gitignore_parser.py

import collections
import os
import re

from os.path import abspath, dirname
from pathlib import Path
import sys
from typing import Reversible, Union

def handle_negation(file_path, rules: Reversible["IgnoreRule"]):
    for rule in reversed(rules):
        if rule.match(file_path):
            return not rule.negation
    return False

def parse_gitignore(full_path, base_dir=None):
    if base_dir is None:
        base_dir = dirname(full_path)
    rules = []
    with open(full_path) as ignore_file:
        counter = 0
        for line in ignore_file:
            counter += 1
            line = line.rstrip('\n')
            rule = rule_from_pattern(line, base_path=Path(base_dir).resolve(),
                                     source=(full_path, counter))
            if rule:
                rules.append(rule)
    if not any(r.negation for r in rules):
        return lambda file_path: any(r.match(file_path) for r in rules)
    else:
        # We have negation rules. We can't use a simple "any" to evaluate them.
        # Later rules override earlier rules.
        return lambda file_path: handle_negation(file_path, rules)

def rule_from_pattern(pattern, base_path=None, source=None):
    """
    Take a .gitignore match pattern, such as "*.py[cod]" or "**/*.bak",
    and return an IgnoreRule suitable for matching against files and
    directories. Patterns which do not match files, such as comments
    and blank lines, will return None.
    Because git allows for nested .gitignore files, a base_path value
    is required for correct behavior. The base path should be absolute.
    """
    if base_path and base_path != Path(base_path).resolve():
        raise ValueError('base_path must be absolute')
    # Store the exact pattern for our repr and string functions
    orig_pattern = pattern
    # Early returns follow
    # Discard comments and separators
    if pattern.strip() == '' or pattern[0] == '#':
        return
    # Strip leading bang before examining double asterisks
    if pattern[0] == '!':
        negation = True
        pattern = pattern[1:]
    else:
        negation = False
    # Multi-asterisks not surrounded by slashes (or at the start/end) should
    # be treated like single-asterisks.
    pattern = re.sub(r'([^/])\*{2,}', r'\1*', pattern)
    pattern = re.sub(r'\*{2,}([^/])', r'*\1', pattern)

    # Special-casing '/', which doesn't match any files or directories
    if pattern.rstrip() == '/':
        return

    directory_only = pattern[-1] == '/'
    # A slash is a sign that we're tied to the base_path of our rule
    # set.
    anchored = '/' in pattern[:-1]
    if pattern[0] == '/':
        pattern = pattern[1:]
    if pattern[0] == '*' and len(pattern) >= 2 and pattern[1] == '*':
        pattern = pattern[2:]
        anchored = False
    if pattern[0] == '/':
        pattern = pattern[1:]
    if pattern[-1] == '/':
        pattern = pattern[:-1]
    # patterns with leading hashes or exclamation marks are escaped with a
    # backslash in front, unescape it
    if pattern[0] == '\\' and pattern[1] in ('#', '!'):
        pattern = pattern[1:]
    # trailing spaces are ignored unless they are escaped with a backslash
    i = len(pattern)-1
    striptrailingspaces = True
    while i > 1 and pattern[i] == ' ':
        if pattern[i-1] == '\\':
            pattern = pattern[:i-1] + pattern[i:]
            i = i - 1
            striptrailingspaces = False
        else:
            if striptrailingspaces:
                pattern = pattern[:i]
        i = i - 1
    regex = fnmatch_pathname_to_regex(
        pattern, directory_only, negation, anchored=bool(anchored)
    )
    return IgnoreRule(
        pattern=orig_pattern,
        regex=regex,
        negation=negation,
        directory_only=directory_only,
        anchored=anchored,
        base_path=_normalize_path(base_path) if base_path else None,
        source=source
    )


