"""Parser for directive options.
This is a highly restricted parser for YAML,
which only allows a subset of YAML to be used for directive options:
- Only block mappings are allowed at the top level
- Mapping keys are parsed as strings (plain or quoted)
- Mapping values are parsed as strings (plain, quoted, literal `|`, folded `>`)
- `#` Comments are allowed and blank lines
Adapted from:
https://github.com/yaml/pyyaml/commit/957ae4d495cf8fcb5475c6c2f1bce801096b68a5
For a good description of multi-line YAML strings, see:
https://stackoverflow.com/a/21699210/5033292
"""
from __future__ import annotations
from collections.abc import Iterable
from dataclasses import dataclass, replace
from typing import ClassVar, Final, Literal, cast
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@dataclass
class Position:
"""Position of a character in a stream."""
index: int
line: int
column: int
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class StreamBuffer:
"""A buffer for a stream of characters."""
def __init__(self, stream: str):
self._buffer = stream + _CHARS_END
self._index = 0
self._line = 0
self._column = 0
@property
def index(self) -> int:
return self._index
@property
def line(self) -> int:
return self._line
@property
def column(self) -> int:
return self._column
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def peek(self, index: int = 0) -> str:
return self._buffer[self._index + index]
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def prefix(self, length: int = 1) -> str:
return self._buffer[self._index : self._index + length]
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def forward(self, length: int = 1) -> None:
while length:
ch = self._buffer[self._index]
self._index += 1
if ch in "\n\x85\u2028\u2029" or (
ch == "\r" and self._buffer[self._index] != "\n"
):
self._line += 1
self._column = 0
elif ch != "\ufeff":
self._column += 1
length -= 1
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def get_position(self) -> Position:
return Position(self._index, self._line, self._column)
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@dataclass
class Token:
"""A parsed token from a directive option stream."""
id: ClassVar[str] = "<unknown>"
start: Position
end: Position
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@dataclass
class KeyToken(Token):
id: ClassVar[str] = "<key>"
value: str
style: Literal[None, "'", '"'] = None
"""The original style of the string."""
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@dataclass
class ValueToken(Token):
id: ClassVar[str] = "<value>"
value: str
style: Literal[None, "'", '"', "|", ">"] = None
"""The original style of the string."""
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@dataclass
class ColonToken(Token):
id: ClassVar[str] = "<colon>"
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class TokenizeError(Exception):
def __init__(
self,
problem: str,
problem_mark: Position,
context: str | None = None,
context_mark: Position | None = None,
):
"""A YAML error with optional context.
:param problem: The problem encountered
:param problem_mark: The position of the problem
:param context: The context of the error, e.g. the parent being scanned
:param context_mark: The position of the context
"""
self.context = context
self.context_mark = context_mark
self.problem = problem
self.problem_mark = problem_mark
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def clone(self, line_offset: int, column_offset: int) -> TokenizeError:
"""Clone the error with the given line and column offsets."""
return TokenizeError(
self.problem,
replace(
self.problem_mark,
line=self.problem_mark.line + line_offset,
column=self.problem_mark.column + column_offset,
),
self.context,
None
if self.context_mark is None
else replace(
self.context_mark,
line=self.context_mark.line + line_offset,
column=self.context_mark.column + column_offset,
),
)
def __str__(self) -> str:
lines = []
if self.context is not None:
lines.append(self.context)
if self.context_mark is not None and (
self.context_mark.line != self.problem_mark.line
or self.context_mark.column != self.problem_mark.column
):
lines.append(
f"at line {self.context_mark.line}, column {self.context_mark.column}"
)
if self.problem is not None:
lines.append(self.problem)
if self.problem_mark is not None:
lines.append(
f"at line {self.problem_mark.line}, column {self.problem_mark.column}"
)
return "\n".join(lines)
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@dataclass
class State:
has_comments: bool = False
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def options_to_items(
text: str, line_offset: int = 0, column_offset: int = 0
) -> tuple[list[tuple[str, str]], State]:
"""Parse a directive option block into (key, value) tuples.
:param text: The directive option text.
:param line_offset: The line offset to apply to the error positions.
:param column_offset: The column offset to apply to the error positions.
:raises: `TokenizeError`
"""
output = []
state = State()
for key_token, value_token in _to_tokens(text, state, line_offset, column_offset):
output.append(
(key_token.value, value_token.value if value_token is not None else "")
)
return output, state
def _to_tokens(
text: str, state: State, line_offset: int = 0, column_offset: int = 0
) -> Iterable[tuple[KeyToken, ValueToken | None]]:
"""Parse a directive option, and yield key/value token pairs.
:param text: The directive option text.
