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

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

src/controllers/plugins/LuaUtilities.hpp

@@ -2,14 +2,19 @@
 
 #ifdef CHATTERINO_HAVE_PLUGINS
 
+#    include "common/QLogging.hpp"
+
 #    include <lua.h>
 #    include <lualib.h>
 #    include <magic_enum/magic_enum.hpp>
 #    include <QList>
 
+#    include <cassert>
+#    include <optional>
 #    include <string>
 #    include <string_view>
 #    include <type_traits>
+#    include <variant>
 #    include <vector>
 struct lua_State;
 class QJsonObject;
@@ -19,6 +24,12 @@ struct CommandContext;
 
 namespace chatterino::lua {
 
+namespace api {
+    struct CompletionList;
+}  // namespace api
+
+constexpr int ERROR_BAD_PEEK = LUA_OK - 1;
+
 /**
  * @brief Dumps the Lua stack into qCDebug(chatterinoLua)
  *
@@ -52,20 +63,136 @@ StackIdx push(lua_State *L, const CommandContext &ctx);
 StackIdx push(lua_State *L, const QString &str);
 StackIdx push(lua_State *L, const std::string &str);
 StackIdx push(lua_State *L, const bool &b);
+StackIdx push(lua_State *L, const int &b);
 
 // returns OK?
+bool peek(lua_State *L, bool *out, StackIdx idx = -1);
 bool peek(lua_State *L, double *out, StackIdx idx = -1);
 bool peek(lua_State *L, QString *out, StackIdx idx = -1);
 bool peek(lua_State *L, QByteArray *out, StackIdx idx = -1);
 bool peek(lua_State *L, std::string *out, StackIdx idx = -1);
+bool peek(lua_State *L, api::CompletionList *out, StackIdx idx = -1);
 
 /**
  * @brief Converts Lua object at stack index idx to a string.
  */
 QString toString(lua_State *L, StackIdx idx = -1);
 
+// This object ensures that the stack is of expected size when it is destroyed
+class StackGuard
+{
+    int expected;
+    lua_State *L;
+
+public:
+    /**
+     * Use this constructor if you expect the stack size to be the same on the
+     * destruction of the object as its creation
+     */
+    StackGuard(lua_State *L)
+        : expected(lua_gettop(L))
+        , L(L)
+    {
+    }
+
+    /**
+     * Use this if you expect the stack size changing, diff is the expected difference
+     * Ex: diff=3 means three elements added to the stack
+     */
+    StackGuard(lua_State *L, int diff)
+        : expected(lua_gettop(L) + diff)
+        , L(L)
+    {
+    }
+
+    ~StackGuard()
+    {
+        if (expected < 0)
+        {
+            return;
+        }
+        int after = lua_gettop(this->L);
+        if (this->expected != after)
+        {
+            stackDump(this->L, "StackGuard check tripped");
+            // clang-format off
+            // clang format likes to insert a new line which means that some builds won't show this message fully
+            assert(false && "internal error: lua stack was not in an expected state");
+            // clang-format on
+        }
+    }
+
+    // This object isn't meant to be passed around
+    StackGuard operator=(StackGuard &) = delete;
+    StackGuard &operator=(StackGuard &&) = delete;
+    StackGuard(StackGuard &) = delete;
+    StackGuard(StackGuard &&) = delete;
+
+    // This function tells the StackGuard that the stack isn't in an expected state but it was handled
+    void handled()
+    {
+        this->expected = -1;
+    }
+};
+
 /// TEMPLATES
 
+template <typename T>
+bool peek(lua_State *L, std::optional<T> *out, StackIdx idx = -1)
+{
+    if (lua_isnil(L, idx))
+    {
+        *out = std::nullopt;
+        return true;
+    }
+
+    *out = T();
+    return peek(L, out->operator->(), idx);
+}
+
+template <typename T>
+bool peek(lua_State *L, std::vector<T> *vec, StackIdx idx = -1)
+{
+    StackGuard guard(L);
+
+    if (!lua_istable(L, idx))
+    {
+        lua::stackDump(L, "!table");
+        qCDebug(chatterinoLua)
+            << "value is not a table, type is" << lua_type(L, idx);
+        return false;
+    }
+    auto len = lua_rawlen(L, idx);
+    if (len == 0)
+    {
+        qCDebug(chatterinoLua) << "value has 0 length";
+        return true;
+    }
+    if (len > 1'000'000)
+    {
+        qCDebug(chatterinoLua) << "value is too long";
+        return false;
+    }
+    // count like lua
+    for (int i = 1; i <= len; i++)
+    {
+        lua_geti(L, idx, i);
+        std::optional<T> obj;
+        if (!lua::peek(L, &obj))
+        {
+            //lua_seti(L, LUA_REGISTRYINDEX, 1);  // lazy
+            qCDebug(chatterinoLua)
+                << "Failed to convert lua object into c++: at array index " << i
+                << ":";
+            stackDump(L, "bad conversion into string");
+            return false;
+        }
+        lua_pop(L, 1);
+        vec->push_back(obj.value());
+    }
+    return true;
+}
+
 /**
  * @brief Converts object at stack index idx to enum given by template parameter T
  */
@@ -150,6 +277,7 @@ StackIdx push(lua_State *L, T inp)
 template <typename T>
 bool pop(lua_State *L, T *out, StackIdx idx = -1)
 {
+    StackGuard guard(L, -1);
     auto ok = peek(L, out, idx);
     if (ok)
     {
@@ -186,6 +314,58 @@ StackIdx pushEnumTable(lua_State *L)
     return out;
 }
 
+// Represents a Lua function on the stack
+template <typename ReturnType, typename... Args>
+class CallbackFunction
+{
+    StackIdx stackIdx_;
+    lua_State *L;
+
+public:
+    CallbackFunction(lua_State *L, StackIdx stackIdx)
+        : stackIdx_(stackIdx)
+        , L(L)
+    {
+    }
+
+    // this type owns the stackidx, it must not be trivially copiable
+    CallbackFunction operator=(CallbackFunction &) = delete;
+    CallbackFunction(CallbackFunction &) = delete;
+
+    // Permit only move
+    CallbackFunction &operator=(CallbackFunction &&) = default;
+    CallbackFunction(CallbackFunction &&) = default;
+
+    ~CallbackFunction()
+    {
+        lua_remove(L, this->stackIdx_);
+    }
+
+    std::variant<int, ReturnType> operator()(Args... arguments)
+    {
+        lua_pushvalue(this->L, this->stackIdx_);
+        (  // apparently this calls lua::push() for every Arg
+            [this, &arguments] {
+                lua::push(this->L, arguments);
+            }(),
+            ...);
+
+        int res = lua_pcall(L, sizeof...(Args), 1, 0);
+        if (res != LUA_OK)
+        {
+            qCDebug(chatterinoLua) << "error is: " << res;
+            return {res};
+        }
+
+        ReturnType val;
+        if (!lua::pop(L, &val))
+        {
+            return {ERROR_BAD_PEEK};
+        }
+        return {val};
+    }
+};
+
 }  // namespace chatterino::lua
 
 #endif