s for object %s",
 340                     sha1_to_hex(note), sha1_to_hex(obj));
 341         if (type != OBJ_BLOB)
 342                 die("blob expected in note %s for object %s",
 343                     sha1_to_hex(note), sha1_to_hex(obj));
 344         write_buf_to_worktree(obj, buf, size);
 345         free(buf);
 346 }
 347
 348 static int ll_merge_in_worktree(struct notes_merge_options *o,
 349                                 struct notes_merge_pair *p)
 350 {
 351         mmbuffer_t result_buf;
 352         mmfile_t base, local, remote;
 353         int status;
 354
 355         read_mmblob(&base, p->base);
 356         read_mmblob(&local, p->local);
 357         read_mmblob(&remote, p->remote);
 358
 359         status = ll_merge(&result_buf, sha1_to_hex(p->obj), &base, NULL,
 360                           &local, o->local_ref, &remote, o->remote_ref, 0);
 361
 362         free(base.ptr);
 363         free(local.ptr);
 364         free(remote.ptr);
 365
 366         if ((status < 0) || !result_buf.ptr)
 367                 die("Failed to execute internal merge");
 368
 369         write_buf_to_worktree(p->obj, result_buf.ptr, result_buf.size);
 370         free(result_buf.ptr);
 371
 372         return status;
 373 }
 374
 375 static int merge_one_change_manual(struct notes_merge_options *o,
 376                                    struct notes_merge_pair *p,
 377                                    struct notes_tree *t)
 378 {
 379         const char *lref = o->local_ref ? o->local_ref : "local version";
 380         const char *rref = o->remote_ref ? o->remote_ref : "remote version";
 381
 382         trace_printf("\t\t\tmerge_one_change_manual(obj = %.7s, base = %.7s, "
 383                "local = %.7s, remote = %.7s)\n",
 384                sha1_to_hex(p->obj), sha1_to_hex(p->base),
 385                sha1_to_hex(p->local), sha1_to_hex(p->remote));
 386
 387         OUTPUT(o, 2, "Auto-merging notes for %s", sha1_to_hex(p->obj));
 388         check_notes_merge_worktree(o);
 389         if (is_null_sha1(p->local)) {
 390                 /* D/F conflict, checkout p->remote */
 391                 assert(!is_null_sha1(p->remote));
 392                 OUTPUT(o, 1, "CONFLICT (delete/modify): Notes for object %s "
 393                        "deleted in %s and modified in %s. Version from %s "
 394                        "left in tree.", sha1_to_hex(p->obj), lref, rref, rref);
 395                 write_note_to_worktree(p->obj, p->remote);
 396         } else if (is_null_sha1(p->remote)) {
 397                 /* D/F conflict, checkout p->local */
 398                 assert(!is_null_sha1(p->local));
 399                 OUTPUT(o, 1, "CONFLICT (delete/modify): Notes for object %s "
 400                        "deleted in %s and modified in %s. Version from %s "
 401                        "left in tree.", sha1_to_hex(p->obj), rref, lref, lref);
 402                 write_note_to_worktree(p->obj, p->local);
 403         } else {
 404                 /* "regular" conflict, checkout result of ll_merge() */
 405                 const char *reason = "content";
 406                 if (is_null_sha1(p->base))
 407                         reason = "add/add";
 408                 assert(!is_null_sha1(p->local));
 409                 assert(!is_null_sha1(p->remote));
 410                 OUTPUT(o, 1, "CONFLICT (%s): Merge conflict in notes for "
 411                        "object %s", reason, sha1_to_hex(p->obj));
 412                 ll_merge_in_worktree(o, p);
 413         }
 414
 415         trace_printf("\t\t\tremoving from partial merge result\n");
 416         remove_note(t, p->obj);
 417
 418         return 1;
 419 }
 420
 421 static int merge_one_change(struct notes_merge_options *o,
 422                             struct notes_merge_pair *p, struct notes_tree *t)
 423 {
 424         /*
 425          * Return 0 if change is successfully resolved (stored in notes_tree).
 426          * Return 1 is change results in a conflict (NOT stored in notes_tree,
 427          * but instead written to NOTES_MERGE_WORKTREE with conflict markers).
