Cannot compile descriptor.proto to php because it is proto2

[Lehren]

What version of protobuf and what language are you using?
Version: v28.3
Language: PHP

What operating system (Linux, Windows, ...) and version?
Mac 15.6.1

What runtime / compiler are you using (e.g., python version or gcc version)
28.3

What did you do?
Steps to reproduce the behavior:

1. Download the 28.3 universal package for osx and install as per the readme
2. Go into the folder
3. Run

 protoc --proto_path=/usr/local/include \
--php_out=../protogen \
google/protobuf/descriptor.proto

4. See error

What did you expect to see
Successful compilation

What did you see instead?
Can't generate PHP code for closed enum google.protobuf.ExtensionRangeOptions.VerificationState. Please use either proto3 or editions without enum_type = CLOSED

Anything else we should know about your project / environment
Additionally, any reference in .proto files to google.protobuf.DescriptorProto get compiled to Google\Protobuf\DescriptorProto , which doesn't exist. It should be Google\Protobuf\Descriptor

[mkruskal-google]

This is unfortunate but WAI. The PHP generator currently doesn't support any features exclusive to proto2 (e.g. closed enums, required fields, groups, extensions). There is no support in the runtime for any of these, so any code we produced would behave incorrectly under various conditions.

Adding support for closed enums might be pretty easy (a lot of runtimes treat all enums as open), but descriptor.proto also has required fields and those would require more work.