git.oblomov.eu Git - git/blob - builtin/difftool.c

   1 /*
   2  * "git difftool" builtin command
   3  *
   4  * This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
   5  * git-difftool--helper script.
   6  *
   7  * This script exports GIT_EXTERNAL_DIFF and GIT_PAGER for use by git.
   8  * The GIT_DIFF* variables are exported for use by git-difftool--helper.
   9  *
  10  * Any arguments that are unknown to this script are forwarded to 'git diff'.
  11  *
  12  * Copyright (C) 2016 Johannes Schindelin
  13  */
  14 #include "cache.h"
  15 #include "builtin.h"
  16 #include "run-command.h"
  17 #include "exec_cmd.h"
  18 #include "parse-options.h"
  19 #include "argv-array.h"
  20 #include "strbuf.h"
  21 #include "lockfile.h"
  22 #include "dir.h"
  23
  24 static char *diff_gui_tool;
  25 static int trust_exit_code;
  26
  27 static const char *const builtin_difftool_usage[] = {
  28         N_("git difftool [<options>] [<commit> [<commit>]] [--] [<path>...]"),
  29         NULL
  30 };
  31
  32 static int difftool_config(const char *var, const char *value, void *cb)
  33 {
  34         if (!strcmp(var, "diff.guitool")) {
  35                 diff_gui_tool = xstrdup(value);
  36                 return 0;
  37         }
  38
  39         if (!strcmp(var, "difftool.trustexitcode")) {
  40                 trust_exit_code = git_config_bool(var, value);
  41                 return 0;
  42         }
  43
  44         return git_default_config(var, value, cb);
  45 }
  46
  47 static int print_tool_help(void)
  48 {
  49         const char *argv[] = { "mergetool", "--tool-help=diff", NULL };
  50         return run_command_v_opt(argv, RUN_GIT_CMD);
  51 }
  52
  53 static int parse_index_info(char *p, int *mode1, int *mode2,
  54                             struct object_id *oid1, struct object_id *oid2,
  55                             char *status)
  56 {
  57         if (*p != ':')
  58                 return error("expected ':', got '%c'", *p);
  59         *mode1 = (int)strtol(p + 1, &p, 8);
  60         if (*p != ' ')
  61                 return error("expected ' ', got '%c'", *p);
  62         *mode2 = (int)strtol(p + 1, &p, 8);
  63         if (*p != ' ')
  64                 return error("expected ' ', got '%c'", *p);
  65         if (get_oid_hex(++p, oid1))
  66                 return error("expected object ID, got '%s'", p + 1);
  67         p += GIT_SHA1_HEXSZ;
  68         if (*p != ' ')
  69                 return error("expected ' ', got '%c'", *p);
  70         if (get_oid_hex(++p, oid2))
  71                 return error("expected object ID, got '%s'", p + 1);
  72         p += GIT_SHA1_HEXSZ;
  73         if (*p != ' ')
  74                 return error("expected ' ', got '%c'", *p);
  75         *status = *++p;
  76         if (!*status)
  77                 return error("missing status");
  78         if (p[1] && !isdigit(p[1]))
  79                 return error("unexpected trailer: '%s'", p + 1);
  80         return 0;
  81 }
  82
  83 /*
  84  * Remove any trailing slash from $workdir
  85  * before starting to avoid double slashes in symlink targets.
  86  */
  87 static void add_path(struct strbuf *buf, size_t base_len, const char *path)
  88 {
  89         strbuf_setlen(buf, base_len);
  90         if (buf->len && buf->buf[buf->len - 1] != '/')
  91                 strbuf_addch(buf, '/');
  92         strbuf_addstr(buf, path);
  93 }
  94
  95 /*
  96  * Determine whether we can simply reuse the file in the worktree.
