`svelte-check`'s `--watch` mode incorrectly ignores directories because of regression from #2807

[abrahamguo]

Describe the bug

in #2807 (@jasonlyu123) (specifically, in refactor(check): clarify snapshot callback and simplify directory watching; ignore .crush), @aewing introduced a regression that can cause svelte-check's watch mode to inadvertently ignore directories.

In that commit, this code was added:

        // If new dir is a parent of existing ones, unwatch children
        const toRemove: string[] = [];
        for (const existing of this.currentWatchedDirs) {
            if (this.isSubdir(existing, dir)) {
                toRemove.push(existing);
            }
        }
        if (toRemove.length) {
            this.watcher.unwatch(toRemove);

this.watcher refers to a chokidar watcher instance.

It's not explicitly documented in Chokidar's documentation, but unwatching a child absolute path, followed by adding a parent absolute path, causes the child paths to remain ignored.

Reproduction

import { watch } from 'chokidar';

const { dirname } = import.meta;
const a = `${dirname}/a`;
const b = `${a}/b`;
watch(b).unwatch(b).add(a).on(`change`, () => console.log(`change!`));

Note that the change handler runs for everything in the a directory, except for changes that happen in the b subdirectory.

Expected behaviour

svelte-check should properly handle parent and child directories when passing to chokidar.

System Info

• OS: macOS

Which package is the issue about?

svelte-check

Additional Information, eg. Screenshots

No response