C++: polish the clipboard patch

- make sure the Platform::Clipboard type is properly documented
 - Use the actual enum in the interface (even though it is
   #[non_exhaustive] so we need to slience a warning)

CC: #3265

api/cpp/include/slint-platform.h

@@ -281,7 +281,6 @@ public:
 class Platform
 {
 public:
-    using Clipboard = cbindgen_private::Clipboard;
     virtual ~Platform() = default;
     Platform(const Platform &) = delete;
     Platform &operator=(const Platform &) = delete;
@@ -290,7 +289,7 @@ public:
     /// Returns a new WindowAdapter
     virtual std::unique_ptr<WindowAdapter> create_window_adapter() = 0;
 
-#ifdef SLINT_FEATURE_FREESTANDING
+#if defined(SLINT_FEATURE_FREESTANDING) || defined(DOXYGEN)
     /// Returns the amount of milliseconds since start of the application.
     ///
     /// This function should only be implemented  if the runtime is compiled with
@@ -301,6 +300,18 @@ public:
     }
 #endif
 
+    /// The type of clipboard used in Platform::clipboard_text and PLatform::set_clipboard_text.
+    enum class Clipboard {
+        /// This is the default clipboard used for text action for Ctrl+V,  Ctrl+C.
+        /// Corresponds to the secondary selection on X11.
+        DefaultClipboard = static_cast<uint8_t>(cbindgen_private::Clipboard::DefaultClipboard),
+        /// This is the clipboard that is used when text is selected
+        /// Corresponds to the primary selection on X11.
+        /// The Platform implementation should do nothing if copy on select is not supported on that
+        /// platform.
+        SelectionClipboard = static_cast<uint8_t>(cbindgen_private::Clipboard::SelectionClipboard),
+    };
+
     /// Sends the given text into the system clipboard.
     ///
     /// If the platform doesn't support the specified clipboard, this function should do nothing
@@ -392,13 +403,13 @@ inline void set_platform(std::unique_ptr<Platform> platform)
                 return reinterpret_cast<const Platform *>(p)->duration_since_start().count();
 #endif
             },
-            [](void *p, const SharedString *text, uint8_t clipboard) {
+            [](void *p, const SharedString *text, cbindgen_private::Clipboard clipboard) {
-                reinterpret_cast<Platform *>(p)->set_clipboard_text(*text,
+                reinterpret_cast<Platform *>(p)->set_clipboard_text(
-                                                                    Platform::Clipboard(clipboard));
+                        *text, static_cast<Platform::Clipboard>(clipboard));
             },
-            [](void *p, SharedString *out_text, uint8_t clipboard) -> bool {
+            [](void *p, SharedString *out_text, cbindgen_private::Clipboard clipboard) -> bool {
                 auto maybe_clipboard = reinterpret_cast<Platform *>(p)->clipboard_text(
-                        Platform::Clipboard(clipboard));
+                        static_cast<Platform::Clipboard>(clipboard));
 
                 bool status = maybe_clipboard.has_value();
                 if (status)

api/cpp/platform.rs

@@ -141,9 +141,11 @@ struct CppPlatform {
     window_factory: unsafe extern "C" fn(PlatformUserData, *mut WindowAdapterRcOpaque),
     #[cfg(not(feature = "std"))]
     duration_since_start: unsafe extern "C" fn(PlatformUserData) -> u64,
-    set_clipboard_text: unsafe extern "C" fn(PlatformUserData, &SharedString, _clipboard: u8),
+    // silent the warning depite `Clipboard` is a `#[non_exhaustive]` enum from another crate.
-    clipboard_text:
+    #[allow(improper_ctypes_definitions)]
-        unsafe extern "C" fn(PlatformUserData, &mut SharedString, _clipboard: u8) -> bool,
+    set_clipboard_text: unsafe extern "C" fn(PlatformUserData, &SharedString, Clipboard),
+    #[allow(improper_ctypes_definitions)]
+    clipboard_text: unsafe extern "C" fn(PlatformUserData, &mut SharedString, Clipboard) -> bool,
     run_event_loop: unsafe extern "C" fn(PlatformUserData),
     quit_event_loop: unsafe extern "C" fn(PlatformUserData),
     invoke_from_event_loop: unsafe extern "C" fn(PlatformUserData, PlatformTaskOpaque),
@@ -185,21 +187,15 @@ impl Platform for CppPlatform {
         }))
     }
 
-    fn set_clipboard_text(&self, _text: &str, _clipboard: Clipboard) {
+    fn set_clipboard_text(&self, text: &str, clipboard: Clipboard) {
-        let shared_text = SharedString::from(_text);
+        let shared_text = SharedString::from(text);
-        unsafe { (self.set_clipboard_text)(self.user_data, &shared_text, _clipboard as u8) }
+        unsafe { (self.set_clipboard_text)(self.user_data, &shared_text, clipboard) }
     }
 
-    fn clipboard_text(&self, _clipboard: Clipboard) -> Option<String> {
+    fn clipboard_text(&self, clipboard: Clipboard) -> Option<String> {
         let mut out_text = SharedString::new();
-        let status =
+        let status = unsafe { (self.clipboard_text)(self.user_data, &mut out_text, clipboard) };
-            unsafe { (self.clipboard_text)(self.user_data, &mut out_text, _clipboard as u8) };
+        status.then(|| out_text.into())
-
-        if !status {
-            None
-        } else {
-            String::from(out_text).into()
-        }
     }
 }
 
@@ -232,18 +228,16 @@ impl i_slint_core::platform::EventLoopProxy for CppEventLoopProxy {
 unsafe impl Send for CppEventLoopProxy {}
 unsafe impl Sync for CppEventLoopProxy {}
 
+// silent the warning depite `Clipboard` is a `#[non_exhaustive]` enum from another crate.
+#[allow(improper_ctypes_definitions)]
 #[no_mangle]
 pub unsafe extern "C" fn slint_platform_register(
     user_data: PlatformUserData,
     drop: unsafe extern "C" fn(PlatformUserData),
     window_factory: unsafe extern "C" fn(PlatformUserData, *mut WindowAdapterRcOpaque),
     #[allow(unused)] duration_since_start: unsafe extern "C" fn(PlatformUserData) -> u64,
-    set_clipboard_text: unsafe extern "C" fn(PlatformUserData, &SharedString, _clipboard: u8),
+    set_clipboard_text: unsafe extern "C" fn(PlatformUserData, &SharedString, Clipboard),
-    clipboard_text: unsafe extern "C" fn(
+    clipboard_text: unsafe extern "C" fn(PlatformUserData, &mut SharedString, Clipboard) -> bool,
-        PlatformUserData,
-        &mut SharedString,
-        _clipboard: u8,
-    ) -> bool,
     run_event_loop: unsafe extern "C" fn(PlatformUserData),
     quit_event_loop: unsafe extern "C" fn(PlatformUserData),
     invoke_from_event_loop: unsafe extern "C" fn(PlatformUserData, PlatformTaskOpaque),