raise instead of overwriting the config file on syntax error

electrum/gui/qt/__init__.py

@@ -27,7 +27,7 @@ import os
 import signal
 import sys
 import threading
-from typing import Optional, TYPE_CHECKING, List, Sequence
+from typing import Optional, TYPE_CHECKING, List, Sequence, Union
 
 try:
     import PyQt6
@@ -582,3 +582,25 @@ class ElectrumGui(BaseElectrumGui, Logger):
         message = _("Text copied to Clipboard") if title is None else _("{} copied to Clipboard").format(title)
         # tooltip cannot be displayed immediately when called from a menu; wait 200ms
         self.timer.singleShot(200, lambda: QToolTip.showText(QCursor.pos(), message, None))
+
+
+def standalone_exception_dialog(exception: Union[str, BaseException]) -> None:
+    app = QApplication.instance()
+    if not app:
+        app = QApplication([])
+
+    msg_box = QMessageBox()
+    msg_box.setWindowTitle(_("Error starting Electrum"))
+    msg_box.setIcon(QMessageBox.Icon.Critical)
+    msg_box.setText(_("An error occurred") + ":")
+    msg_box.setInformativeText(str(exception))
+
+    # Add detailed traceback if available
+    if hasattr(exception, "__traceback__"):
+        import traceback
+        detailed_text = ''.join(traceback.format_exception(
+            type(exception), exception, exception.__traceback__)
+        )
+        msg_box.setDetailedText(detailed_text)
+
+    msg_box.exec()

electrum/simple_config.py

@@ -900,9 +900,7 @@ def read_user_config(path: Optional[str]) -> Dict[str, Any]:
         with open(config_path, "r", encoding='utf-8') as f:
             data = f.read()
         result = json.loads(data)
-    except Exception as exc:
-        _logger.warning(f"Cannot read config file at {config_path}: {exc}")
-        return {}
-    if not type(result) is dict:
-        return {}
+        assert isinstance(result, dict), "config file is not a dict"
+    except Exception as e:
+        raise ValueError(f"Invalid config file at {config_path}: {str(e)}")
     return result

run_electrum

@@ -271,6 +271,25 @@ def sys_exit(i):
         loop_thread.join(timeout=1)
     sys.exit(i)
 
+def read_config(config_options: dict) -> SimpleConfig:
+    """
+    Reads the config file and returns SimpleConfig, on failure it will potentially
+    show a GUI error dialog if a gui is available, and then re-raise the exception.
+    """
+    try:
+        return SimpleConfig(config_options)
+    except Exception as config_error:
+        # parse full cmd to find out which UI is being used
+        full_config_options = parse_command_line(simple_parser=False)
+        if full_config_options.get("cmd") == 'gui':
+            gui_name = full_config_options.get(SimpleConfig.GUI_NAME.key(), 'qt')
+            try:
+                gui = __import__(f'electrum.gui.{gui_name}', fromlist=['electrum'])
+                gui.standalone_exception_dialog(config_error)  # type: ignore
+            except Exception as e:
+                print_stderr(f"Error showing standalone gui dialog: {e}")
+        raise
+
 def parse_command_line(simple_parser=False) -> Dict:
     # parse command line from sys.argv
     if simple_parser:
@@ -371,14 +390,14 @@ def main():
                 sys.argv.remove(x)
         # parse first without plugins
         config_options = parse_command_line(simple_parser=True)
-        tmp_config = SimpleConfig(config_options)
+        tmp_config = read_config(config_options)
         # load (only) the commands modules of plugins so their commands are registered
-        plugin_commands = Plugins(tmp_config, cmd_only=True)
+        _plugin_commands = Plugins(tmp_config, cmd_only=True)
         # re-parse command line
         sys.argv = saved_sys_argv[:]
         config_options = parse_command_line()
 
-    config = SimpleConfig(config_options)
+    config = read_config(config_options)
     cmdname = config.get('cmd')
 
     # set language as early as possible

tests/test_simple_config.py

@@ -6,7 +6,6 @@ import shutil
 from io import StringIO
 
 from electrum.simple_config import SimpleConfig, read_user_config
-from electrum import constants
 
 from . import ElectrumTestCase
 
@@ -250,5 +249,5 @@ class TestUserConfig(ElectrumTestCase):
         with open(thefile, "w") as f:
             f.write(repr(payload))
 
-        result = read_user_config(self.user_dir)
-        self.assertEqual({}, result)
+        with self.assertRaises(ValueError):
+            read_user_config(self.user_dir)