Windows input improvements

src/event/source/windows.rs

@@ -16,6 +16,7 @@ use super::super::{
 pub(crate) struct WindowsEventSource {
     console: Console,
     poll: WinApiPoll,
+    surrogate_buffer: Option<u16>,
 }
 
 impl WindowsEventSource {
@@ -28,6 +29,8 @@ impl WindowsEventSource {
             poll: WinApiPoll::new(),
             #[cfg(feature = "event-stream")]
             poll: WinApiPoll::new()?,
+
+            surrogate_buffer: None,
         })
     }
 }
@@ -41,7 +44,9 @@ impl EventSource for WindowsEventSource {
                 let number = self.console.number_of_console_input_events()?;
                 if event_ready && number != 0 {
                     let event = match self.console.read_single_input_event()? {
-                        InputRecord::KeyEvent(record) => handle_key_event(record),
+                        InputRecord::KeyEvent(record) => {
+                            handle_key_event(record, &mut self.surrogate_buffer)
+                        }
                         InputRecord::MouseEvent(record) => handle_mouse_event(record),
                         InputRecord::WindowBufferSizeEvent(record) => {
                             Some(Event::Resize(record.size.x as u16, record.size.y as u16))

src/event/sys/windows/parse.rs

@@ -1,11 +1,14 @@
 use crossterm_winapi::{ControlKeyState, EventFlags, KeyEventRecord, MouseEvent, ScreenBuffer};
 use winapi::um::{
     wincon::{
-        LEFT_ALT_PRESSED, LEFT_CTRL_PRESSED, RIGHT_ALT_PRESSED, RIGHT_CTRL_PRESSED, SHIFT_PRESSED,
+        CAPSLOCK_ON, LEFT_ALT_PRESSED, LEFT_CTRL_PRESSED, RIGHT_ALT_PRESSED, RIGHT_CTRL_PRESSED,
+        SHIFT_PRESSED,
     },
     winuser::{
-        VK_BACK, VK_CONTROL, VK_DELETE, VK_DOWN, VK_END, VK_ESCAPE, VK_F1, VK_F24, VK_HOME,
-        VK_INSERT, VK_LEFT, VK_MENU, VK_NEXT, VK_PRIOR, VK_RETURN, VK_RIGHT, VK_SHIFT, VK_UP,
+        GetForegroundWindow, GetKeyboardLayout, GetWindowThreadProcessId, ToUnicodeEx, VK_BACK,
+        VK_CONTROL, VK_DELETE, VK_DOWN, VK_END, VK_ESCAPE, VK_F1, VK_F24, VK_HOME, VK_INSERT,
+        VK_LEFT, VK_MENU, VK_NEXT, VK_NUMPAD0, VK_NUMPAD9, VK_PRIOR, VK_RETURN, VK_RIGHT, VK_SHIFT,
+        VK_TAB, VK_UP,
     },
 };
 
@@ -22,18 +25,50 @@ pub(crate) fn handle_mouse_event(mouse_event: MouseEvent) -> Option<Event> {
     None
 }
 
-pub(crate) fn handle_key_event(key_event: KeyEventRecord) -> Option<Event> {
-    if key_event.key_down {
-        if let Some(event) = parse_key_event_record(&key_event) {
-            return Some(Event::Key(event));
+enum WindowsKeyEvent {
+    KeyEvent(KeyEvent),
+    Surrogate(u16),
+}
+
+pub(crate) fn handle_key_event(
+    key_event: KeyEventRecord,
+    surrogate_buffer: &mut Option<u16>,
+) -> Option<Event> {
+    let windows_key_event = parse_key_event_record(&key_event)?;
+    match windows_key_event {
+        WindowsKeyEvent::KeyEvent(key_event) => {
+            // Discard any buffered surrogate value if another valid key event comes before the
+            // next surrogate value.
+            *surrogate_buffer = None;
+            Some(Event::Key(key_event))
+        }
+        WindowsKeyEvent::Surrogate(new_surrogate) => {
+            let ch = handle_surrogate(surrogate_buffer, new_surrogate)?;
+            let modifiers = KeyModifiers::from(&key_event.control_key_state);
+            let key_event = KeyEvent::new(KeyCode::Char(ch), modifiers);
+            Some(Event::Key(key_event))
         }
     }
+}
 
