variant: Fix double-free

gio::Settings::set_value takes over ownership of the Variant sometimes, but in other cases it doesn't. To prevent this being a problem, the custom Variant is made of the type that will never have its ownership taken.

This is not necessarily consistent with what gtk-rs authors intended.

In practice, the ownership is shared by refcounting, and after the Rust reference is dropped, one taken by Settings survives.

src/popover.rs

@@ -91,6 +91,11 @@ mod variants {
             unsafe {
                 let ret = glib_sys::g_variant_builder_end(builder);
                 glib_sys::g_variant_builder_unref(builder);
+                // HACK: This is to prevent C taking ownership
+                // of "floating" Variants,
+                // where Rust gets to keep a stale reference
+                // and crash when trying to drop it.
+                glib_sys::g_variant_ref_sink(ret);
                 glib::Variant::from_glib_full(ret)
             }
         }
@@ -141,7 +146,7 @@ fn set_layout(kind: String, name: String) {
         .chain(inputs).collect();
     settings.set_value(
         "sources",
-        &variants::ArrayPairString(inputs).to_variant()
+        &variants::ArrayPairString(inputs).to_variant(),
     );
     settings.apply();
 }