 428          */
 429         switch (o->strategy) {
 430         case NOTES_MERGE_RESOLVE_MANUAL:
 431                 return merge_one_change_manual(o, p, t);
 432         case NOTES_MERGE_RESOLVE_OURS:
 433                 OUTPUT(o, 2, "Using local notes for %s", sha1_to_hex(p->obj));
 434                 /* nothing to do */
 435                 return 0;
 436         case NOTES_MERGE_RESOLVE_THEIRS:
 437                 OUTPUT(o, 2, "Using remote notes for %s", sha1_to_hex(p->obj));
 438                 if (add_note(t, p->obj, p->remote, combine_notes_overwrite))
 439                         die("BUG: combine_notes_overwrite failed");
 440                 return 0;
 441         case NOTES_MERGE_RESOLVE_UNION:
 442                 OUTPUT(o, 2, "Concatenating local and remote notes for %s",
 443                        sha1_to_hex(p->obj));
 444                 if (add_note(t, p->obj, p->remote, combine_notes_concatenate))
 445                         die("failed to concatenate notes "
 446                             "(combine_notes_concatenate)");
 447                 return 0;
 448         }
 449         die("Unknown strategy (%i).", o->strategy);
 450 }
 451
 452 static int merge_changes(struct notes_merge_options *o,
 453                          struct notes_merge_pair *changes, int *num_changes,
 454                          struct notes_tree *t)
 455 {
 456         int i, conflicts = 0;
 457
 458         trace_printf("\tmerge_changes(num_changes = %i)\n", *num_changes);
 459         for (i = 0; i < *num_changes; i++) {
 460                 struct notes_merge_pair *p = changes + i;
 461                 trace_printf("\t\t%.7s: %.7s -> %.7s/%.7s\n",
 462                        sha1_to_hex(p->obj), sha1_to_hex(p->base),
 463                        sha1_to_hex(p->local), sha1_to_hex(p->remote));
 464
 465                 if (!hashcmp(p->base, p->remote)) {
 466                         /* no remote change; nothing to do */
 467                         trace_printf("\t\t\tskipping (no remote change)\n");
 468                 } else if (!hashcmp(p->local, p->remote)) {
 469                         /* same change in local and remote; nothing to do */
 470                         trace_printf("\t\t\tskipping (local == remote)\n");
 471                 } else if (!hashcmp(p->local, uninitialized) ||
 472                            !hashcmp(p->local, p->base)) {
 473                         /* no local change; adopt remote change */
 474                         trace_printf("\t\t\tno local change, adopted remote\n");
 475                         if (add_note(t, p->obj, p->remote,
 476                                      combine_notes_overwrite))
 477                                 die("BUG: combine_notes_overwrite failed");
 478                 } else {
 479                         /* need file-level merge between local and remote */
 480                         trace_printf("\t\t\tneed content-level merge\n");
 481                         conflicts += merge_one_change(o, p, t);
 482                 }
 483         }
 484
 485         return conflicts;
 486 }
 487
 488 static int merge_from_diffs(struct notes_merge_options *o,
 489                             const unsigned char *base,
 490                             const unsigned char *local,
 491                             const unsigned char *remote, struct notes_tree *t)
 492 {
 493         struct notes_merge_pair *changes;
 494         int num_changes, conflicts;
 495
 496         trace_printf("\tmerge_from_diffs(base = %.7s, local = %.7s, "
 497                "remote = %.7s)\n", sha1_to_hex(base), sha1_to_hex(local),
 498                sha1_to_hex(remote));
 499
 500         changes = diff_tree_remote(o, base, remote, &num_changes);
 501         diff_tree_local(o, changes, num_changes, base, local);
 502
 503         conflicts = merge_changes(o, changes, &num_changes, t);
 504         free(changes);
 505
 506         OUTPUT(o, 4, "Merge result: %i unmerged notes and a %s notes tree",
 507                conflicts, t->dirty ? "dirty" : "clean");
 508
 509         return conflicts ? -1 : 1;
 510 }
 511
 512 void create_notes_commit(struct notes_tree *t, struct commit_list *parents,
 513                          const char *msg, unsigned char *result_sha1)
 514 {
 515         unsigned char tree_sha1[20];
 516
 517         assert(t->initialized);
 518
 519         if (write_notes_tree(t, tree_sha1))
 520                 die("Failed to write notes tree to database");
 521
 522         if (!parents) {
 523                 /* Deduce parent commit from t->ref */
 524                 unsigned char parent_sha1[20];
 525                 if (!read_ref(t->ref, parent_sha1)) {
 526                         struct commit *parent = lookup_commit(parent_sha1);
 527                         if (!parent || parse_commit(parent))
 528                                 die("Failed to find/parse commit %s", t->ref);
 529                         commit_list_insert(parent, &parents);
 530                 }
 531                 /* else: t->ref points to nothing, assume root/orphan commit */
 532         }
 533
 534         if (commit_tree(msg, tree_sha1, parents, result_sha1, NULL))
 535                 die("Failed to commit notes tree to database");
 536 }
 537
 538 int notes_merge(struct notes_merge_options *o,
 539                 struct notes_tree *local_tree,
 540                 unsigned char *result_sha1)
 541 {
 542         unsigned char local_sha1[20], remote_sha1[20];
 543         struct commit *local, *remote;
 544         struct commit_list *bases = NULL;
 545         const unsigned char *base_sha1, *base_tree_sha1;
 546         int result = 0;
 547
 548         assert(o->local_ref && o->remote_ref);
 549         assert(!strcmp(o->local_ref, local_tree->ref));
 550         hashclr(result_sha1);
 551
 552         trace_printf("notes_merge(o->local_ref = %s, o->remote_ref = %s)\n",
 553                o->local_ref, o->remote_ref);
 554
 555         /* Dereference o->local_ref into local_sha1 */
 556         if (!resolve_ref(o->local_ref, local_sha1, 0, NULL))
 557                 die("Failed to resolve local notes ref '%s'", o->local_ref);
 558         else if (!check_ref_format(o->local_ref) && is_null_sha1(local_sha1))
 559                 local = NULL; /* local_sha1 == null_sha1 indicates unborn ref */
 560         else if (!(local = lookup_commit_reference(local_sha1)))
 561                 die("Could not parse local commit %s (%s)",
 562                     sha1_to_hex(local_sha1), o->local_ref);
 563         trace_printf("\tlocal commit: %.7s\n", sha1_to_hex(local_sha1));
 564
 565         /* Dereference o->remote_ref into remote_sha1 */
 566         if (get_sha1(o->remote_ref, remote_sha1)) {
 567                 /*
 568                  * Failed to get remote_sha1. If o->remote_ref looks like an
 569                  * unborn ref, perform the merge using an empty notes tree.
