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+/**
+ * @file lua_function.h
+ * @author Nat Goodspeed
+ * @date 2024-02-05
+ * @brief Definitions useful for coding a new Luau entry point into C++
+ *
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Copyright (c) 2024, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_LUA_FUNCTION_H)
+#define LL_LUA_FUNCTION_H
+
+#include "luau/luacode.h"
+#include "luau/lua.h"
+#include "luau/luaconf.h"
+#include "luau/lualib.h"
+#include "fsyspath.h"
+#include "llerror.h"
+#include "llsd.h"
+#include "stringize.h"
+#include <exception> // std::uncaught_exceptions()
+#include <memory> // std::shared_ptr
+#include <typeindex>
+#include <typeinfo>
+#include <unordered_map>
+#include <utility> // std::pair
+
+class LuaListener;
+
+/*****************************************************************************
+* lluau namespace utility functions
+*****************************************************************************/
+namespace lluau
+{
+ // luau defines luaL_error() as void, but we want to use the Lua idiom of
+ // 'return error(...)'. Wrap luaL_error() in an int function.
+#if __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat-security"
+#endif // __clang__
+ template<typename... Args>
+ int error(lua_State* L, const char* format, Args&&... args)
+ {
+ luaL_error(L, format, std::forward<Args>(args)...);
+#ifndef LL_MSVC
+ return 0;
+#endif
+ }
+#if __clang__
+#pragma clang diagnostic pop
+#endif // __clang__
+
+ // luau removed lua_dostring(), but since we perform the equivalent luau
+ // sequence in multiple places, encapsulate it. desc and text are strings
+ // rather than string_views because dostring() needs pointers to nul-
+ // terminated char arrays.
+ int dostring(lua_State* L, const std::string& desc, const std::string& text);
+ int loadstring(lua_State* L, const std::string& desc, const std::string& text);
+
+ fsyspath source_path(lua_State* L);
+} // namespace lluau
+
+// must be a macro because LL_PRETTY_FUNCTION is context-sensitive
+#define lluau_checkstack(L, n) luaL_checkstack((L), (n), LL_PRETTY_FUNCTION)
+
+std::string lua_tostdstring(lua_State* L, int index);
+void lua_pushstdstring(lua_State* L, const std::string& str);
+LLSD lua_tollsd(lua_State* L, int index);
+void lua_pushllsd(lua_State* L, const LLSD& data);
+
+/*****************************************************************************
+* LuaState
+*****************************************************************************/
+/**
+ * RAII class to manage the lifespan of a lua_State
+ */
+class LuaState
+{
+public:
+ typedef std::function<void(std::string msg)> script_finished_fn;
+
+ LuaState(script_finished_fn cb={});
+
+ LuaState(const LuaState&) = delete;
+ LuaState& operator=(const LuaState&) = delete;
+
+ ~LuaState();
+
+ bool checkLua(const std::string& desc, int r);
+
+ // expr() is for when we want to capture any results left on the stack
+ // by a Lua expression, possibly including multiple return values.
+ // int < 0 means error, and LLSD::asString() is the error message.
+ // int == 0 with LLSD::isUndefined() means the Lua expression returned no
+ // results.
+ // int == 1 means the Lua expression returned one result.
+ // int > 1 with LLSD::isArray() means the Lua expression returned
+ // multiple results, represented as the entries of the array.
+ std::pair<int, LLSD> expr(const std::string& desc, const std::string& text);
+
+ operator lua_State*() const { return mState; }
+
+ // Find or create LuaListener for this LuaState.
+ LuaListener& obtainListener() { return obtainListener(mState); }
+ // Find or create LuaListener for passed lua_State.
+ static LuaListener& obtainListener(lua_State* L);
+
+ // Given lua_State* L, return the LuaState object managing (the main Lua
+ // thread for) L.
+ static LuaState& getParent(lua_State* L);
+
+ void set_interrupts_counter(S32 counter);
+ void check_interrupts_counter();
+
+private:
+ script_finished_fn mCallback;
+ lua_State* mState;
+ std::string mError;
+ S32 mInterrupts{ 0 };
+};
+
+/*****************************************************************************
+* LuaPopper
+*****************************************************************************/
+/**
+ * LuaPopper is an RAII class whose role is to pop some number of entries
+ * from the Lua stack if the calling function exits early.
