format.py

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

"""Python code format's checker.

By default try to follow Guido's style guide :

https://www.python.org/doc/essays/styleguide/

Some parts of the process_token method is based from The Tab Nanny std module.
"""

import tokenize
from functools import reduce
from typing import List

from astroid import nodes

from pylint.checkers import BaseTokenChecker
from pylint.checkers.utils import (
    check_messages,
    is_overload_stub,
    is_protocol_class,
    node_frame_class,
)
from pylint.constants import WarningScope
from pylint.interfaces import IAstroidChecker, IRawChecker, ITokenChecker
from pylint.utils.pragma_parser import OPTION_PO, PragmaParserError, parse_pragma

_ASYNC_TOKEN = "async"
_KEYWORD_TOKENS = [
    "assert",
    "del",
    "elif",
    "except",
    "for",
    "if",
    "in",
    "not",
    "raise",
    "return",
    "while",
    "yield",
    "with",
]

_SPACED_OPERATORS = [
    "==",
    "<",
    ">",
    "!=",
    "<>",
    "<=",
    ">=",
    "+=",
    "-=",
    "*=",
    "**=",
    "/=",
    "//=",
    "&=",
    "|=",
    "^=",
    "%=",
    ">>=",
    "<<=",
]
_OPENING_BRACKETS = ["(", "[", "{"]
_CLOSING_BRACKETS = [")", "]", "}"]
_TAB_LENGTH = 8

_EOL = frozenset([tokenize.NEWLINE, tokenize.NL, tokenize.COMMENT])
_JUNK_TOKENS = (tokenize.COMMENT, tokenize.NL)

# Whitespace checking policy constants
_MUST = 0
_MUST_NOT = 1
_IGNORE = 2

MSGS = {
    "C0301": (
        "Line too long (%s/%s)",
        "line-too-long",
        "Used when a line is longer than a given number of characters.",
    ),
    "C0302": (
        "Too many lines in module (%s/%s)",  # was W0302
        "too-many-lines",
        "Used when a module has too many lines, reducing its readability.",
    ),
    "C0303": (
        "Trailing whitespace",
        "trailing-whitespace",
        "Used when there is whitespace between the end of a line and the newline.",
    ),
    "C0304": (
        "Final newline missing",
        "missing-final-newline",
        "Used when the last line in a file is missing a newline.",
    ),
    "C0305": (
        "Trailing newlines",
        "trailing-newlines",
        "Used when there are trailing blank lines in a file.",
    ),
    "W0311": (
        "Bad indentation. Found %s %s, expected %s",
        "bad-indentation",
        "Used when an unexpected number of indentation's tabulations or "
        "spaces has been found.",
    ),
    "W0301": (
        "Unnecessary semicolon",  # was W0106
        "unnecessary-semicolon",
        'Used when a statement is ended by a semi-colon (";"), which '
        "isn't necessary (that's python, not C ;).",
    ),
    "C0321": (
        "More than one statement on a single line",
        "multiple-statements",
        "Used when more than on statement are found on the same line.",
        {"scope": WarningScope.NODE},
    ),
    "C0325": (
        "Unnecessary parens after %r keyword",
        "superfluous-parens",
        "Used when a single item in parentheses follows an if, for, or "
        "other keyword.",
    ),
    "C0327": (
        "Mixed line endings LF and CRLF",
        "mixed-line-endings",
        "Used when there are mixed (LF and CRLF) newline signs in a file.",
    ),
    "C0328": (
        "Unexpected line ending format. There is '%s' while it should be '%s'.",
        "unexpected-line-ending-format",
        "Used when there is different newline than expected.",
    ),
}


def _last_token_on_line_is(tokens, line_end, token):
    return (
        line_end > 0
        and tokens.token(line_end - 1) == token
        or line_end > 1
        and tokens.token(line_end - 2) == token
        and tokens.type(line_end - 1) == tokenize.COMMENT
    )


