Ensure exceptions are pickleable

src/flake8/exceptions.py

@@ -4,14 +4,10 @@
 class Flake8Exception(Exception):
     """Plain Flake8 exception."""
 
-    pass
-
 
 class EarlyQuit(Flake8Exception):
     """Except raised when encountering a KeyboardInterrupt."""
 
-    pass
-
 
 class ExecutionError(Flake8Exception):
     """Exception raised during execution of Flake8."""
@@ -22,15 +18,15 @@ class FailedToLoadPlugin(Flake8Exception):
 
     FORMAT = 'Flake8 failed to load plugin "%(name)s" due to %(exc)s.'
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, plugin, exception):
         """Initialize our FailedToLoadPlugin exception."""
-        self.plugin = kwargs.pop("plugin")
+        self.plugin = plugin
         self.ep_name = self.plugin.name
-        self.original_exception = kwargs.pop("exception")
-        super(FailedToLoadPlugin, self).__init__(*args, **kwargs)
+        self.original_exception = exception
+        super(FailedToLoadPlugin, self).__init__(plugin, exception)
 
     def __str__(self):
-        """Return a nice string for our exception."""
+        """Format our exception message."""
         return self.FORMAT % {
             "name": self.ep_name,
             "exc": self.original_exception,
@@ -40,9 +36,8 @@ class FailedToLoadPlugin(Flake8Exception):
 class InvalidSyntax(Flake8Exception):
     """Exception raised when tokenizing a file fails."""
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, exception):  # type: (Exception) -> None
         """Initialize our InvalidSyntax exception."""
-        exception = kwargs.pop("exception", None)
         self.original_exception = exception
         self.error_message = "{0}: {1}".format(
             exception.__class__.__name__, exception.args[0]
@@ -50,9 +45,11 @@ class InvalidSyntax(Flake8Exception):
         self.error_code = "E902"
         self.line_number = 1
         self.column_number = 0
-        super(InvalidSyntax, self).__init__(
-            self.error_message, *args, **kwargs
-        )
+        super(InvalidSyntax, self).__init__(exception)
+
+    def __str__(self):
+        """Format our exception message."""
+        return self.error_message
 
 
 class PluginRequestedUnknownParameters(Flake8Exception):
@@ -60,12 +57,12 @@ class PluginRequestedUnknownParameters(Flake8Exception):
 
     FORMAT = '"%(name)s" requested unknown parameters causing %(exc)s'
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, plugin, exception):
         """Pop certain keyword arguments for initialization."""
-        self.original_exception = kwargs.pop("exception")
-        self.plugin = kwargs.pop("plugin")
+        self.plugin = plugin
+        self.original_exception = exception
         super(PluginRequestedUnknownParameters, self).__init__(
-            *args, **kwargs
+            plugin, exception
         )
 
     def __str__(self):
@@ -81,13 +78,11 @@ class PluginExecutionFailed(Flake8Exception):
 
     FORMAT = '"%(name)s" failed during execution due to "%(exc)s"'
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, plugin, exception):
         """Utilize keyword arguments for message generation."""
-        self.original_exception = kwargs.pop("exception")
-        self.plugin = kwargs.pop("plugin")
-        super(PluginExecutionFailed, self).__init__(
-            str(self), *args, **kwargs
-        )
+        self.plugin = plugin
+        self.original_exception = exception
+        super(PluginExecutionFailed, self).__init__(plugin, exception)
 
     def __str__(self):
         """Format our exception message."""
@@ -100,8 +95,6 @@ class PluginExecutionFailed(Flake8Exception):
 class HookInstallationError(Flake8Exception):
     """Parent exception for all hooks errors."""
 
-    pass
-
 
 class GitHookAlreadyExists(HookInstallationError):
     """Exception raised when the git pre-commit hook file already exists."""

src/flake8/processor.py

@@ -118,7 +118,7 @@ class FileProcessor(object):
                     tokenize.generate_tokens(lambda: next(line_iter))
                 )
             except tokenize.TokenError as exc:
-                raise exceptions.InvalidSyntax(exc.message, exception=exc)
+                raise exceptions.InvalidSyntax(exception=exc)
 
         return self._file_tokens
 

tests/unit/test_exceptions.py

@@ -0,0 +1,54 @@
+"""Tests for the flake8.exceptions module."""
+import pickle
+
+import entrypoints
+
+from flake8 import exceptions
+from flake8.plugins import manager as plugins_manager
+
+
+class _ExceptionTest:
+    def test_pickleable(self):
+        """Test that the exception is round-trip pickleable."""
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            new_err = pickle.loads(pickle.dumps(self.err, protocol=proto))
+            assert str(self.err) == str(new_err)
+            orig_e = self.err.original_exception
+            new_e = new_err.original_exception
+            assert (type(orig_e), orig_e.args) == (type(new_e), new_e.args)
+
+
+class TestFailedToLoadPlugin(_ExceptionTest):
+    """Tests for the FailedToLoadPlugin exception."""
+
+    err = exceptions.FailedToLoadPlugin(
+        plugin=plugins_manager.Plugin(
+            'plugin_name',
+            entrypoints.EntryPoint('plugin_name', 'os.path', None),
+        ),
+        exception=ValueError('boom!'),
+    )
+
+
+class TestInvalidSyntax(_ExceptionTest):
+    """Tests for the InvalidSyntax exception."""
+
+    err = exceptions.InvalidSyntax(exception=ValueError('Unexpected token: $'))
+
+
+class TestPluginRequestedUnknownParameters(_ExceptionTest):
+    """Tests for the PluginRequestedUnknownParameters exception."""
+
+    err = exceptions.PluginRequestedUnknownParameters(
+        plugin={'plugin_name': 'plugin_name'},
+        exception=ValueError('boom!'),
+    )
+
+
+class TestPluginExecutionFailed(_ExceptionTest):
+    """Tests for the PluginExecutionFailed exception."""
+
+    err = exceptions.PluginExecutionFailed(
+        plugin={'plugin_name': 'plugin_name'},
+        exception=ValueError('boom!'),
+    )