path: root/checkers/exceptions.py

# Copyright (c) 2003-2013 LOGILAB S.A. (Paris, FRANCE).
# http://www.logilab.fr/ -- mailto:contact@logilab.fr
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation; either version 2 of the License, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
"""exceptions handling (raising, catching, exceptions classes) checker
"""
import sys

from logilab.common.compat import builtins
BUILTINS_NAME = builtins.__name__
import astroid
from astroid import YES, Instance, unpack_infer, List, Tuple

from pylint.checkers import BaseChecker
from pylint.checkers.utils import (
    is_empty, is_raising,
    check_messages, inherit_from_std_ex,
    EXCEPTIONS_MODULE, has_known_bases)
from pylint.interfaces import IAstroidChecker, INFERENCE, INFERENCE_FAILURE

def _annotated_unpack_infer(stmt, context=None):
    """
    Recursively generate nodes inferred by the given statement.
    If the inferred value is a list or a tuple, recurse on the elements.
    Returns an iterator which yields tuples in the format
    ('original node', 'infered node').
    """
    # TODO: the same code as unpack_infer, except for the annotated
    # return. We need this type of annotation only here and
    # there is no point in complicating the API for unpack_infer.
    # If the need arises, this behaviour can be promoted to unpack_infer
    # as well.
    if isinstance(stmt, (List, Tuple)):
        for elt in stmt.elts:
            for infered_elt in unpack_infer(elt, context):
                yield elt, infered_elt
        return
    # if infered is a final node, return it and stop
    infered = next(stmt.infer(context))
    if infered is stmt:
        yield stmt, infered
        return
    # else, infer recursivly, except YES object that should be returned as is
    for infered in stmt.infer(context):
        if infered is YES:
            yield stmt, infered
        else:
            for inf_inf in unpack_infer(infered, context):
                yield stmt, inf_inf


PY3K = sys.version_info >= (3, 0)
OVERGENERAL_EXCEPTIONS = ('Exception',)

MSGS = {
    'E0701': ('Bad except clauses order (%s)',
              'bad-except-order',
              'Used when except clauses are not in the correct order (from the '
              'more specific to the more generic). If you don\'t fix the order, '
              'some exceptions may not be catched by the most specific handler.'),
    'E0702': ('Raising %s while only classes, instances or string are allowed',
              'raising-bad-type',
              'Used when something which is neither a class, an instance or a \
              string is raised (i.e. a `TypeError` will be raised).'),
    'E0703': ('Exception context set to something which is not an '
              'exception, nor None',
              'bad-exception-context',
              'Used when using the syntax "raise ... from ...", '
              'where the exception context is not an exception, '
              'nor None.',
              {'minversion': (3, 0)}),
    'E0710': ('Raising a new style class which doesn\'t inherit from BaseException',
              'raising-non-exception',
              'Used when a new style class which doesn\'t inherit from \
               BaseException is raised.'),
    'E0711': ('NotImplemented raised - should raise NotImplementedError',
              'notimplemented-raised',
              'Used when NotImplemented is raised instead of \
              NotImplementedError'),
    'E0712': ('Catching an exception which doesn\'t inherit from BaseException: %s',
              'catching-non-exception',
              'Used when a class which doesn\'t inherit from \
               BaseException is used as an exception in an except clause.'),

    'W0701': ('Raising a string exception',
              'raising-string',
              'Used when a string exception is raised.'),
    'W0702': ('No exception type(s) specified',
              'bare-except',
              'Used when an except clause doesn\'t specify exceptions type to \
              catch.'),
    'W0703': ('Catching too general exception %s',
              'broad-except',
              'Used when an except catches a too general exception, \
              possibly burying unrelated errors.'),
    'W0704': ('Except doesn\'t do anything',
              'pointless-except',
              'Used when an except clause does nothing but "pass" and there is\
              no "else" clause.'),
    'W0710': ('Exception doesn\'t inherit from standard "Exception" class',
              'nonstandard-exception',
              'Used when a custom exception class is raised but doesn\'t \
              inherit from the builtin "Exception" class.',
              {'maxversion': (3, 0)}),
    'W0711': ('Exception to catch is the result of a binary "%s" operation',
              'binary-op-exception',
              'Used when the exception to catch is of the form \
              "except A or B:".  If intending to catch multiple, \
              rewrite as "except (A, B):"'),
    }


class ExceptionsChecker(BaseChecker):
    """checks for
    * excepts without exception filter
    * type of raise argument : string, Exceptions, other values
    """

    __implements__ = IAstroidChecker

    name = 'exceptions'
    msgs = MSGS
    priority = -4
    options = (('overgeneral-exceptions',
                {'default' : OVERGENERAL_EXCEPTIONS,
                 'type' :'csv', 'metavar' : '<comma-separated class names>',
                 'help' : 'Exceptions that will emit a warning '
                          'when being caught. Defaults to "%s"' % (
                              ', '.join(OVERGENERAL_EXCEPTIONS),)}
               ),
              )