  97  */
  98 static int use_wt_file(const char *workdir, const char *name,
  99                        struct object_id *oid)
 100 {
 101         struct strbuf buf = STRBUF_INIT;
 102         struct stat st;
 103         int use = 0;
 104
 105         strbuf_addstr(&buf, workdir);
 106         add_path(&buf, buf.len, name);
 107
 108         if (!lstat(buf.buf, &st) && !S_ISLNK(st.st_mode)) {
 109                 struct object_id wt_oid;
 110                 int fd = open(buf.buf, O_RDONLY);
 111
 112                 if (fd >= 0 &&
 113                     !index_fd(wt_oid.hash, fd, &st, OBJ_BLOB, name, 0)) {
 114                         if (is_null_oid(oid)) {
 115                                 oidcpy(oid, &wt_oid);
 116                                 use = 1;
 117                         } else if (!oidcmp(oid, &wt_oid))
 118                                 use = 1;
 119                 }
 120         }
 121
 122         strbuf_release(&buf);
 123
 124         return use;
 125 }
 126
 127 struct working_tree_entry {
 128         struct hashmap_entry entry;
 129         char path[FLEX_ARRAY];
 130 };
 131
 132 static int working_tree_entry_cmp(struct working_tree_entry *a,
 133                                   struct working_tree_entry *b, void *keydata)
 134 {
 135         return strcmp(a->path, b->path);
 136 }
 137
 138 /*
 139  * The `left` and `right` entries hold paths for the symlinks hashmap,
 140  * and a SHA-1 surrounded by brief text for submodules.
 141  */
 142 struct pair_entry {
 143         struct hashmap_entry entry;
 144         char left[PATH_MAX], right[PATH_MAX];
 145         const char path[FLEX_ARRAY];
 146 };
 147
 148 static int pair_cmp(struct pair_entry *a, struct pair_entry *b, void *keydata)
 149 {
 150         return strcmp(a->path, b->path);
 151 }
 152
 153 static void add_left_or_right(struct hashmap *map, const char *path,
 154                               const char *content, int is_right)
 155 {
 156         struct pair_entry *e, *existing;
 157
 158         FLEX_ALLOC_STR(e, path, path);
 159         hashmap_entry_init(e, strhash(path));
 160         existing = hashmap_get(map, e, NULL);
 161         if (existing) {
 162                 free(e);
 163                 e = existing;
 164         } else {
 165                 e->left[0] = e->right[0] = '\0';
 166                 hashmap_add(map, e);
 167         }
 168         strlcpy(is_right ? e->right : e->left, content, PATH_MAX);
 169 }
 170
 171 struct path_entry {
 172         struct hashmap_entry entry;
 173         char path[FLEX_ARRAY];
 174 };
 175
 176 static int path_entry_cmp(struct path_entry *a, struct path_entry *b, void *key)
 177 {
 178         return strcmp(a->path, key ? key : b->path);
 179 }
 180
 181 static void changed_files(struct hashmap *result, const char *index_path,
 182                           const char *workdir)
 183 {
 184         struct child_process update_index = CHILD_PROCESS_INIT;
 185         struct child_process diff_files = CHILD_PROCESS_INIT;
 186         struct strbuf index_env = STRBUF_INIT, buf = STRBUF_INIT;
 187         const char *git_dir = absolute_path(get_git_dir()), *env[] = {
 188                 NULL, NULL
 189         };
 190         FILE *fp;
 191
 192         strbuf_addf(&index_env, "GIT_INDEX_FILE=%s", index_path);
 193         env[0] = index_env.buf;
 194
 195         argv_array_pushl(&update_index.args,
 196                          "--git-dir", git_dir, "--work-tree", workdir,
 197                          "update-index", "--really-refresh", "-q",
 198                          "--unmerged", NULL);
 199         update_index.no_stdin = 1;
 200         update_index.no_stdout = 1;
 201         update_index.no_stderr = 1;
 202         update_index.git_cmd = 1;
 203         update_index.use_shell = 0;
 204         update_index.clean_on_exit = 1;
 205         update_index.dir = workdir;
 206         update_index.env = env;
 207         /* Ignore any errors of update-index */
 208         run_command(&update_index);
 209
 210         argv_array_pushl(&diff_files.args,
 211                          "--git-dir", git_dir, "--work-tree", workdir,
 212                          "diff-files", "--name-only", "-z", NULL);
 213         diff_files.no_stdin = 1;
 214         diff_files.git_cmd = 1;
 215         diff_files.use_shell = 0;
 216         diff_files.clean_on_exit = 1;
 217         diff_files.out = -1;
 218         diff_files.dir = workdir;
 219         diff_files.env = env;
 220         if (start_command(&diff_files))
 221                 die("could not obtain raw diff");
 222         fp = xfdopen(diff_files.out, "r");
