[anaconda:master 1/3] Add a simple pointless-override checker to pylint checkers.

mulhern amulhern at redhat.com
Fri Dec 5 14:31:46 UTC 2014


Call it in pylint-one.sh.

Signed-off-by: mulhern <amulhern at redhat.com>
---
 tests/pylint/pointless-override.py | 252 +++++++++++++++++++++++++++++++++++++
 tests/pylint/pylint-one.sh         |   2 +-
 2 files changed, 253 insertions(+), 1 deletion(-)
 create mode 100644 tests/pylint/pointless-override.py

diff --git a/tests/pylint/pointless-override.py b/tests/pylint/pointless-override.py
new file mode 100644
index 0000000..c8d4776
--- /dev/null
+++ b/tests/pylint/pointless-override.py
@@ -0,0 +1,252 @@
+# Pylint checker for pointless class attributes overrides.
+#
+# Copyright (C) 2014  Red Hat, Inc.
+#
+# This copyrighted material is made available to anyone wishing to use,
+# modify, copy, or redistribute it subject to the terms and conditions of
+# the GNU General Public License v.2, or (at your option) any later version.
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY expressed or implied, including the implied warranties 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.  Any Red Hat trademarks that are incorporated in the
+# source code or documentation are not subject to the GNU General Public
+# License and may only be used or replicated with the express permission of
+# Red Hat, Inc.
+#
+# Red Hat Author(s): Anne Mulhern <amulhern at redhat.com>
+#
+
+import abc
+
+from six import add_metaclass
+
+import astroid
+
+from pylint.checkers import BaseChecker
+from pylint.checkers.utils import check_messages
+from pylint.interfaces import IAstroidChecker
+
+ at add_metaclass(abc.ABCMeta)
+class PointlessData(object):
+
+    _DEF_CLASS = abc.abstractproperty(doc="Class of interesting definitions.")
+    message_id = abc.abstractproperty(doc="Pylint message identifier.")
+
+    @classmethod
+    @abc.abstractmethod
+    def _retain_node(cls, node, restrict=True):
+        """ Determines whether to retain a node for the analysis.
+
+            :param node: an AST node
+            :type node: astroid.Class
+            :param restrict bool: True if results returned should be restricted
+            :returns: True if the node should be kept, otherwise False
+            :rtype: bool
+
+            Restricted nodes are candidates for being marked as overridden.
+            Only restricted nodes are put into the initial pool of candidates.
+        """
+        raise NotImplementedError()
+
+    @staticmethod
+    @abc.abstractmethod
+    def _extract_value(node):
+        """ Return the node that contains the assignment's value.
+
+            :param node: an AST node
+            :type node: astroid.Class
+            :returns: the node corresponding to the value
+            :rtype: bool
+        """
+        raise NotImplementedError()
+
+    @staticmethod
+    @abc.abstractmethod
+    def _extract_targets(node):
+        """ Generates the names being assigned to.
+
+            :param node: an AST node
+            :type node: astroid.Class
+            :returns: a list of assignment target names
+            :rtype: generator of str
+        """
+        raise NotImplementedError()
+
+    @classmethod
+    def get_data(cls, node, restrict=True):
+        """ Find relevant nodes for this analysis.
+
+            :param node: an AST node
+            :type node: astroid.Class
+            :param restrict bool: True if results returned should be restricted
+
+            :rtype: generator of astroid.Class
+            :returns: a generator of interesting nodes.
+
+            Note that all nodes returned are guaranteed to be instances of
+            some class in self._DEF_CLASS.
+        """
+        nodes = (n for n in node.body if isinstance(n, cls._DEF_CLASS))
+        for n in nodes:
+            if cls._retain_node(n, restrict):
+                for name in cls._extract_targets(n):
+                    yield (name, cls._extract_value(n))
+
+    @classmethod
+    @abc.abstractmethod
+    def check_equal(cls, node, other):
+        """ Check whether the two nodes are considered equal.
+
+            :param node: some ast node
+            :param other: some ast node
+
+            :rtype: bool
+            :returns: True if the nodes are considered equal, otherwise False
+
+            If the method returns True, the nodes are actually equal, but it
+            may return False when the nodes are equal.
+        """
+        raise NotImplementedError()
+
+class PointlessFunctionDefinition(PointlessData):
+    """ Looking for pointless function definitions. """
+
+    _DEF_CLASS = astroid.Function
+    message_id = "W9952"
+
+    @classmethod
+    def _retain_node(cls, node, restrict=True):
+        return not restrict or \
+           (len(node.body) == 1 and isinstance(node.body[0], astroid.Pass))
+
+    @classmethod
+    def check_equal(cls, node, other):
+        return len(node.body) == 1 and isinstance(node.body[0], astroid.Pass) and \
+           len(other.body) == 1 and isinstance(other.body[0], astroid.Pass)
+
+    @staticmethod
+    def _extract_value(node):
+        return node
+
+    @staticmethod
