[commands] Don't raise ExtensionNotFound for ImportErrors in modules

Now loading an extension that _contains_ a failed import will fail
with ExtensionFailed, rather than ExtensionNotFound.

discord/ext/commands/bot.py

@@ -27,7 +27,7 @@
 import asyncio
 import collections
 import inspect
-import importlib
+import importlib.util
 import sys
 import traceback
 import re
@@ -588,12 +588,17 @@ def _call_module_finalizers(self, lib, key):
                 if _is_submodule(name, module):
                     del sys.modules[module]
 
-    def _load_from_module_spec(self, lib, key):
+    def _load_from_module_spec(self, spec, key):
         # precondition: key not in self.__extensions
+        lib = importlib.util.module_from_spec(spec)
+        try:
+            spec.loader.exec_module(lib)
+        except Exception as e:
+            raise errors.ExtensionFailed(key, e) from e
+
         try:
             setup = getattr(lib, 'setup')
         except AttributeError:
-            del sys.modules[key]
             raise errors.NoEntryPointError(key)
 
         try:
@@ -603,7 +608,7 @@ def _load_from_module_spec(self, lib, key):
             self._call_module_finalizers(lib, key)
             raise errors.ExtensionFailed(key, e) from e
         else:
-            self.__extensions[key] = lib
+            sys.modules[key] = self.__extensions[key] = lib
 
     def load_extension(self, name):
         """Loads an extension.
@@ -637,12 +642,11 @@ def load_extension(self, name):
         if name in self.__extensions:
             raise errors.ExtensionAlreadyLoaded(name)
 
-        try:
-            lib = importlib.import_module(name)
-        except ImportError as e:
-            raise errors.ExtensionNotFound(name, e) from e
-        else:
-            self._load_from_module_spec(lib, name)
+        spec = importlib.util.find_spec(name)
+        if spec is None:
+            raise errors.ExtensionNotFound(name)
+
+        self._load_from_module_spec(spec, name)
 
     def unload_extension(self, name):
         """Unloads an extension.

discord/ext/commands/errors.py

@@ -503,7 +503,7 @@ def __init__(self, name):
         super().__init__("Extension {!r} has no 'setup' function.".format(name), name=name)
 
 class ExtensionFailed(ExtensionError):
-    """An exception raised when an extension failed to load during execution of the ``setup`` entry point.
+    """An exception raised when an extension failed to load during execution of the module or ``setup`` entry point.
 
     This inherits from :exc:`ExtensionError`
 
@@ -521,19 +521,21 @@ def __init__(self, name, original):
         super().__init__(fmt.format(name, original), name=name)
 
 class ExtensionNotFound(ExtensionError):
-    """An exception raised when an extension failed to be imported.
+    """An exception raised when an extension is not found.
 
     This inherits from :exc:`ExtensionError`
 
+    .. versionchanged:: 1.3.0
+        Made the ``original`` attribute always None.
+
     Attributes
     -----------
     name: :class:`str`
         The extension that had the error.
-    original: :exc:`ImportError`
-        The original exception that was raised. You can also get this via
-        the ``__cause__`` attribute.
+    original: :class:`NoneType`
+        Always ``None`` for backwards compatibility.
     """
-    def __init__(self, name, original):
-        self.original = original
+    def __init__(self, name, original=None):
+        self.original = None
         fmt = 'Extension {0!r} could not be loaded.'
         super().__init__(fmt.format(name), name=name)