design_analysis.py

# -*- coding: utf-8 -*-
# Copyright (c) 2006, 2009-2010, 2012-2015 LOGILAB S.A. (Paris, FRANCE) <contact@logilab.fr>
# Copyright (c) 2012, 2014 Google, Inc.
# Copyright (c) 2014-2020 Claudiu Popa <pcmanticore@gmail.com>
# Copyright (c) 2014 Arun Persaud <arun@nubati.net>
# Copyright (c) 2015 Ionel Cristian Maries <contact@ionelmc.ro>
# Copyright (c) 2016 Łukasz Rogalski <rogalski.91@gmail.com>
# Copyright (c) 2017 ahirnish <ahirnish@gmail.com>
# Copyright (c) 2018 Lucas Cimon <lucas.cimon@gmail.com>
# Copyright (c) 2018 Mike Frysinger <vapier@gmail.com>
# Copyright (c) 2018 Mark Miller <725mrm@gmail.com>
# Copyright (c) 2018 Ashley Whetter <ashley@awhetter.co.uk>
# Copyright (c) 2018 Ville Skyttä <ville.skytta@iki.fi>
# Copyright (c) 2018 Jakub Wilk <jwilk@jwilk.net>
# Copyright (c) 2019 Pierre Sassoulas <pierre.sassoulas@gmail.com>
# Copyright (c) 2019 Michael Scott Cuthbert <cuthbert@mit.edu>
# Copyright (c) 2020 Anthony Sottile <asottile@umich.edu>

# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/PyCQA/pylint/blob/master/COPYING

"""check for signs of poor design"""

import re
from collections import defaultdict

import astroid
from astroid import BoolOp, If, decorators

from pylint import utils
from pylint.checkers import BaseChecker
from pylint.checkers.utils import check_messages
from pylint.interfaces import IAstroidChecker

MSGS = {
    "R0901": (
        "Too many ancestors (%s/%s)",
        "too-many-ancestors",
        "Used when class has too many parent classes, try to reduce "
        "this to get a simpler (and so easier to use) class.",
    ),
    "R0902": (
        "Too many instance attributes (%s/%s)",
        "too-many-instance-attributes",
        "Used when class has too many instance attributes, try to reduce "
        "this to get a simpler (and so easier to use) class.",
    ),
    "R0903": (
        "Too few public methods (%s/%s)",
        "too-few-public-methods",
        "Used when class has too few public methods, so be sure it's "
        "really worth it.",
    ),
    "R0904": (
        "Too many public methods (%s/%s)",
        "too-many-public-methods",
        "Used when class has too many public methods, try to reduce "
        "this to get a simpler (and so easier to use) class.",
    ),
    "R0911": (
        "Too many return statements (%s/%s)",
        "too-many-return-statements",
        "Used when a function or method has too many return statement, "
        "making it hard to follow.",
    ),
    "R0912": (
        "Too many branches (%s/%s)",
        "too-many-branches",
        "Used when a function or method has too many branches, "
        "making it hard to follow.",
    ),
    "R0913": (
        "Too many arguments (%s/%s)",
        "too-many-arguments",
        "Used when a function or method takes too many arguments.",
    ),
    "R0914": (
        "Too many local variables (%s/%s)",
        "too-many-locals",
        "Used when a function or method has too many local variables.",
    ),
    "R0915": (
        "Too many statements (%s/%s)",
        "too-many-statements",
        "Used when a function or method has too many statements. You "
        "should then split it in smaller functions / methods.",
    ),
    "R0916": (
        "Too many boolean expressions in if statement (%s/%s)",
        "too-many-boolean-expressions",
        "Used when an if statement contains too many boolean expressions.",
    ),
}
SPECIAL_OBJ = re.compile("^_{2}[a-z]+_{2}$")
DATACLASSES_DECORATORS = frozenset({"dataclass", "attrs"})
DATACLASS_IMPORT = "dataclasses"
TYPING_NAMEDTUPLE = "typing.NamedTuple"


def _is_exempt_from_public_methods(node: astroid.ClassDef) -> bool:
    """Check if a class is exempt from too-few-public-methods"""

    # If it's a typing.Namedtuple or an Enum
    for ancestor in node.ancestors():
        if ancestor.name == "Enum" and ancestor.root().name == "enum":
            return True
        if ancestor.qname() == TYPING_NAMEDTUPLE:
            return True

