checkout: FORCE doesn't halt on dirty index

If the index is dirty, allow `GIT_CHECKOUT_FORCE` to obliterate unsaved
changes.  This is in keeping with its name and description.

src/checkout.c

@@ -2412,16 +2412,25 @@ static int checkout_data_init(
 		 * and those should not be overwritten.)
 		 */
 		if (data->index != git_iterator_index(target)) {
-			if ((error = git_index_read_safely(data->index)) < 0)
-				goto cleanup;
-
-			/* cannot checkout if unresolved conflicts exist */
-			if ((data->opts.checkout_strategy & GIT_CHECKOUT_FORCE) == 0 &&
-				git_index_has_conflicts(data->index)) {
-				error = GIT_ECONFLICT;
-				giterr_set(GITERR_CHECKOUT,
-					"unresolved conflicts exist in the index");
-				goto cleanup;
+			if (data->opts.checkout_strategy & GIT_CHECKOUT_FORCE) {
+				/* When forcing, we can blindly re-read the index */
+				if ((error = git_index_read(data->index, false)) < 0)
+					goto cleanup;
+			} else {
+				/*
+				 * When not being forced, we need to check for unresolved
+				 * conflicts and unsaved changes in the index before
+				 * proceeding.
+				 */
+				if (git_index_has_conflicts(data->index)) {
+					error = GIT_ECONFLICT;
+					giterr_set(GITERR_CHECKOUT,
+						"unresolved conflicts exist in the index");
+					goto cleanup;
+				}
+
+				if ((error = git_index_read_safely(data->index)) < 0)
+					goto cleanup;
 			}
 
 			/* clean conflict data in the current index */

tests/checkout/tree.c

@@ -672,12 +672,9 @@ void test_checkout_tree__can_cancel_checkout_from_notify(void)
 	git_checkout_options opts = GIT_CHECKOUT_OPTIONS_INIT;
 	git_oid oid;
 	git_object *obj = NULL;
-	git_index *index = NULL;
 
 	assert_on_branch(g_repo, "master");
 
-	cl_git_pass(git_repository_index(&index, g_repo));
-
 	cl_git_pass(git_reference_name_to_id(&oid, g_repo, "refs/heads/dir"));
 	cl_git_pass(git_object_lookup(&obj, g_repo, &oid, GIT_OBJ_ANY));
 
@@ -704,8 +701,6 @@ void test_checkout_tree__can_cancel_checkout_from_notify(void)
 	else
 		cl_assert_equal_i(4, ca.count);
 
-	cl_git_pass(git_index_read(index, 1));
-
 	/* and again with a different stopping point and return code */
 	ca.filename = "README";
 	ca.error = 123;
@@ -721,7 +716,6 @@ void test_checkout_tree__can_cancel_checkout_from_notify(void)
 		cl_assert_equal_i(1, ca.count);
 
 	git_object_free(obj);
-	git_index_free(index);
 }
 
 void test_checkout_tree__can_checkout_with_last_workdir_item_missing(void)
@@ -1502,11 +1496,9 @@ void test_checkout_tree__baseline_is_empty_when_no_index(void)
 	git_reference *head;
 	git_object *obj;
 	size_t conflicts = 0;
-	git_index *index;
 
 	assert_on_branch(g_repo, "master");
 
-	cl_git_pass(git_repository_index(&index, g_repo));
 	cl_git_pass(git_repository_head(&head, g_repo));
 	cl_git_pass(git_reference_peel(&obj, head, GIT_OBJ_COMMIT));
 
@@ -1525,8 +1517,6 @@ void test_checkout_tree__baseline_is_empty_when_no_index(void)
 	cl_git_fail_with(GIT_ECONFLICT, git_checkout_tree(g_repo, obj, &opts));
 	cl_assert_equal_i(4, conflicts);
 
-	cl_git_pass(git_index_read(index, 1));
-
 	/* but force should succeed and update the index */
 	opts.checkout_strategy |= GIT_CHECKOUT_FORCE;
 	cl_git_pass(git_checkout_tree(g_repo, obj, &opts));
@@ -1535,7 +1525,6 @@ void test_checkout_tree__baseline_is_empty_when_no_index(void)
 
 	git_object_free(obj);
 	git_reference_free(head);
-	git_index_free(index);
 }
 
 void test_checkout_tree__mode_change_is_force_updated(void)

tests/checkout/typechange.c

@@ -259,7 +259,6 @@ static int make_submodule_dirty(git_submodule *sm, const char *name, void *paylo
 void test_checkout_typechange__checkout_with_conflicts(void)
 {
 	int i;
-	git_index *index;
 	git_object *obj;
 	git_checkout_options opts = GIT_CHECKOUT_OPTIONS_INIT;
 	notify_counts cts = {0};
@@ -290,10 +289,6 @@ void test_checkout_typechange__checkout_with_conflicts(void)
 		cl_assert_equal_i(cts.updates, 0);
 		cl_assert_equal_i(cts.ignored, 0);
 
-		cl_git_pass(git_repository_index(&index, g_repo));
-		cl_git_pass(git_index_read(index, 1));
-		git_index_free(index);
-
 		opts.checkout_strategy =
 			GIT_CHECKOUT_FORCE | GIT_CHECKOUT_REMOVE_UNTRACKED;
 		memset(&cts, 0, sizeof(cts));