Playground has many classes and interfaces referring to similar concept of PHP. There’s:

• IsomorphicLocalPHP - sync interface for running PHP in the current process
• IsomorphicRemotePHP - same as above but async for running PHP remotely, e.g. in a worker
• BasePHP - base implementation of IsomorphicLocalPHP
• WebPHP - ditto, but with browser specific methods
• NodePHP - ditto, but with node specific methods
• UniversalPHP – an interface with common parts from all of the above that returns either synchronously or asynchronously
• WebPHPEndpoint - Async implementation of IsomorphicRemotePHP that calls WebPHP running in a worker. Used by client apps
• PlaygroundClient – A postMessage facade that calls WebPHPEndpoint from another frame
• ...and probably more.

I saw developers get very confused about this structure, especially with regard to why UniversalPHP and PlaygroundClient are often interchangeable. It is difficult to understand the structure and easy to update one but forget about another (and miss it in a review, see #490).

Let’s discuss and see if there can be a simpler structure that allows for:

• Isomorphic PHP interface that supports web, node, and other runtimes
• Same-thread PHP execution with synchronous method
• Remote PHP execution, e.g. in a worker, with asynchronous methods

If it cannot be simplified, then at least let’s find a way to raise alarm bells in TypeScript if the PR makes a change in BasePHP but not in the other ones.

cc @eliot-akira @dmsnell @wojtekn