Merge branch 'nd/checkout-m-doc-update'

Doc about the above.

* nd/checkout-m-doc-update:
  checkout.txt: note about losing staged changes with --merge

Documentation/git-checkout.txt

@@ -242,6 +242,8 @@ should result in deletion of the path).
 +
 When checking out paths from the index, this option lets you recreate
 the conflicted merge in the specified paths.
++
+When switching branches with `--merge`, staged changes may be lost.
 
 --conflict=<style>::
 	The same as --merge option above, but changes the way the

builtin/checkout.c

@@ -726,6 +726,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			struct tree *result;
 			struct tree *work;
 			struct merge_options o;
+			struct strbuf sb = STRBUF_INIT;
+
 			if (!opts->merge)
 				return 1;
 
@@ -736,6 +738,13 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			if (!old_branch_info->commit)
 				return 1;
 
+			if (repo_index_has_changes(the_repository,
+						   get_commit_tree(old_branch_info->commit),
+						   &sb))
+				warning(_("staged changes in the following files may be lost: %s"),
+					sb.buf);
+			strbuf_release(&sb);
+
 			/* Do more real merge */
 
 			/*