Add VALIDATE_LUA as a function in lpxserver and lpxclient

luprex/cpp/core/enginewrapper.hpp

@@ -32,6 +32,7 @@ enum class AccessKind {
     INVOKE_LUA_SOURCE,
     PROBE_LUA_CALL,
     CONNECT_TO_SERVER,
+    VALIDATE_LUA,
 };
 
 class DrivenEngine;

luprex/cpp/core/lpxclient.cpp

@@ -20,14 +20,21 @@ public:
     LuaConsole console_;
     PrintChanneler print_channeler_;
     eng::vector<Invocation> delayed_invocations_;
+    lua_State *lua_syntax_checker_;
 
 public:
     LpxClient() {
+        lua_syntax_checker_ = LuaCoreStack::newstate(eng::l_alloc);
+
         set_console_prompt(console_.get_prompt());
 
         set_initial_state_standalone();
     }
 
+    ~LpxClient() {
+        lua_close(lua_syntax_checker_);
+    }
+
     void set_initial_state_connect(const eng::string &hostspec) {
         // Create the world model.
         world_.reset(new World(WORLD_TYPE_PREDICTIVE));
@@ -256,6 +263,13 @@ public:
                 set_initial_state_connect(util::ss("nocert:", datapk, ":8085"));
                 break;
             }
+            case AccessKind::VALIDATE_LUA: {
+                LuaVar closure;
+                LuaDefStack LS(lua_syntax_checker_, closure);
+                eng::string errmsg = LS.load(closure, datapk, "stdin");
+                retpk->write_bytes(errmsg);
+                break;
+            }
             default: {
                 util::dprint("Invalid event_access: ", int(kind));
             }

luprex/cpp/core/lpxserver.cpp

@@ -6,6 +6,7 @@
 #include "luaconsole.hpp"
 #include "util.hpp"
 #include "printbuffer.hpp"
+#include "luastack.hpp"
 
 #include <memory>
 
@@ -33,10 +34,14 @@ public:
     eng::vector<Invocation> delayed_invocations_;
     int64_t admin_id_ = 0;
     double next_tick_ = 0;
+    lua_State *lua_syntax_checker_;
 
 public:
     LpxServer()
     {
+        // Create a little lua interpreter for syntax checking only.
+        lua_syntax_checker_ = LuaCoreStack::newstate(eng::l_alloc);
+
         // Create the master world model.
         master_.reset(new World(WORLD_TYPE_MASTER));
 
@@ -62,6 +67,10 @@ public:
         rescan_lua_source(true);
     }
 
+    ~LpxServer() {
+        lua_close(lua_syntax_checker_);
+    }
+
     virtual void do_syntax_error(std::string_view error) override {
         stdostream() << "Syntax error: " << error << std::endl;
     }
@@ -178,6 +187,13 @@ public:
                 master_->rollback();
                 break;
             }
+            case AccessKind::VALIDATE_LUA: {
+                LuaVar closure;
+                LuaDefStack LS(lua_syntax_checker_, closure);
+                eng::string errmsg = LS.load(closure, datapk, "stdin");
+                retpk->write_bytes(errmsg);
+                break;
+            }
             default: {
                 stdostream() << "Invalid event_access: " << int(kind) << std::endl;
             }

luprex/cpp/core/luaconsole.cpp

@@ -89,26 +89,23 @@ void LuaConsole::add(eng::string line) {
     }
 
     // Try to parse the lua expression
-    int top = lua_gettop(lua_state_);
-    int status = luaL_loadbuffer(lua_state_, partial.c_str(), partial.size(), "=stdin");
-    if (status == LUA_ERRSYNTAX)
     {
-        const char *eof = "<eof>";
-        int leof = strlen(eof);
-        size_t lmsg;
-        const char *msg = lua_tolstring(lua_state_, -1, &lmsg);
-        const char *tp = msg + lmsg - leof;
-        if (strstr(msg, eof) != tp) {
+        LuaVar result;
+        LuaDefStack LS(lua_state_, result);
+        eng::string errmsg = LS.load(result, partial, "stdin");
+        if (errmsg.empty()) {
+            words_.push_back(lua_mode);
+            words_.emplace_back(sv::rtrim(partial));
+            clear_raw_input();
+        } else if (errmsg.find("<eof>") != std::string::npos) {
+            // We have an incomplete expression.
+            // Do nothing, just let the user type more stuff.
+        } else {
             words_.push_back("syntax");
-            words_.push_back(msg);
+            words_.push_back(errmsg);
             clear_raw_input();
         }
-    } else {
-        words_.push_back(lua_mode);
-        words_.emplace_back(sv::rtrim(partial));
-        clear_raw_input();
     }
-    lua_settop(lua_state_, top);
 }
 
