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import re
import sys
def negate(condition):
"""
Returns a CPP conditional that is the opposite of the conditional passed in.
"""
if condition.startswith('!'):
return condition[1:]
return "!" + condition
class Monitor:
"""
A simple C preprocessor that scans C source and computes, line by line,
what the current C preprocessor #if state is.
Doesn't handle everything--for example, if you have /* inside a C string,
without a matching */ (also inside a C string), or with a */ inside a C
string but on another line and with preprocessor macros in between...
the parser will get lost.
Anyway this implementation seems to work well enough for the CPython sources.
"""
is_a_simple_defined = re.compile(r'^defined\s*\(\s*[A-Za-z0-9_]+\s*\)$').match
def __init__(self, filename=None, *, verbose=False):
self.stack = []
self.in_comment = False
self.continuation = None
self.line_number = 0
self.filename = filename
self.verbose = verbose
def __repr__(self):
return ''.join((
'<Monitor ',
str(id(self)),
" line=", str(self.line_number),
" condition=", repr(self.condition()),
">"))
def status(self):
return str(self.line_number).rjust(4) + ": " + self.condition()
def condition(self):
"""
Returns the current preprocessor state, as a single #if condition.
"""
return " && ".join(condition for token, condition in self.stack)
def fail(self, *a):
if self.filename:
filename = " " + self.filename
else:
filename = ''
print("Error at" + filename, "line", self.line_number, ":")
print(" ", ' '.join(str(x) for x in a))
sys.exit(-1)
def close(self):
if self.stack:
self.fail("Ended file while still in a preprocessor conditional block!")
def write(self, s):
for line in s.split("\n"):
self.writeline(line)
def writeline(self, line):
self.line_number += 1
line = line.strip()
def pop_stack():
if not self.stack:
self.fail("#" + token + " without matching #if / #ifdef / #ifndef!")
return self.stack.pop()
if self.continuation:
line = self.continuation + line
self.continuation = None
if not line:
return
if line.endswith('\\'):
self.continuation = line[:-1].rstrip() + " "
return
# we have to ignore preprocessor commands inside comments
#
# we also have to handle this:
# /* start
# ...
# */ /* <-- tricky!
# ...
# */
# and this:
# /* start
# ...
# */ /* also tricky! */
if self.in_comment:
if '*/' in line:
# snip out the comment and continue
#
# GCC allows
# /* comment
# */ #include <stdio.h>
# maybe other compilers too?
_, _, line = line.partition('*/')
self.in_comment = False
while True:
if '/*' in line:
if self.in_comment:
self.fail("Nested block comment!")
before, _, remainder = line.partition('/*')
comment, comment_ends, after = remainder.partition('*/')
if comment_ends:
# snip out the comment
line = before.rstrip() + ' ' + after.lstrip()
continue
# comment continues to eol
self.in_comment = True
line = before.rstrip()
break
# we actually have some // comments
# (but block comments take precedence)
before, line_comment, comment = line.partition('//')
if line_comment:
line = before.rstrip()
if not line.startswith('#'):
return
line = line[1:].lstrip()
assert line
fields = line.split()
token = fields[0].lower()
condition = ' '.join(fields[1:]).strip()
if_tokens = {'if', 'ifdef', 'ifndef'}
all_tokens = if_tokens | {'elif', 'else', 'endif'}
if token not in all_tokens:
return
# cheat a little here, to reuse the implementation of if
if token == 'elif':
pop_stack()
token = 'if'
if token in if_tokens:
if not condition:
self.fail("Invalid format for #" + token + " line: no argument!")
if token == 'if':
if not self.is_a_simple_defined(condition):
condition = "(" + condition + ")"
else:
fields = condition.split()
if len(fields) != 1:
self.fail("Invalid format for #" + token + " line: should be exactly one argument!")
symbol = fields[0]
condition = 'defined(' + symbol + ')'
if token == 'ifndef':
condition = '!' + condition
self.stack.append(("if", condition))
if self.verbose:
print(self.status())
return
previous_token, previous_condition = pop_stack()
if token == 'else':
self.stack.append(('else', negate(previous_condition)))
elif token == 'endif':
pass
if self.verbose:
print(self.status())
if __name__ == '__main__':
for filename in sys.argv[1:]:
with open(filename, "rt") as f:
cpp = Monitor(filename, verbose=True)
print()
print(filename)
for line_number, line in enumerate(f.read().split('\n'), 1):
cpp.writeline(line)
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