-    None
+fn handle_surrogate(surrogate_buffer: &mut Option<u16>, new_surrogate: u16) -> Option<char> {
+    match *surrogate_buffer {
+        Some(buffered_surrogate) => {
+            *surrogate_buffer = None;
+            std::char::decode_utf16([buffered_surrogate, new_surrogate])
+                .next()
+                .unwrap()
+                .ok()
+        }
+        None => {
+            *surrogate_buffer = Some(new_surrogate);
+            None
+        }
+    }
 }
 
-impl From<ControlKeyState> for KeyModifiers {
-    fn from(state: ControlKeyState) -> Self {
+impl From<&ControlKeyState> for KeyModifiers {
+    fn from(state: &ControlKeyState) -> Self {
         let shift = state.has_state(SHIFT_PRESSED);
         let alt = state.has_state(LEFT_ALT_PRESSED | RIGHT_ALT_PRESSED);
         let control = state.has_state(LEFT_CTRL_PRESSED | RIGHT_CTRL_PRESSED);
@@ -54,12 +89,147 @@ impl From<ControlKeyState> for KeyModifiers {
     }
 }
 
-fn parse_key_event_record(key_event: &KeyEventRecord) -> Option<KeyEvent> {
-    let modifiers = KeyModifiers::from(key_event.control_key_state);
+enum CharCase {
+    LowerCase,
+    UpperCase,
+}
+
+fn try_ensure_char_case(ch: char, desired_case: CharCase) -> char {
+    match desired_case {
+        CharCase::LowerCase if ch.is_uppercase() => {
+            let mut iter = ch.to_lowercase();
+            // Unwrap is safe; iterator yields one or more chars.
+            let ch_lower = iter.next().unwrap();
+            if iter.next() == None {
+                ch_lower
+            } else {
+                ch
+            }
+        }
+        CharCase::UpperCase if ch.is_lowercase() => {
+            let mut iter = ch.to_uppercase();
+            // Unwrap is safe; iterator yields one or more chars.
+            let ch_upper = iter.next().unwrap();
+            if iter.next() == None {
+                ch_upper
+            } else {
+                ch
+            }
+        }
+        _ => ch,
+    }
+}
+
+// Attempts to return the character for a key event accounting for the user's keyboard layout.
+// The returned character (if any) is capitalized (if applicable) based on shift and capslock state.
+// Returns None if the key doesn't map to a character or if it is a dead key.
+// We use the *currently* active keyboard layout (if it can be determined). This layout may not
+// correspond to the keyboard layout that was active when the user typed their input, since console
+// applications get their input asynchronously from the terminal. By the time a console application
+// can process a key input, the user may have changed the active layout. In this case, the character
+// returned might not correspond to what the user expects, but there is no way for a console
+// application to know what the keyboard layout actually was for a key event, so this is our best
+// effort. If a console application processes input in a timely fashion, then it is unlikely that a
+// user has time to change their keyboard layout before a key event is processed.
+fn get_char_for_key(key_event: &KeyEventRecord) -> Option<char> {
+    let virtual_key_code = key_event.virtual_key_code as u32;
+    let virtual_scan_code = key_event.virtual_scan_code as u32;
+    let key_state = [0u8; 256];
+    let mut utf16_buf = [0u16, 16];
+    let dont_change_kernel_keyboard_state = 0x4;
+
+    // Best-effort attempt at determining the currently active keyboard layout.
+    // At the time of writing, this works for a console application running in Windows Terminal, but
+    // doesn't work under a Conhost terminal. For Conhost, the window handle returned by
+    // GetForegroundWindow() does not appear to actually be the foreground window which has the