:param line_offset: The line offset to apply to the error positions.
:param column_offset: The column offset to apply to the error positions.
:raises: `TokenizeError`
"""
key_token: KeyToken | None = None
try:
for token in _tokenize(text, state):
if isinstance(token, KeyToken):
if key_token is not None:
yield key_token, None
key_token = token
elif isinstance(token, ValueToken):
if key_token is None:
raise TokenizeError("expected key before value", token.start)
yield key_token, token
key_token = None
if key_token is not None:
yield key_token, None
except TokenizeError as exc:
if line_offset or column_offset:
raise exc.clone(line_offset, column_offset) from exc
raise
def _tokenize(text: str, state: State) -> Iterable[Token]:
"""Yield tokens from a directive option stream."""
stream = StreamBuffer(text)
while True:
_scan_to_next_token(stream, state)
if stream.peek() == _CHARS_END:
break
if not stream.column == 0:
raise TokenizeError(
"expected key to start at column 0", stream.get_position()
)
# find key
ch = stream.peek()
if ch in ("'", '"'):
yield _scan_flow_scalar(stream, cast(Literal['"', "'"], ch), is_key=True)
else:
yield _scan_plain_scalar(stream, state, is_key=True)
_scan_to_next_token(stream, state)
# check next char is colon + space
if stream.peek() != ":":
raise TokenizeError("expected ':' after key", stream.get_position())
start_mark = stream.get_position()
stream.forward()
end_mark = stream.get_position()
yield ColonToken(start_mark, end_mark)
_scan_to_next_token(stream, state)
# now find value
ch = stream.peek()
if stream.column == 0:
pass
elif ch in ("|", ">"):
yield _scan_block_scalar(stream, cast(Literal["|", ">"], ch), state)
elif ch in ("'", '"'):
yield _scan_flow_scalar(stream, cast(Literal['"', "'"], ch), is_key=False)
else:
yield _scan_plain_scalar(stream, state, is_key=False)
def _scan_to_next_token(stream: StreamBuffer, state: State) -> None:
"""Skip spaces, line breaks and comments.
The byte order mark is also stripped,
if it's the first character in the stream.
"""
if stream.index == 0 and stream.peek() == "\ufeff":
stream.forward()
found = False
while not found:
while stream.peek() == " ":
stream.forward()
if stream.peek() == "#":
state.has_comments = True
while stream.peek() not in _CHARS_END_NEWLINE:
stream.forward()
if not _scan_line_break(stream):
found = True
def _scan_plain_scalar(
stream: StreamBuffer, state: State, is_key: bool = False
) -> KeyToken | ValueToken:
chunks = []
start_mark = stream.get_position()
end_mark = start_mark
indent = 0 if is_key else 1
spaces: list[str] = []
while True:
length = 0
if stream.peek() == "#":
state.has_comments = True
break
while True:
ch = stream.peek(length)
if ch in _CHARS_END_SPACE_TAB_NEWLINE or (
is_key
and ch == ":"
and stream.peek(length + 1) in _CHARS_END_SPACE_TAB_NEWLINE
):
break
length += 1
if length == 0:
break
chunks.extend(spaces)
chunks.append(stream.prefix(length))
stream.forward(length)
end_mark = stream.get_position()
spaces = _scan_plain_spaces(stream, allow_newline=(not is_key))
if not spaces or stream.peek() == "#" or (stream.column < indent):
if stream.peek() == "#":
state.has_comments = True
break
return (
KeyToken(start_mark, end_mark, "".join(chunks))
if is_key
else ValueToken(start_mark, end_mark, "".join(chunks))
)
def _scan_plain_spaces(stream: StreamBuffer, allow_newline: bool = True) -> list[str]:
chunks = []
length = 0
while stream.peek(length) == " ":
length += 1
whitespaces = stream.prefix(length)
stream.forward(length)
ch = stream.peek()
if allow_newline and ch in _CHARS_NEWLINE:
line_break = _scan_line_break(stream)
breaks = []
while stream.peek() in _CHARS_SPACE_NEWLINE:
if stream.peek() == " ":
stream.forward()
else:
breaks.append(_scan_line_break(stream))
if line_break != "\n":
chunks.append(line_break)
elif not breaks:
chunks.append(" ")
chunks.extend(breaks)
elif whitespaces:
chunks.append(whitespaces)
return chunks
def _scan_line_break(stream: StreamBuffer) -> str:
# Transforms:
# '\r\n' : '\n'
# '\r' : '\n'
# '\n' : '\n'
# '\x85' : '\n'
# '\u2028' : '\u2028'
# '\u2029 : '\u2029'
# default : ''
ch = stream.peek()
if ch in "\r\n\x85":
if stream.prefix(2) == "\r\n":
stream.forward(2)
else:
stream.forward()
return "\n"
elif ch in "\u2028\u2029":
stream.forward()
return ch
return ""
def _scan_flow_scalar(
stream: StreamBuffer, style: Literal["'", '"'], is_key: bool = False
) -> KeyToken | ValueToken:
double = style == '"'
chunks = []
start_mark = stream.get_position()
quote = stream.peek()
stream.forward()
chunks.extend(_scan_flow_scalar_non_spaces(stream, double, start_mark))
while stream.peek() != quote:
chunks.extend(_scan_flow_scalar_spaces(stream, start_mark))
chunks.extend(_scan_flow_scalar_non_spaces(stream, double, start_mark))
stream.forward()
end_mark = stream.get_position()
return (
KeyToken(start_mark, end_mark, "".join(chunks), style)
if is_key
else ValueToken(start_mark, end_mark, "".join(chunks), style)
)
def _scan_flow_scalar_non_spaces(
stream: StreamBuffer, double: bool, start_mark: Position
) -> list[str]:
chunks = []
while True:
length = 0
while stream.peek(length) not in "'\"\\" + _CHARS_END_SPACE_TAB_NEWLINE:
length += 1
if length:
chunks.append(stream.prefix(length))
stream.forward(length)
ch = stream.peek()
if not double and ch == "'" and stream.peek(1) == "'":
chunks.append("'")
stream.forward(2)
elif (double and ch == "'") or (not double and ch in '"\\'):
chunks.append(ch)
stream.forward()
elif double and ch == "\\":
stream.forward()
ch = stream.peek()
if ch in _ESCAPE_REPLACEMENTS:
chunks.append(_ESCAPE_REPLACEMENTS[ch])
stream.forward()
elif ch in _ESCAPE_CODES:
length = _ESCAPE_CODES[ch]
stream.forward()
for k in range(length):
if stream.peek(k) not in "0123456789ABCDEFabcdef":
raise TokenizeError(
"expected escape sequence of %d hexadecimal numbers, but found %r"
% (length, stream.peek(k)),
stream.get_position(),
"while scanning a double-quoted scalar",
start_mark,
)
code = int(stream.prefix(length), 16)
chunks.append(chr(code))
stream.forward(length)
elif ch in _CHARS_NEWLINE:
_scan_line_break(stream)
chunks.extend(_scan_flow_scalar_breaks(stream))
else:
raise TokenizeError(
f"found unknown escape character {ch!r}",
stream.get_position(),
"while scanning a double-quoted scalar",
start_mark,
)
else:
return chunks
def _scan_flow_scalar_spaces(stream: StreamBuffer, start_mark: Position) -> list[str]:
chunks = []
length = 0
while stream.peek(length) in " \t":
length += 1
whitespaces = stream.prefix(length)
stream.forward(length)
ch = stream.peek()
if ch == _CHARS_END:
raise TokenizeError(
"found unexpected end of stream",
stream.get_position(),
"while scanning a quoted scalar",
start_mark,
)
elif ch in _CHARS_NEWLINE:
line_break = _scan_line_break(stream)
breaks = _scan_flow_scalar_breaks(stream)
if line_break != "\n":
chunks.append(line_break)
elif not breaks:
chunks.append(" ")
chunks.extend(breaks)
else:
chunks.append(whitespaces)
return chunks
def _scan_flow_scalar_breaks(stream: StreamBuffer) -> list[str]:
chunks = []
while True:
while stream.peek() in " \t":
stream.forward()
if stream.peek() in _CHARS_NEWLINE:
chunks.append(_scan_line_break(stream))
else:
return chunks
def _scan_block_scalar(
stream: StreamBuffer, style: Literal["|", ">"], state: State
) -> ValueToken:
indent = 0
folded = style == ">"
chunks = []
start_mark = stream.get_position()
# Scan the header.
stream.forward()
chomping, increment = _scan_block_scalar_indicators(stream, start_mark)
_scan_block_scalar_ignored_line(stream, start_mark, state)
# Determine the indentation level and go to the first non-empty line.
min_indent = indent + 1
if min_indent < 1:
min_indent = 1
if increment is None:
breaks, max_indent, end_mark = _scan_block_scalar_indentation(stream)
indent = max(min_indent, max_indent)
else:
indent = min_indent + increment - 1
breaks, end_mark = _scan_block_scalar_breaks(stream, indent)
line_break = ""
