waf/waflib/Tools/c_preproc.py

#!/usr/bin/env python
# encoding: utf-8
# Thomas Nagy, 2006-2010 (ita)

"""
C/C++ preprocessor for finding dependencies

Reasons for using the Waf preprocessor by default

#. Some c/c++ extensions (Qt) require a custom preprocessor for obtaining the dependencies (.moc files)
#. Not all compilers provide .d files for obtaining the dependencies (portability)
#. A naive file scanner will not catch the constructs such as "#include foo()"
#. A naive file scanner will catch unnecessary dependencies (change an unused header -> recompile everything)

Regarding the speed concerns:

* the preprocessing is performed only when files must be compiled
* the macros are evaluated only for #if/#elif/#include
* system headers are not scanned by default

Now if you do not want the Waf preprocessor, the tool +gccdeps* uses the .d files produced
during the compilation to track the dependencies (useful when used with the boost libraries).
It only works with gcc >= 4.4 though.

A dumb preprocessor is also available in the tool *c_dumbpreproc*
"""
# TODO: more varargs, pragma once

import re, sys, os, string, traceback
from waflib import Logs, Build, Utils, Errors
from waflib.Logs import debug, error

class PreprocError(Errors.WafError):
	pass

POPFILE = '-'
"Constant representing a special token used in :py:meth:`waflib.Tools.c_preproc.c_parser.start` iteration to switch to a header read previously"

recursion_limit = 150
"Limit on the amount of files to read in the dependency scanner"

go_absolute = False
"Set to True to track headers on files in /usr/include, else absolute paths are ignored (but it becomes very slow)"

standard_includes = ['/usr/include']
if Utils.is_win32:
	standard_includes = []

use_trigraphs = 0
"""Apply trigraph rules (False by default)"""

strict_quotes = 0
"""Reserve the "#include <>" quotes for system includes (do not search for those includes). False by default."""

g_optrans = {
'not':'!',
'and':'&&',
'bitand':'&',
'and_eq':'&=',
'or':'||',
'bitor':'|',
'or_eq':'|=',
'xor':'^',
'xor_eq':'^=',
'compl':'~',
}
"""Operators such as and/or/xor for c++. Set an empty dict to disable."""

# ignore #warning and #error
re_lines = re.compile(
	'^[ \t]*(#|%:)[ \t]*(ifdef|ifndef|if|else|elif|endif|include|import|define|undef|pragma)[ \t]*(.*)\r*$',
	re.IGNORECASE | re.MULTILINE)
"""Match #include lines"""

re_mac = re.compile("^[a-zA-Z_]\w*")
"""Match macro definitions"""

re_fun = re.compile('^[a-zA-Z_][a-zA-Z0-9_]*[(]')
"""Match macro functions"""

re_pragma_once = re.compile('^\s*once\s*', re.IGNORECASE)
"""Match #pragma once statements"""

re_nl = re.compile('\\\\\r*\n', re.MULTILINE)
"""Match newlines"""

re_cpp = re.compile(
	r"""(/\*[^*]*\*+([^/*][^*]*\*+)*/)|//[^\n]*|("(\\.|[^"\\])*"|'(\\.|[^'\\])*'|.[^/"'\\]*)""",
	re.MULTILINE)
"""Filter C/C++ comments"""

trig_def = [('??'+a, b) for a, b in zip("=-/!'()<>", r'#~\|^[]{}')]
"""Trigraph definitions"""

chr_esc = {'0':0, 'a':7, 'b':8, 't':9, 'n':10, 'f':11, 'v':12, 'r':13, '\\':92, "'":39}
"""Escape characters"""

NUM   = 'i'
"""Number token"""

OP    = 'O'
"""Operator token"""

IDENT = 'T'
"""Identifier token"""

STR   = 's'
"""String token"""

CHAR  = 'c'
"""Character token"""

tok_types = [NUM, STR, IDENT, OP]
"""Token types"""

exp_types = [
	r"""0[xX](?P<hex>[a-fA-F0-9]+)(?P<qual1>[uUlL]*)|L*?'(?P<char>(\\.|[^\\'])+)'|(?P<n1>\d+)[Ee](?P<exp0>[+-]*?\d+)(?P<float0>[fFlL]*)|(?P<n2>\d*\.\d+)([Ee](?P<exp1>[+-]*?\d+))?(?P<float1>[fFlL]*)|(?P<n4>\d+\.\d*)([Ee](?P<exp2>[+-]*?\d+))?(?P<float2>[fFlL]*)|(?P<oct>0*)(?P<n0>\d+)(?P<qual2>[uUlL]*)""",
	r'L?"([^"\\]|\\.)*"',
	r'[a-zA-Z_]\w*',
	r'%:%:|<<=|>>=|\.\.\.|<<|<%|<:|<=|>>|>=|\+\+|\+=|--|->|-=|\*=|/=|%:|%=|%>|==|&&|&=|\|\||\|=|\^=|:>|!=|##|[\(\)\{\}\[\]<>\?\|\^\*\+&=:!#;,%/\-\?\~\.]',
]
"""Expression types"""