+    // keyboard layout associated with it (or perhaps it is, but also has special protection that
+    // doesn't allow us to query it).
+    // When this determination fails, the returned keyboard layout handle will be null, which is an
+    // acceptable input for ToUnicodeEx, as that argument is optional. In this case ToUnicodeEx
+    // appears to use the keyboard layout associated with the current thread, which will be the
+    // layout that was inherited when the console application started (or possibly when the current
+    // thread was spawned). This is then unfortunately not updated when the user changes their
+    // keyboard layout in the terminal, but it's what we get.
+    let active_keyboard_layout = unsafe {
+        let foreground_window = GetForegroundWindow();
+        let foreground_thread = GetWindowThreadProcessId(foreground_window, std::ptr::null_mut());
+        GetKeyboardLayout(foreground_thread)
+    };
+
+    let ret = unsafe {
+        ToUnicodeEx(
+            virtual_key_code,
+            virtual_scan_code,
+            key_state.as_ptr(),
+            utf16_buf.as_mut_ptr(),
+            utf16_buf.len() as i32,
+            dont_change_kernel_keyboard_state,
+            active_keyboard_layout,
+        )
+    };
+
+    // -1 indicates a dead key.
+    // 0 indicates no character for this key.
+    if ret < 1 {
+        return None;
+    }
+
+    let mut ch_iter = std::char::decode_utf16(utf16_buf.into_iter().take(ret as usize));
+    let mut ch = ch_iter.next()?.ok()?;
+    if ch_iter.next() != None {
+        // Key doesn't map to a single char.
+        return None;
+    }
+
+    let is_shift_pressed = key_event.control_key_state.has_state(SHIFT_PRESSED);
+    let is_capslock_on = key_event.control_key_state.has_state(CAPSLOCK_ON);
+    let desired_case = if is_shift_pressed ^ is_capslock_on {
+        CharCase::UpperCase
+    } else {
+        CharCase::LowerCase
+    };
+    ch = try_ensure_char_case(ch, desired_case);
+    Some(ch)
+}
+
+fn parse_key_event_record(key_event: &KeyEventRecord) -> Option<WindowsKeyEvent> {
+    let modifiers = KeyModifiers::from(&key_event.control_key_state);
+    let virtual_key_code = key_event.virtual_key_code as i32;
+
+    // We normally ignore all key release events, but we will make an exception for an Alt key
+    // release if it carries a u_char value, as this indicates an Alt code.
+    let is_alt_code = virtual_key_code == VK_MENU && !key_event.key_down && key_event.u_char != 0;
+    if is_alt_code {
+        let utf16 = key_event.u_char;
+        match utf16 {
+            surrogate @ 0xD800..=0xDFFF => {
+                return Some(WindowsKeyEvent::Surrogate(surrogate));
+            }
+            unicode_scalar_value => {
+                // Unwrap is safe: We tested for surrogate values above and those are the only
+                // u16 values that are invalid when directly interpreted as unicode scalar
+                // values.
+                let ch = std::char::from_u32(unicode_scalar_value as u32).unwrap();
+                let key_code = KeyCode::Char(ch);
+                let key_event = KeyEvent::new(key_code, modifiers);
+                return Some(WindowsKeyEvent::KeyEvent(key_event));
+            }
+        }
+    }
 
-    let key_code = key_event.virtual_key_code as i32;
+    // Don't generate events for numpad key presses when they're producing Alt codes.
+    let is_numpad_numeric_key = (VK_NUMPAD0..=VK_NUMPAD9).contains(&virtual_key_code);
+    let is_only_alt_modifier = modifiers.contains(KeyModifiers::ALT)
+        && !modifiers.contains(KeyModifiers::SHIFT | KeyModifiers::CONTROL);
+    if is_only_alt_modifier && is_numpad_numeric_key {
+        return None;
+    }
 