IGNORE_RULE_FIELDS = [
    'pattern', 'regex',  # Basic values
    'negation', 'directory_only', 'anchored',  # Behavior flags
    'base_path',  # Meaningful for gitignore-style behavior
    'source'  # (file, line) tuple for reporting
]


class IgnoreRule(collections.namedtuple('IgnoreRule_', IGNORE_RULE_FIELDS)):
    def __str__(self):
        return self.pattern

    def __repr__(self):
        return ''.join(['IgnoreRule(\'', self.pattern, '\')'])

    def match(self, abs_path: Union[str, Path]):
        matched = False
        if self.base_path:
            rel_path = _normalize_path(abs_path).relative_to(self.base_path).as_posix()
        else:
            rel_path = _normalize_path(abs_path).as_posix()
        # Path() strips the trailing following symbols on windows, so we need to
        # preserve it: ' ', '.'
        if sys.platform.startswith('win'):
            rel_path += ' ' * _count_trailing_symbol(' ', abs_path)
            rel_path += '.' * _count_trailing_symbol('.', abs_path)
        # Path() strips the trailing slash, so we need to preserve it
        # in case of directory-only negation
        if self.negation and type(abs_path) == str and abs_path[-1] == '/':
            rel_path += '/'
        if rel_path.startswith('./'):
            rel_path = rel_path[2:]
        if re.search(self.regex, rel_path):
            matched = True
        return matched


# Frustratingly, python's fnmatch doesn't provide the FNM_PATHNAME
# option that .gitignore's behavior depends on.
def fnmatch_pathname_to_regex(
    pattern, directory_only: bool, negation: bool, anchored: bool = False
):
    """
    Implements fnmatch style-behavior, as though with FNM_PATHNAME flagged;
    the path separator will not match shell-style '*' and '.' wildcards.
    """
    i, n = 0, len(pattern)

    seps = [re.escape(os.sep)]
    if os.altsep is not None:
        seps.append(re.escape(os.altsep))
    seps_group = '[' + '|'.join(seps) + ']'
    nonsep = r'[^{}]'.format('|'.join(seps))

    res = []
    while i < n:
        c = pattern[i]
        i += 1
        if c == '*':
            try:
                if pattern[i] == '*':
                    i += 1
                    if i < n and pattern[i] == '/':
                        i += 1
                        res.append(''.join(['(.*', seps_group, ')?']))
                    else:
                        res.append('.*')
                else:
                    res.append(''.join([nonsep, '*']))
            except IndexError:
                res.append(''.join([nonsep, '*']))
        elif c == '?':
            res.append(nonsep)
        elif c == '/':
            res.append(seps_group)
        elif c == '[':
            j = i
            if j < n and pattern[j] == '!':
                j += 1
            if j < n and pattern[j] == ']':
                j += 1
            while j < n and pattern[j] != ']':
                j += 1
            if j >= n:
                res.append('\\[')
            else:
                stuff = pattern[i:j].replace('\\', '\\\\').replace('/', '')
                i = j + 1
                if stuff[0] == '!':
                    stuff = ''.join(['^', stuff[1:]])
                elif stuff[0] == '^':
                    stuff = ''.join('\\' + stuff)
                res.append('[{}]'.format(stuff))
        else:
            res.append(re.escape(c))

    if anchored:
        res.insert(0, '^')
    else:
        res.insert(0, f"(^|{seps_group})")
    
    if directory_only and not pattern.endswith('/'):
        res.append(f"($|{seps_group}.*)")
    elif not directory_only:
        res.append('$')
    elif directory_only and negation:
        res.append('/$')
    else:
        res.append('($|\\/)')
    
    return ''.join(res)


def _normalize_path(path: Union[str, Path]) -> Path:
    """Normalize a path without resolving symlinks.

    This is equivalent to `Path.resolve()` except that it does not resolve symlinks.
    Note that this simplifies paths by removing double slashes, `..`, `.` etc. like
    `Path.resolve()` does.
    """
    return Path(abspath(path))


def _count_trailing_symbol(symbol: str, text: str) -> int:
    """Count the number of trailing characters in a string."""
    count = 0
    for char in reversed(str(text)):
        if char == symbol:
            count += 1
        else:
            break
    return count