Rather than using Greg's birthday, use null to indicate that the
existing format/compression should be retained. For the format
simply using zero would be sufficient, but as the documentation
explicitly says that NULL is allowed here, we may as well make
that the truth.
In other words, don't automatically unserialize when the magic
phar:// stream wrappers are used.
RFC: https://wiki.php.net/rfc/phar_stop_autoloading_metadata
Also, change the signature from `getMetadata()`
to `getMetadata(array $unserialize_options = [])`.
Start throwing earlier if setMetadata() is called and serialization threw.
See https://externals.io/message/110856 and
https://bugs.php.net/bug.php?id=76774
This was refactored to add a phar_metadata_tracker for the following reasons:
- The way to properly copy a zval was previously implicit and undocumented
(e.g. is it a pointer to a raw string or an actual value)
- Avoid unnecessary serialization and unserialization in the most common case
- If a metadata value is serialized once while saving a new/modified phar file,
this allows reusing the same serialized string.
- Have as few ways to copy/clone/lazily parse metadata (etc.) as possible,
so that code changes can be limited to only a few places in the future.
- Performance is hopefully not a concern - copying a string should be faster
than unserializing a value, and metadata should be rare in most cases.
Remove unnecessary skip in a test(Compression's unused)
Add additional assertions about usage of persistent phars
Improve robustness of `Phar*->setMetadata()`
- Add sanity checks for edge cases freeing metadata, when destructors
or serializers modify the phar recursively.
- Typical use cases of php have phar.readonly=1 and would not be affected.
Closes GH-5855