 223         while (!strbuf_getline_nul(&buf, fp)) {
 224                 struct path_entry *entry;
 225                 FLEX_ALLOC_STR(entry, path, buf.buf);
 226                 hashmap_entry_init(entry, strhash(buf.buf));
 227                 hashmap_add(result, entry);
 228         }
 229         if (finish_command(&diff_files))
 230                 die("diff-files did not exit properly");
 231         strbuf_release(&index_env);
 232         strbuf_release(&buf);
 233 }
 234
 235 static NORETURN void exit_cleanup(const char *tmpdir, int exit_code)
 236 {
 237         struct strbuf buf = STRBUF_INIT;
 238         strbuf_addstr(&buf, tmpdir);
 239         remove_dir_recursively(&buf, 0);
 240         if (exit_code)
 241                 warning(_("failed: %d"), exit_code);
 242         exit(exit_code);
 243 }
 244
 245 static int ensure_leading_directories(char *path)
 246 {
 247         switch (safe_create_leading_directories(path)) {
 248                 case SCLD_OK:
 249                 case SCLD_EXISTS:
 250                         return 0;
 251                 default:
 252                         return error(_("could not create leading directories "
 253                                        "of '%s'"), path);
 254         }
 255 }
 256
 257 static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 258                         int argc, const char **argv)
 259 {
 260         char tmpdir[PATH_MAX];
 261         struct strbuf info = STRBUF_INIT, lpath = STRBUF_INIT;
 262         struct strbuf rpath = STRBUF_INIT, buf = STRBUF_INIT;
 263         struct strbuf ldir = STRBUF_INIT, rdir = STRBUF_INIT;
 264         struct strbuf wtdir = STRBUF_INIT;
 265         size_t ldir_len, rdir_len, wtdir_len;
 266         struct cache_entry *ce = xcalloc(1, sizeof(ce) + PATH_MAX + 1);
 267         const char *workdir, *tmp;
 268         int ret = 0, i;
 269         FILE *fp;
 270         struct hashmap working_tree_dups, submodules, symlinks2;
 271         struct hashmap_iter iter;
 272         struct pair_entry *entry;
 273         enum object_type type;
 274         unsigned long size;
 275         struct index_state wtindex;
 276         struct checkout lstate, rstate;
 277         int rc, flags = RUN_GIT_CMD, err = 0;
 278         struct child_process child = CHILD_PROCESS_INIT;
 279         const char *helper_argv[] = { "difftool--helper", NULL, NULL, NULL };
 280         struct hashmap wt_modified, tmp_modified;
 281         int indices_loaded = 0;
 282
 283         workdir = get_git_work_tree();
 284
 285         /* Setup temp directories */
 286         tmp = getenv("TMPDIR");
 287         xsnprintf(tmpdir, sizeof(tmpdir), "%s/git-difftool.XXXXXX", tmp ? tmp : "/tmp");
 288         if (!mkdtemp(tmpdir))
 289                 return error("could not create '%s'", tmpdir);
 290         strbuf_addf(&ldir, "%s/left/", tmpdir);
 291         strbuf_addf(&rdir, "%s/right/", tmpdir);
 292         strbuf_addstr(&wtdir, workdir);
 293         if (!wtdir.len || !is_dir_sep(wtdir.buf[wtdir.len - 1]))
 294                 strbuf_addch(&wtdir, '/');
 295         mkdir(ldir.buf, 0700);
 296         mkdir(rdir.buf, 0700);
 297
 298         memset(&wtindex, 0, sizeof(wtindex));
 299
 300         memset(&lstate, 0, sizeof(lstate));
 301         lstate.base_dir = ldir.buf;
 302         lstate.base_dir_len = ldir.len;
 303         lstate.force = 1;
 304         memset(&rstate, 0, sizeof(rstate));
 305         rstate.base_dir = rdir.buf;
 306         rstate.base_dir_len = rdir.len;
 307         rstate.force = 1;
 308
 309         ldir_len = ldir.len;
 310         rdir_len = rdir.len;
 311         wtdir_len = wtdir.len;
 312
 313         hashmap_init(&working_tree_dups,
 314                      (hashmap_cmp_fn)working_tree_entry_cmp, 0);
 315         hashmap_init(&submodules, (hashmap_cmp_fn)pair_cmp, 0);
 316         hashmap_init(&symlinks2, (hashmap_cmp_fn)pair_cmp, 0);
 317
 318         child.no_stdin = 1;
 319         child.git_cmd = 1;
 320         child.use_shell = 0;
 321         child.clean_on_exit = 1;
 322         child.dir = prefix;
 323         child.out = -1;
 324         argv_array_pushl(&child.args, "diff", "--raw", "--no-abbrev", "-z",
 325                          NULL);
 326         for (i = 0; i < argc; i++)
 327                 argv_array_push(&child.args, argv[i]);
 328         if (start_command(&child))
 329                 die("could not obtain raw diff");
 330         fp = xfdopen(child.out, "r");
 331
 332         /* Build index info for left and right sides of the diff */
 333         i = 0;
 334         while (!strbuf_getline_nul(&info, fp)) {
