Nasal: support for module reload via command

This won’t work for all modules, depending on what inter-dependencies
exist.

src/Main/fg_commands.cxx

@@ -1036,6 +1036,17 @@ do_profiler_stop(const SGPropertyNode *arg, SGPropertyNode *root)
 #endif
 }
 
+static bool do_reload_nasal_module(const SGPropertyNode* arg, SGPropertyNode*)
+{
+    auto nasalSys = globals->get_subsystem<FGNasalSys>();
+    if (!nasalSys) {
+        SG_LOG(SG_GUI, SG_ALERT, "reloadModuleFromFile command: Nasal subsystem not found");
+        return false;
+    }
+
+    return nasalSys->reloadModuleFromFile(arg->getStringValue("module"));
+}
+
 
 ////////////////////////////////////////////////////////////////////////
 // Command setup.
@@ -1054,6 +1065,7 @@ static struct {
 } built_ins[] = {
     {"null", do_null},
     {"nasal", do_nasal},
+    {"nasal-module-reload", do_reload_nasal_module},
     {"pause", do_pause},
     {"load", do_load},
     {"save", do_save},

src/Scripting/NasalSys.cxx

@@ -800,7 +800,7 @@ public:
         _sys->gcRelease(_gcRoot);
     }
 
-    virtual bool operator()(const SGPropertyNode* aNode, SGPropertyNode * root)
+    bool operator()(const SGPropertyNode* aNode, SGPropertyNode* root) override
     {
         _sys->setCmdArg(const_cast<SGPropertyNode*>(aNode));
         naRef args[1];
@@ -1541,8 +1541,12 @@ bool FGNasalSys::createModule(const char* moduleName, const char* fileName,
     if (!naHash_get(_globals, modname, &locals))
         locals = naNewHash(ctx);
 
-    _cmdArg = (SGPropertyNode*)cmdarg;
+    // store the filename in the module hash, so we could reload it
+    naRef modFilePath = naNewString(ctx);
+    naStr_fromdata(modFilePath, (char*)fileName, strlen(fileName));
+    hashset(locals, "__moduleFilePath", modFilePath);
 
+    _cmdArg = (SGPropertyNode*)cmdarg;
     callWithContext(ctx, code, argc, args, locals);
     hashset(_globals, moduleName, locals);
 
@@ -1565,6 +1569,28 @@ void FGNasalSys::deleteModule(const char* moduleName)
     naFreeContext(ctx);
 }
 
+bool FGNasalSys::reloadModuleFromFile(const std::string& moduleName)
+{
+    if (!_inited || naIsNil(_globals)) {
+        return false;
+    }
+
+    naRef locals = naHash_cget(_globals, (char*)moduleName.c_str());
+    if (naIsNil(locals)) {
+        // no such module
+        return false;
+    }
+
+    naRef filePath = naHash_cget(locals, (char*)"__moduleFilePath");
+    if (naIsNil(filePath)) {
+        return false;
+    }
+
+    SGPath path = SGPath::fromUtf8(naStr_data(filePath));
+    deleteModule(moduleName.c_str());
+    return loadModule(path, moduleName.c_str());
+}
+
 naRef FGNasalSys::getModule(const std::string& moduleName) const
 {
     naRef mod = naHash_cget(_globals, (char*)moduleName.c_str());

src/Scripting/NasalSys.hxx

@@ -163,6 +163,8 @@ public:
      */
     static naRef getPropertyValue(naContext c, SGPropertyNode* node);
 
+    bool reloadModuleFromFile(const std::string& moduleName);
+
 private:
     void initLogLevelConstants();
 
@@ -176,6 +178,7 @@ private:
                std::string& errors);
     naRef genPropsModule();
 
+
 private:
     //friend class FGNasalScript;
     friend class FGNasalListener;