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

* 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

builtin/merge.c

@@ -608,6 +608,14 @@ static void write_tree_trivial(unsigned char *sha1)
 		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)
@@ -628,11 +636,11 @@ int try_merge_command(const char *strategy, size_t xopts_nr,
 		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);

builtin/revert.c

@@ -408,8 +408,6 @@ static int do_pick_commit(void)
 	discard_cache();
 
 	if (!commit->parents) {
-		if (action == REVERT)
-			die (_("Cannot revert a root commit"));
 		parent = NULL;
 	}
 	else if (commit->parents->next) {
@@ -467,7 +465,7 @@ static int do_pick_commit(void)
 		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
 		strbuf_addstr(&msgbuf, sha1_to_hex(commit->object.sha1));
 
-		if (commit->parents->next) {
+		if (commit->parents && commit->parents->next) {
 			strbuf_addstr(&msgbuf, ", reversing\nchanges made to ");
 			strbuf_addstr(&msgbuf, sha1_to_hex(parent->object.sha1));
 		}

t/t3503-cherry-pick-root.sh

 #!/bin/sh
 
-test_description='test cherry-picking a root commit'
+test_description='test cherry-picking (and reverting) a root commit'
 
 . ./test-lib.sh
 
@@ -23,7 +23,30 @@ test_expect_success setup '
 test_expect_success 'cherry-pick a root commit' '
 
 	git cherry-pick master &&
-	test first = $(cat file1)
+	echo first >expect &&
+	test_cmp expect file1
+
+'
+
+test_expect_success 'revert a root commit' '
+
+	git revert master &&
+	test_path_is_missing file1
+
+'
+
+test_expect_success 'cherry-pick a root commit with an external strategy' '
+
+	git cherry-pick --strategy=resolve master &&
+	echo first >expect &&
+	test_cmp expect file1
+
+'
+
+test_expect_success 'revert a root commit with an external strategy' '
+
+	git revert --strategy=resolve master &&
+	test_path_is_missing file1
 
 '