path: root/pylint/checkers/design_analysis.py

# 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) 2019-2021 Pierre Sassoulas <pierre.sassoulas@gmail.com>
# Copyright (c) 2019 Michael Scott Cuthbert <cuthbert@mit.edu>
# Copyright (c) 2020 hippo91 <guillaume.peillex@gmail.com>
# 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 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"
TYPING_TYPEDDICT = "typing.TypedDict"


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, typing.TypedDict or an Enum
    for ancestor in node.ancestors():
        if ancestor.name == "Enum" and ancestor.root().name == "enum":
            return True
        if ancestor.qname() in (TYPING_NAMEDTUPLE, TYPING_TYPEDDICT):
            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, astroid.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

    @astroid.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], astroid.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, astroid.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))