    # Or if it's a dataclass
    if not node.decorators:
        return False

    root_locals = set(node.root().locals)
    for decorator in node.decorators.nodes:
        if isinstance(decorator, astroid.Call):
            decorator = decorator.func
        if not isinstance(decorator, (astroid.Name, astroid.Attribute)):
            continue
        if isinstance(decorator, astroid.Name):
            name = decorator.name
        else:
            name = decorator.attrname
        if name in DATACLASSES_DECORATORS and (
            root_locals.intersection(DATACLASSES_DECORATORS)
            or DATACLASS_IMPORT in root_locals
        ):
            return True
    return False


def _count_boolean_expressions(bool_op):
    """Counts the number of boolean expressions in BoolOp `bool_op` (recursive)

    example: a and (b or c or (d and e)) ==> 5 boolean expressions
    """
    nb_bool_expr = 0
    for bool_expr in bool_op.get_children():
        if isinstance(bool_expr, BoolOp):
            nb_bool_expr += _count_boolean_expressions(bool_expr)
        else:
            nb_bool_expr += 1
    return nb_bool_expr


def _count_methods_in_class(node):
    all_methods = sum(1 for method in node.methods() if not method.name.startswith("_"))
    # Special methods count towards the number of public methods,
    # but don't count towards there being too many methods.
    for method in node.mymethods():
        if SPECIAL_OBJ.search(method.name) and method.name != "__init__":
            all_methods += 1
    return all_methods


class MisdesignChecker(BaseChecker):
    """checks for sign of poor/misdesign:
    * number of methods, attributes, local variables...
    * size, complexity of functions, methods
    """

    __implements__ = (IAstroidChecker,)

    # configuration section name
    name = "design"
    # messages
    msgs = MSGS
    priority = -2
    # configuration options
    options = (
        (
            "max-args",
            {
                "default": 5,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of arguments for function / method.",
            },
        ),
        (
            "max-locals",
            {
                "default": 15,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of locals for function / method body.",
            },
        ),
        (
            "max-returns",
            {
                "default": 6,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of return / yield for function / "
                "method body.",
            },
        ),
        (
            "max-branches",
            {
                "default": 12,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of branch for function / method body.",
            },
        ),
        (
            "max-statements",
            {
                "default": 50,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of statements in function / method " "body.",
            },
        ),
        (
            "max-parents",
            {
                "default": 7,
                "type": "int",
                "metavar": "<num>",
                "help": "Maximum number of parents for a class (see R0901).",
            },
        ),
        (
            "max-attributes",
            {
                "default": 7,
                "type": "int",
                "metavar": "<num>",
                "help": "Maximum number of attributes for a class \
(see R0902).",
            },
        ),
        (
            "min-public-methods",
            {
                "default": 2,
                "type": "int",
                "metavar": "<num>",
                "help": "Minimum number of public methods for a class \
(see R0903).",
            },
        ),
        (
            "max-public-methods",
            {
                "default": 20,
                "type": "int",
                "metavar": "<num>",
                "help": "Maximum number of public methods for a class \
(see R0904).",
            },
        ),
        (
            "max-bool-expr",
            {
                "default": 5,
                "type": "int",
                "metavar": "<num>",
                "help": "Maximum number of boolean expressions in an if "
                "statement (see R0916).",
            },
        ),
    )

    def __init__(self, linter=None):
        BaseChecker.__init__(self, linter)
        self.stats = None
        self._returns = None
        self._branches = None
        self._stmts = None

    def open(self):
        """initialize visit variables"""
        self.stats = self.linter.add_stats()
        self._returns = []
        self._branches = defaultdict(int)
        self._stmts = []

    def _inc_all_stmts(self, amount):
        for i in range(len(self._stmts)):
            self._stmts[i] += amount

    @decorators.cachedproperty
    def _ignored_argument_names(self):
        return utils.get_global_option(self, "ignored-argument-names", default=None)

    @check_messages(
        "too-many-ancestors",
        "too-many-instance-attributes",
        "too-few-public-methods",
        "too-many-public-methods",
    )
    def visit_classdef(self, node):
        """check size of inheritance hierarchy and number of instance attributes
        """
        nb_parents = len(list(node.ancestors()))
        if nb_parents > self.config.max_parents:
            self.add_message(
                "too-many-ancestors",
                node=node,
                args=(nb_parents, self.config.max_parents),
            )

        if len(node.instance_attrs) > self.config.max_attributes:
            self.add_message(
                "too-many-instance-attributes",
                node=node,
                args=(len(node.instance_attrs), self.config.max_attributes),
            )

    @check_messages("too-few-public-methods", "too-many-public-methods")
    def leave_classdef(self, node):
        """check number of public methods"""
        my_methods = sum(
            1 for method in node.mymethods() if not method.name.startswith("_")
        )

        # Does the class contain less than n public methods ?
        # This checks only the methods defined in the current class,
        # since the user might not have control over the classes
        # from the ancestors. It avoids some false positives
        # for classes such as unittest.TestCase, which provides
        # a lot of assert methods. It doesn't make sense to warn
        # when the user subclasses TestCase to add his own tests.
        if my_methods > self.config.max_public_methods:
            self.add_message(
                "too-many-public-methods",
                node=node,
                args=(my_methods, self.config.max_public_methods),
            )

