RFE: optional alternate game id in playlists for cores where the core manages the game list

First and foremost consider this:

• Only RetroArch bugs should be filed here. Not core bugs or game bugs
• This is not a forum or a help section, this is strictly developer oriented

Description

Basically I want a clarification if the playlist format is fixed, or if there is no problem replacing the 'path' or adding a 'extra' property (either/or) that specific cores would take advantage of if playlists with that property were produced. One would think that this would be possible, because the playlists are json, but i believe that retroarch is currently managing the launching of cores by passing the path, and thus it 'has to be real file'. I'm asking if it's possible to use or specify a alternate way of launching that passes the entire json entry into the core.

This idea is intended (at least at start) for the scummvm core, where the current way to launch games from outside the core requires the creation of files in the game directory just for that, which is user hostile because users have to create them manually. My project here https://github.com/i30817/libretro-mkscumm handles that, but while i was writing it, i started to wonder why couldn't the playlist just record the id for cores like this.

Obviously, it 'can't' because the retroarch scanner can't or isn't prepared to write a id instead of a file because those ids are de-facto created by scummvm code. However, you are already required to add games from the scummvm core GUI for they to work, and then are required to put those ids into files to appease the manual scanner to finally get the games into playlists.

Removing the need to create those files in the directory, even if the RA scanner can't handle their creation (yet?) would allow my tool to create the playlist without creating files in the games directory which i think would be a win, for cases where the games are in read-only mediums.

My questions then are: could RA pass another 'entry' instead of 'path' when launching the core for selected cores? Or even better, pass the whole json entry so the cores does whatever it wants with the fallbacks it wants?

Start by tracing RetroArch’s playlist scanner and core-launch path, focusing on how the existing path field is passed to cores. Compare that flow with the scummvm core GUI workflow described here; done means establishing whether an alternate id or full playlist entry can be supported, including for read-only game directories.