Restore reporting of unhandled exceptions during GUI application startup on windows

Not as nice as it was previously since errors importing the site module
will not be reported, but the python API provides no hooks for this in
Py_RunMain

bypy/run-python.h

@@ -170,6 +170,7 @@ typedef struct {
 #endif
 	const wchar_t *basename, *module, *function;
 	int argc;
+    PyObject* (*calibre_os_module)(void);
 #ifdef _WIN32
 	wchar_t* const *argv;
 #else
@@ -237,6 +238,11 @@ run_interpreter() {
     status = PyConfig_SetBytesArgv(&config, interpreter_data.argc, interpreter_data.argv);
 #endif
     CHECK_STATUS;
+    if (interpreter_data.calibre_os_module) {
+        if (PyImport_AppendInittab("calibre_os_module", interpreter_data.calibre_os_module) == -1) {
+            fatal("Failed to add calibre_os_module to the init table");
+        }
+    }
     status = Py_InitializeFromConfig(&config);
     CHECK_STATUS;
 

bypy/windows/site.py

@@ -85,4 +85,13 @@ def main():
 
 
 if __name__ == '__main__':
-    main()
+    try:
+        main()
+    except Exception:
+        if sys.gui_app:
+            import traceback
+            import calibre_os_module
+            calibre_os_module.gui_error_message(
+                f"Unhandled exception running {sys.calibre_basename}",
+                traceback.format_exc())
+        raise

bypy/windows/util.c

@@ -115,6 +115,42 @@ redirect_out_stream(FILE *stream) {
     }
 }
 
+static PyObject*
+gui_error_message(PyObject *self, PyObject *args) {
+    PyObject *pt, *pm;
+    if (!PyArg_ParseTuple(args, "UU", &pt, &pm)) return NULL;
+    wchar_t title[256] = {0}, text[4096] = {0};
+    PyUnicode_AsWideChar(pt, title, arraysz(title)-1);
+    PyUnicode_AsWideChar(pm, text, arraysz(text)-1);
+    MessageBoxW(NULL, text, title, MB_ICONERROR|MB_OK);
+    return PyBool_FromLong(1);
+}
+
+static PyMethodDef methods[] = {
+    {"gui_error_message", (PyCFunction)gui_error_message, METH_VARARGS,
+     "gui_error_message(title, msg) -> Show a GUI based error message."
+    },
+    {NULL}  /* Sentinel */
+};
+
+
+static struct PyModuleDef module = {
+    /* m_base     */ PyModuleDef_HEAD_INIT,
+    /* m_name     */ "calibre_os_module",
+    /* m_doc      */ "Integration with OS facilities during startup",
+    /* m_size     */ -1,
+    /* m_methods  */ methods,
+    /* m_slots    */ 0,
+    /* m_traverse */ 0,
+    /* m_clear    */ 0,
+    /* m_free     */ 0,
+};
+
+PyObject*
+calibre_os_module(void) {
+    return PyModule_Create(&module);
+}
+
 static void
 null_invalid_parameter_handler(
    const wchar_t * expression,
@@ -151,6 +187,7 @@ execute_python_entrypoint(const wchar_t *basename, const wchar_t *module, const
     interpreter_data.argv = CommandLineToArgvW(GetCommandLineW(), &interpreter_data.argc);
     if (interpreter_data.argv == NULL) ExitProcess(show_last_error(L"Failed to get command line"));
     interpreter_data.basename = basename; interpreter_data.module = module; interpreter_data.function = function;
+    interpreter_data.calibre_os_module = calibre_os_module;
     load_python_dll();
     pre_initialize_interpreter(is_gui_app);
 	run_interpreter();