fix: add support for ELECTRON_OZONE_PLATFORM_HINT environment variable

[vially]

Description of Change

Add support for the ELECTRON_OZONE_PLATFORM_HINT environment variable in order to make it easier for users to enable Wayland support for all Electron apps without having to manually patch application .desktop files (or other similar workarounds #30897).

The accepted values are the same as upstream, with the special auto value being recommended for most users (especially for those switching between X11 and Wayland environments).

When both the --ozone-platform-hint command line flag and the ELECTRON_OZONE_PLATFORM_HINT environment variable are specified, the command line flag has higher priority.

Fixes #30897

Checklist

• PR description included and stakeholders cc'd (@ckerr @deepak1556 @zcbenz)
• npm test passes
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Added support for ELECTRON_OZONE_PLATFORM_HINT environment variable on Linux.

[deepak1556]

Can we instead set --ozone-platform-hint=auto by default in Electron ? We seem to have a resonable fallback to use X11 when wayland server is not found/running

electron/shell/browser/electron_browser_main_parts_linux.cc

Lines 56 to 110 in 730d918

	// Evaluates the environment and returns the effective platform name for the
	// given |ozone_platform_hint|.
	// For the "auto" value, returns "wayland" if the XDG session type is "wayland",
	// "x11" otherwise.
	// For the "wayland" value, checks if the Wayland server is available, and
	// returns "x11" if it is not.
	// See https://crbug.com/1246928.
	std::string MaybeFixPlatformName(const std::string& ozone_platform_hint) {
	#if BUILDFLAG(OZONE_PLATFORM_WAYLAND)
	// Wayland is selected if both conditions below are true:
	// 1. The user selected either 'wayland' or 'auto'.
	// 2. The XDG session type is 'wayland', OR the user has selected 'wayland'
	// explicitly and a Wayland server is running.
	// Otherwise, fall back to X11.
	if (ozone_platform_hint == kPlatformWayland ||
	ozone_platform_hint == "auto") {
	auto env(base::Environment::Create());
	std::string xdg_session_type;
	const bool has_xdg_session_type =
	env->GetVar(base::nix::kXdgSessionTypeEnvVar, &xdg_session_type) &&
	!xdg_session_type.empty();
	if ((has_xdg_session_type && xdg_session_type == "wayland") ||
	(ozone_platform_hint == kPlatformWayland &&
	HasWaylandDisplay(env.get()))) {
	return kPlatformWayland;
	}
	}
	#endif // BUILDFLAG(OZONE_PLATFORM_WAYLAND)
	#if BUILDFLAG(OZONE_PLATFORM_X11)
	if (ozone_platform_hint == kPlatformX11) {
	return kPlatformX11;
	}
	#if BUILDFLAG(OZONE_PLATFORM_WAYLAND)
	if (ozone_platform_hint == kPlatformWayland ||
	ozone_platform_hint == "auto") {
	// We are here if:
	// - The binary has both X11 and Wayland backends.
	// - The user wanted Wayland but that did not work, otherwise it would have
	// been returned above.
	if (ozone_platform_hint == kPlatformWayland) {
	LOG(WARNING) << "No Wayland server is available. Falling back to X11.";
	} else {
	LOG(WARNING) << "This is not a Wayland session. Falling back to X11. "
	"If you need to run Chrome on Wayland using some "
	"embedded compositor, e. g., Weston, please specify "
	"Wayland as your preferred Ozone platform, or use "
	"--ozone-platform=wayland.";
	}
	return kPlatformX11;
	}
	#endif // BUILDFLAG(OZONE_PLATFORM_WAYLAND)
	#endif // BUILDFLAG(OZONE_PLATFORM_X11)

, also --ozone-platform takes precedence over --ozone-platform-hint which still gives applications control over the default behavior of Electron for any edge cases they encounter. Seems like a default of --ozone-platform-hint=auto in Electron would cover all use cases mentioned in the linked issue.

[vially]

Can we instead set --ozone-platform-hint=auto by default in Electron?

I've created #35630 which does that (set --ozone-platform-hint to auto by default). I think either one of these two pull-requests (#35614, #35630) will address #30897, but I'm personally more in favor of #35630.

[ckerr]

I think I'd prefer #35630 over this PR and from #35614 (comment) it sounds like @deepak1556 would lean in the same direction

[deepak1556]

Yup I prefer #35630 over the environment variable. Maybe we close this and revisit if #35630 is not viable.

[parcelcat]

Since #35630 looks premature until Chromium changes the default ozone platform value, could we please reopen this pull request?

@ckerr @deepak1556 @vially

[ZtereoHYPE]

This feels way overdue considering chromium seems nowhere close to enabling their default ozone platform hint.