wizard,hw: tell user about errors during plugin init

see #4817 (issuecomment-434765570)

electrum/base_wizard.py

@@ -228,14 +228,7 @@ class BaseWizard(object):
     def choose_hw_device(self, purpose=HWD_SETUP_NEW_WALLET):
         title = _('Hardware Keystore')
         # check available plugins
-        support = self.plugins.get_hardware_support()
+        supported_plugins = self.plugins.get_hardware_support()
-        if not support:
-            msg = '\n'.join([
-                _('No hardware wallet support found on your system.'),
-                _('Please install the relevant libraries (eg python-trezor for Trezor).'),
-            ])
-            self.confirm_dialog(title=title, message=msg, run_next= lambda x: self.choose_hw_device(purpose))
-            return
         # scan devices
         devices = []
         devmgr = self.plugins.device_manager
@@ -246,14 +239,24 @@ class BaseWizard(object):
             debug_msg = '  {}:\n    {}'.format(_('Error scanning devices'), e)
         else:
             debug_msg = ''
-            for name, description, plugin in support:
+            for splugin in supported_plugins:
+                name, plugin = splugin.name, splugin.plugin
+                # plugin init errored?
+                if not plugin:
+                    e = splugin.exception
+                    indented_error_msg = '    '.join([''] + str(e).splitlines(keepends=True))
+                    debug_msg += f'  {name}: (error during plugin init)\n'
+                    debug_msg += '    {}\n'.format(_('You might have an incompatible library.'))
+                    debug_msg += f'{indented_error_msg}\n'
+                    continue
+                # see if plugin recognizes 'scanned_devices'
                 try:
                     # FIXME: side-effect: unpaired_device_info sets client.handler
                     u = devmgr.unpaired_device_infos(None, plugin, devices=scanned_devices)
                 except BaseException as e:
-                    devmgr.print_error('error getting device infos for {}: {}'.format(name, e))
+                    devmgr.print_error(f'error getting device infos for {name}: {e}')
                     indented_error_msg = '    '.join([''] + str(e).splitlines(keepends=True))
-                    debug_msg += '  {}:\n{}\n'.format(plugin.name, indented_error_msg)
+                    debug_msg += f'  {name}: (error getting device infos)\n{indented_error_msg}\n'
                     continue
                 devices += list(map(lambda x: (name, x), u))
         if not debug_msg:

electrum/plugin.py

@@ -28,7 +28,7 @@ import os
 import pkgutil
 import time
 import threading
-from typing import NamedTuple, Any, Union
+from typing import NamedTuple, Any, Union, TYPE_CHECKING, Optional
 
 from .i18n import _
 from .util import (profiler, PrintError, DaemonThread, UserCancelled,
@@ -37,6 +37,9 @@ from . import bip32
 from . import plugins
 from .simple_config import SimpleConfig
 
+if TYPE_CHECKING:
+    from .plugins.hw_wallet import HW_PluginBase
+
 
 plugin_loaders = {}
 hook_names = set()
@@ -148,10 +151,17 @@ class Plugins(DaemonThread):
                 try:
                     p = self.get_plugin(name)
                     if p.is_enabled():
-                        out.append([name, details[2], p])
+                        out.append(HardwarePluginToScan(name=name,
-                except:
+                                                        description=details[2],
+                                                        plugin=p,
+                                                        exception=None))
+                except Exception as e:
                     traceback.print_exc()
                     self.print_error("cannot load plugin for:", name)
+                    out.append(HardwarePluginToScan(name=name,
+                                                    description=details[2],
+                                                    plugin=None,
+                                                    exception=e))
         return out
 
     def register_wallet_type(self, name, gui_good, wallet_type):
@@ -277,6 +287,13 @@ class DeviceInfo(NamedTuple):
     initialized: bool
 
 
+class HardwarePluginToScan(NamedTuple):
+    name: str
+    description: str
+    plugin: Optional['HW_PluginBase']
+    exception: Optional[Exception]
+
+
 class DeviceMgr(ThreadJob, PrintError):
     '''Manages hardware clients.  A client communicates over a hardware
     channel with the device.

run_electrum

@@ -165,18 +165,20 @@ def init_cmdline(config_options, server):
 
 
 def get_connected_hw_devices(plugins):
-    support = plugins.get_hardware_support()
+    supported_plugins = plugins.get_hardware_support()
-    if not support:
-        print_msg('No hardware wallet support found on your system.')
-        sys.exit(1)
     # scan devices
     devices = []
     devmgr = plugins.device_manager
-    for name, description, plugin in support:
+    for splugin in supported_plugins:
+        name, plugin = splugin.name, splugin.plugin
+        if not plugin:
+            e = splugin.exception
+            print_stderr(f"{name}: error during plugin init: {repr(e)}")
+            continue
         try:
             u = devmgr.unpaired_device_infos(None, plugin)
         except:
-            devmgr.print_error("error", name)
+            devmgr.print_error(f'error getting device infos for {name}: {e}')
             continue
         devices += list(map(lambda x: (name, x), u))
     return devices