# The contexts for hanging indents.
# A hanging indented dictionary value after :
HANGING_DICT_VALUE = "dict-value"
# Hanging indentation in an expression.
HANGING = "hanging"
# Hanging indentation in a block header.
HANGING_BLOCK = "hanging-block"
# Continued indentation inside an expression.
CONTINUED = "continued"
# Continued indentation in a block header.
CONTINUED_BLOCK = "continued-block"

SINGLE_LINE = "single"
WITH_BODY = "multi"


class TokenWrapper:
    """A wrapper for readable access to token information."""

    def __init__(self, tokens):
        self._tokens = tokens

    def token(self, idx):
        return self._tokens[idx][1]

    def type(self, idx):
        return self._tokens[idx][0]

    def start_line(self, idx):
        return self._tokens[idx][2][0]

    def start_col(self, idx):
        return self._tokens[idx][2][1]

    def line(self, idx):
        return self._tokens[idx][4]


class FormatChecker(BaseTokenChecker):
    """checks for :
    * unauthorized constructions
    * strict indentation
    * line length
    """

    __implements__ = (ITokenChecker, IAstroidChecker, IRawChecker)

    # configuration section name
    name = "format"
    # messages
    msgs = MSGS
    # configuration options
    # for available dict keys/values see the optik parser 'add_option' method
    options = (
        (
            "max-line-length",
            {
                "default": 100,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of characters on a single line.",
            },
        ),
        (
            "ignore-long-lines",
            {
                "type": "regexp",
                "metavar": "<regexp>",
                "default": r"^\s*(# )?<?https?://\S+>?$",
                "help": (
                    "Regexp for a line that is allowed to be longer than the limit."
                ),
            },
        ),
        (
            "single-line-if-stmt",
            {
                "default": False,
                "type": "yn",
                "metavar": "<y or n>",
                "help": (
                    "Allow the body of an if to be on the same "
                    "line as the test if there is no else."
                ),
            },
        ),
        (
            "single-line-class-stmt",
            {
                "default": False,
                "type": "yn",
                "metavar": "<y or n>",
                "help": (
                    "Allow the body of a class to be on the same "
                    "line as the declaration if body contains "
                    "single statement."
                ),
            },
        ),
        (
            "max-module-lines",
            {
                "default": 1000,
                "type": "int",
                "metavar": "<int>",
                "help": "Maximum number of lines in a module.",
            },
        ),
        (
            "indent-string",
            {
                "default": "    ",
                "type": "non_empty_string",
                "metavar": "<string>",
                "help": "String used as indentation unit. This is usually "
                '"    " (4 spaces) or "\\t" (1 tab).',
            },
        ),
        (
            "indent-after-paren",
            {
                "type": "int",
                "metavar": "<int>",
                "default": 4,
                "help": "Number of spaces of indent required inside a hanging "
                "or continued line.",
            },
        ),
        (
            "expected-line-ending-format",
            {
                "type": "choice",
                "metavar": "<empty or LF or CRLF>",
                "default": "",
                "choices": ["", "LF", "CRLF"],
                "help": (
                    "Expected format of line ending, "
                    "e.g. empty (any line ending), LF or CRLF."
                ),
            },
        ),
    )

    def __init__(self, linter=None):
        super().__init__(linter)
        self._lines = None
        self._visited_lines = None
        self._bracket_stack = [None]

    def new_line(self, tokens, line_end, line_start):
        """a new line has been encountered, process it if necessary"""
        if _last_token_on_line_is(tokens, line_end, ";"):
            self.add_message("unnecessary-semicolon", line=tokens.start_line(line_end))

        line_num = tokens.start_line(line_start)
        line = tokens.line(line_start)
        if tokens.type(line_start) not in _JUNK_TOKENS:
            self._lines[line_num] = line.split("\n")[0]
        self.check_lines(line, line_num)

    def process_module(self, _node: nodes.Module) -> None:
        pass

    def _check_keyword_parentheses(
        self, tokens: List[tokenize.TokenInfo], start: int
    ) -> None:
        """Check that there are not unnecessary parentheses after a keyword.

