Add support for explicit menu selection from the UI

the JsonUI now supports a "menu_select(int)" RPC call that should
trigger explicit selection of the provided item index.

As discussed for issue #2019.

doc/json_ui.asciidoc

@@ -60,3 +60,4 @@ The requests that the json ui can interpret on stdin are:
 * mouse(String type, int line, int column): mouse event, type
   can be: 'move', 'press', 'release', 'wheel_up', 'wheel_down',
   line, column is the cursor position.
+* menu_select(int index): explicit select of given menu entry

src/input_handler.cc

@@ -837,9 +837,8 @@ public:
                 m_refresh_completion_pending = true;
             }
         }
-        else if (key == Key::Tab or key == shift(Key::Tab)) // tab completion
+        else if (key == Key::Tab or key == shift(Key::Tab) or key.modifiers == Key::Modifiers::MenuSelect) // completion
         {
-            const bool reverse = (key == shift(Key::Tab));
             CandidateList& candidates = m_completions.candidates;
             // first try, we need to ask our completer for completions
             if (candidates.empty())
@@ -853,7 +852,10 @@ public:
             if (candidates.empty())
                 return;
 
-            if (not reverse and ++m_current_completion >= candidates.size())
+            const bool reverse = (key == shift(Key::Tab));
+            if (key.modifiers == Key::Modifiers::MenuSelect)
+                m_current_completion = clamp<int>(key.key, 0, candidates.size() - 1);
+            else if (not reverse and ++m_current_completion >= candidates.size())
                 m_current_completion = 0;
             else if (reverse and --m_current_completion < 0)
                 m_current_completion = candidates.size()-1;
@@ -1222,13 +1224,19 @@ public:
         else if (key == ctrl('n'))
         {
             last_insert().keys.pop_back();
-            m_completer.select(1, last_insert().keys);
+            m_completer.select(1, true, last_insert().keys);
             update_completions = false;
         }
         else if (key == ctrl('p'))
         {
             last_insert().keys.pop_back();
-            m_completer.select(-1, last_insert().keys);
+            m_completer.select(-1, true, last_insert().keys);
+            update_completions = false;
+        }
+        else if (key.modifiers == Key::Modifiers::MenuSelect)
+        {
+            last_insert().keys.pop_back();
+            m_completer.select(key.key, false, last_insert().keys);
             update_completions = false;
         }
         else if (key == ctrl('x'))

src/insert_completer.cc

@@ -407,13 +407,13 @@ InsertCompleter::~InsertCompleter()
     m_options.unregister_watcher(*this);
 }
 
-void InsertCompleter::select(int offset, Vector<Key>& keystrokes)
+void InsertCompleter::select(int index, bool relative, Vector<Key>& keystrokes)
 {
     if (not setup_ifn())
         return;
 
     auto& buffer = m_context.buffer();
-    m_current_candidate = (m_current_candidate + offset) % (int)m_completions.candidates.size();
+    m_current_candidate = (relative ? m_current_candidate + index : index) % (int)m_completions.candidates.size();
     if (m_current_candidate < 0)
         m_current_candidate += m_completions.candidates.size();
     const InsertCompletion::Candidate& candidate = m_completions.candidates[m_current_candidate];

src/insert_completer.hh

@@ -82,7 +82,7 @@ public:
     InsertCompleter& operator=(const InsertCompleter&) = delete;
     ~InsertCompleter();
 
-    void select(int offset, Vector<Key>& keystrokes);
+    void select(int index, bool relative, Vector<Key>& keystrokes);
     void update();
     void reset();
 

src/json_ui.cc

@@ -410,6 +410,12 @@ void JsonUI::eval_json(const Value& json)
         else
             throw runtime_error(format("invalid mouse event type: {}", type));
     }
+    else if (method == "menu_select")
+    {
+        if (params.size() != 1)
+            throw runtime_error("menu_select needs the item index");
+        m_on_key({Key::Modifiers::MenuSelect, (Codepoint)params[0].as<int>()});
+    }
     else if (method == "resize")
     {
         if (params.size() != 2)

src/keys.hh

@@ -30,6 +30,7 @@ struct Key
                      MouseWheelDown | MouseWheelUp,
 
         Resize = 1 << 8,
+        MenuSelect = 1 << 9,
     };
     enum NamedKey : Codepoint
     {