fix: add support for --ozone-platform-hint flag on Linux

shell/browser/electron_browser_main_parts.cc

@@ -77,9 +77,16 @@
 #include "ui/gtk/gtk_compat.h"  // nogncheck
 #include "ui/gtk/gtk_util.h"    // nogncheck
 #include "ui/ozone/public/ozone_platform.h"
+#include "ui/ozone/public/ozone_switches.h"
 #include "ui/views/linux_ui/linux_ui.h"
 #include "ui/views/linux_ui/linux_ui_factory.h"
-#endif
+#if BUILDFLAG(OZONE_PLATFORM_WAYLAND)
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/nix/xdg_util.h"
+#include "base/threading/thread_restrictions.h"
+#endif  // BUILDFLAG(OZONE_PLATFORM_WAYLAND)
+#endif  // BUILDFLAG(IS_LINUX)
 
 #if BUILDFLAG(IS_WIN)
 #include "ui/base/l10n/l10n_util_win.h"
@@ -108,6 +115,42 @@
 #include "chrome/browser/spellchecker/spellcheck_factory.h"  // nogncheck
 #endif
 
+#if BUILDFLAG(IS_LINUX)
+#if BUILDFLAG(OZONE_PLATFORM_WAYLAND)
+
+constexpr char kPlatformWayland[] = "wayland";
+
+bool HasWaylandDisplay(base::Environment* env) {
+  std::string wayland_display;
+  const bool has_wayland_display =
+      env->GetVar("WAYLAND_DISPLAY", &wayland_display) &&
+      !wayland_display.empty();
+  if (has_wayland_display)
+    return true;
+
+  std::string xdg_runtime_dir;
+  const bool has_xdg_runtime_dir =
+      env->GetVar("XDG_RUNTIME_DIR", &xdg_runtime_dir) &&
+      !xdg_runtime_dir.empty();
+  if (has_xdg_runtime_dir) {
+    auto wayland_server_pipe =
+        base::FilePath(xdg_runtime_dir).Append("wayland-0");
+    // Normally, this should happen exactly once, at the startup of the main
+    // process.
+    base::ScopedAllowBlocking allow_blocking;
+    return base::PathExists(wayland_server_pipe);
+  }
+
+  return false;
+}
+
+#endif  // BUILDFLAG(OZONE_PLATFORM_WAYLAND)
+
+#if BUILDFLAG(OZONE_PLATFORM_X11)
+constexpr char kPlatformX11[] = "x11";
+#endif
+#endif  // BUILDFLAG(IS_LINUX)
+
 namespace electron {
 
 namespace {
@@ -160,7 +203,66 @@ void UpdateDarkThemeSetting() {
   // Pass it to Web Theme, to make "prefers-color-scheme" media query work.
   ui::NativeTheme::GetInstanceForWeb()->set_use_dark_colors(is_dark);
 }
-#endif
+
+// 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)
+
+  return ozone_platform_hint;
+}
+#endif  // BUILDFLAG(IS_LINUX)
 
 }  // namespace
 
@@ -217,6 +319,21 @@ int ElectronBrowserMainParts::PreEarlyInitialization() {
   HandleSIGCHLD();
 #endif
 #if BUILDFLAG(IS_LINUX)
+  auto* const command_line = base::CommandLine::ForCurrentProcess();
+  if (!command_line->HasSwitch(switches::kOzonePlatform)) {
+    const auto ozone_platform_hint =
+        command_line->GetSwitchValueASCII(switches::kOzonePlatformHint);
+    if (!ozone_platform_hint.empty()) {
+      command_line->AppendSwitchASCII(
+          switches::kOzonePlatform, MaybeFixPlatformName(ozone_platform_hint));
+    }
+  }
+
+  auto env = base::Environment::Create();
+  std::string desktop_startup_id;
+  if (env->GetVar("DESKTOP_STARTUP_ID", &desktop_startup_id))
+    command_line->AppendSwitchASCII("desktop-startup-id", desktop_startup_id);
+
   ui::OzonePlatform::PreEarlyInitialization();
 #endif
 #if BUILDFLAG(IS_MAC)