        Parens are unnecessary if there is exactly one balanced outer pair on a
        line, and it is followed by a colon, and contains no commas (i.e. is not a
        tuple).

        Args:
        tokens: list of Tokens; the entire list of Tokens.
        start: int; the position of the keyword in the token list.
        """
        # If the next token is not a paren, we're fine.
        if self._bracket_stack[-1] == ":" and tokens[start].string == "for":
            self._bracket_stack.pop()
        if tokens[start + 1].string != "(":
            return
        found_and_or = False
        contains_walrus_operator = False
        walrus_operator_depth = 0
        contains_double_parens = 0
        depth = 0
        keyword_token = str(tokens[start].string)
        line_num = tokens[start].start[0]
        for i in range(start, len(tokens) - 1):
            token = tokens[i]

            # If we hit a newline, then assume any parens were for continuation.
            if token.type == tokenize.NL:
                return
            # Since the walrus operator doesn't exist below python3.8, the tokenizer
            # generates independent tokens
            if (
                token.string == ":="  # <-- python3.8+ path
                or token.string + tokens[i + 1].string == ":="
            ):
                contains_walrus_operator = True
                walrus_operator_depth = depth
            if token.string == "(":
                depth += 1
                if tokens[i + 1].string == "(":
                    contains_double_parens = 1
            elif token.string == ")":
                depth -= 1
                if depth:
                    if contains_double_parens and tokens[i + 1].string == ")":
                        # For walrus operators in `if (not)` conditions and comprehensions
                        if keyword_token in {"in", "if", "not"}:
                            continue
                        return
                    contains_double_parens -= 1
                    continue
                # ')' can't happen after if (foo), since it would be a syntax error.
                if tokens[i + 1].string in {":", ")", "]", "}", "in"} or tokens[
                    i + 1
                ].type in {tokenize.NEWLINE, tokenize.ENDMARKER, tokenize.COMMENT}:
                    if contains_walrus_operator and walrus_operator_depth - 1 == depth:
                        return
                    # The empty tuple () is always accepted.
                    if i == start + 2:
                        return
                    if keyword_token == "not":
                        if not found_and_or:
                            self.add_message(
                                "superfluous-parens", line=line_num, args=keyword_token
                            )
                    elif keyword_token in {"return", "yield"}:
                        self.add_message(
                            "superfluous-parens", line=line_num, args=keyword_token
                        )
                    elif not found_and_or and keyword_token != "in":
                        self.add_message(
                            "superfluous-parens", line=line_num, args=keyword_token
                        )
                return
            elif depth == 1:
                # This is a tuple, which is always acceptable.
                if token[1] == ",":
                    return
                # 'and' and 'or' are the only boolean operators with lower precedence
                # than 'not', so parens are only required when they are found.
                if token[1] in {"and", "or"}:
                    found_and_or = True
                # A yield inside an expression must always be in parentheses,
                # quit early without error.
                elif token[1] == "yield":
                    return
                # A generator expression always has a 'for' token in it, and
                # the 'for' token is only legal inside parens when it is in a
                # generator expression.  The parens are necessary here, so bail
                # without an error.
                elif token[1] == "for":
                    return
                # A generator expression can have an 'else' token in it.
                # We check the rest of the tokens to see if any problems incure after
                # the 'else'.
                elif token[1] == "else":
                    if "(" in (i.string for i in tokens[i:]):
                        self._check_keyword_parentheses(tokens[i:], 0)
                    return

    def _prepare_token_dispatcher(self):
        dispatch = {}
        for tokens, handler in ((_KEYWORD_TOKENS, self._check_keyword_parentheses),):
            for token in tokens:
                dispatch[token] = handler
        return dispatch

    def process_tokens(self, tokens):
        """process tokens and search for :