 void CommonCommands::do_command(const StringVec &words) {

luprex/cpp/core/luastack.cpp

@@ -323,6 +323,29 @@ bool LuaCoreStack::next(LuaSlot tab, LuaSlot key, LuaSlot value) const {
     return (ret != 0);
 }
 
+eng::string LuaCoreStack::load(LuaSlot result, std::string_view code, std::string_view context)
+{
+    eng::string fullcontext = eng::string("=") + eng::string(context);
+    luaL_loadbuffer(L_, code.data(), code.size(), fullcontext.c_str());
+    int type = lua_type(L_, -1);
+    if (type == LUA_TFUNCTION) {
+        // compiler returned a closure.
+        lua_replace(L_, result.index());
+        return "";
+    } else if (type == LUA_TSTRING) {
+        // compiler returned an error message.
+        size_t len;
+        const char *str = lua_tolstring(L_, -1, &len);
+        eng::string message(str, len);
+        lua_pop(L_, 1);
+        if (message.empty()) message = "unknown compiler error";
+        set(result, message);
+        return message;
+    } else {
+        assert(false && "lua compiler didn't return a closure, but didn't return an error message either");
+    }
+}
+
 void LuaCoreStack::getglobaltable(LuaSlot target) const {
     lua_pushglobaltable(L_);
     lua_replace(L_, target);

luprex/cpp/core/luastack.hpp

@@ -792,6 +792,19 @@ public:
     //
     bool next(LuaSlot tab, LuaSlot key, LuaSlot val) const;
 
+    // Compile lua code.
+    //
+    // If the code contains a syntax error, then the result variable
+    // is set to the error message, and the error message is returned.
+    //
+    // If the code is valid, then the result variable is set to a
+    // closure, and an empty string is returned.
+    //
+    // If a syntax error occurs, the error message may contain the
+    // token <eof>.  If so, the problem is an incomplete expression.
+    //
+    eng::string load(LuaSlot result, std::string_view code, std::string_view context);
+
     // Return true if the int64 can be stored losslessly in a lua_Number.
     //
     // Lua numbers are actually double-precision floating point.  double

luprex/cpp/core/source.cpp

@@ -78,9 +78,7 @@ static void calculate_loadresult(LuaCoreStack &LS0, LuaSlot info, const eng::str
     if (code == "") {
         LS.rawset(info, "loadresult", "missing or empty source file");
     } else {
-        eng::string chunk = "=" + fn;
-        luaL_loadbuffer(LS.state(), code.c_str(), code.size(), chunk.c_str());
-        lua_replace(LS.state(), loadresult.index());
+        LS.load(loadresult, code, fn);
         LS.rawset(info, "loadresult", loadresult);
     }
 }

luprex/cpp/core/world-core.cpp

@@ -377,14 +377,10 @@ eng::string World::probe_lua_expr(int64_t actor_id, std::string_view lua) {
 
     LuaVar closure;
     LuaExtStack LS(L, closure);
-
-    // create the compiled closure.
-    int status = luaL_loadbuffer(L, lua.data(), lua.size(), "=probe");
-    lua_replace(L, closure.index());
-    if (status != LUA_OK) {
-        // The closure is actually an error message. Do nothing.
-        // This should normally not happen: LuaConsole should filter
-        // out syntax errors.
+    eng::string errmsg = LS.load(closure, lua, "probe");
+    if (!errmsg.empty()) {
+        // This should normally not happen: the front end should
+        // filter expressions for syntactic lua validity.
         return "";
     }