Investigate XDG BaseDir integration

[Screwtapello]

Currently, bsnes more-or-less supports the XDG BaseDir specification for storing configuration on Linux - it keeps some things in ~/.config/bsnes/ and some in ~/.local/share/bsnes/ and since #103 landed it even respects $XDG_CONFIG_HOME and $XDG_DATA_HOME.

However, bsnes' external-resource handling is really designed for the Windows model, where resources tend to be next to the executable, or in the user's home directory, and the distinction between config/data/cache and the user/system/vendor hierarchy don't really exist. I recall that bsnes and higan have at different times put everything in ~/.config or put everything in ~/.local/share for simplicity's sake, and I don't know if they're any more rigorous now.

Updating bsnes to properly follow the XDG BaseDir spec on Linux without regressing Windows or macOS may be difficult, but I'd like to get an idea for how difficult it would be:

• [x] Investigate all the places where bsnes loads an external resource
  • a good start would be finding all the things that call functions in nall/path.hpp and tracing their callers
• [x] figure out their access (read/write), and their type (config/data/cache)
• [ ] figure out a search algorithm for each combination of categories (read config, write config, read data, ...)
• [ ] check whether nall provides all the ingredients for discovering the paths required by the search algorithm (I think the raw parts are in nall/path.hpp and the path construction operations are in nall/location.hpp but it would be good to check)

Once we have a good idea of where we are, and where we want to be, we can estimate how much work it would be to get from one to the other, and whether that investment is worth making.

[Screwtapello]

I expect the outcome of this issue to be a new issue ("Implement XDG BaseDir integration") that describes exactly the work to be done. If it turns out to be a lot of work, and something easier like #110 is a net improvement, we might just go for that instead.

[ghisvail]

Subscribed. Thank you for this very good summary!

Regarding #110, another approach could be to just copy the default stuff installed under /usr/share/bsnes to their relevant location under $XDG_CONFIG_HOME and $XDG_DATA_HOME and not override the search paths in locate. This could be easily done with a wrapper script doing this check first, copy if data is absent, and finally execute the binary. Since both locations are r/w, it should be fine.

[Screwtapello]

Copy-at-first startup is what (I think) Linux packagers have traditionally done, but I hope someday we can do better than that.

[ghisvail]

Locations where either locate or nall::Path, broken down with file, function, line and access (ro = read-only, rw = read-write)

Uses of nall::Path

Path	Function	Usage	r/w
bsnes/target-bsnes/bsnes.cpp	locate(string) -> string
bsnes/target-bsnes/movies.cpp	Program::moviePlay	dialog.setPath(Path::desktop())	ro
bsnes/target-bsnes/movies.cpp	Program::movieStop	dialog.setPath(Path::desktop())	ro
bsnes/target-bsnes/utility.cpp	Program::selectPath	dialog.setPath(Path::desktop())	ro
bsnes/target-bsnes/utility.cpp	Program::selectPath	window.setPath(Path::desktop())	ro
hiro/browser-dialog.cpp	BrowserDialogWindow::run	file::read({Path::userSettings(), "hiro/browser-dialog.bml"})	rw
hiro/browser-dialog.cpp	BrowserDialogWindow::setPath	Path::root()	ro
hiro/browser-dialog.cpp	BrowserDialog::_run()	Path::user()	ro
hiro/gtk/settings.cpp	Settings::Settings	Path::userSettings()	ro
hiro/gtk/settings.cpp	Settings::~Settings	Path::userSettings()	rw
hiro/gtk/window.cpp	pWindow::construct()	Path::user()	ro
hiro/qt/settings.cpp	Settings::Settings	Path::userSettings()	ro
hiro/qt/settings.cpp	Settings::~Settings	Path::userSettings()	rw
hiro/qt/window.cpp	pWindow::construct()	Path::user()	ro
hiro/windows/settings.cpp	Settings::Settings	Path::userSettings()	ro
hiro/windows/settings.cpp	Settings::~Settings	Path::userSettings()	rw
nall/arguments.hpp	Aguments::construct()	Path::real(programArgument)	ro
nall/dl.hpp	library::open	Path::user()	ro
nall/run.hpp	invoke	Path::program()	ro

Uses of locate

Path	Function	Usage	r/w
bsnes/target-bsnes/bsnes.cpp	nall::main	locate("settings.bml")	rw
bsnes/target-bsnes/bsnes.cpp	nall::main	locate("Locale/")	ro
bsnes/target-bsnes/presentation/presentation.cpp	Presentation::updateShaders	locate("Shaders/")	ro
bsnes/target-bsnes/program/game-rom.cpp	Program::openRomSuperFamicom	locate({"Firmware/", ...})	ro
bsnes/target-bsnes/program/game.cpp	Program::loadSuperFamicom	locate("Database/Super Famicom.bml")	ro
bsnes/target-bsnes/program/game.cpp	Program::loadGameBoy	locate("Database/Game Boy.bml")	ro
bsnes/target-bsnes/program/game.cpp	Program::loadGameBoy	locate("Database/Game Boy Color.bml")	ro
bsnes/target-bsnes/program/game.cpp	Program::loadBSMemory	locate(""Database/BS Memory.bml"")	ro
bsnes/target-bsnes/program/game.cpp	Program::loadSufamiTurboA	locate("Database/Sufami Turbo.bml")	ro
bsnes/target-bsnes/program/game.cpp	Program::loadSufamiTurboB	locate("Database/Sufami Turbo.bml")	ro
bsnes/target-bsnes/settings/settings.cpp	Settings::save	locate("settings.bml")	rw
bsnes/target-bsnes/tools/cheat-editor.cpp	CheatDatabase::findCheats	locate("Database/Cheat Codes.bml")	ro
bsnes/target-bsnes/tools/cheat-editor.cpp	CheatEditor::create	locate("Database/Cheat Codes.bml")	ro