desktop: Make trait SessionPortal public

Make SessionPortal public so that users can use it in bounds
Apply the sealed trait trick so that users are unable to implement it

src/desktop/global_shortcuts.rs

@@ -316,4 +316,5 @@ impl<'a> std::ops::Deref for GlobalShortcuts<'a> {
     }
 }
 
+impl crate::Sealed for GlobalShortcuts<'_> {}
 impl SessionPortal for GlobalShortcuts<'_> {}

src/desktop/inhibit.rs

@@ -251,4 +251,5 @@ impl<'a> std::ops::Deref for InhibitProxy<'a> {
     }
 }
 
+impl crate::Sealed for InhibitProxy<'_> {}
 impl SessionPortal for InhibitProxy<'_> {}

src/desktop/input_capture.rs

@@ -732,4 +732,5 @@ impl<'a> std::ops::Deref for InputCapture<'a> {
     }
 }
 
+impl crate::Sealed for InputCapture<'_> {}
 impl SessionPortal for InputCapture<'_> {}

src/desktop/location.rs

@@ -285,6 +285,7 @@ impl<'a> LocationProxy<'a> {
     }
 }
 
+impl crate::Sealed for LocationProxy<'_> {}
 impl SessionPortal for LocationProxy<'_> {}
 
 impl<'a> std::ops::Deref for LocationProxy<'a> {

src/desktop/mod.rs

@@ -4,7 +4,7 @@ mod session;
 pub(crate) use self::handle_token::HandleToken;
 pub use self::{
     request::{Request, Response, ResponseError, ResponseType},
-    session::Session,
+    session::{Session, SessionPortal},
 };
 mod color;
 pub use color::Color;

src/desktop/remote_desktop.rs

@@ -695,4 +695,5 @@ impl<'a> std::ops::Deref for RemoteDesktop<'a> {
     }
 }
 
+impl crate::Sealed for RemoteDesktop<'_> {}
 impl SessionPortal for RemoteDesktop<'_> {}

src/desktop/screencast.rs

@@ -424,6 +424,7 @@ impl<'a> std::ops::Deref for Screencast<'a> {
     }
 }
 
+impl crate::Sealed for Screencast<'_> {}
 impl SessionPortal for Screencast<'_> {}
 
 /// Defines which portals session can be used in a screen-cast.

src/desktop/session.rs

@@ -101,7 +101,7 @@ where
 }
 
 /// Portals that have a long-lived interaction
-pub trait SessionPortal {}
+pub trait SessionPortal: crate::Sealed {}
 
 /// A response to a `create_session` request.
 #[derive(Type, Debug)]

src/lib.rs

@@ -78,3 +78,10 @@ pub async fn is_sandboxed() -> bool {
 }
 
 pub use self::error::{Error, PortalError};
+
+mod sealed {
+    /// Use as a supertrait for public traits that users should not be able to implement
+    pub trait Sealed {}
+}
+
+pub(crate) use sealed::Sealed;