+    def _extract_targets(node):
+        yield node.name
+
+class PointlessAssignment(PointlessData):
+
+    _DEF_CLASS = astroid.Assign
+    message_id = "W9951"
+
+    _VALUE_CLASSES = (
+        astroid.Const,
+        astroid.Dict,
+        astroid.List,
+        astroid.Tuple
+    )
+
+    @classmethod
+    def _retain_node(cls, node, restrict=True):
+        return not restrict or isinstance(node.value, cls._VALUE_CLASSES)
+
+    @classmethod
+    def check_equal(cls, node, other):
+        if type(node) != type(other):
+            return False
+        if isinstance(node, astroid.Const):
+            return node.value == other.value
+        if isinstance(node, (astroid.List, astroid.Tuple)):
+            return len(node.elts) == len(other.elts) and \
+               all(cls.check_equal(n, o) for (n, o) in zip(node.elts, other.elts))
+        if isinstance(node, astroid.Dict):
+            return len(node.items) == len(other.items)
+        return False
+
+    @staticmethod
+    def _extract_value(node):
+        return node.value
+
+    @staticmethod
+    def _extract_targets(node):
+        for target in node.targets:
+            yield target.name
+
+class PointlessClassAttributeOverrideChecker(BaseChecker):
+    """ If the nearest definition of the class attribute in the MRO assigns
+        it the same value, then the overriding definition is said to be
+        pointless.
+
+        The algorithm for detecting a pointless attribute override is the following.
+
+        * For each class, C:
+           - For each attribute assignment,
+               name_1 = name_2 ... name_n = l (where l is a literal):
+              * For each n in (n_1, n_2):
+                - Traverse the linearization of the MRO until the first
+                   matching assignment n = l' is identified. If l is equal to l',
+                   then consider that the assignment to l in C is a
+                   pointless override.
+
+        The algorithm for detecting a pointless method override has the same
+        general structure, and the same defects discussed below.
+
+        Note that this analysis is neither sound nor complete. It is unsound
+        under multiple inheritance. Consider the following class hierarchy::
+
+            class A(object):
+                _attrib = False
+
+            class B(A):
+                _attrib = False
+
+            class C(A):
+                _attrib = True
+
+            class D(B,C):
+                pass
+
+        In this  case, starting from B, B._attrib = False would be considered
+        pointless. However, for D the MRO is B, C, A, and removing the assignment
+        B._attrib = False would change the inherited value of D._attrib from
+        False to True.
+
+        The analysis is incomplete because it will find some values unequal when
+        actually they are equal.
+
+        The analysis is both incomplete and unsound because it expects that
+        assignments will always be made by means of the same syntax.
+    """
+
+    __implements__ = (IAstroidChecker,)
+
+    name = "pointless class attribute override checker"
+    msgs = {
+       "W9951":
+       (
+          "Assignment to class attribute %s overrides identical assignment in ancestor.",
+          "pointless-class-attribute-override",
+          "Assignment to class attribute  that overrides assignment in ancestor that assigns identical value has no effect."
+       ),
+       "W9952":
+       (
+          "definition of %s method overrides identical method definition in ancestor",
+          "pointless-method-definition-override",
+          "Overriding empty method definition with another empty method definition has no effect."
+       )
+    }
+
+    @check_messages("W9951", "W9952")
+    def visit_class(self, node):
+        for checker in (PointlessAssignment, PointlessFunctionDefinition):
+            for (name, value) in checker.get_data(node):
+                for a in node.ancestors():
+                    match = next((v for (n, v) in checker.get_data(a, False) if n == name), None)
+                    if match is not None:
+                        if checker.check_equal(value, match):
+                            self.add_message(checker.message_id, node=value, args=(name,))
+                        break
+
+def register(linter):
+    linter.register_checker(PointlessClassAttributeOverrideChecker(linter))
diff --git a/tests/pylint/pylint-one.sh b/tests/pylint/pylint-one.sh
index 7235674..7c7b8c2 100755
--- a/tests/pylint/pylint-one.sh
+++ b/tests/pylint/pylint-one.sh
@@ -18,7 +18,7 @@ pylint_output="$(pylint \
     --dummy-variables-rgx=_ \
     --ignored-classes=DefaultInstall,Popen,QueueFactory,TransactionSet \
     --defining-attr-methods=__init__,_grabObjects,initialize,reset,start,setUp \
-    --load-plugins=intl,preconf,markup,eintr \
+    --load-plugins=intl,preconf,markup,eintr,pointless-override \
     --init-hook=\
 'import gi.overrides, os;
 gi.overrides.__path__[0:0] = (os.environ["ANACONDA_WIDGETS_OVERRIDES"].split(":") if "ANACONDA_WIDGETS_OVERRIDES" in os.environ else [])' \
-- 
1.9.3



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