Introduce InputModeChange hook

InputModeChange <old mode>:<new mode> is intended to replace the various
<Mode>Begin/<Mode>End hooks.

Fixes #1772

doc/pages/hooks.asciidoc

@@ -120,6 +120,9 @@ of the given *group*.
 *RuntimeError* `error message`::
     an error was encountered while executing a user command
 
+*InputModeChange* `<old mode>:<new mode>`::
+    Triggered whenever the current input mode changes
+
 *KakBegin*::
     kakoune has started, this hook is called just after reading the user
     configuration files

src/commands.cc

@@ -756,7 +756,7 @@ static constexpr auto hooks = {
     "InsertBegin", "InsertChar", "InsertDelete", "InsertEnd", "InsertIdle", "InsertKey",
     "InsertMove", "InsertCompletionHide", "InsertCompletionShow", "InsertCompletionSelect",
     "KakBegin", "KakEnd", "FocusIn", "FocusOut", "RuntimeError", "PromptIdle",
-    "NormalBegin", "NormalEnd", "NormalIdle", "NormalKey", "RawKey",
+    "NormalBegin", "NormalEnd", "NormalIdle", "NormalKey", "InputModeChange", "RawKey",
     "WinClose", "WinCreate", "WinDisplay", "WinResize", "WinSetOption",
 };
 

src/input_handler.cc

@@ -39,6 +39,8 @@ public:
 
     virtual KeymapMode keymap_mode() const = 0;
 
+    virtual StringView name() const = 0;
+
     virtual std::pair<CursorMode, DisplayCoord> get_cursor_info() const
     {
         const auto cursor = context().selections().main().cursor();
@@ -332,6 +334,8 @@ public:
 
     KeymapMode keymap_mode() const override { return KeymapMode::Normal; }
 
+    StringView name() const override { return "normal"; }
+
 private:
     friend struct InputHandler::ScopedForceNormal;
 
@@ -652,6 +656,8 @@ public:
 
     KeymapMode keymap_mode() const override { return KeymapMode::Menu; }
 
+    StringView name() const override { return "menu"; }
+
 private:
     MenuCallback m_callback;
 
@@ -893,6 +899,8 @@ public:
 
     KeymapMode keymap_mode() const override { return KeymapMode::Prompt; }
 
+    StringView name() const override { return "prompt"; }
+
     std::pair<CursorMode, DisplayCoord> get_cursor_info() const override
     {
         DisplayCoord coord{0_line, m_prompt.column_length() + m_line_editor.cursor_display_column()};
@@ -1026,6 +1034,8 @@ public:
 
     KeymapMode keymap_mode() const override { return m_keymap_mode; }
 
+    StringView name() const override { return "next-key"; }
+
 private:
     KeyCallback m_callback;
     KeymapMode m_keymap_mode;
@@ -1266,6 +1276,8 @@ public:
 
     KeymapMode keymap_mode() const override { return KeymapMode::Insert; }
 
+    StringView name() const override { return "insert"; }
+
 private:
     template<typename Type>
     void move(Type offset)
@@ -1395,9 +1407,13 @@ InputHandler::~InputHandler() = default;
 
 void InputHandler::push_mode(InputMode* new_mode)
 {
+    StringView prev_name = current_mode().name();
+
     current_mode().on_disabled(true);
     m_mode_stack.emplace_back(new_mode);
     new_mode->on_enabled();
+
+    context().hooks().run_hook("InputModeChange", format("{}:{}", prev_name, new_mode->name()), context());
 }
 
 void InputHandler::pop_mode(InputMode* mode)
@@ -1405,20 +1421,27 @@ void InputHandler::pop_mode(InputMode* mode)
     kak_assert(m_mode_stack.back().get() == mode);
     kak_assert(m_mode_stack.size() > 1);
 
+    StringView prev_name = mode->name();
+
     current_mode().on_disabled(false);
     m_mode_stack.pop_back();
     current_mode().on_enabled();
+
+    context().hooks().run_hook("InputModeChange", format("{}:{}", prev_name, current_mode().name()), context());
 }
 
 void InputHandler::reset_normal_mode()
 {
-    if (m_mode_stack.size() > 1)
+    kak_assert(dynamic_cast<InputModes::Normal*>(m_mode_stack[0].get()) != nullptr);
-    {
+    if (m_mode_stack.size() == 1)
-        current_mode().on_disabled(false);
+        return;
-        m_mode_stack.resize(1);
+
-    }
+    StringView prev_name = current_mode().name();
-    kak_assert(dynamic_cast<InputModes::Normal*>(&current_mode()) != nullptr);
+    current_mode().on_disabled(false);
+    m_mode_stack.resize(1);
     current_mode().on_enabled();
+
+    context().hooks().run_hook("InputModeChange", format("{}:{}", prev_name, current_mode().name()), context());
 }
 
 void InputHandler::insert(InsertMode mode, int count)