Merge branch 'nd/maint-sparse-errors'

* nd/maint-sparse-errors:
Add explanation why we do not allow to sparse checkout to empty working tree
sparse checkout: show error messages when worktree shaping fails

diff --combined t/t1011-read-tree-sparse-checkout.sh
index 018c3546b6f05228a20dfb5ec9364d0a1575e4ff,efcd8abd2f97458cfe06900d1723910bc59ac6dc..5c0053a20bf2fbf1dd466ace5dc933e38ce3544d
--- 1/t/t1011-read-tree-sparse-checkout.sh
--- 2/t/t1011-read-tree-sparse-checkout.sh
+++ b/t/t1011-read-tree-sparse-checkout.sh
@@@ -234,4 -234,19 +234,20 @@@ test_expect_success 'read-tree --reset 
        test_cmp empty result
  '
  
+ test_expect_success 'print errors when failed to update worktree' '
+       echo sub >.git/info/sparse-checkout &&
+       git checkout -f init &&
+       mkdir sub &&
+       touch sub/added sub/addedtoo &&
+       test_must_fail git checkout top 2>actual &&
+       cat >expected <<\EOF &&
+ error: The following untracked working tree files would be overwritten by checkout:
+       sub/added
+       sub/addedtoo
+ Please move or remove them before you can switch branches.
++Aborting
+ EOF
+       test_cmp expected actual
+ '
+ 
  test_done

diff --combined unpack-trees.c
index 237aed8c766638c55d8d6b870c86ef2ad13a74d3,0f205903e170388d800e71d155ac99dccc101846..8282f5e5f6c615460e1c340d66e395c2d57aef73
--- 1/unpack-trees.c
--- 2/unpack-trees.c
+++ b/unpack-trees.c
@@@ -159,7 -159,7 +159,7 @@@ static void display_error_msgs(struct u
                string_list_clear(rejects, 0);
        }
        if (something_displayed)
 -              printf("Aborting\n");
 +              fprintf(stderr, "Aborting\n");
  }
  
  /*
@@@ -444,7 -444,6 +444,7 @@@ static int traverse_trees_recursive(in
  
        newinfo = *info;
        newinfo.prev = info;
 +      newinfo.pathspec = info->pathspec;
        newinfo.name = *p;
        newinfo.pathlen += tree_entry_len(p->path, p->sha1) + 1;
        newinfo.conflicts |= df_conflicts;
@@@ -594,7 -593,7 +594,7 @@@ static int unpack_nondirectories(int n
  static int unpack_failed(struct unpack_trees_options *o, const char *message)
  {
        discard_index(&o->result);
 -      if (!o->gently) {
 +      if (!o->gently && !o->exiting_early) {
                if (message)
                        return error("%s", message);
                return -1;
@@@ -1041,7 -1040,6 +1041,7 @@@ int unpack_trees(unsigned len, struct t
                info.fn = unpack_callback;
                info.data = o;
                info.show_all_errors = o->show_all_errors;
 +              info.pathspec = o->pathspec;
  
                if (o->prefix) {
                        /*
@@@ -1091,6 -1089,7 +1091,7 @@@
                 */
                mark_new_skip_worktree(o->el, &o->result, CE_ADDED, CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
  
+               ret = 0;
                for (i = 0; i < o->result.cache_nr; i++) {
                        struct cache_entry *ce = o->result.cache[i];
  
@@@ -1103,19 -1102,30 +1104,30 @@@
                         * correct CE_NEW_SKIP_WORKTREE
                         */
                        if (ce->ce_flags & CE_ADDED &&
-                           verify_absent(ce, ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o))
-                                       return -1;
+                           verify_absent(ce, ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
+                               if (!o->show_all_errors)
+                                       goto return_failed;
+                               ret = -1;
+                       }
  
                        if (apply_sparse_checkout(ce, o)) {
+                               if (!o->show_all_errors)
+                                       goto return_failed;
                                ret = -1;
-                               goto done;
                        }
                        if (!ce_skip_worktree(ce))
                                empty_worktree = 0;
  
                }
+               if (ret < 0)
+                       goto return_failed;
+               /*
+                * Sparse checkout is meant to narrow down checkout area
+                * but it does not make sense to narrow down to empty working
+                * tree. This is usually a mistake in sparse checkout rules.
+                * Do not allow users to do that.
+                */
                if (o->result.cache_nr && empty_worktree) {
-                       /* dubious---why should this fail??? */
                        ret = unpack_failed(o, "Sparse checkout leaves no entry on working directory");
                        goto done;
                }
@@@ -1135,8 -1145,6 +1147,8 @@@ return_failed
                display_error_msgs(o);
        mark_all_ce_unused(o->src_index);
        ret = unpack_failed(o, NULL);
 +      if (o->exiting_early)
 +              ret = 0;
        goto done;
  }
  
@@@ -1170,22 -1178,11 +1182,22 @@@ static int verify_uptodate_1(struct cac
  {
        struct stat st;
  
 -      if (o->index_only || (!((ce->ce_flags & CE_VALID) || ce_skip_worktree(ce)) && (o->reset || ce_uptodate(ce))))
 +      if (o->index_only)
 +              return 0;
 +
 +      /*
 +       * CE_VALID and CE_SKIP_WORKTREE cheat, we better check again
 +       * if this entry is truly up-to-date because this file may be
 +       * overwritten.
 +       */
 +      if ((ce->ce_flags & CE_VALID) || ce_skip_worktree(ce))
 +              ; /* keep checking */
 +      else if (o->reset || ce_uptodate(ce))
                return 0;
  
        if (!lstat(ce->name, &st)) {
 -              unsigned changed = ie_match_stat(o->src_index, ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 +              int flags = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE;
 +              unsigned changed = ie_match_stat(o->src_index, ce, &st, flags);
                if (!changed)
                        return 0;
                /*