+ */
+class LuaPopper
+{
+public:
+ LuaPopper(lua_State* L, int count):
+ mState(L),
+ mCount(count)
+ {}
+
+ LuaPopper(const LuaPopper&) = delete;
+ LuaPopper& operator=(const LuaPopper&) = delete;
+
+ ~LuaPopper();
+
+ void disarm() { set(0); }
+ void set(int count) { mCount = count; }
+
+private:
+ lua_State* mState;
+ int mCount;
+};
+
+/*****************************************************************************
+* LuaRemover
+*****************************************************************************/
+/**
+ * Remove a particular stack index on exit from enclosing scope.
+ * If you pass a negative index (meaning relative to the current stack top),
+ * converts to an absolute index. The point of LuaRemover is to remove the
+ * entry at the specified index regardless of subsequent pushes to the stack.
+ */
+class LuaRemover
+{
+public:
+ LuaRemover(lua_State* L, int index):
+ mState(L),
+ mIndex(lua_absindex(L, index))
+ {}
+ LuaRemover(const LuaRemover&) = delete;
+ LuaRemover& operator=(const LuaRemover&) = delete;
+ ~LuaRemover()
+ {
+ lua_remove(mState, mIndex);
+ }
+
+private:
+ lua_State* mState;
+ int mIndex;
+};
+
+/*****************************************************************************
+* LuaStackDelta
+*****************************************************************************/
+/**
+ * Instantiate LuaStackDelta in a block to compare the Lua data stack depth on
+ * entry (LuaStackDelta construction) and exit. Optionally, pass the expected
+ * depth increment. (But be aware that LuaStackDelta cannot observe the effect
+ * of a LuaPopper or LuaRemover declared previously in the same block.)
+ */
+class LuaStackDelta
+{
+public:
+ LuaStackDelta(lua_State* L, const std::string& where, int delta=0);
+ LuaStackDelta(const LuaStackDelta&) = delete;
+ LuaStackDelta& operator=(const LuaStackDelta&) = delete;
+
+ ~LuaStackDelta();
+
+private:
+ lua_State* L;
+ std::string mWhere;
+ int mDepth, mDelta;
+};
+
+#define lua_checkdelta(L, ...) LuaStackDelta delta(L, LL_PRETTY_FUNCTION, ##__VA_ARGS__)
+
+/*****************************************************************************
+* lua_push() wrappers for generic code
+*****************************************************************************/
+inline
+void lua_push(lua_State* L, bool b)
+{
+ lua_pushboolean(L, int(b));
+}
+
+inline
+void lua_push(lua_State* L, lua_CFunction fn)
+{
+ lua_pushcfunction(L, fn, "");
+}
+
+inline
+void lua_push(lua_State* L, lua_Integer n)
+{
+ lua_pushinteger(L, n);
+}
+
+inline
+void lua_push(lua_State* L, void* p)
+{
+ lua_pushlightuserdata(L, p);
+}
+
+inline
+void lua_push(lua_State* L, const LLSD& data)
+{
+ lua_pushllsd(L, data);
+}
+
+inline
+void lua_push(lua_State* L, const char* s, size_t len)
+{
+ lua_pushlstring(L, s, len);
+}
+
+inline
+void lua_push(lua_State* L)
+{
+ lua_pushnil(L);
+}
+
+inline
+void lua_push(lua_State* L, lua_Number n)
+{
+ lua_pushnumber(L, n);
+}
+
+inline
+void lua_push(lua_State* L, const std::string& s)
+{
+ lua_pushstdstring(L, s);
+}
+
+inline
+void lua_push(lua_State* L, const char* s)
+{
+ lua_pushstring(L, s);
+}
+
+/*****************************************************************************
+* lua_to() wrappers for generic code
+*****************************************************************************/
+template <typename T>
+auto lua_to(lua_State* L, int index);
+
+template <>
+inline
+auto lua_to<bool>(lua_State* L, int index)
+{
+ return lua_toboolean(L, index);
+}
+
+template <>
+inline
+auto lua_to<lua_CFunction>(lua_State* L, int index)
+{
+ return lua_tocfunction(L, index);
+}
+
+template <>
+inline
+auto lua_to<lua_Integer>(lua_State* L, int index)
+{
+ return lua_tointeger(L, index);
+}
+
+template <>
+inline
+auto lua_to<LLSD>(lua_State* L, int index)
+{
+ return lua_tollsd(L, index);
+}
+
+template <>
+inline
+auto lua_to<lua_Number>(lua_State* L, int index)
+{
+ return lua_tonumber(L, index);
+}
+
+template <>
+inline
+auto lua_to<std::string>(lua_State* L, int index)
+{
+ return lua_tostdstring(L, index);
+}
+
+template <>
+inline
+auto lua_to<void*>(lua_State* L, int index)
+{
+ return lua_touserdata(L, index);
+}
+
+/*****************************************************************************
+* field operations
+*****************************************************************************/
+// return to C++, from table at index, the value of field k
+template <typename T>
+auto lua_getfieldv(lua_State* L, int index, const char* k)