 335                 int lmode, rmode;
 336                 struct object_id loid, roid;
 337                 char status;
 338                 const char *src_path, *dst_path;
 339                 size_t src_path_len, dst_path_len;
 340
 341                 if (starts_with(info.buf, "::"))
 342                         die(N_("combined diff formats('-c' and '--cc') are "
 343                                "not supported in\n"
 344                                "directory diff mode('-d' and '--dir-diff')."));
 345
 346                 if (parse_index_info(info.buf, &lmode, &rmode, &loid, &roid,
 347                                      &status))
 348                         break;
 349                 if (strbuf_getline_nul(&lpath, fp))
 350                         break;
 351                 src_path = lpath.buf;
 352                 src_path_len = lpath.len;
 353
 354                 i++;
 355                 if (status != 'C' && status != 'R') {
 356                         dst_path = src_path;
 357                         dst_path_len = src_path_len;
 358                 } else {
 359                         if (strbuf_getline_nul(&rpath, fp))
 360                                 break;
 361                         dst_path = rpath.buf;
 362                         dst_path_len = rpath.len;
 363                 }
 364
 365                 if (S_ISGITLINK(lmode) || S_ISGITLINK(rmode)) {
 366                         strbuf_reset(&buf);
 367                         strbuf_addf(&buf, "Subproject commit %s",
 368                                     oid_to_hex(&loid));
 369                         add_left_or_right(&submodules, src_path, buf.buf, 0);
 370                         strbuf_reset(&buf);
 371                         strbuf_addf(&buf, "Subproject commit %s",
 372                                     oid_to_hex(&roid));
 373                         if (!oidcmp(&loid, &roid))
 374                                 strbuf_addstr(&buf, "-dirty");
 375                         add_left_or_right(&submodules, dst_path, buf.buf, 1);
 376                         continue;
 377                 }
 378
 379                 if (S_ISLNK(lmode)) {
 380                         char *content = read_sha1_file(loid.hash, &type, &size);
 381                         add_left_or_right(&symlinks2, src_path, content, 0);
 382                         free(content);
 383                 }
 384
 385                 if (S_ISLNK(rmode)) {
 386                         char *content = read_sha1_file(roid.hash, &type, &size);
 387                         add_left_or_right(&symlinks2, dst_path, content, 1);
 388                         free(content);
 389                 }
 390
 391                 if (lmode && status != 'C') {
 392                         ce->ce_mode = lmode;
 393                         oidcpy(&ce->oid, &loid);
 394                         strcpy(ce->name, src_path);
 395                         ce->ce_namelen = src_path_len;
 396                         if (checkout_entry(ce, &lstate, NULL))
 397                                 return error("could not write '%s'", src_path);
 398                 }
 399
 400                 if (rmode) {
 401                         struct working_tree_entry *entry;
 402
 403                         /* Avoid duplicate working_tree entries */
 404                         FLEX_ALLOC_STR(entry, path, dst_path);
 405                         hashmap_entry_init(entry, strhash(dst_path));
 406                         if (hashmap_get(&working_tree_dups, entry, NULL)) {
 407                                 free(entry);
 408                                 continue;
 409                         }
 410                         hashmap_add(&working_tree_dups, entry);
 411
 412                         if (!use_wt_file(workdir, dst_path, &roid)) {
 413                                 ce->ce_mode = rmode;
 414                                 oidcpy(&ce->oid, &roid);
 415                                 strcpy(ce->name, dst_path);
 416                                 ce->ce_namelen = dst_path_len;
 417                                 if (checkout_entry(ce, &rstate, NULL))
 418                                         return error("could not write '%s'",
 419                                                      dst_path);
 420                         } else if (!is_null_oid(&roid)) {
 421                                 /*
 422                                  * Changes in the working tree need special
 423                                  * treatment since they are not part of the
 424                                  * index.
