Bug 1695453 - Rename IsWaylandDisabled to IsWaylandEnabled, r=stransky

Inversed logic has been proven to be more difficult to read,
so use the simple positive variant.

Also add a simple sanity check for `WAYLAND_DISPLAY` so if people
set `MOZ_ENABLE_WAYLAND` in a X11 session don't get undesired behavior.

While on it, change a check for `XDG_SESSION_TYPE` to also use
`WAYLAND_DISPLAY`, improving behavior when launching FF from a TTY
or a TTY-launched session (e.g. via `weston-launch`).

`WAYLAND_DISPLAY` and `DISPLAY` are not expected to be set if
no Wayland or X11 server is available, so using them makes us behave
more predictable.

Differential Revision: https://phabricator.services.mozilla.com/D106726

dom/ipc/BrowserChild.cpp

@@ -2184,7 +2184,7 @@ RefPtr<VsyncChild> BrowserChild::GetVsyncChild() {
   // given platform. Note: this only makes sense if nsWindow returns a
   // window-specific VsyncSource.
 #if defined(MOZ_WAYLAND)
-  if (!IsWaylandDisabled() && !mVsyncChild) {
+  if (IsWaylandEnabled() && !mVsyncChild) {
     PVsyncChild* actor = SendPVsyncConstructor();
     mVsyncChild = static_cast<VsyncChild*>(actor);
   }

dom/ipc/ContentChild.cpp

@@ -661,11 +661,11 @@ bool ContentChild::Init(MessageLoop* aIOLoop, base::ProcessId aParentPid,
   if (!gfxPlatform::IsHeadless()) {
     const char* display_name = PR_GetEnv("MOZ_GDK_DISPLAY");
     if (!display_name) {
-      bool waylandDisabled = true;
+      bool waylandEnabled = false;
 #  ifdef MOZ_WAYLAND
-      waylandDisabled = IsWaylandDisabled();
+      waylandEnabled = IsWaylandEnabled();
 #  endif
-      if (waylandDisabled) {
+      if (!waylandEnabled) {
         display_name = PR_GetEnv("DISPLAY");
       }
     }

gfx/ipc/GPUParent.cpp

@@ -275,11 +275,11 @@ mozilla::ipc::IPCResult GPUParent::RecvInit(
 #if defined(MOZ_WIDGET_GTK)
   char* display_name = PR_GetEnv("MOZ_GDK_DISPLAY");
   if (!display_name) {
-    bool waylandDisabled = true;
+    bool waylandEnabled = false;
 #  ifdef MOZ_WAYLAND
-    waylandDisabled = IsWaylandDisabled();
+    waylandEnabled = IsWaylandEnabled();
 #  endif
-    if (waylandDisabled) {
+    if (!waylandEnabled) {
       display_name = PR_GetEnv("DISPLAY");
     }
   }

toolkit/xre/glxtest.cpp

@@ -26,7 +26,7 @@
 #include <unistd.h>
 
 #include "mozilla/Unused.h"
-#include "nsAppRunner.h"  // for IsWaylandDisabled on IsX11EGLEnabled
+#include "nsAppRunner.h"  // for IsWaylandEnabled on IsX11EGLEnabled
 #include "stdint.h"
 
 #ifdef __SUNPRO_CC
@@ -1200,7 +1200,7 @@ int childgltest() {
   int pci_count = get_pci_status();
 
 #ifdef MOZ_WAYLAND
-  if (!IsWaylandDisabled()) {
+  if (IsWaylandEnabled()) {
     wayland_egltest();
   } else
 #endif

toolkit/xre/nsAppRunner.cpp

@@ -4157,7 +4157,12 @@ static void PR_CALLBACK ReadAheadDlls_ThreadStart(void* arg) {
 #endif
 
 #if defined(MOZ_WAYLAND)
-bool IsWaylandDisabled() {
+bool IsWaylandEnabled() {
+  const char* waylandDisplay = PR_GetEnv("WAYLAND_DISPLAY");
+  if (!waylandDisplay) {
+    return false;
+  }
+
   // MOZ_ENABLE_WAYLAND is our primary Wayland on/off switch.
   const char* waylandPref = PR_GetEnv("MOZ_ENABLE_WAYLAND");
   bool enableWayland = (waylandPref && *waylandPref);
@@ -4173,7 +4178,7 @@ bool IsWaylandDisabled() {
   if (enableWayland && gtk_check_version(3, 22, 0) != nullptr) {
     NS_WARNING("Running Wayland backen on Gtk3 < 3.22. Expect issues/glitches");
   }
-  return !enableWayland;
+  return enableWayland;
 }
 #endif
 
@@ -4362,13 +4367,13 @@ int XREMain::XRE_mainStartup(bool* aExitFlag) {
       saveDisplayArg = true;
     }
 
-    bool disableWayland = true;
+    bool waylandEnabled = false;
 #  if defined(MOZ_WAYLAND)
-    disableWayland = IsWaylandDisabled();
+    waylandEnabled = IsWaylandEnabled();
 #  endif
     // On Wayland disabled builds read X11 DISPLAY env exclusively
     // and don't care about different displays.
-    if (disableWayland && !display_name) {
+    if (!waylandEnabled && !display_name) {
       display_name = PR_GetEnv("DISPLAY");
       if (!display_name) {
         PR_fprintf(PR_STDERR,

toolkit/xre/nsAppRunner.h

@@ -167,7 +167,7 @@ void setASanReporterPath(nsIFile* aDir);
 #endif
 
 #ifdef MOZ_WAYLAND
-bool IsWaylandDisabled();
+bool IsWaylandEnabled();
 #endif
 
 #endif  // nsAppRunner_h__

widget/GfxInfoX11.cpp

@@ -462,7 +462,7 @@ void GfxInfo::GetData() {
   mAdapterDescription.Assign(glRenderer);
 #ifdef MOZ_WAYLAND
   mIsWayland = gdk_display_get_default() &&
-               !GDK_IS_X11_DISPLAY(gdk_display_get_default());
+               GDK_IS_WAYLAND_DISPLAY(gdk_display_get_default());
   if (mIsWayland) {
     mIsWaylandDRM = GetDMABufDevice()->IsDMABufVAAPIEnabled() ||
                     GetDMABufDevice()->IsDMABufWebGLEnabled() ||
@@ -473,8 +473,8 @@ void GfxInfo::GetData() {
   // Make a best effort guess at whether or not we are using the XWayland compat
   // layer. For all intents and purposes, we should otherwise believe we are
   // using X11.
-  const char* windowEnv = getenv("XDG_SESSION_TYPE");
-  mIsXWayland = windowEnv && strcmp(windowEnv, "wayland") == 0;
+  const char* waylandDisplay = getenv("WAYLAND_DISPLAY");
+  mIsXWayland = !mIsWayland && waylandDisplay;
 
   // Make a best effort guess at the desktop environment in use. Sadly there
   // does not appear to be a standard way to do this, so we check a few