    @check_messages('raising-string', 'nonstandard-exception',
                    'raising-bad-type', 'raising-non-exception',
                    'notimplemented-raised', 'bad-exception-context')
    def visit_raise(self, node):
        """visit raise possibly inferring value"""
        # ignore empty raise
        if node.exc is None:
            return
        if PY3K and node.cause:
            try:
                cause = next(node.cause.infer())
            except astroid.InferenceError:
                pass
            else:
                if cause is YES:
                    return
                if isinstance(cause, astroid.Const):
                    if cause.value is not None:
                        self.add_message('bad-exception-context',
                                         node=node)
                elif (not isinstance(cause, astroid.Class) and
                      not inherit_from_std_ex(cause)):
                    self.add_message('bad-exception-context',
                                     node=node)
        expr = node.exc
        if self._check_raise_value(node, expr):
            return
        else:
            try:
                value = next(unpack_infer(expr))
            except astroid.InferenceError:
                return
            self._check_raise_value(node, value)

    def _check_raise_value(self, node, expr):
        """check for bad values, string exception and class inheritance
        """
        value_found = True
        if isinstance(expr, astroid.Const):
            value = expr.value
            if isinstance(value, str):
                self.add_message('raising-string', node=node)
            else:
                self.add_message('raising-bad-type', node=node,
                                 args=value.__class__.__name__)
        elif (isinstance(expr, astroid.Name) and \
                 expr.name in ('None', 'True', 'False')) or \
                 isinstance(expr, (astroid.List, astroid.Dict, astroid.Tuple,
                                   astroid.Module, astroid.Function)):
            self.add_message('raising-bad-type', node=node, args=expr.name)
        elif ((isinstance(expr, astroid.Name) and expr.name == 'NotImplemented')
              or (isinstance(expr, astroid.CallFunc) and
                  isinstance(expr.func, astroid.Name) and
                  expr.func.name == 'NotImplemented')):
            self.add_message('notimplemented-raised', node=node)
        elif isinstance(expr, astroid.BinOp) and expr.op == '%':
            self.add_message('raising-string', node=node)
        elif isinstance(expr, (Instance, astroid.Class)):
            if isinstance(expr, Instance):
                expr = expr._proxied
            if (isinstance(expr, astroid.Class) and
                    not inherit_from_std_ex(expr) and
                    expr.root().name != BUILTINS_NAME):
                if expr.newstyle:
                    self.add_message('raising-non-exception', node=node)
                else:
                    self.add_message(
                        'nonstandard-exception', node=node,
                         confidence=INFERENCE if has_known_bases(expr) else INFERENCE_FAILURE)
            else:
                value_found = False
        else:
            value_found = False
        return value_found

    @check_messages('bare-except', 'broad-except', 'pointless-except',
                    'binary-op-exception', 'bad-except-order',
                    'catching-non-exception')
    def visit_tryexcept(self, node):
        """check for empty except"""
        exceptions_classes = []
        nb_handlers = len(node.handlers)
        for index, handler in enumerate(node.handlers):
            # single except doing nothing but "pass" without else clause
            if is_empty(handler.body) and not node.orelse:
                self.add_message('pointless-except',
                                 node=handler.type or handler.body[0])
            if handler.type is None:
                if not is_raising(handler.body):
                    self.add_message('bare-except', node=handler)
                # check if a "except:" is followed by some other
                # except
                if index < (nb_handlers - 1):
                    msg = 'empty except clause should always appear last'
                    self.add_message('bad-except-order', node=node, args=msg)

            elif isinstance(handler.type, astroid.BoolOp):
                self.add_message('binary-op-exception',
                                 node=handler, args=handler.type.op)
            else:
                try:
                    excs = list(_annotated_unpack_infer(handler.type))
                except astroid.InferenceError:
                    continue
                for part, exc in excs:
                    if exc is YES:
                        continue
                    if isinstance(exc, astroid.Instance) and inherit_from_std_ex(exc):
                        exc = exc._proxied
                    if not isinstance(exc, astroid.Class):
                        # Don't emit the warning if the infered stmt
                        # is None, but the exception handler is something else,
                        # maybe it was redefined.
                        if (isinstance(exc, astroid.Const) and
                                exc.value is None):
                            if ((isinstance(handler.type, astroid.Const) and
                                     handler.type.value is None) or
                                     handler.type.parent_of(exc)):
                                # If the exception handler catches None or
                                # the exception component, which is None, is
                                # defined by the entire exception handler, then
                                # emit a warning.
                                self.add_message('catching-non-exception',
                                                 node=handler.type,
                                                 args=(part.as_string(), ))
                        else:
                            self.add_message('catching-non-exception',
                                             node=handler.type,
                                             args=(part.as_string(), ))
                        continue

                    exc_ancestors = [anc for anc in exc.ancestors()
                                     if isinstance(anc, astroid.Class)]
                    for previous_exc in exceptions_classes:
                        if previous_exc in exc_ancestors:
                            msg = '%s is an ancestor class of %s' % (
                                previous_exc.name, exc.name)
                            self.add_message('bad-except-order',
                                             node=handler.type, args=msg)
                    if (exc.name in self.config.overgeneral_exceptions
                            and exc.root().name == EXCEPTIONS_MODULE
                            and not is_raising(handler.body)):
                        self.add_message('broad-except',
                                         args=exc.name, node=handler.type)

                    if (not inherit_from_std_ex(exc) and
                            exc.root().name != BUILTINS_NAME):
                        if has_known_bases(exc):
                            self.add_message('catching-non-exception',
                                             node=handler.type,
                                             args=(exc.name, ))

                exceptions_classes += [exc for _, exc in excs]


def register(linter):
    """required method to auto register this checker"""
    linter.register_checker(ExceptionsChecker(linter))