wt-status: actually ignore submodules when requested

Since ff6f1f564 (submodule-config: lazy-load a repository's .gitmodules
file, 2017-08-03) rebase interactive fails if there are any submodules
with unstaged changes which have been configured with a value for
'submodule.<name>.ignore' in the repository's config.

This is due to how configured values of 'submodule.<name>.ignore' are
handled in addition to a change in how the submodule config is loaded.
When the diff machinery hits a submodule (gitlink as well as a
corresponding entry in the submodule subsystem) it will read the value
of 'submodule.<name>.ignore' stored in the repository's config and if
the config is present it will clear the 'IGNORE_SUBMODULES' (which is
the flag explicitly requested by rebase interactive),
'IGNORE_UNTRACKED_IN_SUBMODULES', and 'IGNORE_DIRTY_SUBMODULES' diff
flags and then set one of them based on the configured value.

Historically this wasn't a problem because the submodule subsystem
wasn't initialized because the .gitmodules file wasn't explicitly loaded
by the rebase interactive command.  So when the diff machinery hit a
submodule it would skip over reading any configured values of
'submodule.<name>.ignore'.

In order to preserve the behavior of submodules being ignored by rebase
interactive, also set the 'OVERRIDE_SUBMODULE_CONFIG' diff flag when
submodules are requested to be ignored when checking for unstaged
changes.

Reported-by: Orgad Shaneh <orgads@gmail.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3426-rebase-submodule.sh

@@ -40,4 +40,21 @@ git_rebase_interactive () {
 
 test_submodule_switch "git_rebase_interactive"
 
+test_expect_success 'rebase interactive ignores modified submodules' '
+	test_when_finished "rm -rf super sub" &&
+	git init sub &&
+	git -C sub commit --allow-empty -m "Initial commit" &&
+	git init super &&
+	git -C super submodule add ../sub &&
+	git -C super config submodule.sub.ignore dirty &&
+	>super/foo &&
+	git -C super add foo &&
+	git -C super commit -m "Initial commit" &&
+	test_commit -C super a &&
+	test_commit -C super b &&
+	test_commit -C super/sub c &&
+	set_fake_editor &&
+	git -C super rebase -i HEAD^^
+'
+
 test_done

wt-status.c

@@ -2262,8 +2262,10 @@ int has_unstaged_changes(int ignore_submodules)
 	int result;
 
 	init_revisions(&rev_info, NULL);
-	if (ignore_submodules)
+	if (ignore_submodules) {
 		DIFF_OPT_SET(&rev_info.diffopt, IGNORE_SUBMODULES);
+		DIFF_OPT_SET(&rev_info.diffopt, OVERRIDE_SUBMODULE_CONFIG);
+	}
 	DIFF_OPT_SET(&rev_info.diffopt, QUICK);
 	diff_setup_done(&rev_info.diffopt);
 	result = run_diff_files(&rev_info, 0);