 425                                  */
 426                                 struct cache_entry *ce2 =
 427                                         make_cache_entry(rmode, roid.hash,
 428                                                          dst_path, 0, 0);
 429
 430                                 add_index_entry(&wtindex, ce2,
 431                                                 ADD_CACHE_JUST_APPEND);
 432
 433                                 add_path(&rdir, rdir_len, dst_path);
 434                                 if (ensure_leading_directories(rdir.buf))
 435                                         return error("could not create "
 436                                                      "directory for '%s'",
 437                                                      dst_path);
 438                                 add_path(&wtdir, wtdir_len, dst_path);
 439                                 if (symlinks) {
 440                                         if (symlink(wtdir.buf, rdir.buf)) {
 441                                                 ret = error_errno("could not symlink '%s' to '%s'", wtdir.buf, rdir.buf);
 442                                                 goto finish;
 443                                         }
 444                                 } else {
 445                                         struct stat st;
 446                                         if (stat(wtdir.buf, &st))
 447                                                 st.st_mode = 0644;
 448                                         if (copy_file(rdir.buf, wtdir.buf,
 449                                                       st.st_mode)) {
 450                                                 ret = error("could not copy '%s' to '%s'", wtdir.buf, rdir.buf);
 451                                                 goto finish;
 452                                         }
 453                                 }
 454                         }
 455                 }
 456         }
 457
 458         if (finish_command(&child)) {
 459                 ret = error("error occurred running diff --raw");
 460                 goto finish;
 461         }
 462
 463         if (!i)
 464                 return 0;
 465
 466         /*
 467          * Changes to submodules require special treatment.This loop writes a
 468          * temporary file to both the left and right directories to show the
 469          * change in the recorded SHA1 for the submodule.
 470          */
 471         hashmap_iter_init(&submodules, &iter);
 472         while ((entry = hashmap_iter_next(&iter))) {
 473                 if (*entry->left) {
 474                         add_path(&ldir, ldir_len, entry->path);
 475                         ensure_leading_directories(ldir.buf);
 476                         write_file(ldir.buf, "%s", entry->left);
 477                 }
 478                 if (*entry->right) {
 479                         add_path(&rdir, rdir_len, entry->path);
 480                         ensure_leading_directories(rdir.buf);
 481                         write_file(rdir.buf, "%s", entry->right);
 482                 }
 483         }
 484
 485         /*
 486          * Symbolic links require special treatment.The standard "git diff"
 487          * shows only the link itself, not the contents of the link target.
 488          * This loop replicates that behavior.
 489          */
 490         hashmap_iter_init(&symlinks2, &iter);
 491         while ((entry = hashmap_iter_next(&iter))) {
 492                 if (*entry->left) {
 493                         add_path(&ldir, ldir_len, entry->path);
 494                         ensure_leading_directories(ldir.buf);
 495                         write_file(ldir.buf, "%s", entry->left);
 496                 }
 497                 if (*entry->right) {
 498                         add_path(&rdir, rdir_len, entry->path);
 499                         ensure_leading_directories(rdir.buf);
 500                         write_file(rdir.buf, "%s", entry->right);
 501                 }
 502         }
 503
 504         strbuf_release(&buf);
 505
 506         strbuf_setlen(&ldir, ldir_len);
 507         helper_argv[1] = ldir.buf;
 508         strbuf_setlen(&rdir, rdir_len);
 509         helper_argv[2] = rdir.buf;
 510
 511         if (extcmd) {
 512                 helper_argv[0] = extcmd;
 513                 flags = 0;
 514         } else
 515                 setenv("GIT_DIFFTOOL_DIRDIFF", "true", 1);
 516         rc = run_command_v_opt(helper_argv, flags);
 517
 518         /*
 519          * If the diff includes working copy files and those
 520          * files were modified during the diff, then the changes
 521          * should be copied back to the working tree.