# Scan the inner part of the block scalar.
while stream.column == indent and stream.peek() != _CHARS_END:
chunks.extend(breaks)
leading_non_space = stream.peek() not in " \t"
length = 0
while stream.peek(length) not in _CHARS_END_NEWLINE:
length += 1
chunks.append(stream.prefix(length))
stream.forward(length)
line_break = _scan_line_break(stream)
breaks, end_mark = _scan_block_scalar_breaks(stream, indent)
if stream.column == indent and stream.peek() != _CHARS_END:
if (
folded
and line_break == "\n"
and leading_non_space
and stream.peek() not in " \t"
):
if not breaks:
chunks.append(" ")
else:
chunks.append(line_break)
else:
break
# Chomp the tail.
if chomping is not False:
chunks.append(line_break)
if chomping is True:
chunks.extend(breaks)
# We are done.
return ValueToken(start_mark, end_mark, "".join(chunks), style)
def _scan_block_scalar_indicators(
stream: StreamBuffer, start_mark: Position
) -> tuple[bool | None, int | None]:
chomping = None
increment = None
ch = stream.peek()
if ch in "+-":
chomping = ch == "+"
stream.forward()
ch = stream.peek()
if ch in "0123456789":
increment = int(ch)
if increment == 0:
raise TokenizeError(
"expected indentation indicator in the range 1-9, but found 0",
stream.get_position(),
"while scanning a block scalar",
start_mark,
)
stream.forward()
elif ch in "0123456789":
increment = int(ch)
if increment == 0:
raise TokenizeError(
"expected indentation indicator in the range 1-9, but found 0",
stream.get_position(),
"while scanning a block scalar",
start_mark,
)
stream.forward()
ch = stream.peek()
if ch in "+-":
chomping = ch == "+"
stream.forward()
ch = stream.peek()
if ch not in _CHARS_END_SPACE_NEWLINE:
raise TokenizeError(
f"expected chomping or indentation indicators, but found {ch!r}",
stream.get_position(),
"while scanning a block scalar",
start_mark,
)
return chomping, increment
def _scan_block_scalar_ignored_line(
stream: StreamBuffer, start_mark: Position, state: State
) -> None:
while stream.peek() == " ":
stream.forward()
if stream.peek() == "#":
state.has_comments = True
while stream.peek() not in _CHARS_END_NEWLINE:
stream.forward()
ch = stream.peek()
if ch not in _CHARS_END_NEWLINE:
raise TokenizeError(
f"expected a comment or a line break, but found {ch!r}",
stream.get_position(),
"while scanning a block scalar",
start_mark,
)
_scan_line_break(stream)
def _scan_block_scalar_indentation(
stream: StreamBuffer,
) -> tuple[list[str], int, Position]:
chunks = []
max_indent = 0
end_mark = stream.get_position()
while stream.peek() in _CHARS_SPACE_NEWLINE:
if stream.peek() != " ":
chunks.append(_scan_line_break(stream))
end_mark = stream.get_position()
else:
stream.forward()
if stream.column > max_indent:
max_indent = stream.column
return chunks, max_indent, end_mark
def _scan_block_scalar_breaks(
stream: StreamBuffer, indent: int
) -> tuple[list[str], Position]:
chunks = []
end_mark = stream.get_position()
while stream.column < indent and stream.peek() == " ":
stream.forward()
while stream.peek() in _CHARS_NEWLINE:
chunks.append(_scan_line_break(stream))
end_mark = stream.get_position()
while stream.column < indent and stream.peek() == " ":
stream.forward()
return chunks, end_mark
_CHARS_END: Final[str] = "\0"
_CHARS_NEWLINE: Final[str] = "\r\n\x85\u2028\u2029"
_CHARS_END_NEWLINE: Final[str] = "\0\r\n\x85\u2028\u2029"
_CHARS_SPACE_NEWLINE: Final[str] = " \r\n\x85\u2028\u2029"
_CHARS_END_SPACE_NEWLINE: Final[str] = "\0 \r\n\x85\u2028\u2029"
_CHARS_END_SPACE_TAB_NEWLINE: Final[str] = "\0 \t\r\n\x85\u2028\u2029"
_ESCAPE_REPLACEMENTS: Final[dict[str, str]] = {
"0": "\0",
"a": "\x07",
"b": "\x08",
"t": "\x09",
"\t": "\x09",
"n": "\x0a",
"v": "\x0b",
"f": "\x0c",
"r": "\x0d",
"e": "\x1b",
" ": "\x20",
'"': '"',
"\\": "\\",
"/": "/",
"N": "\x85",
"_": "\xa0",
"L": "\u2028",
"P": "\u2029",
}
_ESCAPE_CODES: Final[dict[str, int]] = {
"x": 2,
"u": 4,
"U": 8,
}
