restore: invalidate cache-tree when removing entries with --staged

When "git restore --staged <path>" removes a path that's in the index,
it marks the entry with CE_REMOVE, but we don't do anything to
invalidate the cache-tree. In the non-staged case, we end up in
checkout_worktree(), which calls remove_marked_cache_entries(). That
actually drops the entries from the index, as well as invalidating the
cache-tree and untracked-cache.

But with --staged, we never call checkout_worktree(), and the CE_REMOVE
entries remain. Interestingly, they are dropped when we write out the
index, but that means the resulting index is inconsistent: its
cache-tree will not match the actual entries, and running "git commit"
immediately after will create the wrong tree.

We can solve this by calling remove_marked_cache_entries() ourselves
before writing out the index. Note that we can't just hoist it out of
checkout_worktree(); that function needs to iterate over the CE_REMOVE
entries (to drop their matching worktree files) before removing them.

One curiosity about the test: without this patch, it actually triggers a
BUG() when running git-restore:

  BUG: cache-tree.c:810: new1 with flags 0x4420000 should not be in cache-tree

But in the original problem report, which used a similar recipe,
git-restore actually creates the bogus index (and the commit is created
with the wrong tree). I'm not sure why the test here behaves differently
than my out-of-suite reproduction, but what's here should catch either
symptom (and the fix corrects both cases).

Reported-by: Torsten Krah <krah.tm@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -521,6 +521,8 @@ static int checkout_paths(const struct checkout_opts *opts,
 	/* Now we are committed to check them out */
 	if (opts->checkout_worktree)
 		errs |= checkout_worktree(opts);
+	else
+		remove_marked_cache_entries(&the_index, 1);
 
 	/*
 	 * Allow updating the index when checking out from the index.

t/t2070-restore.sh

@@ -95,4 +95,21 @@ test_expect_success 'restore --ignore-unmerged ignores unmerged entries' '
 	)
 '
 
+test_expect_success 'restore --staged invalidates cache tree for deletions' '
+	test_when_finished git reset --hard &&
+	>new1 &&
+	>new2 &&
+	git add new1 new2 &&
+
+	# It is important to commit and then reset here, so that the index
+	# contains a valid cache-tree for the "both" tree.
+	git commit -m both &&
+	git reset --soft HEAD^ &&
+
+	git restore --staged new1 &&
+	git commit -m "just new2" &&
+	git rev-parse HEAD:new2 &&
+	test_must_fail git rev-parse HEAD:new1
+'
+
 test_done