+{
+ lua_checkdelta(L);
+ lluau_checkstack(L, 1);
+ lua_getfield(L, index, k);
+ LuaPopper pop(L, 1);
+ return lua_to<T>(L, -1);
+}
+
+// set in table at index, as field k, the specified C++ value
+template <typename T>
+auto lua_setfieldv(lua_State* L, int index, const char* k, const T& value)
+{
+ lua_checkdelta(L);
+ lluau_checkstack(L, 1);
+ lua_push(L, value);
+ lua_setfield(L, index, k);
+}
+
+// return to C++, from table at index, the value of field k (without metamethods)
+template <typename T>
+auto lua_rawgetfield(lua_State* L, int index, const std::string_view& k)
+{
+ lua_checkdelta(L);
+ lluau_checkstack(L, 1);
+ lua_pushlstring(L, k.data(), k.length());
+ lua_rawget(L, index);
+ LuaPopper pop(L, 1);
+ return lua_to<T>(L, -1);
+}
+
+// set in table at index, as field k, the specified C++ value (without metamethods)
+template <typename T>
+void lua_rawsetfield(lua_State* L, int index, const std::string_view& k, const T& value)
+{
+ lua_checkdelta(L);
+ lluau_checkstack(L, 2);
+ lua_pushlstring(L, k.data(), k.length());
+ lua_push(L, value);
+ lua_rawset(L, index);
+}
+
+/*****************************************************************************
+* lua_function (and helper class LuaFunction)
+*****************************************************************************/
+/**
+ * LuaFunction is a base class containing a static registry of its static
+ * subclass call() methods. call() is NOT virtual: instead, each subclass
+ * constructor passes a pointer to its distinct call() method to the base-
+ * class constructor, along with a name by which to register that method.
+ *
+ * The init() method walks the registry and registers each such name with the
+ * passed lua_State.
+ */
+class LuaFunction
+{
+public:
+ LuaFunction(const std::string_view& name, lua_CFunction function,
+ const std::string_view& helptext);
+
+ static void init(lua_State* L);
+
+ static lua_CFunction get(const std::string& key);
+
+protected:
+ using Registry = std::map<std::string, std::pair<lua_CFunction, std::string>>;
+ using Lookup = std::map<lua_CFunction, std::string>;
+ static std::pair<const Registry&, const Lookup&> getRState() { return getState(); }
+
+private:
+ static std::pair<Registry&, Lookup&> getState();
+};
+
+/**
+ * lua_function(name, helptext) is a macro to facilitate defining C++ functions
+ * available to Lua. It defines a subclass of LuaFunction and declares a
+ * static instance of that subclass, thereby forcing the compiler to call its
+ * constructor at module initialization time. The constructor passes the
+ * stringized instance name to its LuaFunction base-class constructor, along
+ * with a pointer to the static subclass call() method. It then emits the
+ * call() method definition header, to be followed by a method body enclosed
+ * in curly braces as usual.
+ */
+#define lua_function(name, helptext) \
+static struct name##_luasub : public LuaFunction \
+{ \
+ name##_luasub(): LuaFunction(#name, &call, helptext) {} \
+ static int call(lua_State* L); \
+} name##_lua; \
+int name##_luasub::call(lua_State* L)
+// {
+// ... supply method body here, referencing 'L' ...
+// }
+
+/*****************************************************************************
+* lua_emplace<T>(), lua_toclass<T>()
+*****************************************************************************/
+// Every instance of DistinctInt has a different int value, barring int
+// wraparound.
+class DistinctInt
+{
+public:
+ DistinctInt(): mValue(++mValues) {}
+ int get() const { return mValue; }
+ operator int() const { return mValue; }
+private:
+ static int mValues;
+ int mValue;
+};
+
+namespace {
+
+template <typename T>
+struct TypeTag
+{
+ // For (std::is_same<T, U>), &TypeTag<T>::value == &TypeTag<U>::value.
+ // For (! std::is_same<T, U>), &TypeTag<T>::value != &TypeTag<U>::value.
+ // And every distinct instance of DistinctInt has a distinct value.
+ // Therefore, TypeTag<T>::value is an int uniquely associated with each
+ // distinct T.
+ static DistinctInt value;
+};
+
+template <typename T>
+DistinctInt TypeTag<T>::value;
+
+} // anonymous namespace
+
+/**
+ * On the stack belonging to the passed lua_State, push a Lua userdata object
+ * containing a newly-constructed C++ object T(args...). The userdata has a
+ * Luau destructor guaranteeing that the new T instance is destroyed when the
+ * userdata is garbage-collected, no later than when the LuaState is
+ * destroyed.