 570                  */
 571                 if (!check_ref_format(o->remote_ref)) {
 572                         hashclr(remote_sha1);
 573                         remote = NULL;
 574                 } else {
 575                         die("Failed to resolve remote notes ref '%s'",
 576                             o->remote_ref);
 577                 }
 578         } else if (!(remote = lookup_commit_reference(remote_sha1))) {
 579                 die("Could not parse remote commit %s (%s)",
 580                     sha1_to_hex(remote_sha1), o->remote_ref);
 581         }
 582         trace_printf("\tremote commit: %.7s\n", sha1_to_hex(remote_sha1));
 583
 584         if (!local && !remote)
 585                 die("Cannot merge empty notes ref (%s) into empty notes ref "
 586                     "(%s)", o->remote_ref, o->local_ref);
 587         if (!local) {
 588                 /* result == remote commit */
 589                 hashcpy(result_sha1, remote_sha1);
 590                 goto found_result;
 591         }
 592         if (!remote) {
 593                 /* result == local commit */
 594                 hashcpy(result_sha1, local_sha1);
 595                 goto found_result;
 596         }
 597         assert(local && remote);
 598
 599         /* Find merge bases */
 600         bases = get_merge_bases(local, remote, 1);
 601         if (!bases) {
 602                 base_sha1 = null_sha1;
 603                 base_tree_sha1 = (unsigned char *)EMPTY_TREE_SHA1_BIN;
 604                 OUTPUT(o, 4, "No merge base found; doing history-less merge");
 605         } else if (!bases->next) {
 606                 base_sha1 = bases->item->object.sha1;
 607                 base_tree_sha1 = bases->item->tree->object.sha1;
 608                 OUTPUT(o, 4, "One merge base found (%.7s)",
 609                        sha1_to_hex(base_sha1));
 610         } else {
 611                 /* TODO: How to handle multiple merge-bases? */
 612                 base_sha1 = bases->item->object.sha1;
 613                 base_tree_sha1 = bases->item->tree->object.sha1;
 614                 OUTPUT(o, 3, "Multiple merge bases found. Using the first "
 615                        "(%.7s)", sha1_to_hex(base_sha1));
 616         }
 617
 618         OUTPUT(o, 4, "Merging remote commit %.7s into local commit %.7s with "
 619                "merge-base %.7s", sha1_to_hex(remote->object.sha1),
 620                sha1_to_hex(local->object.sha1), sha1_to_hex(base_sha1));
 621
 622         if (!hashcmp(remote->object.sha1, base_sha1)) {
 623                 /* Already merged; result == local commit */
 624                 OUTPUT(o, 2, "Already up-to-date!");
 625                 hashcpy(result_sha1, local->object.sha1);
 626                 goto found_result;
 627         }
 628         if (!hashcmp(local->object.sha1, base_sha1)) {
 629                 /* Fast-forward; result == remote commit */
 630                 OUTPUT(o, 2, "Fast-forward");
 631                 hashcpy(result_sha1, remote->object.sha1);
 632                 goto found_result;
 633         }
 634
 635         result = merge_from_diffs(o, base_tree_sha1, local->tree->object.sha1,
 636                                   remote->tree->object.sha1, local_tree);
 637
 638         if (result != 0) { /* non-trivial merge (with or without conflicts) */
 639                 /* Commit (partial) result */
 640                 struct commit_list *parents = NULL;
 641                 commit_list_insert(remote, &parents); /* LIFO order */
 642                 commit_list_insert(local, &parents);
 643                 create_notes_commit(local_tree, parents, o->commit_msg,
 644                                     result_sha1);
 645         }
 646
 647 found_result:
 648         free_commit_list(bases);
 649         trace_printf("notes_merge(): result = %i, result_sha1 = %.7s\n",
 650                result, sha1_to_hex(result_sha1));
 651         return result;
 652 }