 522          * Do not copy back files when symlinks are used and the
 523          * external tool did not replace the original link with a file.
 524          *
 525          * These hashes are loaded lazily since they aren't needed
 526          * in the common case of --symlinks and the difftool updating
 527          * files through the symlink.
 528          */
 529         hashmap_init(&wt_modified, (hashmap_cmp_fn)path_entry_cmp,
 530                      wtindex.cache_nr);
 531         hashmap_init(&tmp_modified, (hashmap_cmp_fn)path_entry_cmp,
 532                      wtindex.cache_nr);
 533
 534         for (i = 0; i < wtindex.cache_nr; i++) {
 535                 struct hashmap_entry dummy;
 536                 const char *name = wtindex.cache[i]->name;
 537                 struct stat st;
 538
 539                 add_path(&rdir, rdir_len, name);
 540                 if (lstat(rdir.buf, &st))
 541                         continue;
 542
 543                 if ((symlinks && S_ISLNK(st.st_mode)) || !S_ISREG(st.st_mode))
 544                         continue;
 545
 546                 if (!indices_loaded) {
 547                         static struct lock_file lock;
 548                         strbuf_reset(&buf);
 549                         strbuf_addf(&buf, "%s/wtindex", tmpdir);
 550                         if (hold_lock_file_for_update(&lock, buf.buf, 0) < 0 ||
 551                             write_locked_index(&wtindex, &lock, COMMIT_LOCK)) {
 552                                 ret = error("could not write %s", buf.buf);
 553                                 rollback_lock_file(&lock);
 554                                 goto finish;
 555                         }
 556                         changed_files(&wt_modified, buf.buf, workdir);
 557                         strbuf_setlen(&rdir, rdir_len);
 558                         changed_files(&tmp_modified, buf.buf, rdir.buf);
 559                         add_path(&rdir, rdir_len, name);
 560                         indices_loaded = 1;
 561                 }
 562
 563                 hashmap_entry_init(&dummy, strhash(name));
 564                 if (hashmap_get(&tmp_modified, &dummy, name)) {
 565                         add_path(&wtdir, wtdir_len, name);
 566                         if (hashmap_get(&wt_modified, &dummy, name)) {
 567                                 warning(_("both files modified: '%s' and '%s'."),
 568                                         wtdir.buf, rdir.buf);
 569                                 warning(_("working tree file has been left."));
 570                                 warning("%s", "");
 571                                 err = 1;
 572                         } else if (unlink(wtdir.buf) ||
 573                                    copy_file(wtdir.buf, rdir.buf, st.st_mode))
 574                                 warning_errno(_("could not copy '%s' to '%s'"),
 575                                               rdir.buf, wtdir.buf);
 576                 }
 577         }
 578
 579         if (err) {
 580                 warning(_("temporary files exist in '%s'."), tmpdir);
 581                 warning(_("you may want to cleanup or recover these."));
 582                 exit(1);
 583         } else
 584                 exit_cleanup(tmpdir, rc);
 585
 586 finish:
 587         free(ce);
 588         strbuf_release(&ldir);
 589         strbuf_release(&rdir);
 590         strbuf_release(&wtdir);
 591         strbuf_release(&buf);
 592
 593         return ret;
 594 }
 595
 596 static int run_file_diff(int prompt, const char *prefix,
 597                          int argc, const char **argv)
 598 {
 599         struct argv_array args = ARGV_ARRAY_INIT;
 600         const char *env[] = {
 601                 "GIT_PAGER=", "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL,
 602                 NULL
 603         };
 604         int ret = 0, i;
 605
 606         if (prompt > 0)
 607                 env[2] = "GIT_DIFFTOOL_PROMPT=true";
 608         else if (!prompt)
 609                 env[2] = "GIT_DIFFTOOL_NO_PROMPT=true";