-    let parse_result = match key_code {
+    if !key_event.key_down {
+        return None;
+    }
+
+    let parse_result = match virtual_key_code {
         VK_SHIFT | VK_CONTROL | VK_MENU => None,
         VK_BACK => Some(KeyCode::Backspace),
         VK_ESCAPE => Some(KeyCode::Esc),
@@ -75,55 +245,36 @@ fn parse_key_event_record(key_event: &KeyEventRecord) -> Option<KeyEvent> {
         VK_END => Some(KeyCode::End),
         VK_DELETE => Some(KeyCode::Delete),
         VK_INSERT => Some(KeyCode::Insert),
+        VK_TAB if modifiers.contains(KeyModifiers::SHIFT) => Some(KeyCode::BackTab),
+        VK_TAB => Some(KeyCode::Tab),
         _ => {
-            // Modifier Keys (Ctrl, Alt, Shift) Support
-            let character_raw = key_event.u_char;
-
-            if character_raw < 255 {
-                // Invalid character
-                if character_raw == 0 {
-                    return None;
+            let utf16 = key_event.u_char;
+            match utf16 {
+                0x00..=0x1f => {
+                    // Some key combinations generate either no u_char value or generate control
+                    // codes. To deliver back a KeyCode::Char(...) event we want to know which
+                    // character the key normally maps to on the user's keyboard layout.
+                    // The keys that intentionally generate control codes (ESC, ENTER, TAB, etc.)
+                    // are handled by their virtual key codes above.
+                    get_char_for_key(key_event).map(KeyCode::Char)
                 }
-
-                let mut character = character_raw as u8 as char;
-
-                if modifiers.contains(KeyModifiers::CONTROL)
-                    && !modifiers.contains(KeyModifiers::ALT)
-                {
-                    // we need to do some parsing
-                    // Control character will take the ASCII code produced by the key and bitwise AND
-                    // it with 31, forcing bits 6 and bits 7 to zero.
-                    // So we can make a bitwise OR back to see what's the raw control character.
-                    let c = character_raw as u8;
-                    if c <= b'\x1F' {
-                        character = (c | b'\x40') as char;
-                        // if we press something like ctrl-g, we will get `character` with value `G`.
-                        // in this case, convert the `character` to lowercase `g`.
-                        if character.is_ascii_uppercase()
-                            && !modifiers.contains(KeyModifiers::SHIFT)
-                        {
-                            character.make_ascii_lowercase();
-                        }
-                    } else {
-                        return None;
-                    }
+                surrogate @ 0xD800..=0xDFFF => {
+                    return Some(WindowsKeyEvent::Surrogate(surrogate));
                 }
-
-                if modifiers.contains(KeyModifiers::SHIFT) && character == '\t' {
-                    Some(KeyCode::BackTab)
-                } else if character == '\t' {
-                    Some(KeyCode::Tab)
-                } else {
-                    Some(KeyCode::Char(character))
+                unicode_scalar_value => {
+                    // Unwrap is safe: We tested for surrogate values above and those are the only
+                    // u16 values that are invalid when directly interpreted as unicode scalar
+                    // values.
+                    let ch = std::char::from_u32(unicode_scalar_value as u32).unwrap();
+                    Some(KeyCode::Char(ch))
                 }
-            } else {
-                std::char::from_u32(character_raw as u32).map(KeyCode::Char)
             }
         }
     };
 
     if let Some(key_code) = parse_result {
-        return Some(KeyEvent::new(key_code, modifiers));
+        let key_event = KeyEvent::new(key_code, modifiers);
+        return Some(WindowsKeyEvent::KeyEvent(key_event));
     }
 
     None
@@ -137,7 +288,7 @@ pub fn parse_relative_y(y: i16) -> Result<i16> {
 }
 
 fn parse_mouse_event_record(event: &MouseEvent) -> Result<Option<crate::event::MouseEvent>> {
-    let modifiers = KeyModifiers::from(event.control_key_state);
+    let modifiers = KeyModifiers::from(&event.control_key_state);
 
     let xpos = event.mouse_position.x as u16;
     let ypos = parse_relative_y(event.mouse_position.y)? as u16;