Dead keys: act on compose status at press time

- Two dead keys that compose (´´ → ´) type the result right away; a dead
  key that can't continue the sequence types the old accents and starts anew
- With Ctrl/Alt/Super, a dead key sends its dead keysym, as the physical
  key does, not the spacing accent from its label

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/input/DeadKeys.cpp

@@ -37,11 +37,36 @@ DeadKeys::DeadKeys(const QString &locale)
 
 DeadKeys::~DeadKeys() = default;
 
-void DeadKeys::press(quint32 deadKeysym)
+QString DeadKeys::press(quint32 deadKeysym)
 {
-    m_pending += deadKeyText(deadKeysym);
-    if (m_state)
-        xkb_compose_state_feed(m_state.get(), deadKeysym);
+    if (!m_state) {
+        m_pending += deadKeyText(deadKeysym);
+        return {};
+    }
+    xkb_compose_state_feed(m_state.get(), deadKeysym);
+    switch (xkb_compose_state_get_status(m_state.get())) {
+    case XKB_COMPOSE_COMPOSED: {
+        const QString composed = composedText();
+        cancel();
+        return composed;
+    }
+    case XKB_COMPOSE_CANCELLED: {
+        // No sequence goes on like this: type the old accents, start anew.
+        const QString accents = m_pending;
+        cancel();
+        return accents + press(deadKeysym);
+    }
+    default:
+        m_pending += deadKeyText(deadKeysym);
+        return {};
+    }
+}
+
+QString DeadKeys::composedText() const
+{
+    char utf8[64];
+    xkb_compose_state_get_utf8(m_state.get(), utf8, sizeof utf8);
+    return QString::fromUtf8(utf8);
 }
 
 QString DeadKeys::compose(const QString &text)
@@ -50,11 +75,8 @@ QString DeadKeys::compose(const QString &text)
     if (m_state && !text.isEmpty()) {
         const char32_t ucs = text.toUcs4().first();
         xkb_compose_state_feed(m_state.get(), xkb_utf32_to_keysym(ucs));
-        if (xkb_compose_state_get_status(m_state.get()) == XKB_COMPOSE_COMPOSED) {
-            char utf8[64];
-            xkb_compose_state_get_utf8(m_state.get(), utf8, sizeof utf8);
-            result = QString::fromUtf8(utf8) + text.mid(QString::fromUcs4(&ucs, 1).size());
-        }
+        if (xkb_compose_state_get_status(m_state.get()) == XKB_COMPOSE_COMPOSED)
+            result = composedText() + text.mid(QString::fromUcs4(&ucs, 1).size());
     }
     cancel();
     return result;