Add duk_fatal_exception for C++ uncaught/fatal

src-input/duk_error_longjmp.c

@@ -76,14 +76,9 @@ DUK_INTERNAL void duk_err_longjmp(duk_hthread *thr) {
 
 	DUK_DD(DUK_DDPRINT("about to longjmp, pf_prevent_count=%ld", (long) thr->heap->pf_prevent_count));
 
-#if !defined(DUK_USE_CPP_EXCEPTIONS)
 	/* If we don't have a jmpbuf_ptr, there is little we can do except
 	 * cause a fatal error.  The caller's expectation is that we never
 	 * return.
-	 *
-	 * With C++ exceptions we now just propagate an uncaught error
-	 * instead of invoking the fatal error handler.  Because there's
-	 * a dummy jmpbuf for C++ exceptions now, this could be changed.
 	 */
 	if (!thr->heap->lj.jmpbuf_ptr) {
 		DUK_D(DUK_DPRINT("uncaught error: type=%d iserror=%d value1=%!T value2=%!T",
@@ -97,16 +92,12 @@ DUK_INTERNAL void duk_err_longjmp(duk_hthread *thr) {
 #endif
 		DUK_UNREACHABLE();
 	}
-#endif  /* DUK_USE_CPP_EXCEPTIONS */
 
 #if defined(DUK_USE_CPP_EXCEPTIONS)
-	{
-		duk_internal_exception exc;  /* dummy */
-		throw exc;
-	}
-#else  /* DUK_USE_CPP_EXCEPTIONS */
+	throw duk_internal_exception();  /* dummy */
+#else
 	DUK_LONGJMP(thr->heap->lj.jmpbuf_ptr->jb);
-#endif  /* DUK_USE_CPP_EXCEPTIONS */
+#endif
 
 	DUK_UNREACHABLE();
 }

src-input/duk_error_macros.c

@@ -113,10 +113,18 @@ DUK_INTERNAL DUK_COLD void duk_default_fatal_handler(void *udata, const char *ms
 	DUK_UNREF(udata);
 	DUK_UNREF(msg);
 
+	msg = msg ? msg : "NULL";
+
 #if defined(DUK_USE_FATAL_HANDLER)
 	/* duk_config.h provided a custom default fatal handler. */
-	DUK_D(DUK_DPRINT("custom default fatal error handler called: %s", msg ? msg : "NULL"));
+	DUK_D(DUK_DPRINT("custom default fatal error handler called: %s", msg));
 	DUK_USE_FATAL_HANDLER(udata, msg);
+#elif defined(DUK_USE_CPP_EXCEPTIONS)
+	/* With C++ use a duk_fatal_exception which user code can catch in
+	 * a natural way.
+	 */
+	DUK_D(DUK_DPRINT("built-in default C++ fatal error handler called: %s", msg));
+	throw duk_fatal_exception(msg);
 #else
 	/* Default behavior is to abort() on error.  There's no printout
 	 * which makes this awkward, so it's always recommended to use an
@@ -133,7 +141,7 @@ DUK_INTERNAL DUK_COLD void duk_default_fatal_handler(void *udata, const char *ms
 	 *   - http://duktape.org/api.html#taglist-protected
 	 * ====================================================================
 	 */
-	DUK_D(DUK_DPRINT("built-in default fatal error handler called: %s", msg ? msg : "NULL"));
+	DUK_D(DUK_DPRINT("built-in default fatal error handler called: %s", msg));
 	DUK_ABORT();
 #endif
 

src-input/duk_exception.h

@@ -1,18 +1,30 @@
 /*
- *  Exception for Duktape internal throws when C++ exceptions are used
+ *  Exceptions for Duktape internal throws when C++ exceptions are used
  *  for long control transfers.
- *
- *  Doesn't inherit from any exception base class to minimize the chance
- *  that user code would accidentally catch this exception.
  */
 
 #if !defined(DUK_EXCEPTION_H_INCLUDED)
 #define DUK_EXCEPTION_H_INCLUDED
 
 #if defined(DUK_USE_CPP_EXCEPTIONS)
+/* Internal exception used as a setjmp-longjmp replacement.  User code should
+ * NEVER see or catch this exception, so it doesn't inherit from any base
+ * class which should minimize the chance of user code accidentally catching
+ * the exception.
+ */
 class duk_internal_exception {
 	/* intentionally empty */
 };
+
+/* Fatal error, thrown as a specific C++ exception with C++ exceptions
+ * enabled.  It is unsafe to continue; doing so may cause crashes or memory
+ * leaks.  This is intended to be either uncaught, or caught by user code
+ * aware of the "unsafe to continue" semantics.
+ */
+class duk_fatal_exception : public virtual std::runtime_error {
+ public:
+	duk_fatal_exception(const char *message) : std::runtime_error(message) {}
+};
 #endif
 
 #endif  /* DUK_EXCEPTION_H_INCLUDED */

src-input/duk_js_call.c

@@ -2724,7 +2724,10 @@ DUK_INTERNAL duk_int_t duk_handle_safe_call(duk_hthread *thr,
 		retval = DUK_EXEC_ERROR;
 	}
 #if defined(DUK_USE_CPP_EXCEPTIONS)
-	catch (std::exception &exc) {
+	catch (duk_fatal_exception &exc) {
+		DUK_D(DUK_DPRINT("rethrow duk_fatal_exception"));
+		throw;
+	} catch (std::exception &exc) {
 		const char *what = exc.what();
 		DUK_ASSERT((duk_size_t) ((duk_uint8_t *) thr->valstack_end - (duk_uint8_t *) thr->valstack) >= entry_valstack_end_byteoff);
 		DUK_STATS_INC(thr->heap, stats_safecall_throw);

src-input/duk_js_executor.c

@@ -2937,7 +2937,10 @@ DUK_INTERNAL void duk_js_execute_bytecode(duk_hthread *exec_thr) {
 			                           entry_jmpbuf_ptr);
 		}
 #if defined(DUK_USE_CPP_EXCEPTIONS)
-		catch (std::exception &exc) {
+		catch (duk_fatal_exception &exc) {
+			DUK_D(DUK_DPRINT("rethrow duk_fatal_exception"));
+			throw;
+		} catch (std::exception &exc) {
 			const char *what = exc.what();
 			if (!what) {
 				what = "unknown";