Merge branch 'mm/fetch-show-error-message-on-unadvertised-object'
[gitweb.git] / builtin / difftool.c
index 53870bbaf7528546fb862fe0ea501bdbf437cdcc..d13350ce832cd8c0064c8a5b2d3c9be64f876b8d 100644 (file)
  *
  * Copyright (C) 2016 Johannes Schindelin
  */
+#include "cache.h"
 #include "builtin.h"
 #include "run-command.h"
 #include "exec_cmd.h"
+#include "parse-options.h"
+#include "argv-array.h"
+#include "strbuf.h"
+#include "lockfile.h"
+#include "dir.h"
+
+static char *diff_gui_tool;
+static int trust_exit_code;
+
+static const char *const builtin_difftool_usage[] = {
+       N_("git difftool [<options>] [<commit> [<commit>]] [--] [<path>...]"),
+       NULL
+};
+
+static int difftool_config(const char *var, const char *value, void *cb)
+{
+       if (!strcmp(var, "diff.guitool")) {
+               diff_gui_tool = xstrdup(value);
+               return 0;
+       }
+
+       if (!strcmp(var, "difftool.trustexitcode")) {
+               trust_exit_code = git_config_bool(var, value);
+               return 0;
+       }
+
+       return git_default_config(var, value, cb);
+}
+
+static int print_tool_help(void)
+{
+       const char *argv[] = { "mergetool", "--tool-help=diff", NULL };
+       return run_command_v_opt(argv, RUN_GIT_CMD);
+}
+
+static int parse_index_info(char *p, int *mode1, int *mode2,
+                           struct object_id *oid1, struct object_id *oid2,
+                           char *status)
+{
+       if (*p != ':')
+               return error("expected ':', got '%c'", *p);
+       *mode1 = (int)strtol(p + 1, &p, 8);
+       if (*p != ' ')
+               return error("expected ' ', got '%c'", *p);
+       *mode2 = (int)strtol(p + 1, &p, 8);
+       if (*p != ' ')
+               return error("expected ' ', got '%c'", *p);
+       if (get_oid_hex(++p, oid1))
+               return error("expected object ID, got '%s'", p + 1);
+       p += GIT_SHA1_HEXSZ;
+       if (*p != ' ')
+               return error("expected ' ', got '%c'", *p);
+       if (get_oid_hex(++p, oid2))
+               return error("expected object ID, got '%s'", p + 1);
+       p += GIT_SHA1_HEXSZ;
+       if (*p != ' ')
+               return error("expected ' ', got '%c'", *p);
+       *status = *++p;
+       if (!*status)
+               return error("missing status");
+       if (p[1] && !isdigit(p[1]))
+               return error("unexpected trailer: '%s'", p + 1);
+       return 0;
+}
 
 /*
- * NEEDSWORK: this function can go once the legacy-difftool Perl script is
- * retired.
- *
- * We intentionally avoid reading the config directly here, to avoid messing up
- * the GIT_* environment variables when we need to fall back to exec()ing the
- * Perl script.
+ * Remove any trailing slash from $workdir
+ * before starting to avoid double slashes in symlink targets.
+ */
+static void add_path(struct strbuf *buf, size_t base_len, const char *path)
+{
+       strbuf_setlen(buf, base_len);
+       if (buf->len && buf->buf[buf->len - 1] != '/')
+               strbuf_addch(buf, '/');
+       strbuf_addstr(buf, path);
+}
+
+/*
+ * Determine whether we can simply reuse the file in the worktree.
