Merge branch 'jk/http-auth' into next
[git] / 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 }