+ *
+ * Usage:
+ * lua_emplace<T>(L, T constructor args...);
+ * // L's Lua stack top is now a userdata containing T
+ */
+template <class T, typename... ARGS>
+void lua_emplace(lua_State* L, ARGS&&... args)
+{
+ lua_checkdelta(L, 1);
+ lluau_checkstack(L, 1);
+ int tag{ TypeTag<T>::value };
+ if (! lua_getuserdatadtor(L, tag))
+ {
+ // We haven't yet told THIS lua_State the destructor to use for this tag.
+ lua_setuserdatadtor(
+ L, tag,
+ [](lua_State*, void* ptr)
+ {
+ // destroy the contained T instance
+ static_cast<T*>(ptr)->~T();
+ });
+ }
+ auto ptr = lua_newuserdatatagged(L, sizeof(T), tag);
+ // stack is uninitialized userdata
+ // For now, assume (but verify) that lua_newuserdata() returns a
+ // conservatively-aligned ptr. If that turns out not to be the case, we
+ // might have to discard the new userdata, overallocate its successor and
+ // perform manual alignment -- but only if we must.
+ llassert((uintptr_t(ptr) % alignof(T)) == 0);
+ // Construct our T there using placement new
+ new (ptr) T(std::forward<ARGS>(args)...);
+ // stack is now initialized userdata containing our T instance -- return
+ // that
+}
+
+/**
+ * If the value at the passed acceptable index is a full userdata created by
+ * lua_emplace<T>(), return a pointer to the contained T instance. Otherwise
+ * (index is not a full userdata; userdata is not of type T) return nullptr.
+ */
+template <class T>
+T* lua_toclass(lua_State* L, int index)
+{
+ lua_checkdelta(L);
+ // get void* pointer to userdata (if that's what it is)
+ void* ptr{ lua_touserdatatagged(L, index, TypeTag<T>::value) };
+ // Derive the T* from ptr. If in future lua_emplace() must manually
+ // align our T* within the Lua-provided void*, adjust accordingly.
+ return static_cast<T*>(ptr);
+}
+
+/*****************************************************************************
+* lua_what()
+*****************************************************************************/
+// Usage: std::cout << lua_what(L, stackindex) << ...;
+// Reports on the Lua value found at the passed stackindex.
+// If cast to std::string, returns the corresponding string value.
+class lua_what
+{
+public:
+ lua_what(lua_State* state, int idx):
+ L(state),
+ index(idx)
+ {}
+
+ friend std::ostream& operator<<(std::ostream& out, const lua_what& self);
+
+ operator std::string() const { return stringize(*this); }
+
+private:
+ lua_State* L;
+ int index;
+};
+
+/*****************************************************************************
+* lua_stack()
+*****************************************************************************/
+// Usage: std::cout << lua_stack(L) << ...;
+// Reports on the contents of the Lua stack.
+// If cast to std::string, returns the corresponding string value.
+class lua_stack
+{
+public:
+ lua_stack(lua_State* state):
+ L(state)
+ {}
+
+ friend std::ostream& operator<<(std::ostream& out, const lua_stack& self);
+
+ operator std::string() const { return stringize(*this); }
+
+private:
+ lua_State* L;
+};
+
+/*****************************************************************************
+* LuaLog
+*****************************************************************************/
+// adapted from indra/test/debug.h
+// can't generalize Debug::operator() target because it's a variadic template
+class LuaLog
+{
+public:
+ template <typename... ARGS>
+ LuaLog(lua_State* L, ARGS&&... args):
+ L(L),
+ mBlock(stringize(std::forward<ARGS>(args)...))
+ {
+ (*this)("entry ", lua_stack(L));
+ }
+
+ // non-copyable
+ LuaLog(const LuaLog&) = delete;
+ LuaLog& operator=(const LuaLog&) = delete;
+
+ ~LuaLog()
+ {
+ auto exceptional{ std::uncaught_exceptions()? "exceptional " : "" };
+ (*this)(exceptional, "exit ", lua_stack(L));
+ }
+
+ template <typename... ARGS>
+ void operator()(ARGS&&... args)
+ {
+ LL_DEBUGS("Lua") << mBlock << ' ';
+ stream_to(LL_CONT, std::forward<ARGS>(args)...);
+ LL_ENDL;
+ }
+
+private:
+ lua_State* L;
+ const std::string mBlock;
+};
+
+#endif /* ! defined(LL_LUA_FUNCTION_H) */
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