  */
-static int use_builtin_difftool(void) {
-       struct child_process cp = CHILD_PROCESS_INIT;
-       struct strbuf out = STRBUF_INIT;
-       int ret;
-
-       argv_array_pushl(&cp.args,
-                        "config", "--bool", "difftool.usebuiltin", NULL);
-       cp.git_cmd = 1;
-       if (capture_command(&cp, &out, 6))
+static int use_wt_file(const char *workdir, const char *name,
+                      struct object_id *oid)
+{
+       struct strbuf buf = STRBUF_INIT;
+       struct stat st;
+       int use = 0;
+
+       strbuf_addstr(&buf, workdir);
+       add_path(&buf, buf.len, name);
+
+       if (!lstat(buf.buf, &st) && !S_ISLNK(st.st_mode)) {
+               struct object_id wt_oid;
+               int fd = open(buf.buf, O_RDONLY);
+
+               if (fd >= 0 &&
+                   !index_fd(wt_oid.hash, fd, &st, OBJ_BLOB, name, 0)) {
+                       if (is_null_oid(oid)) {
+                               oidcpy(oid, &wt_oid);
+                               use = 1;
+                       } else if (!oidcmp(oid, &wt_oid))
+                               use = 1;
+               }
+       }
+
+       strbuf_release(&buf);
+
+       return use;
+}
+
+struct working_tree_entry {
+       struct hashmap_entry entry;
+       char path[FLEX_ARRAY];
+};
+
+static int working_tree_entry_cmp(struct working_tree_entry *a,
+                                 struct working_tree_entry *b, void *keydata)
+{
+       return strcmp(a->path, b->path);
+}
+
+/*
+ * The `left` and `right` entries hold paths for the symlinks hashmap,
+ * and a SHA-1 surrounded by brief text for submodules.
+ */
+struct pair_entry {
+       struct hashmap_entry entry;
+       char left[PATH_MAX], right[PATH_MAX];
+       const char path[FLEX_ARRAY];
+};
+
+static int pair_cmp(struct pair_entry *a, struct pair_entry *b, void *keydata)
+{
+       return strcmp(a->path, b->path);
+}
+
+static void add_left_or_right(struct hashmap *map, const char *path,
+                             const char *content, int is_right)
+{
+       struct pair_entry *e, *existing;
+
+       FLEX_ALLOC_STR(e, path, path);
+       hashmap_entry_init(e, strhash(path));
+       existing = hashmap_get(map, e, NULL);
+       if (existing) {
+               free(e);
+               e = existing;
+       } else {
+               e->left[0] = e->right[0] = '\0';
+               hashmap_add(map, e);
+       }
+       strlcpy(is_right ? e->right : e->left, content, PATH_MAX);
+}
+
+struct path_entry {
+       struct hashmap_entry entry;
+       char path[FLEX_ARRAY];
+};
+
+static int path_entry_cmp(struct path_entry *a, struct path_entry *b, void *key)
+{
+       return strcmp(a->path, key ? key : b->path);
+}
+
+static void changed_files(struct hashmap *result, const char *index_path,
+                         const char *workdir)
+{
+       struct child_process update_index = CHILD_PROCESS_INIT;
+       struct child_process diff_files = CHILD_PROCESS_INIT;
+       struct strbuf index_env = STRBUF_INIT, buf = STRBUF_INIT;
+       const char *git_dir = absolute_path(get_git_dir()), *env[] = {
+               NULL, NULL
+       };
+       FILE *fp;
+
+       strbuf_addf(&index_env, "GIT_INDEX_FILE=%s", index_path);
+       env[0] = index_env.buf;
+
+       argv_array_pushl(&update_index.args,
+                        "--git-dir", git_dir, "--work-tree", workdir,
+                        "update-index", "--really-refresh", "-q",
+                        "--unmerged", NULL);
+       update_index.no_stdin = 1;
+       update_index.no_stdout = 1;
+       update_index.no_stderr = 1;
+       update_index.git_cmd = 1;
+       update_index.use_shell = 0;
+       update_index.clean_on_exit = 1;
+       update_index.dir = workdir;
+       update_index.env = env;
+       /* Ignore any errors of update-index */
+       run_command(&update_index);
+
+       argv_array_pushl(&diff_files.args,
+                        "--git-dir", git_dir, "--work-tree", workdir,
+                        "diff-files", "--name-only", "-z", NULL);
+       diff_files.no_stdin = 1;
+       diff_files.git_cmd = 1;
+       diff_files.use_shell = 0;
+       diff_files.clean_on_exit = 1;
+       diff_files.out = -1;
+       diff_files.dir = workdir;