 610
 611
 612         argv_array_push(&args, "diff");
 613         for (i = 0; i < argc; i++)
 614                 argv_array_push(&args, argv[i]);
 615         ret = run_command_v_opt_cd_env(args.argv, RUN_GIT_CMD, prefix, env);
 616         exit(ret);
 617 }
 618
 619 int cmd_difftool(int argc, const char **argv, const char *prefix)
 620 {
 621         int use_gui_tool = 0, dir_diff = 0, prompt = -1, symlinks = 0,
 622             tool_help = 0;
 623         static char *difftool_cmd = NULL, *extcmd = NULL;
 624         struct option builtin_difftool_options[] = {
 625                 OPT_BOOL('g', "gui", &use_gui_tool,
 626                          N_("use `diff.guitool` instead of `diff.tool`")),
 627                 OPT_BOOL('d', "dir-diff", &dir_diff,
 628                          N_("perform a full-directory diff")),
 629                 { OPTION_SET_INT, 'y', "no-prompt", &prompt, NULL,
 630                         N_("do not prompt before launching a diff tool"),
 631                         PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 0},
 632                 { OPTION_SET_INT, 0, "prompt", &prompt, NULL, NULL,
 633                         PARSE_OPT_NOARG | PARSE_OPT_NONEG | PARSE_OPT_HIDDEN,
 634                         NULL, 1 },
 635                 OPT_BOOL(0, "symlinks", &symlinks,
 636                          N_("use symlinks in dir-diff mode")),
 637                 OPT_STRING('t', "tool", &difftool_cmd, N_("<tool>"),
 638                            N_("use the specified diff tool")),
 639                 OPT_BOOL(0, "tool-help", &tool_help,
 640                          N_("print a list of diff tools that may be used with "
 641                             "`--tool`")),
 642                 OPT_BOOL(0, "trust-exit-code", &trust_exit_code,
 643                          N_("make 'git-difftool' exit when an invoked diff "
 644                             "tool returns a non - zero exit code")),
 645                 OPT_STRING('x', "extcmd", &extcmd, N_("<command>"),
 646                            N_("specify a custom command for viewing diffs")),
 647                 OPT_END()
 648         };
 649
 650         git_config(difftool_config, NULL);
 651         symlinks = has_symlinks;
 652
 653         argc = parse_options(argc, argv, prefix, builtin_difftool_options,
 654                              builtin_difftool_usage, PARSE_OPT_KEEP_UNKNOWN |
 655                              PARSE_OPT_KEEP_DASHDASH);
 656
 657         if (tool_help)
 658                 return print_tool_help();
 659
 660         /* NEEDSWORK: once we no longer spawn anything, remove this */
 661         setenv(GIT_DIR_ENVIRONMENT, absolute_path(get_git_dir()), 1);
 662         setenv(GIT_WORK_TREE_ENVIRONMENT, absolute_path(get_git_work_tree()), 1);
 663
 664         if (use_gui_tool && diff_gui_tool && *diff_gui_tool)
 665                 setenv("GIT_DIFF_TOOL", diff_gui_tool, 1);
 666         else if (difftool_cmd) {
 667                 if (*difftool_cmd)
 668                         setenv("GIT_DIFF_TOOL", difftool_cmd, 1);
 669                 else
 670                         die(_("no <tool> given for --tool=<tool>"));
 671         }
 672
 673         if (extcmd) {
 674                 if (*extcmd)
 675                         setenv("GIT_DIFFTOOL_EXTCMD", extcmd, 1);
 676                 else
 677                         die(_("no <cmd> given for --extcmd=<cmd>"));
 678         }
 679
 680         setenv("GIT_DIFFTOOL_TRUST_EXIT_CODE",
 681                trust_exit_code ? "true" : "false", 1);
 682
 683         /*
 684          * In directory diff mode, 'git-difftool--helper' is called once
 685          * to compare the a / b directories. In file diff mode, 'git diff'
 686          * will invoke a separate instance of 'git-difftool--helper' for
 687          * each file that changed.
 688          */
 689         if (dir_diff)
 690                 return run_dir_diff(extcmd, symlinks, prefix, argc, argv);
 691         return run_file_diff(prompt, prefix, argc, argv);
 692 }