Handle _selected_range sent to NSTextInputClient.setMarkedText(). (#3619)

Co-authored-by: Mads Marquart <mads@marquart.dk>

src/changelog/unreleased.md

@@ -56,3 +56,4 @@ changelog entry.
 
 - On macOS, fix panic on exit when dropping windows outside the event loop.
 - On macOS, fix window dragging glitches when dragging across a monitor boundary with different scale factor.
+- On macOS, fix the range in `Ime::Preedit`.

src/platform_impl/macos/view.rs

@@ -270,19 +270,20 @@ declare_class!(
         fn set_marked_text(
             &self,
             string: &NSObject,
-            _selected_range: NSRange,
+            selected_range: NSRange,
             _replacement_range: NSRange,
         ) {
+            // TODO: Use _replacement_range, requires changing the event to report surrounding text.
             trace_scope!("setMarkedText:selectedRange:replacementRange:");
 
             // SAFETY: This method is guaranteed to get either a `NSString` or a `NSAttributedString`.
-            let (marked_text, preedit_string) = if string.is_kind_of::<NSAttributedString>() {
+            let (marked_text, string) = if string.is_kind_of::<NSAttributedString>() {
                 let string: *const NSObject = string;
                 let string: *const NSAttributedString = string.cast();
                 let string = unsafe { &*string };
                 (
                     NSMutableAttributedString::from_attributed_nsstring(string),
-                    string.string().to_string(),
+                    string.string(),
                 )
             } else {
                 let string: *const NSObject = string;
@@ -290,7 +291,7 @@ declare_class!(
                 let string = unsafe { &*string };
                 (
                     NSMutableAttributedString::from_nsstring(string),
-                    string.to_string(),
+                    string.copy(),
                 )
             };
 
@@ -310,16 +311,21 @@ declare_class!(
                 self.ivars().ime_state.set(ImeState::Ground);
             }
 
-            // Empty string basically means that there's no preedit, so indicate that by sending
-            // `None` cursor range.
-            let cursor_range = if preedit_string.is_empty() {
+            let cursor_range = if string.is_empty() {
+                // An empty string basically means that there's no preedit, so indicate that by
+                // sending a `None` cursor range.
                 None
             } else {
-                Some((preedit_string.len(), preedit_string.len()))
+                // Convert the selected range from UTF-16 indices to UTF-8 indices.
+                let sub_string_a = unsafe { string.substringToIndex(selected_range.location) };
+                let sub_string_b = unsafe { string.substringToIndex(selected_range.end()) };
+                let lowerbound_utf8 = sub_string_a.len();
+                let upperbound_utf8 = sub_string_b.len();
+                Some((lowerbound_utf8, upperbound_utf8))
             };
 
             // Send WindowEvent for updating marked text
-            self.queue_event(WindowEvent::Ime(Ime::Preedit(preedit_string, cursor_range)));
+            self.queue_event(WindowEvent::Ime(Ime::Preedit(string.to_string(), cursor_range)));
         }
 
         #[method(unmarkText)]
@@ -379,6 +385,7 @@ declare_class!(
 
         #[method(insertText:replacementRange:)]
         fn insert_text(&self, string: &NSObject, _replacement_range: NSRange) {
+            // TODO: Use _replacement_range, requires changing the event to report surrounding text.
             trace_scope!("insertText:replacementRange:");
 
             // SAFETY: This method is guaranteed to get either a `NSString` or a `NSAttributedString`.