+       diff_files.env = env;
+       if (start_command(&diff_files))
+               die("could not obtain raw diff");
+       fp = xfdopen(diff_files.out, "r");
+       while (!strbuf_getline_nul(&buf, fp)) {
+               struct path_entry *entry;
+               FLEX_ALLOC_STR(entry, path, buf.buf);
+               hashmap_entry_init(entry, strhash(buf.buf));
+               hashmap_add(result, entry);
+       }
+       if (finish_command(&diff_files))
+               die("diff-files did not exit properly");
+       strbuf_release(&index_env);
+       strbuf_release(&buf);
+}
+
+static NORETURN void exit_cleanup(const char *tmpdir, int exit_code)
+{
+       struct strbuf buf = STRBUF_INIT;
+       strbuf_addstr(&buf, tmpdir);
+       remove_dir_recursively(&buf, 0);
+       if (exit_code)
+               warning(_("failed: %d"), exit_code);
+       exit(exit_code);
+}
+
+static int ensure_leading_directories(char *path)
+{
+       switch (safe_create_leading_directories(path)) {
+               case SCLD_OK:
+               case SCLD_EXISTS:
+                       return 0;
+               default:
+                       return error(_("could not create leading directories "
+                                      "of '%s'"), path);
+       }
+}
+
+static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
+                       int argc, const char **argv)
+{
+       char tmpdir[PATH_MAX];
+       struct strbuf info = STRBUF_INIT, lpath = STRBUF_INIT;
+       struct strbuf rpath = STRBUF_INIT, buf = STRBUF_INIT;
+       struct strbuf ldir = STRBUF_INIT, rdir = STRBUF_INIT;
+       struct strbuf wtdir = STRBUF_INIT;
+       size_t ldir_len, rdir_len, wtdir_len;
+       struct cache_entry *ce = xcalloc(1, sizeof(ce) + PATH_MAX + 1);
+       const char *workdir, *tmp;
+       int ret = 0, i;
+       FILE *fp;
+       struct hashmap working_tree_dups, submodules, symlinks2;
+       struct hashmap_iter iter;
+       struct pair_entry *entry;
+       enum object_type type;
+       unsigned long size;
+       struct index_state wtindex;
+       struct checkout lstate, rstate;
+       int rc, flags = RUN_GIT_CMD, err = 0;
+       struct child_process child = CHILD_PROCESS_INIT;
+       const char *helper_argv[] = { "difftool--helper", NULL, NULL, NULL };
+       struct hashmap wt_modified, tmp_modified;
+       int indices_loaded = 0;
+
+       workdir = get_git_work_tree();
+
+       /* Setup temp directories */
+       tmp = getenv("TMPDIR");
+       xsnprintf(tmpdir, sizeof(tmpdir), "%s/git-difftool.XXXXXX", tmp ? tmp : "/tmp");
+       if (!mkdtemp(tmpdir))
+               return error("could not create '%s'", tmpdir);
+       strbuf_addf(&ldir, "%s/left/", tmpdir);
+       strbuf_addf(&rdir, "%s/right/", tmpdir);
+       strbuf_addstr(&wtdir, workdir);
+       if (!wtdir.len || !is_dir_sep(wtdir.buf[wtdir.len - 1]))
+               strbuf_addch(&wtdir, '/');
+       mkdir(ldir.buf, 0700);
+       mkdir(rdir.buf, 0700);
+
+       memset(&wtindex, 0, sizeof(wtindex));
+
+       memset(&lstate, 0, sizeof(lstate));
+       lstate.base_dir = ldir.buf;
+       lstate.base_dir_len = ldir.len;
+       lstate.force = 1;
+       memset(&rstate, 0, sizeof(rstate));
+       rstate.base_dir = rdir.buf;
+       rstate.base_dir_len = rdir.len;
+       rstate.force = 1;
+
+       ldir_len = ldir.len;
+       rdir_len = rdir.len;
+       wtdir_len = wtdir.len;
+
+       hashmap_init(&working_tree_dups,
+                    (hashmap_cmp_fn)working_tree_entry_cmp, 0);
+       hashmap_init(&submodules, (hashmap_cmp_fn)pair_cmp, 0);
+       hashmap_init(&symlinks2, (hashmap_cmp_fn)pair_cmp, 0);
+
+       child.no_stdin = 1;
+       child.git_cmd = 1;
+       child.use_shell = 0;
+       child.clean_on_exit = 1;
+       child.dir = prefix;
+       child.out = -1;
+       argv_array_pushl(&child.args, "diff", "--raw", "--no-abbrev", "-z",
+                        NULL);
+       for (i = 0; i < argc; i++)
+               argv_array_push(&child.args, argv[i]);
+       if (start_command(&child))
+               die("could not obtain raw diff");
+       fp = xfdopen(child.out, "r");
+
+       /* Build index info for left and right sides of the diff */
+       i = 0;
