Add a new completion API for experimental plugins feature. (#5000)

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/controllers/plugins/LuaAPI.hpp

@@ -1,14 +1,18 @@
 #pragma once
 
 #ifdef CHATTERINO_HAVE_PLUGINS
+#    include <QString>
+
+#    include <vector>
 
 struct lua_State;
 namespace chatterino::lua::api {
-// names in this namespace reflect what's visible inside Lua and follow the lua naming scheme
+// function names in this namespace reflect what's visible inside Lua and follow the lua naming scheme
 
 // NOLINTBEGIN(readability-identifier-naming)
 // Following functions are exposed in c2 table.
 int c2_register_command(lua_State *L);
+int c2_register_callback(lua_State *L);
 int c2_send_msg(lua_State *L);
 int c2_system_msg(lua_State *L);
 int c2_log(lua_State *L);
@@ -23,6 +27,24 @@ int g_import(lua_State *L);
 // Represents "calls" to qCDebug, qCInfo ...
 enum class LogLevel { Debug, Info, Warning, Critical };
 
+// Exposed as c2.EventType
+// Represents callbacks c2 can do into lua world
+enum class EventType {
+    CompletionRequested,
+};
+
+/**
+ * This is for custom completion, a registered function returns this type
+ * however in Lua array part (value) and object part (hideOthers) are in the same
+ * table.
+ */
+struct CompletionList {
+    std::vector<QString> values{};
+
+    // exposed as hide_others
+    bool hideOthers{};
+};
+
 }  // namespace chatterino::lua::api
 
 #endif