Merge branch 'jc/read-tree-empty-with-m' into maint

"git read-tree -m" (no tree-ish) gave a nonsense suggestion "use
--empty if you want to clear the index".  With "-m", such a request
will still fail anyway, as you'd need to name at least one tree-ish
to be merged.

* jc/read-tree-empty-with-m:
read-tree: "read-tree -m --empty" does not make sense

diff --combined builtin/read-tree.c
index 38344256791a1232963f6153bea3bbfcf94481e7,ce5265dde20705cc6e03029bbf6e6994d352056e..a52a9e11bb13c6685a7c1fbf98258792eef74ff3
--- 1/builtin/read-tree.c
--- 2/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@@ -15,13 -15,10 +15,13 @@@
  #include "builtin.h"
  #include "parse-options.h"
  #include "resolve-undo.h"
 +#include "submodule.h"
 +#include "submodule-config.h"
  
  static int nr_trees;
  static int read_empty;
  static struct tree *trees[MAX_UNPACK_TREES];
 +static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
  
  static int list_tree(unsigned char *sha1)
  {
@@@ -81,7 -78,7 +81,7 @@@ static void debug_stage(const char *lab
        else
                printf("%06o #%d %s %.8s\n",
                       ce->ce_mode, ce_stage(ce), ce->name,
 -                     sha1_to_hex(ce->sha1));
 +                     oid_to_hex(&ce->oid));
  }
  
  static int debug_merge(const struct cache_entry * const *stages,
@@@ -99,23 -96,6 +99,23 @@@
        return 0;
  }
  
 +static int option_parse_recurse_submodules(const struct option *opt,
 +                                         const char *arg, int unset)
 +{
 +      if (unset) {
 +              recurse_submodules = RECURSE_SUBMODULES_OFF;
 +              return 0;
 +      }
 +      if (arg)
 +              recurse_submodules =
 +                      parse_update_recurse_submodules_arg(opt->long_name,
 +                                                          arg);
 +      else
 +              recurse_submodules = RECURSE_SUBMODULES_ON;
 +
 +      return 0;
 +}
 +
  static struct lock_file lock_file;
  
  int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@@ -129,37 -109,34 +129,37 @@@
                { OPTION_CALLBACK, 0, "index-output", NULL, N_("file"),
                  N_("write resulting index to <file>"),
                  PARSE_OPT_NONEG, index_output_cb },
 -              OPT_SET_INT(0, "empty", &read_empty,
 -                          N_("only empty the index"), 1),
 +              OPT_BOOL(0, "empty", &read_empty,
 +                          N_("only empty the index")),
                OPT__VERBOSE(&opts.verbose_update, N_("be verbose")),
                OPT_GROUP(N_("Merging")),
 -              OPT_SET_INT('m', NULL, &opts.merge,
 -                          N_("perform a merge in addition to a read"), 1),
 -              OPT_SET_INT(0, "trivial", &opts.trivial_merges_only,
 -                          N_("3-way merge if no file level merging required"), 1),
 -              OPT_SET_INT(0, "aggressive", &opts.aggressive,
 -                          N_("3-way merge in presence of adds and removes"), 1),
 -              OPT_SET_INT(0, "reset", &opts.reset,
 -                          N_("same as -m, but discard unmerged entries"), 1),
 +              OPT_BOOL('m', NULL, &opts.merge,
 +                       N_("perform a merge in addition to a read")),
 +              OPT_BOOL(0, "trivial", &opts.trivial_merges_only,
 +                       N_("3-way merge if no file level merging required")),
 +              OPT_BOOL(0, "aggressive", &opts.aggressive,
 +                       N_("3-way merge in presence of adds and removes")),
 +              OPT_BOOL(0, "reset", &opts.reset,
 +                       N_("same as -m, but discard unmerged entries")),
                { OPTION_STRING, 0, "prefix", &opts.prefix, N_("<subdirectory>/"),
                  N_("read the tree into the index under <subdirectory>/"),
                  PARSE_OPT_NONEG | PARSE_OPT_LITERAL_ARGHELP },
 -              OPT_SET_INT('u', NULL, &opts.update,
 -                          N_("update working tree with merge result"), 1),
 +              OPT_BOOL('u', NULL, &opts.update,
 +                       N_("update working tree with merge result")),
                { OPTION_CALLBACK, 0, "exclude-per-directory", &opts,
                  N_("gitignore"),
                  N_("allow explicitly ignored files to be overwritten"),
                  PARSE_OPT_NONEG, exclude_per_directory_cb },
 -              OPT_SET_INT('i', NULL, &opts.index_only,
 -                          N_("don't check the working tree after merging"), 1),
 +              OPT_BOOL('i', NULL, &opts.index_only,
 +                       N_("don't check the working tree after merging")),
                OPT__DRY_RUN(&opts.dry_run, N_("don't update the index or the work tree")),
 -              OPT_SET_INT(0, "no-sparse-checkout", &opts.skip_sparse_checkout,
 -                          N_("skip applying sparse checkout filter"), 1),
 -              OPT_SET_INT(0, "debug-unpack", &opts.debug_unpack,
 -                          N_("debug unpack-trees"), 1),
 +              OPT_BOOL(0, "no-sparse-checkout", &opts.skip_sparse_checkout,
 +                       N_("skip applying sparse checkout filter")),
 +              OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 +                       N_("debug unpack-trees")),
 +              { OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
 +                          "checkout", "control recursive updating of submodules",
 +                          PARSE_OPT_OPTARG, option_parse_recurse_submodules },
                OPT_END()
        };
  
@@@ -173,13 -150,7 +173,13 @@@
        argc = parse_options(argc, argv, unused_prefix, read_tree_options,
                             read_tree_usage, 0);
  
 -      hold_locked_index(&lock_file, 1);
 +      hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 +
 +      if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
 +              gitmodules_config();
 +              git_config(submodule_config, NULL);
 +              set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
 +      }
  
        prefix_set = opts.prefix ? 1 : 0;
        if (1 < opts.merge + opts.reset + prefix_set)
@@@ -210,7 -181,7 +210,7 @@@
                        die("failed to unpack tree object %s", arg);
                stage++;
        }
-       if (nr_trees == 0 && !read_empty)
+       if (!nr_trees && !read_empty && !opts.merge)
                warning("read-tree: emptying the index with no arguments is deprecated; use --empty");
        else if (nr_trees > 0 && read_empty)
                die("passing trees as arguments contradicts --empty");
@@@ -226,10 -197,9 +226,10 @@@
                setup_work_tree();
  
        if (opts.merge) {
 -              if (stage < 2)
 -                      die("just how do you expect me to merge %d trees?", stage-1);
                switch (stage - 1) {
 +              case 0:
 +                      die("you must specify at least one tree to merge");
 +                      break;
                case 1:
                        opts.fn = opts.prefix ? bind_merge : oneway_merge;
                        break;