        _ too long lines (i.e. longer than <max_chars>)
        _ optionally bad construct (if given, bad_construct must be a compiled
          regular expression).
        """
        self._bracket_stack = [None]
        indents = [0]
        check_equal = False
        line_num = 0
        self._lines = {}
        self._visited_lines = {}
        token_handlers = self._prepare_token_dispatcher()
        self._last_line_ending = None
        last_blank_line_num = 0
        for idx, (tok_type, token, start, _, line) in enumerate(tokens):
            if start[0] != line_num:
                line_num = start[0]
                # A tokenizer oddity: if an indented line contains a multi-line
                # docstring, the line member of the INDENT token does not contain
                # the full line; therefore we check the next token on the line.
                if tok_type == tokenize.INDENT:
                    self.new_line(TokenWrapper(tokens), idx - 1, idx + 1)
                else:
                    self.new_line(TokenWrapper(tokens), idx - 1, idx)

            if tok_type == tokenize.NEWLINE:
                # a program statement, or ENDMARKER, will eventually follow,
                # after some (possibly empty) run of tokens of the form
                #     (NL | COMMENT)* (INDENT | DEDENT+)?
                # If an INDENT appears, setting check_equal is wrong, and will
                # be undone when we see the INDENT.
                check_equal = True
                self._check_line_ending(token, line_num)
            elif tok_type == tokenize.INDENT:
                check_equal = False
                self.check_indent_level(token, indents[-1] + 1, line_num)
                indents.append(indents[-1] + 1)
            elif tok_type == tokenize.DEDENT:
                # there's nothing we need to check here!  what's important is
                # that when the run of DEDENTs ends, the indentation of the
                # program statement (or ENDMARKER) that triggered the run is
                # equal to what's left at the top of the indents stack
                check_equal = True
                if len(indents) > 1:
                    del indents[-1]
            elif tok_type == tokenize.NL:
                if not line.strip("\r\n"):
                    last_blank_line_num = line_num
            elif tok_type not in (tokenize.COMMENT, tokenize.ENCODING):
                # This is the first concrete token following a NEWLINE, so it
                # must be the first token of the next program statement, or an
                # ENDMARKER; the "line" argument exposes the leading whitespace
                # for this statement; in the case of ENDMARKER, line is an empty
                # string, so will properly match the empty string with which the
                # "indents" stack was seeded
                if check_equal:
                    check_equal = False
                    self.check_indent_level(line, indents[-1], line_num)

            if tok_type == tokenize.NUMBER and token.endswith("l"):
                self.add_message("lowercase-l-suffix", line=line_num)

            try:
                handler = token_handlers[token]
            except KeyError:
                pass
            else:
                handler(tokens, idx)

        line_num -= 1  # to be ok with "wc -l"
        if line_num > self.config.max_module_lines:
            # Get the line where the too-many-lines (or its message id)
            # was disabled or default to 1.
            message_definition = self.linter.msgs_store.get_message_definitions(
                "too-many-lines"
            )[0]
            names = (message_definition.msgid, "too-many-lines")
            line = next(
                filter(None, (self.linter._pragma_lineno.get(name) for name in names)),
                1,
            )
            self.add_message(
                "too-many-lines",
                args=(line_num, self.config.max_module_lines),
                line=line,
            )