+       while (!strbuf_getline_nul(&info, fp)) {
+               int lmode, rmode;
+               struct object_id loid, roid;
+               char status;
+               const char *src_path, *dst_path;
+               size_t src_path_len, dst_path_len;
+
+               if (starts_with(info.buf, "::"))
+                       die(N_("combined diff formats('-c' and '--cc') are "
+                              "not supported in\n"
+                              "directory diff mode('-d' and '--dir-diff')."));
+
+               if (parse_index_info(info.buf, &lmode, &rmode, &loid, &roid,
+                                    &status))
+                       break;
+               if (strbuf_getline_nul(&lpath, fp))
+                       break;
+               src_path = lpath.buf;
+               src_path_len = lpath.len;
+
+               i++;
+               if (status != 'C' && status != 'R') {
+                       dst_path = src_path;
+                       dst_path_len = src_path_len;
+               } else {
+                       if (strbuf_getline_nul(&rpath, fp))
+                               break;
+                       dst_path = rpath.buf;
+                       dst_path_len = rpath.len;
+               }
+
+               if (S_ISGITLINK(lmode) || S_ISGITLINK(rmode)) {
+                       strbuf_reset(&buf);
+                       strbuf_addf(&buf, "Subproject commit %s",
+                                   oid_to_hex(&loid));
+                       add_left_or_right(&submodules, src_path, buf.buf, 0);
+                       strbuf_reset(&buf);
+                       strbuf_addf(&buf, "Subproject commit %s",
+                                   oid_to_hex(&roid));
+                       if (!oidcmp(&loid, &roid))
+                               strbuf_addstr(&buf, "-dirty");
+                       add_left_or_right(&submodules, dst_path, buf.buf, 1);
+                       continue;
+               }
+
+               if (S_ISLNK(lmode)) {
+                       char *content = read_sha1_file(loid.hash, &type, &size);
+                       add_left_or_right(&symlinks2, src_path, content, 0);
+                       free(content);
+               }
+
+               if (S_ISLNK(rmode)) {
+                       char *content = read_sha1_file(roid.hash, &type, &size);
+                       add_left_or_right(&symlinks2, dst_path, content, 1);
+                       free(content);
+               }
+
+               if (lmode && status != 'C') {
+                       ce->ce_mode = lmode;
+                       oidcpy(&ce->oid, &loid);
+                       strcpy(ce->name, src_path);
+                       ce->ce_namelen = src_path_len;
+                       if (checkout_entry(ce, &lstate, NULL))
+                               return error("could not write '%s'", src_path);
+               }
+
+               if (rmode) {
+                       struct working_tree_entry *entry;
+
+                       /* Avoid duplicate working_tree entries */
+                       FLEX_ALLOC_STR(entry, path, dst_path);
+                       hashmap_entry_init(entry, strhash(dst_path));
+                       if (hashmap_get(&working_tree_dups, entry, NULL)) {
+                               free(entry);
+                               continue;
+                       }
+                       hashmap_add(&working_tree_dups, entry);
+
+                       if (!use_wt_file(workdir, dst_path, &roid)) {
+                               ce->ce_mode = rmode;
+                               oidcpy(&ce->oid, &roid);
+                               strcpy(ce->name, dst_path);
+                               ce->ce_namelen = dst_path_len;
+                               if (checkout_entry(ce, &rstate, NULL))
+                                       return error("could not write '%s'",
+                                                    dst_path);
+                       } else if (!is_null_oid(&roid)) {
+                               /*
+                                * Changes in the working tree need special
+                                * treatment since they are not part of the
+                                * index.
