Address review: add call stack and filename to wrapped script exceptions

- Catch Boxed_Value in AST_Node_Impl::eval() and wrap in eval_error so
  call stack accumulates as the exception propagates through the AST chain
- Add eval_error constructor accepting filename + Boxed_Value
- Populate filename on wrapped eval_error in chaiscript_engine::eval()
- Extract original boxed value in Try_AST_Node for script try/catch semantics
- Unwrap boxed value in internal_eval/internal_eval_file to preserve
  script-level exception identity across nested eval() calls
- Add tests for call stack presence, filename population, and
  exception_specification backward compatibility

Requested by @lefticus in PR #682 review.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

include/chaiscript/language/chaiscript_common.hpp

@@ -341,11 +341,18 @@ namespace chaiscript {
       }
 
       eval_error(const std::string &t_why, Boxed_Value t_bv) noexcept
-          : std::runtime_error("Error: \"" + t_why + "\" ")
+          : std::runtime_error(format_why(t_why) + " " + format_filename("__EVAL__"))
           , reason(t_why)
           , m_boxed_value(std::move(t_bv)) {
       }
 
+      eval_error(const std::string &t_why, const std::string &t_fname, Boxed_Value t_bv) noexcept
+          : std::runtime_error(format_why(t_why) + " " + format_filename(t_fname))
+          , reason(t_why)
+          , filename(t_fname)
+          , m_boxed_value(std::move(t_bv)) {
+      }
+
       eval_error(const eval_error &) = default;
 
       bool has_boxed_value() const noexcept { return !m_boxed_value.is_undef(); }

include/chaiscript/language/chaiscript_engine.hpp

@@ -100,6 +100,9 @@ namespace chaiscript {
         } catch (const exception::file_not_found_error &) {
           // failed to load, try the next path
         } catch (const exception::eval_error &t_ee) {
+          if (t_ee.has_boxed_value()) {
+            throw Boxed_Value(t_ee.boxed_value());
+          }
           throw Boxed_Value(t_ee);
         }
       }
@@ -113,6 +116,9 @@ namespace chaiscript {
       try {
         return do_eval(t_e, "__EVAL__", true);
       } catch (const exception::eval_error &t_ee) {
+        if (t_ee.has_boxed_value()) {
+          throw Boxed_Value(t_ee.boxed_value());
+        }
         throw Boxed_Value(t_ee);
       }
     }
@@ -691,11 +697,21 @@ namespace chaiscript {
     eval(const std::string &t_input, const Exception_Handler &t_handler = Exception_Handler(), const std::string &t_filename = "__EVAL__") {
       try {
         return do_eval(t_input, t_filename);
+      } catch (exception::eval_error &ee) {
+        if (ee.has_boxed_value()) {
+          if (ee.filename.empty()) {
+            ee.filename = t_filename;
+          }
+          if (t_handler) {
+            t_handler->handle(ee.boxed_value(), m_engine);
+          }
+        }
+        throw;
       } catch (Boxed_Value &bv) {
         if (t_handler) {
           t_handler->handle(bv, m_engine);
         }
-        throw exception::eval_error("Exception thrown during evaluation", bv);
+        throw exception::eval_error("Exception thrown during evaluation", t_filename, bv);
       }
     }
 

include/chaiscript/language/chaiscript_eval.hpp

@@ -142,6 +142,10 @@ namespace chaiscript {
         } catch (exception::eval_error &ee) {
           ee.call_stack.push_back(*this);
           throw;
+        } catch (const Boxed_Value &bv) {
+          exception::eval_error ee("Exception thrown during evaluation", bv);
+          ee.call_stack.push_back(*this);
+          throw ee;
         }
       }
 
@@ -1358,7 +1362,11 @@ namespace chaiscript {
           try {
             retval = this->children[0]->eval(t_ss);
           } catch (const exception::eval_error &e) {
-            retval = handle_exception(t_ss, Boxed_Value(std::ref(e)));
+            if (e.has_boxed_value()) {
+              retval = handle_exception(t_ss, e.boxed_value());
+            } else {
+              retval = handle_exception(t_ss, Boxed_Value(std::ref(e)));
+            }
           } catch (const std::runtime_error &e) {
             retval = handle_exception(t_ss, Boxed_Value(std::ref(e)));
           } catch (const std::out_of_range &e) {

unittests/compiled_tests.cpp

@@ -320,6 +320,43 @@ TEST_CASE("eval_error without boxed_value has_boxed_value returns false") {
   CHECK_FALSE(ee.has_boxed_value());
 }
 
+TEST_CASE("eval_error wrapping script throw includes call stack") {
+  chaiscript::ChaiScript_Basic chai(create_chaiscript_stdlib(), create_chaiscript_parser());
+
+  try {
+    chai.eval("def foo() { throw(42); } \n foo();");
+    REQUIRE(false);
+  } catch (const chaiscript::exception::eval_error &ee) {
+    REQUIRE(ee.has_boxed_value());
+    CHECK_FALSE(ee.call_stack.empty());
+    const auto pretty = ee.pretty_print();
+    CHECK(pretty.find("foo") != std::string::npos);
+  }
+}
+
+TEST_CASE("eval_error wrapping script throw includes filename") {
+  chaiscript::ChaiScript_Basic chai(create_chaiscript_stdlib(), create_chaiscript_parser());
+
+  try {
+    chai.eval("throw(99);", chaiscript::Exception_Handler(), "test_script.chai");
+    REQUIRE(false);
+  } catch (const chaiscript::exception::eval_error &ee) {
+    REQUIRE(ee.has_boxed_value());
+    CHECK(ee.filename == "test_script.chai");
+  }
+}
+
+TEST_CASE("exception_specification still auto-unboxes for backward compatibility") {
+  chaiscript::ChaiScript_Basic chai(create_chaiscript_stdlib(), create_chaiscript_parser());
+
+  try {
+    chai.eval("throw(1)", chaiscript::exception_specification<int>());
+    REQUIRE(false);
+  } catch (const int e) {
+    CHECK(e == 1);
+  }
+}
+
 TEST_CASE("Deduction of pointer return types") {
   int val = 5;
   int *val_ptr = &val;