Emscripten ports have broken backward compatibility

[TelpeNight]

We use current latest version of emscripten (1.27) with SDL2 port (USE_SDL=2). We have been using cached version of SDL from ~/.emscripten_ports until now. Few days ago we tried to fetch the latest version of SDL port from github by manually clearing cache. Now our project is broken in all browsers.
Please, see #3060 and emscripten-ports/SDL2#2. The problem is that emscripten 1.27 still has the old buggy code:

var rect = (target === window) ? { left: 0, top: 0 } : target.getBoundingClientRect();

But SDL port relies on latest changes (see emscripten-ports/SDL2@8d47621). So latest emscripten 1.27 and master branch of SDL post are not compatible.
We don't want to switch to emscripten's master branch, and 1.27 is the latest version available in emsdk. So we had to manually patch emscripten's sources to be compatible with SDL port.

I have 2 suggestion:

1. Provide each emscripten version with some stable and well tested tags of ports.
2. Allow developers to configure repository, branch and tag of each port. So developers can use their own forks for quick bug fixes and testing.

Right now we are going to modify local sdl.py. We will use our own sdl port fork to increase stability.

[kripken]

True, we should make ports use a version specific to the emscripten version. Will try to get to that today.

[kripken]

Done. I don't think we'll backport this, but going forward, emscripten versions will use specific ports versions.

[TelpeNight]

I still suggest to allow developers to configure repository, branch and tag of each port. Should I open it as a separate feature request?

[kripken]

No need, we can reopen this. Perhaps I didn't fully understand, then. How specifically are you suggesting the user would define those things?

[TelpeNight]

Dunno exactly. Maybe by specifying some config file as a build option. Something like --port-config some_file. some_file would allow to override repo and/or tags of each port.

var Ports = {
    SDL2 : {
        repo: 'AlisGames',
        tag: 'stable', /* or branch: 'stabe' */
    }
}

mergeInto(PortManager.ports, Ports);

For example you can use this library-like syntax. I'm not sure, that this is the best way. Maybe you can find better solution.

[kripken]

Perhaps. Let's see what other people think/suggest.