+                                */
+                               struct cache_entry *ce2 =
+                                       make_cache_entry(rmode, roid.hash,
+                                                        dst_path, 0, 0);
+
+                               add_index_entry(&wtindex, ce2,
+                                               ADD_CACHE_JUST_APPEND);
+
+                               add_path(&rdir, rdir_len, dst_path);
+                               if (ensure_leading_directories(rdir.buf))
+                                       return error("could not create "
+                                                    "directory for '%s'",
+                                                    dst_path);
+                               add_path(&wtdir, wtdir_len, dst_path);
+                               if (symlinks) {
+                                       if (symlink(wtdir.buf, rdir.buf)) {
+                                               ret = error_errno("could not symlink '%s' to '%s'", wtdir.buf, rdir.buf);
+                                               goto finish;
+                                       }
+                               } else {
+                                       struct stat st;
+                                       if (stat(wtdir.buf, &st))
+                                               st.st_mode = 0644;
+                                       if (copy_file(rdir.buf, wtdir.buf,
+                                                     st.st_mode)) {
+                                               ret = error("could not copy '%s' to '%s'", wtdir.buf, rdir.buf);
+                                               goto finish;
+                                       }
+                               }
+                       }
+               }
+       }
+
+       if (finish_command(&child)) {
+               ret = error("error occurred running diff --raw");
+               goto finish;
+       }
+
+       if (!i)
                return 0;
-       strbuf_trim(&out);
-       ret = !strcmp("true", out.buf);
-       strbuf_release(&out);
+
+       /*
+        * Changes to submodules require special treatment.This loop writes a
+        * temporary file to both the left and right directories to show the
+        * change in the recorded SHA1 for the submodule.
+        */
+       hashmap_iter_init(&submodules, &iter);
+       while ((entry = hashmap_iter_next(&iter))) {
+               if (*entry->left) {
+                       add_path(&ldir, ldir_len, entry->path);
+                       ensure_leading_directories(ldir.buf);
+                       write_file(ldir.buf, "%s", entry->left);
+               }
+               if (*entry->right) {
+                       add_path(&rdir, rdir_len, entry->path);
+                       ensure_leading_directories(rdir.buf);
+                       write_file(rdir.buf, "%s", entry->right);
+               }
+       }
+
+       /*
+        * Symbolic links require special treatment.The standard "git diff"
+        * shows only the link itself, not the contents of the link target.
+        * This loop replicates that behavior.
+        */
+       hashmap_iter_init(&symlinks2, &iter);
+       while ((entry = hashmap_iter_next(&iter))) {
+               if (*entry->left) {
+                       add_path(&ldir, ldir_len, entry->path);
+                       ensure_leading_directories(ldir.buf);
+                       write_file(ldir.buf, "%s", entry->left);
+               }
+               if (*entry->right) {
+                       add_path(&rdir, rdir_len, entry->path);
+                       ensure_leading_directories(rdir.buf);
+                       write_file(rdir.buf, "%s", entry->right);
+               }
+       }
+
+       strbuf_release(&buf);
+
+       strbuf_setlen(&ldir, ldir_len);
+       helper_argv[1] = ldir.buf;
+       strbuf_setlen(&rdir, rdir_len);
+       helper_argv[2] = rdir.buf;
+
+       if (extcmd) {
+               helper_argv[0] = extcmd;
+               flags = 0;
+       } else
+               setenv("GIT_DIFFTOOL_DIRDIFF", "true", 1);
+       rc = run_command_v_opt(helper_argv, flags);
+
+       /*
+        * If the diff includes working copy files and those
+        * files were modified during the diff, then the changes
+        * should be copied back to the working tree.
