Detect and prevent crashes due to CSS

src/Previewer/Internal.js

@@ -250,8 +250,7 @@ export default function Internal({
 // it would be great to keep the ast around and pass that to prettier
 // so there is no need to re-parse but that's not supported yet
 // https://github.com/prettier/prettier/issues/9114
-// We are not using https://github.com/pazams/postcss-scopify
-// because it's not compatible with postcss 8
+// TODO: Consider using https://github.com/pazams/postcss-scopify instead
 function scopeStylesheet(style, id) {
   const ast = postcss.parse(style);
   for (const node of ast.nodes) {

src/Previewer/Previewer.js

@@ -189,9 +189,13 @@ export default function Previewer({
 
     if (settings.get_boolean("safe-mode")) {
       // console.time("detectCrash");
-      const crashed = await detectCrash(text, target_id);
-      if (crashed) return;
+      const crashed = await detectCrash({
+        xml: text,
+        css: code_view_css.buffer.text,
+        object_id: target_id,
+      });
       // console.timeEnd("detectCrash");
+      if (crashed) return;
     }
 
     const builder = new Gtk.Builder();

src/Previewer/crasher.vala

@@ -3,12 +3,33 @@ public void main (string[] args) {
 
     var builder = new Gtk.Builder ();
     var output = new Gtk.Window ();
+    var provider = new Gtk.CssProvider ();
 
     try {
         builder.add_from_string (args[1], -1);
-        var object = builder.get_object (args[2]) as Gtk.Widget;
+        print("1\n");
+        provider.load_from_string (args[2]);
+        print("2\n");
+        Gtk.StyleContext.add_provider_for_display (
+            output.get_display(),
+            provider,
+            Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION
+        );
+        print("3\n");
+        var object = builder.get_object (args[3]) as Gtk.Widget;
         output.set_child (object);
     } catch (Error e) {
         GLib.error (e.message);
     }
+
+    //output.opacity = 0;
+    output.present();
+
+    // run pending work so CSS/style errors surface
+    var ctx = MainContext.default ();
+    while (ctx.pending ()) {
+        ctx.iteration (false);
+    }
+
+    output.destroy();
 }

src/Previewer/utils.js

@@ -151,11 +151,29 @@ function assertObjectBuildable(el_object, is_root) {
   }
 }
 
-export async function detectCrash(str, object_id) {
-  // const flags =
-  //   Gio.SubprocessFlags.STDOUT_SILENCE | Gio.SubprocessFlags.STDERR_SILENCE;
-  const flags = Gio.SubprocessFlags.NONE;
-  const proc = Gio.Subprocess.new(["workbench-crasher", str, object_id], flags);
+const BROADWAY_DISPLAY = ":5";
+let broadwayd = null;
+
+function ensureBroadway() {
+  if (broadwayd) return;
+  // GTK4's daemon is gtk4-broadwayd (broadwayd is the GTK3 one)
+  broadwayd = Gio.Subprocess.new(
+    ["gtk4-broadwayd", BROADWAY_DISPLAY],
+    Gio.SubprocessFlags.STDOUT_SILENCE | Gio.SubprocessFlags.STDERR_SILENCE,
+  );
+}
+
+export async function detectCrash({ xml, css, object_id }) {
+  ensureBroadway();
+
+  const launcher = new Gio.SubprocessLauncher({
+    flags: Gio.SubprocessFlags.NONE,
+  });
+  launcher.setenv("GDK_BACKEND", "broadway", true);
+  launcher.setenv("BROADWAY_DISPLAY", BROADWAY_DISPLAY, true);
+  launcher.setenv("G_DEBUG", "fatal-criticals", true); // optional: make criticals fail
+
+  const proc = launcher.spawnv(["workbench-crasher", xml, css, object_id]);
 
   const success = await proc.wait_check_async(null).catch((_err) => {
     return false;