        # See if there are any trailing lines.  Do not complain about empty
        # files like __init__.py markers.
        if line_num == last_blank_line_num and line_num > 0:
            self.add_message("trailing-newlines", line=line_num)

    def _check_line_ending(self, line_ending, line_num):
        # check if line endings are mixed
        if self._last_line_ending is not None:
            # line_ending == "" indicates a synthetic newline added at
            # the end of a file that does not, in fact, end with a
            # newline.
            if line_ending and line_ending != self._last_line_ending:
                self.add_message("mixed-line-endings", line=line_num)

        self._last_line_ending = line_ending

        # check if line ending is as expected
        expected = self.config.expected_line_ending_format
        if expected:
            # reduce multiple \n\n\n\n to one \n
            line_ending = reduce(lambda x, y: x + y if x != y else x, line_ending, "")
            line_ending = "LF" if line_ending == "\n" else "CRLF"
            if line_ending != expected:
                self.add_message(
                    "unexpected-line-ending-format",
                    args=(line_ending, expected),
                    line=line_num,
                )

    @check_messages("multiple-statements")
    def visit_default(self, node: nodes.NodeNG) -> None:
        """check the node line number and check it if not yet done"""
        if not node.is_statement:
            return
        if not node.root().pure_python:
            return
        prev_sibl = node.previous_sibling()
        if prev_sibl is not None:
            prev_line = prev_sibl.fromlineno
        # The line on which a finally: occurs in a try/finally
        # is not directly represented in the AST. We infer it
        # by taking the last line of the body and adding 1, which
        # should be the line of finally:
        elif (
            isinstance(node.parent, nodes.TryFinally) and node in node.parent.finalbody
        ):
            prev_line = node.parent.body[0].tolineno + 1
        else:
            prev_line = node.parent.statement().fromlineno
        line = node.fromlineno
        assert line, node
        if prev_line == line and self._visited_lines.get(line) != 2:
            self._check_multi_statement_line(node, line)
            return
        if line in self._visited_lines:
            return
        try:
            tolineno = node.blockstart_tolineno
        except AttributeError:
            tolineno = node.tolineno
        assert tolineno, node
        lines = []
        for line in range(line, tolineno + 1):
            self._visited_lines[line] = 1
            try:
                lines.append(self._lines[line].rstrip())
            except KeyError:
                lines.append("")

    def _check_multi_statement_line(self, node, line):
        """Check for lines containing multiple statements."""
        # Do not warn about multiple nested context managers
        # in with statements.
        if isinstance(node, nodes.With):
            return
        # For try... except... finally..., the two nodes
        # appear to be on the same line due to how the AST is built.
        if isinstance(node, nodes.TryExcept) and isinstance(
            node.parent, nodes.TryFinally
        ):
            return
        if (
            isinstance(node.parent, nodes.If)
            and not node.parent.orelse
            and self.config.single_line_if_stmt
        ):
            return
        if (
            isinstance(node.parent, nodes.ClassDef)
            and len(node.parent.body) == 1
            and self.config.single_line_class_stmt
        ):
            return

        # Function overloads that use ``Ellipsis`` are exempted.
        if (
            isinstance(node, nodes.Expr)
            and isinstance(node.value, nodes.Const)
            and node.value.value is Ellipsis
        ):
            frame = node.frame()
            if is_overload_stub(frame) or is_protocol_class(node_frame_class(frame)):
                return

        self.add_message("multiple-statements", node=node)
        self._visited_lines[line] = 2

    def check_line_ending(self, line: str, i: int) -> None:
        """
        Check that the final newline is not missing and that there is no trailing whitespace.
        """
        if not line.endswith("\n"):
            self.add_message("missing-final-newline", line=i)
            return
        # exclude \f (formfeed) from the rstrip
        stripped_line = line.rstrip("\t\n\r\v ")
        if line[len(stripped_line) :] not in ("\n", "\r\n"):
            self.add_message(
                "trailing-whitespace", line=i, col_offset=len(stripped_line)
            )

    def check_line_length(self, line: str, i: int, checker_off: bool) -> None:
        """
        Check that the line length is less than the authorized value
        """
        max_chars = self.config.max_line_length
        ignore_long_line = self.config.ignore_long_lines
        line = line.rstrip()
        if len(line) > max_chars and not ignore_long_line.search(line):
            if checker_off:
                self.linter.add_ignored_message("line-too-long", i)
            else:
                self.add_message("line-too-long", line=i, args=(len(line), max_chars))