+        * Do not copy back files when symlinks are used and the
+        * external tool did not replace the original link with a file.
+        *
+        * These hashes are loaded lazily since they aren't needed
+        * in the common case of --symlinks and the difftool updating
+        * files through the symlink.
+        */
+       hashmap_init(&wt_modified, (hashmap_cmp_fn)path_entry_cmp,
+                    wtindex.cache_nr);
+       hashmap_init(&tmp_modified, (hashmap_cmp_fn)path_entry_cmp,
+                    wtindex.cache_nr);
+
+       for (i = 0; i < wtindex.cache_nr; i++) {
+               struct hashmap_entry dummy;
+               const char *name = wtindex.cache[i]->name;
+               struct stat st;
+
+               add_path(&rdir, rdir_len, name);
+               if (lstat(rdir.buf, &st))
+                       continue;
+
+               if ((symlinks && S_ISLNK(st.st_mode)) || !S_ISREG(st.st_mode))
+                       continue;
+
+               if (!indices_loaded) {
+                       static struct lock_file lock;
+                       strbuf_reset(&buf);
+                       strbuf_addf(&buf, "%s/wtindex", tmpdir);
+                       if (hold_lock_file_for_update(&lock, buf.buf, 0) < 0 ||
+                           write_locked_index(&wtindex, &lock, COMMIT_LOCK)) {
+                               ret = error("could not write %s", buf.buf);
+                               rollback_lock_file(&lock);
+                               goto finish;
+                       }
+                       changed_files(&wt_modified, buf.buf, workdir);
+                       strbuf_setlen(&rdir, rdir_len);
+                       changed_files(&tmp_modified, buf.buf, rdir.buf);
+                       add_path(&rdir, rdir_len, name);
+                       indices_loaded = 1;
+               }
+
+               hashmap_entry_init(&dummy, strhash(name));
+               if (hashmap_get(&tmp_modified, &dummy, name)) {
+                       add_path(&wtdir, wtdir_len, name);
+                       if (hashmap_get(&wt_modified, &dummy, name)) {
+                               warning(_("both files modified: '%s' and '%s'."),
+                                       wtdir.buf, rdir.buf);
+                               warning(_("working tree file has been left."));
+                               warning("%s", "");
+                               err = 1;
+                       } else if (unlink(wtdir.buf) ||
+                                  copy_file(wtdir.buf, rdir.buf, st.st_mode))
+                               warning_errno(_("could not copy '%s' to '%s'"),
+                                             rdir.buf, wtdir.buf);
+               }
+       }
+
+       if (err) {
+               warning(_("temporary files exist in '%s'."), tmpdir);
+               warning(_("you may want to cleanup or recover these."));
+               exit(1);
+       } else
+               exit_cleanup(tmpdir, rc);
+
+finish:
+       free(ce);
+       strbuf_release(&ldir);
+       strbuf_release(&rdir);
+       strbuf_release(&wtdir);
+       strbuf_release(&buf);
+
        return ret;
 }
 
+static int run_file_diff(int prompt, const char *prefix,
+                        int argc, const char **argv)
+{
+       struct argv_array args = ARGV_ARRAY_INIT;
+       const char *env[] = {
+               "GIT_PAGER=", "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL,
+               NULL
+       };
+       int ret = 0, i;
+
+       if (prompt > 0)
+               env[2] = "GIT_DIFFTOOL_PROMPT=true";
+       else if (!prompt)
+               env[2] = "GIT_DIFFTOOL_NO_PROMPT=true";
+
+
+       argv_array_push(&args, "diff");
+       for (i = 0; i < argc; i++)
+               argv_array_push(&args, argv[i]);
+       ret = run_command_v_opt_cd_env(args.argv, RUN_GIT_CMD, prefix, env);
+       exit(ret);
+}
+
 int cmd_difftool(int argc, const char **argv, const char *prefix)
 {
-       /*
-        * NEEDSWORK: Once the builtin difftool has been tested enough
-        * and git-legacy-difftool.perl is retired to contrib/, this preamble
-        * can be removed.
