submodule deinit: unset core.worktree

When a submodule is deinit'd, the working tree is gone, so the setting of
core.worktree is bogus. Unset it. As we covered the only other case in
which a submodule loses its working tree in the earlier step
(i.e. switching branches of top-level project to move to a commit that did
not have the submodule), this makes the code always maintain
core.worktree correctly unset when there is no working tree
for a submodule.

This re-introduces 984cd77 (submodule deinit: unset core.worktree,
2018-06-18), which was reverted as part of f178c13 (Revert "Merge
branch 'sb/submodule-core-worktree'", 2018-09-07)

The whole series was reverted as the offending commit e983175
(submodule: ensure core.worktree is set after update, 2018-06-18)
was relied on by other commits such as 984cd77.

Keep the offending commit reverted, but its functionality came back via
4d6d6ef (Merge branch 'sb/submodule-update-in-c', 2018-09-17), such
that we can reintroduce 984cd77 now.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/submodule--helper.c

@@ -1131,6 +1131,8 @@ static void deinit_submodule(const char *path, const char *prefix,
 		if (!(flags & OPT_QUIET))
 			printf(format, displaypath);
 
+		submodule_unset_core_worktree(sub);
+
 		strbuf_release(&sb_rm);
 	}
 

t/lib-submodule-update.sh

@@ -235,7 +235,7 @@ reset_work_tree_to_interested () {
 	then
 		mkdir -p submodule_update/.git/modules/sub1/modules &&
 		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
-		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+		# core.worktree is unset for sub2 as it is not checked out
 	fi &&
 	# indicate we are interested in the submodule:
 	git -C submodule_update config submodule.sub1.url "bogus" &&

t/t7400-submodule-basic.sh

@@ -984,6 +984,11 @@ test_expect_success 'submodule deinit should remove the whole submodule section
 	rmdir init
 '
 
+test_expect_success 'submodule deinit should unset core.worktree' '
+	test_path_is_file .git/modules/example/config &&
+	test_must_fail git config -f .git/modules/example/config core.worktree
+'
+
 test_expect_success 'submodule deinit from subdirectory' '
 	git submodule update --init &&
 	git config submodule.example.foo bar &&