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1import contextlib
2import re
3from dataclasses import dataclass
4from typing import Dict, Iterator, NoReturn, Optional, Tuple, Union
5
6from .specifiers import Specifier
7
8
9@dataclass
10class Token:
11 name: str
12 text: str
13 position: int
14
15
16class ParserSyntaxError(Exception):
17 """The provided source text could not be parsed correctly."""
18
19 def __init__(
20 self,
21 message: str,
22 *,
23 source: str,
24 span: Tuple[int, int],
25 ) -> None:
26 self.span = span
27 self.message = message
28 self.source = source
29
30 super().__init__()
31
32 def __str__(self) -> str:
33 marker = " " * self.span[0] + "~" * (self.span[1] - self.span[0]) + "^"
34 return "\n ".join([self.message, self.source, marker])
35
36
37DEFAULT_RULES: "Dict[str, Union[str, re.Pattern[str]]]" = {
38 "LEFT_PARENTHESIS": r"\(",
39 "RIGHT_PARENTHESIS": r"\)",
40 "LEFT_BRACKET": r"\[",
41 "RIGHT_BRACKET": r"\]",
42 "SEMICOLON": r";",
43 "COMMA": r",",
44 "QUOTED_STRING": re.compile(
45 r"""
46 (
47 ('[^']*')
48 |
49 ("[^"]*")
50 )
51 """,
52 re.VERBOSE,
53 ),
54 "OP": r"(===|==|~=|!=|<=|>=|<|>)",
55 "BOOLOP": r"\b(or|and)\b",
56 "IN": r"\bin\b",
57 "NOT": r"\bnot\b",
58 "VARIABLE": re.compile(
59 r"""
60 \b(
61 python_version
62 |python_full_version
63 |os[._]name
64 |sys[._]platform
65 |platform_(release|system)
66 |platform[._](version|machine|python_implementation)
67 |python_implementation
68 |implementation_(name|version)
69 |extra
70 )\b
71 """,
72 re.VERBOSE,
73 ),
74 "SPECIFIER": re.compile(
75 Specifier._operator_regex_str + Specifier._version_regex_str,
76 re.VERBOSE | re.IGNORECASE,
77 ),
78 "AT": r"\@",
79 "URL": r"[^ \t]+",
80 "IDENTIFIER": r"\b[a-zA-Z0-9][a-zA-Z0-9._-]*\b",
81 "VERSION_PREFIX_TRAIL": r"\.\*",
82 "VERSION_LOCAL_LABEL_TRAIL": r"\+[a-z0-9]+(?:[-_\.][a-z0-9]+)*",
83 "WS": r"[ \t]+",
84 "END": r"$",
85}
86
87
88class Tokenizer:
89 """Context-sensitive token parsing.
90
91 Provides methods to examine the input stream to check whether the next token
92 matches.
93 """
94
95 def __init__(
96 self,
97 source: str,
98 *,
99 rules: "Dict[str, Union[str, re.Pattern[str]]]",
100 ) -> None:
101 self.source = source
102 self.rules: Dict[str, re.Pattern[str]] = {
103 name: re.compile(pattern) for name, pattern in rules.items()
104 }
105 self.next_token: Optional[Token] = None
106 self.position = 0
107
108 def consume(self, name: str) -> None:
109 """Move beyond provided token name, if at current position."""
110 if self.check(name):
111 self.read()
112
113 def check(self, name: str, *, peek: bool = False) -> bool:
114 """Check whether the next token has the provided name.
115
116 By default, if the check succeeds, the token *must* be read before
117 another check. If `peek` is set to `True`, the token is not loaded and
118 would need to be checked again.
119 """
120 assert (
121 self.next_token is None
122 ), f"Cannot check for {name!r}, already have {self.next_token!r}"
123 assert name in self.rules, f"Unknown token name: {name!r}"
124
125 expression = self.rules[name]
126
127 match = expression.match(self.source, self.position)
128 if match is None:
129 return False
130 if not peek:
131 self.next_token = Token(name, match[0], self.position)
132 return True
133
134 def expect(self, name: str, *, expected: str) -> Token:
135 """Expect a certain token name next, failing with a syntax error otherwise.
136
137 The token is *not* read.
138 """
139 if not self.check(name):
140 raise self.raise_syntax_error(f"Expected {expected}")
141 return self.read()
142
143 def read(self) -> Token:
144 """Consume the next token and return it."""
145 token = self.next_token
146 assert token is not None
147
148 self.position += len(token.text)
149 self.next_token = None
150
151 return token
152
153 def raise_syntax_error(
154 self,
155 message: str,
156 *,
157 span_start: Optional[int] = None,
158 span_end: Optional[int] = None,
159 ) -> NoReturn:
160 """Raise ParserSyntaxError at the given position."""
161 span = (
162 self.position if span_start is None else span_start,
163 self.position if span_end is None else span_end,
164 )
165 raise ParserSyntaxError(
166 message,
167 source=self.source,
168 span=span,
169 )
170
171 @contextlib.contextmanager
172 def enclosing_tokens(
173 self, open_token: str, close_token: str, *, around: str
174 ) -> Iterator[None]:
175 if self.check(open_token):
176 open_position = self.position
177 self.read()
178 else:
179 open_position = None
180
181 yield
182
183 if open_position is None:
184 return
185
186 if not self.check(close_token):
187 self.raise_syntax_error(
188 f"Expected matching {close_token} for {open_token}, after {around}",
189 span_start=open_position,
190 )
191
192 self.read()