Console: Use a REPL environment to run code

In the REPL environment, we set `print` to print to the UI console
instead of stdout.

Source/lua/repl.cpp

@@ -1,6 +1,8 @@
 #ifdef _DEBUG
 #include "lua/repl.hpp"
 
+#include <cstddef>
+#include <optional>
 #include <string>
 #include <string_view>
 
@@ -9,16 +11,49 @@
 #include <sol/utility/to_string.hpp>
 
 #include "lua/lua.hpp"
+#include "panels/console.hpp"
 #include "utils/str_cat.hpp"
 
 namespace devilution {
 
 namespace {
 
+std::optional<sol::environment> replEnv;
+
+int LuaPrintToConsole(lua_State *state)
+{
+	std::string result;
+	const int n = lua_gettop(state);
+	for (int i = 1; i <= n; i++) {
+		size_t l;
+		const char *s = luaL_tolstring(state, i, &l);
+		if (i > 1)
+			result += '\t';
+		result.append(s, l);
+		lua_pop(state, 1);
+	}
+	PrintToConsole(result);
+	return 0;
+}
+
+void CreateReplEnvironment()
+{
+	sol::state &lua = LuaState();
+	replEnv.emplace(lua, sol::create, lua.globals());
+	replEnv->set("print", LuaPrintToConsole);
+}
+
+sol::environment &ReplEnvironment()
+{
+	if (!replEnv.has_value())
+		CreateReplEnvironment();
+	return *replEnv;
+}
+
 sol::protected_function_result TryRunLuaAsExpressionThenStatement(std::string_view code)
 {
 	// Try to compile as an expression first. This also how the `lua` repl is implemented.
-	const sol::state &lua = LuaState();
+	sol::state &lua = LuaState();
 	std::string expression = StrCat("return ", code, ";");
 	sol::detail::typical_chunk_name_t basechunkname = {};
 	sol::load_status status = static_cast<sol::load_status>(
@@ -35,6 +70,7 @@ sol::protected_function_result TryRunLuaAsExpressionThenStatement(std::string_vi
 		}
 	}
 	sol::stack_aligned_protected_function fn(lua.lua_state(), -1);
+	sol::set_environment(ReplEnvironment(), fn);
 	return fn();
 }
 

Source/panels/console.cpp

@@ -132,9 +132,8 @@ void AddConsoleLine(ConsoleLine &&consoleLine)
 void SendInput()
 {
 	const std::string_view input = ConsoleInputState.value();
-	tl::expected<std::string, std::string> result = RunLuaReplLine(input);
-
 	AddConsoleLine(ConsoleLine { .type = ConsoleLine::Input, .text = StrCat(Prompt, input) });
+	tl::expected<std::string, std::string> result = RunLuaReplLine(input);
 
 	if (result.has_value()) {
 		if (!result->empty()) {
@@ -465,5 +464,10 @@ void DrawConsole(const Surface &out)
 	BltFast(&sdlRect, &sdlRect);
 }
 
+void PrintToConsole(std::string_view text)
+{
+	AddConsoleLine(ConsoleLine { .type = ConsoleLine::Output, .text = std::string(text) });
+}
+
 } // namespace devilution
 #endif // _DEBUG

Source/panels/console.hpp

@@ -1,6 +1,8 @@
 #ifdef _DEBUG
 #pragma once
 
+#include <string_view>
+
 #include <SDL.h>
 
 #include "engine/surface.hpp"
@@ -11,6 +13,7 @@ bool IsConsoleOpen();
 void OpenConsole();
 bool ConsoleHandleEvent(const SDL_Event &event);
 void DrawConsole(const Surface &out);
+void PrintToConsole(std::string_view text);
 
 } // namespace devilution
 #endif // _DEBUG