Add "readonly" as a keyword for PHP and add previous classnames to descriptor pool

[bshaffer]

See #10038

This PR adds compatibility for PHP 8.1 by identifying "readonly" as a reserved word, and by adding forwards compatibility for any ReadOnly classes generated with a previous protobuf version (see new tests / new test protos).

It should be noted that in the past when we added a new keyword, forwards compatibility was not preserved. We only realized it now because we have several libraries (Spanner/Datastore/Firestore) which use the keyword readonly for message names.

Summary

• Makes ReadOnly a reserved keyword for PHP 8.1
  • Added in fix: reserve "ReadOnly" keyword for PHP 8.1 and add compatibility #9633
  • When the forwards-compatibility issue was discovered, we reverted this in Revert "fix: reserve "ReadOnly" keyword for PHP 8.1 and add compatibi…lity (#9633)" #10036
• Adds the "previously unreserved name" to the descriptor pool to preserve forwards compatibility.
• Adds tests with previously generated classes to verify it works
• Updates the protobuf.so extension as well!

BC file for the previously unreserved classnames

In the file ReadOnly.php, where there used to generate class ReadOnly, there is now the following code to create an alias for the new classname:

<?php
# Generated by the protocol buffer compiler.  DO NOT EDIT!
# source: proto/test_reserved_message_lower.proto

namespace Lower;

class_exists(PBReadOnly::class); // autoload the new class, which will also create an alias to the deprecated class
@trigger_error(__NAMESPACE__ . '\ReadOnly is deprecated and will be removed in the next major release. Use PBReadOnly instead', E_USER_DEPRECATED);

This ensures that anyone still using the name Readme on previous versions of PHP will not be broken.

Alias declaration in new class file to the previously unreserved classnames

Likewise, at the bottom of the new PBReadOnly.php file/class, we create an alias to the old one:

/**
 * Generated from protobuf message <code>readonly</code>
 */
class PBReadOnly extends \Google\Protobuf\Internal\Message
{

    /**
     * Constructor.
     *
     * @param array $data {
     *     Optional. Data for populating the Message object.
     *
     * }
     */
    public function __construct($data = NULL) {
        \GPBMetadata\Proto\TestReservedMessageLower::initOnce();
        parent::__construct($data);
    }

}

// Adding a class alias for backwards compatibility with the "readonly" keyword.
class_alias(ReadOnly::class, __NAMESPACE__ . '\ReadOnly');

NOTE: The classname "readonly" is still valid, but the syntax for declaring it (e.g. class ReadOnly {}) is not. That means that creating an alias for it, and instantiating the class directly, is still valid in PHP 8.1.

Previously unreserved classnames

The previously unreserved classnames function the same way as any other type of reserved word, with the exception that they also get added to the descriptor pool. This is to maintain backwards compatibility.

In order for Protobuf to be able to know and handle any messages defined using the previous classname (e.g. ReadOnly) for versions of any library that are still using the older versions, we've added the previous names to the descriptor pool in both the native PHP and the C-extension implementations.

[bshaffer]

Looks like I need to add some of the new test files to the distribution file! Should be an easy fix.

[bshaffer]

@haberman This is ready for another test run!

[zeriyoshi]

make: *** [initialize_submodule] Error 1

It seems to be a network problem or something.
Re-run kokoro, maybe it will succeed.

[bshaffer]

@zeriyoshi I see the following errors:

-- Performing Test HAVE_CXX_FLAG_WD654 - Failed
-- Performing Test HAVE_THREAD_SAFETY_ATTRIBUTES -- failed to compile
-- Performing Test HAVE_GNU_POSIX_REGEX -- failed to compile
CMake Error at CMakeLists.txt:34 (message):
  Did not find Google Test sources! Either pass correct path in
  GOOGLETEST_PATH, or enable BENCHMARK_DOWNLOAD_DEPENDENCIES, or disable
  BENCHMARK_USE_BUNDLED_GTEST, or disable BENCHMARK_ENABLE_GTEST_TESTS /
  BENCHMARK_ENABLE_TESTING.

Could these be what is causing the make error?

[bshaffer]

@zeriyoshi okay I fixed it, for some reason in my commit there was an update to the third_party/benchmarks submodule. I don't know how that got in there, but I removed the change and that should do the trick!

[fowles]

this looks to duplicate the code above. Can you add well named helper?

[bshaffer]

There are subtle enough differences that I do not think it would be advantageous to add a helper

[bshaffer]

@fowles I've addressed all your review comments, PTAL (also @haberman)