is_readable() returns writability, not readability (breaks dirlist on read-only dirs)

[remyperona]

Summary

VirtualFilesystemDirect::is_readable() returns a file's writability, not its readability. A read-only entry (e.g. 0444) is readable but not writable, so it is wrongly reported as "not readable".

// VirtualFilesystemDirect.php
public function is_readable( $file ) {
    return is_writeable( $this->getUrl( $file ) ); // ← wrong predicate
}

Impact

This is not purely cosmetic. dirlist() gates on is_readable():

// VirtualFilesystemDirect.php (dirlist)
if ( ! $this->is_dir( $path ) || ! $this->is_readable( $path ) ) {
    return false;
}

So listing a read-only directory returns false — precisely the kind of permission scenario a filesystem mock exists to reproduce. Any consumer test that sets a directory read-only and asserts on its listing gets a false negative.

Why it hasn't surfaced

The unit test only covers 0777 (→ true) and 000 (→ false), both of which happen to pass under the buggy delegation. A 0444 (read-only) case would fail. See Tests/Unit/VirtualFilesystemDirect/isReadable.php.

Failure scenario

$file = $this->filesystem->getFile( 'baz/index.html' );
$file->chmod( 0444 );                                   // read-only
$this->assertTrue( $this->filesystem->is_readable( 'baz/index.html' ) ); // FAILS (returns false)

Proposed fix

public function is_readable( $file ) {
    return is_readable( $this->getUrl( $file ) );
}

Plus regression coverage:

• isReadable.php: add a 0444 case asserting true.
• isWritable.php: add a 0444 case asserting false (guards against the inverse regression).
• dirlist.php: add a read-only directory case asserting the listing is returned, not false.

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Found during an audit of WP Rocket's integration test suite, which depends on this package.