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# build-aux/measurestack/vcg.py - Parse the "VCG" language
#
# Copyright (C) 2024-2025 Luke T. Shumaker <lukeshu@lukeshu.com>
# SPDX-License-Identifier: AGPL-3.0-or-later
import re
import typing
# pylint: disable=unused-variable
__all__ = [
"VCGElem",
"parse_vcg",
]
# Parse the "VCG" language
#
# https://www.rw.cdl.uni-saarland.de/people/sander/private/html/gsvcg1.html
#
# The formal syntax is found at
# ftp://ftp.cs.uni-sb.de/pub/graphics/vcg/vcg.tgz `doc/grammar.txt`.
class VCGElem:
typ: str
lineno: int
attrs: dict[str, str]
re_beg = re.compile(r"(edge|node):\s*\{\s*")
_re_tok = r"[a-zA-Z_][a-zA-Z0-9_]*"
_re_str = r'"(?:[^\"]|\\.)*"'
re_attr = re.compile("(" + _re_tok + r")\s*:\s*(" + _re_tok + "|" + _re_str + r")\s*")
re_end = re.compile(r"\}\s*$")
re_skip = re.compile(r"(graph:\s*\{\s*title\s*:\s*" + _re_str + r"\s*|\})\s*")
re_esc = re.compile(r"\\.")
def parse_vcg(reader: typing.TextIO) -> typing.Iterator[VCGElem]:
for lineno, line in enumerate(reader):
pos = 0
def _raise(msg: str) -> typing.NoReturn:
nonlocal lineno
nonlocal line
nonlocal pos
e = SyntaxError(msg)
e.lineno = lineno
e.offset = pos
e.text = line
raise e
if re_skip.fullmatch(line):
continue
elem = VCGElem()
elem.lineno = lineno
m = re_beg.match(line, pos=pos)
if not m:
_raise("does not look like a VCG line")
elem.typ = m.group(1)
pos = m.end()
elem.attrs = {}
while True:
if re_end.match(line, pos=pos):
break
m = re_attr.match(line, pos=pos)
if not m:
_raise("unexpected character")
k = m.group(1)
v = m.group(2)
if k in elem.attrs:
_raise(f"duplicate key: {k!r}")
if v.startswith('"'):
def unesc(esc: re.Match[str]) -> str:
match esc.group(0)[1:]:
case "n":
return "\n"
case '"':
return '"'
case "\\":
return "\\"
case _:
_raise(f"invalid escape code {esc.group(0)!r}")
v = re_esc.sub(unesc, v[1:-1])
elem.attrs[k] = v
pos = m.end()
del _raise
del pos
del line
del lineno
yield elem
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