        # Stop here for exception, metaclass, interface classes and other
        # classes for which we don't need to count the methods.
        if node.type != "class" or _is_exempt_from_public_methods(node):
            return

        # Does the class contain more than n public methods ?
        # This checks all the methods defined by ancestors and
        # by the current class.
        all_methods = _count_methods_in_class(node)
        if all_methods < self.config.min_public_methods:
            self.add_message(
                "too-few-public-methods",
                node=node,
                args=(all_methods, self.config.min_public_methods),
            )

    @check_messages(
        "too-many-return-statements",
        "too-many-branches",
        "too-many-arguments",
        "too-many-locals",
        "too-many-statements",
        "keyword-arg-before-vararg",
    )
    def visit_functiondef(self, node):
        """check function name, docstring, arguments, redefinition,
        variable names, max locals
        """
        # init branch and returns counters
        self._returns.append(0)
        # check number of arguments
        args = node.args.args
        ignored_argument_names = self._ignored_argument_names
        if args is not None:
            ignored_args_num = 0
            if ignored_argument_names:
                ignored_args_num = sum(
                    1 for arg in args if ignored_argument_names.match(arg.name)
                )

            argnum = len(args) - ignored_args_num
            if argnum > self.config.max_args:
                self.add_message(
                    "too-many-arguments",
                    node=node,
                    args=(len(args), self.config.max_args),
                )
        else:
            ignored_args_num = 0
        # check number of local variables
        locnum = len(node.locals) - ignored_args_num
        if locnum > self.config.max_locals:
            self.add_message(
                "too-many-locals", node=node, args=(locnum, self.config.max_locals)
            )
        # init new statements counter
        self._stmts.append(1)

    visit_asyncfunctiondef = visit_functiondef

    @check_messages(
        "too-many-return-statements",
        "too-many-branches",
        "too-many-arguments",
        "too-many-locals",
        "too-many-statements",
    )
    def leave_functiondef(self, node):
        """most of the work is done here on close:
        checks for max returns, branch, return in __init__
        """
        returns = self._returns.pop()
        if returns > self.config.max_returns:
            self.add_message(
                "too-many-return-statements",
                node=node,
                args=(returns, self.config.max_returns),
            )
        branches = self._branches[node]
        if branches > self.config.max_branches:
            self.add_message(
                "too-many-branches",
                node=node,
                args=(branches, self.config.max_branches),
            )
        # check number of statements
        stmts = self._stmts.pop()
        if stmts > self.config.max_statements:
            self.add_message(
                "too-many-statements",
                node=node,
                args=(stmts, self.config.max_statements),
            )

    leave_asyncfunctiondef = leave_functiondef

    def visit_return(self, _):
        """count number of returns"""
        if not self._returns:
            return  # return outside function, reported by the base checker
        self._returns[-1] += 1

    def visit_default(self, node):
        """default visit method -> increments the statements counter if
        necessary
        """
        if node.is_statement:
            self._inc_all_stmts(1)

    def visit_tryexcept(self, node):
        """increments the branches counter"""
        branches = len(node.handlers)
        if node.orelse:
            branches += 1
        self._inc_branch(node, branches)
        self._inc_all_stmts(branches)

    def visit_tryfinally(self, node):
        """increments the branches counter"""
        self._inc_branch(node, 2)
        self._inc_all_stmts(2)

    @check_messages("too-many-boolean-expressions")
    def visit_if(self, node):
        """increments the branches counter and checks boolean expressions"""
        self._check_boolean_expressions(node)
        branches = 1
        # don't double count If nodes coming from some 'elif'
        if node.orelse and (len(node.orelse) > 1 or not isinstance(node.orelse[0], If)):
            branches += 1
        self._inc_branch(node, branches)
        self._inc_all_stmts(branches)

    def _check_boolean_expressions(self, node):
        """Go through "if" node `node` and counts its boolean expressions

        if the "if" node test is a BoolOp node
        """
        condition = node.test
        if not isinstance(condition, BoolOp):
            return
        nb_bool_expr = _count_boolean_expressions(condition)
        if nb_bool_expr > self.config.max_bool_expr:
            self.add_message(
                "too-many-boolean-expressions",
                node=condition,
                args=(nb_bool_expr, self.config.max_bool_expr),
            )

    def visit_while(self, node):
        """increments the branches counter"""
        branches = 1
        if node.orelse:
            branches += 1
        self._inc_branch(node, branches)

    visit_for = visit_while

    def _inc_branch(self, node, branchesnum=1):
        """increments the branches counter"""
        self._branches[node.scope()] += branchesnum


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