[Bug] Faulty detection logic if both file creation and deletion happens between detection calls

[Hiroko103]

Hi!

The logic behind change detection is flawed.
It becomes an issue if both file deletion and creation happens between two 'findChanges' call.
(Theoretically it can be prevented by polling for changes fast enough, but I can't rely on it, since many file operations can happen even in a few milliseconds, and polling can be expensive.)

Problematic source part:

resource-watcher/src/ResourceWatcher.php

Lines 135 to 143 in fda1c53

	if (count($finderFileHashes) > count($cacheFileHashes)) {
	foreach ($finderFileHashes as $file => $hash) {
	$this->processFileFromFilesystem($file, $hash);
	}
	} else {
	foreach ($cacheFileHashes as $file => $hash) {
	$this->processFileFromCache($file, $hash);
	}
	}

Based just on the file count, it is not possible to detect all 3 cases (addition, deletion, updates) at once.
The code should compare differences from the perspective of both of them.
- Cache compared to actual files
- Actual files compared to cache

The library wrongly assumes that if:
"Current count of files" > "file count in cache", then only these two could have happened:

• Any/some file was updated
• New file has been added

AND IF

"Current count of files" <= "file count in cache", then only these two could have happened:

• Any/some file was updated
• Some files were deleted

Examples:

1. Library initialized
2. Files in folder: ['a.txt', 'b.txt', 'c.txt']
3. Delete: 'c.txt'
4. Add: 'd.txt'
5. Detect changes

In this case, the library will report that 'c.txt' has been deleted, but won't report that 'd.txt' have been added.

Another similar example:

1. Library initialized
2. Files in folder: ['a.txt', 'b.txt', 'c.txt']
3. Delete: 'c.txt'
4. Add: 'd.txt'
5. Add: 'e.txt'
6. Detect changes

Now the library will report that 'd.txt' and 'e.txt' have been added, but won't report that 'c.txt' have been deleted.

I'm attaching a test script with the example scenario.

index.zip

[ruudk]

Noticed the same, this fixes the problem it seems:

private function findChangesAgainstCache() : void
    {
        $this->calculateHashOfFilesFromFinder();

        $finderFileHashes = $this->fileHashesFromFinder;
        $cacheFileHashes = $this->cache->getAll();

        foreach (array_diff_key($finderFileHashes, $cacheFileHashes) as $file => $hash) {
            $this->cache->write($file, $hash);
            $this->newFiles[] = $file;
        }

        foreach (array_diff_key($cacheFileHashes, $finderFileHashes) as $file => $hash) {
            $this->cache->delete($file);
            $this->deletedFiles[] = $file;
        }

        foreach (array_intersect_key($finderFileHashes, $cacheFileHashes) as $file => $hash) {
            if ($hash === $cacheFileHashes[$file]) {
                continue;
            }

            $this->cache->write($file, $hash);
            $this->updatedFiles[] = $file;
        }
    }

Just sharing it here. Don't want to create a PR because I already copied this code into my project. Don't want to have a dependency.

[Hiroko103]

Thank you for sharing it. I really appreciate it. :)