debugger on autoCallFunction error

src/libcmd/command.cc

@@ -79,24 +79,28 @@ ref<EvalState> EvalCommand::getEvalState()
     return ref<EvalState>(evalState);
 }
 */
-EvalCommand::EvalCommand()
-{
-    addFlag({
-        .longName = "debugger",
-        .description = "start an interactive environment if evaluation fails",
-        .handler = {&startReplOnEvalErrors, true},
-    });
-}
 // ref<EvalState> EvalCommand::getEvalState()
 // {
 //     if (!evalState)
 //         evalState = std::make_shared<EvalState>(searchPath, getStore());
 //     return ref<EvalState>(evalState);
 // }
+
+
+EvalCommand::EvalCommand()
+{
+    // std::cout << "EvalCommand::EvalCommand()" << std::endl;
+    addFlag({
+        .longName = "debugger",
+        .description = "start an interactive environment if evaluation fails",
+        .handler = {&startReplOnEvalErrors, true},
+    });
+}
 extern std::function<void(const Error & error, const std::map<std::string, Value *> & env)> debuggerHook;
 
 ref<EvalState> EvalCommand::getEvalState()
 {
+    std::cout << " EvalCommand::getEvalState()" << startReplOnEvalErrors << std::endl;
     if (!evalState) {
         evalState = std::make_shared<EvalState>(searchPath, getStore());
         if (startReplOnEvalErrors)

src/libexpr/eval.cc

@@ -1398,12 +1398,28 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
             if (j != args.end()) {
                 actualArgs->attrs->push_back(*j);
             } else if (!i.def) {
-                throwMissingArgumentError(i.pos, R"(cannot evaluate a function that has an argument without a value ('%1%')
+                auto error = MissingArgumentError({
+                            .msg = hintfmt(R"(cannot evaluate a function that has an argument without a value ('%1%')
 
 Nix attempted to evaluate a function as a top level expression; in
 this case it must have its arguments supplied either by default
 values, or passed explicitly with '--arg' or '--argstr'. See
-https://nixos.org/manual/nix/stable/#ss-functions.)", i.name);
+https://nixos.org/manual/nix/stable/#ss-functions.)", i.name),
+                            .errPos = i.pos
+                        });
+                
+//                 throwMissingArgumentError(i.pos
+//                                           , R"(cannot evaluate a function that has an argument without a value ('%1%')
+
+// Nix attempted to evaluate a function as a top level expression; in
+// this case it must have its arguments supplied either by default
+// values, or passed explicitly with '--arg' or '--argstr'. See
+// https://nixos.org/manual/nix/stable/#ss-functions.)", i.name);
+
+                if (debuggerHook)
+                    debuggerHook(error, {{"fun", &fun}});
+
+                throw error;
 
             }
         }