Merge branch 'jk/cherry-pick-root-with-resolve' into maint

* jk/cherry-pick-root-with-resolve:
t3503: test cherry picking and reverting root commits
revert: allow reverting a root commit
cherry-pick: handle root commits with external strategies

diff --combined builtin/merge.c
index 0f03dff1160f68de6f406f038c1b5c2bbd6529c8,8a0f6901f90c9728fb7521121ead030325ce3a45..a437ecba297e76eab1b72a2966b2b0b1cf3b49bc
--- 1/builtin/merge.c
--- 2/builtin/merge.c
+++ b/builtin/merge.c
@@@ -56,7 -56,6 +56,7 @@@ static size_t use_strategies_nr, use_st
  static const char **xopts;
  static size_t xopts_nr, xopts_alloc;
  static const char *branch;
 +static char *branch_mergeoptions;
  static int option_renormalize;
  static int verbosity;
  static int allow_rerere_auto;
@@@ -504,34 -503,26 +504,34 @@@ cleanup
        strbuf_release(&bname);
  }
  
 +static void parse_branch_merge_options(char *bmo)
 +{
 +      const char **argv;
 +      int argc;
 +
 +      if (!bmo)
 +              return;
 +      argc = split_cmdline(bmo, &argv);
 +      if (argc < 0)
 +              die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 +                  split_cmdline_strerror(argc));
 +      argv = xrealloc(argv, sizeof(*argv) * (argc + 2));
 +      memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 +      argc++;
 +      argv[0] = "branch.*.mergeoptions";
 +      parse_options(argc, argv, NULL, builtin_merge_options,
 +                    builtin_merge_usage, 0);
 +      free(argv);
 +}
 +
  static int git_merge_config(const char *k, const char *v, void *cb)
  {
        if (branch && !prefixcmp(k, "branch.") &&
                !prefixcmp(k + 7, branch) &&
                !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
 -              const char **argv;
 -              int argc;
 -              char *buf;
 -
 -              buf = xstrdup(v);
 -              argc = split_cmdline(buf, &argv);
 -              if (argc < 0)
 -                      die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 -                          split_cmdline_strerror(argc));
 -              argv = xrealloc(argv, sizeof(*argv) * (argc + 2));
 -              memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 -              argc++;
 -              parse_options(argc, argv, NULL, builtin_merge_options,
 -                            builtin_merge_usage, 0);
 -              free(buf);
 +              free(branch_mergeoptions);
 +              branch_mergeoptions = xstrdup(v);
 +              return 0;
        }
  
        if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
@@@ -599,6 -590,14 +599,14 @@@ static void write_tree_trivial(unsigne
                die(_("git write-tree failed to write a tree"));
  }
  
+ static const char *merge_argument(struct commit *commit)
+ {
+       if (commit)
+               return sha1_to_hex(commit->object.sha1);
+       else
+               return EMPTY_TREE_SHA1_HEX;
+ }
+ 
  int try_merge_command(const char *strategy, size_t xopts_nr,
                      const char **xopts, struct commit_list *common,
                      const char *head_arg, struct commit_list *remotes)
@@@ -619,11 -618,11 +627,11 @@@
                args[i++] = s;
        }
        for (j = common; j; j = j->next)
-               args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
+               args[i++] = xstrdup(merge_argument(j->item));
        args[i++] = "--";
        args[i++] = head_arg;
        for (j = remotes; j; j = j->next)
-               args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
+               args[i++] = xstrdup(merge_argument(j->item));
        args[i] = NULL;
        ret = run_command_v_opt(args, RUN_GIT_CMD);
        strbuf_release(&buf);
@@@ -1019,8 -1018,6 +1027,8 @@@ int cmd_merge(int argc, const char **ar
        if (diff_use_color_default == -1)
                diff_use_color_default = git_use_color_default;
  
 +      if (branch_mergeoptions)
 +              parse_branch_merge_options(branch_mergeoptions);
        argc = parse_options(argc, argv, prefix, builtin_merge_options,
                        builtin_merge_usage, 0);