    @staticmethod
    def remove_pylint_option_from_lines(options_pattern_obj) -> str:
        """
        Remove the `# pylint ...` pattern from lines
        """
        lines = options_pattern_obj.string
        purged_lines = (
            lines[: options_pattern_obj.start(1)].rstrip()
            + lines[options_pattern_obj.end(1) :]
        )
        return purged_lines

    @staticmethod
    def is_line_length_check_activated(pylint_pattern_match_object) -> bool:
        """
        Return true if the line length check is activated
        """
        try:
            for pragma in parse_pragma(pylint_pattern_match_object.group(2)):
                if pragma.action == "disable" and "line-too-long" in pragma.messages:
                    return False
        except PragmaParserError:
            # Printing useful information dealing with this error is done in the lint package
            pass
        return True

    @staticmethod
    def specific_splitlines(lines: str) -> List[str]:
        """
        Split lines according to universal newlines except those in a specific sets
        """
        unsplit_ends = {
            "\v",
            "\x0b",
            "\f",
            "\x0c",
            "\x1c",
            "\x1d",
            "\x1e",
            "\x85",
            "\u2028",
            "\u2029",
        }
        res = []
        buffer = ""
        for atomic_line in lines.splitlines(True):
            if atomic_line[-1] not in unsplit_ends:
                res.append(buffer + atomic_line)
                buffer = ""
            else:
                buffer += atomic_line
        return res

    def check_lines(self, lines: str, lineno: int) -> None:
        """
        Check lines have :
            - a final newline
            - no trailing whitespace
            - less than a maximum number of characters
        """
        # we're first going to do a rough check whether any lines in this set
        # go over the line limit. If none of them do, then we don't need to
        # parse out the pylint options later on and can just assume that these
        # lines are clean

        # we'll also handle the line ending check here to avoid double-iteration
        # unless the line lengths are suspect

        max_chars = self.config.max_line_length

        split_lines = self.specific_splitlines(lines)

        for offset, line in enumerate(split_lines):
            self.check_line_ending(line, lineno + offset)

        # hold onto the initial lineno for later
        potential_line_length_warning = False
        for offset, line in enumerate(split_lines):
            # this check is purposefully simple and doesn't rstrip
            # since this is running on every line you're checking it's
            # advantageous to avoid doing a lot of work
            if len(line) > max_chars:
                potential_line_length_warning = True
                break

        # if there were no lines passing the max_chars config, we don't bother
        # running the full line check (as we've met an even more strict condition)
        if not potential_line_length_warning:
            return

        # Line length check may be deactivated through `pylint: disable` comment
        mobj = OPTION_PO.search(lines)
        checker_off = False
        if mobj:
            if not self.is_line_length_check_activated(mobj):
                checker_off = True
            # The 'pylint: disable whatever' should not be taken into account for line length count
            lines = self.remove_pylint_option_from_lines(mobj)

        # here we re-run specific_splitlines since we have filtered out pylint options above
        for offset, line in enumerate(self.specific_splitlines(lines)):
            self.check_line_length(line, lineno + offset, checker_off)

    def check_indent_level(self, string, expected, line_num):
        """return the indent level of the string"""
        indent = self.config.indent_string
        if indent == "\\t":  # \t is not interpreted in the configuration file
            indent = "\t"
        level = 0
        unit_size = len(indent)
        while string[:unit_size] == indent:
            string = string[unit_size:]
            level += 1
        suppl = ""
        while string and string[0] in " \t":
            suppl += string[0]
            string = string[1:]
        if level != expected or suppl:
            i_type = "spaces"
            if indent[0] == "\t":
                i_type = "tabs"
            self.add_message(
                "bad-indentation",
                line=line_num,
                args=(level * unit_size + len(suppl), i_type, expected * unit_size),
            )


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