-        */
-       if (!use_builtin_difftool()) {
-               const char *path = mkpath("%s/git-legacy-difftool",
-                                         git_exec_path());
+       int use_gui_tool = 0, dir_diff = 0, prompt = -1, symlinks = 0,
+           tool_help = 0;
+       static char *difftool_cmd = NULL, *extcmd = NULL;
+       struct option builtin_difftool_options[] = {
+               OPT_BOOL('g', "gui", &use_gui_tool,
+                        N_("use `diff.guitool` instead of `diff.tool`")),
+               OPT_BOOL('d', "dir-diff", &dir_diff,
+                        N_("perform a full-directory diff")),
+               { OPTION_SET_INT, 'y', "no-prompt", &prompt, NULL,
+                       N_("do not prompt before launching a diff tool"),
+                       PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 0},
+               { OPTION_SET_INT, 0, "prompt", &prompt, NULL, NULL,
+                       PARSE_OPT_NOARG | PARSE_OPT_NONEG | PARSE_OPT_HIDDEN,
+                       NULL, 1 },
+               OPT_BOOL(0, "symlinks", &symlinks,
+                        N_("use symlinks in dir-diff mode")),
+               OPT_STRING('t', "tool", &difftool_cmd, N_("<tool>"),
+                          N_("use the specified diff tool")),
+               OPT_BOOL(0, "tool-help", &tool_help,
+                        N_("print a list of diff tools that may be used with "
+                           "`--tool`")),
+               OPT_BOOL(0, "trust-exit-code", &trust_exit_code,
+                        N_("make 'git-difftool' exit when an invoked diff "
+                           "tool returns a non - zero exit code")),
+               OPT_STRING('x', "extcmd", &extcmd, N_("<command>"),
+                          N_("specify a custom command for viewing diffs")),
+               OPT_END()
+       };
 
-               if (sane_execvp(path, (char **)argv) < 0)
-                       die_errno("could not exec %s", path);
+       git_config(difftool_config, NULL);
+       symlinks = has_symlinks;
 
-               return 0;
+       argc = parse_options(argc, argv, prefix, builtin_difftool_options,
+                            builtin_difftool_usage, PARSE_OPT_KEEP_UNKNOWN |
+                            PARSE_OPT_KEEP_DASHDASH);
+
+       if (tool_help)
+               return print_tool_help();
+
+       /* NEEDSWORK: once we no longer spawn anything, remove this */
+       setenv(GIT_DIR_ENVIRONMENT, absolute_path(get_git_dir()), 1);
+       setenv(GIT_WORK_TREE_ENVIRONMENT, absolute_path(get_git_work_tree()), 1);
+
+       if (use_gui_tool && diff_gui_tool && *diff_gui_tool)
+               setenv("GIT_DIFF_TOOL", diff_gui_tool, 1);
+       else if (difftool_cmd) {
+               if (*difftool_cmd)
+                       setenv("GIT_DIFF_TOOL", difftool_cmd, 1);
+               else
+                       die(_("no <tool> given for --tool=<tool>"));
+       }
+
+       if (extcmd) {
+               if (*extcmd)
+                       setenv("GIT_DIFFTOOL_EXTCMD", extcmd, 1);
+               else
+                       die(_("no <cmd> given for --extcmd=<cmd>"));
        }
-       prefix = setup_git_directory();
-       trace_repo_setup(prefix);
-       setup_work_tree();
 
-       die("TODO");
+       setenv("GIT_DIFFTOOL_TRUST_EXIT_CODE",
+              trust_exit_code ? "true" : "false", 1);
+
+       /*
+        * In directory diff mode, 'git-difftool--helper' is called once
+        * to compare the a / b directories. In file diff mode, 'git diff'
+        * will invoke a separate instance of 'git-difftool--helper' for
+        * each file that changed.
+        */
+       if (dir_diff)
+               return run_dir_diff(extcmd, symlinks, prefix, argc, argv);
+       return run_file_diff(prompt, prefix, argc, argv);
 }