re_clexer = re.compile('|'.join(["(?P<%s>%s)" % (name, part) for name, part in zip(tok_types, exp_types)]), re.M)
"""Match expressions into tokens"""

accepted  = 'a'
"""Parser state is *accepted*"""

ignored   = 'i'
"""Parser state is *ignored*, for example preprocessor lines in an #if 0 block"""

undefined = 'u'
"""Parser state is *undefined* at the moment"""

skipped   = 's'
"""Parser state is *skipped*, for example preprocessor lines in a #elif 0 block"""

def repl(m):
	"""Replace function used with :py:attr:`waflib.Tools.c_preproc.re_cpp`"""
	s = m.group(1)
	if s:
		return ' '
	return m.group(3) or ''

def filter_comments(filename):
	"""
	Filter the comments from a c/h file, and return the preprocessor lines.
	The regexps :py:attr:`waflib.Tools.c_preproc.re_cpp`, :py:attr:`waflib.Tools.c_preproc.re_nl` and :py:attr:`waflib.Tools.c_preproc.re_lines` are used internally.

	:return: the preprocessor directives as a list of (keyword, line)
	:rtype: a list of string pairs
	"""
	# return a list of tuples : keyword, line
	code = Utils.readf(filename)
	if use_trigraphs:
		for (a, b) in trig_def: code = code.split(a).join(b)
	code = re_nl.sub('', code)
	code = re_cpp.sub(repl, code)
	return [(m.group(2), m.group(3)) for m in re.finditer(re_lines, code)]

prec = {}
"""
Operator precendence rules required for parsing expressions of the form::

	#if 1 && 2 != 0
"""
ops = ['* / %', '+ -', '<< >>', '< <= >= >', '== !=', '& | ^', '&& ||', ',']
for x in range(len(ops)):
	syms = ops[x]
	for u in syms.split():
		prec[u] = x

def trimquotes(s):
	"""
	Remove the single quotes around an expression::

		trimquotes("'test'") == "test"

	:param s: expression to transform
	:type s: string
	:rtype: string
	"""
	if not s: return ''
	s = s.rstrip()
	if s[0] == "'" and s[-1] == "'": return s[1:-1]
	return s

def reduce_nums(val_1, val_2, val_op):
	"""
	Apply arithmetic rules to compute a result

	:param val1: input parameter
	:type val1: int or string
	:param val2: input parameter
	:type val2: int or string
	:param val_op: C operator in *+*, */*, *-*, etc
	:type val_op: string
	:rtype: int
	"""
	#print val_1, val_2, val_op

	# now perform the operation, make certain a and b are numeric
	try:    a = 0 + val_1
	except TypeError: a = int(val_1)
	try:    b = 0 + val_2
	except TypeError: b = int(val_2)

	d = val_op
	if d == '%':  c = a%b
	elif d=='+':  c = a+b
	elif d=='-':  c = a-b
	elif d=='*':  c = a*b
	elif d=='/':  c = a/b
	elif d=='^':  c = a^b
	elif d=='|':  c = a|b
	elif d=='||': c = int(a or b)
	elif d=='&':  c = a&b
	elif d=='&&': c = int(a and b)
	elif d=='==': c = int(a == b)
	elif d=='!=': c = int(a != b)
	elif d=='<=': c = int(a <= b)
	elif d=='<':  c = int(a < b)
	elif d=='>':  c = int(a > b)
	elif d=='>=': c = int(a >= b)
	elif d=='^':  c = int(a^b)
	elif d=='<<': c = a<<b
	elif d=='>>': c = a>>b
	else: c = 0
	return c

def get_num(lst):
	"""
	Try to obtain a number from a list of tokens. The token types are defined in :py:attr:`waflib.Tools.ccroot.tok_types`.

	:param lst: list of preprocessor tokens
	:type lst: list of tuple (tokentype, value)
	:return: a pair containing the number and the rest of the list
	:rtype: tuple(value, list)
	"""
	if not lst: raise PreprocError("empty list for get_num")
	(p, v) = lst[0]
	if p == OP:
		if v == '(':
			count_par = 1
			i = 1
			while i < len(lst):
				(p, v) = lst[i]

				if p == OP:
					if v == ')':
						count_par -= 1
						if count_par == 0:
							break
					elif v == '(':
						count_par += 1
				i += 1
			else:
				raise PreprocError("rparen expected %r" % lst)

			(num, _) = get_term(lst[1:i])
			return (num, lst[i+1:])

		elif v == '+':
			return get_num(lst[1:])
		elif v == '-':
			num, lst = get_num(lst[1:])
			return (reduce_nums('-1', num, '*'), lst)
		elif v == '!':
			num, lst = get_num(lst[1:])
			return (int(not int(num)), lst)
		elif v == '~':
			num, lst = get_num(lst[1:])
			return (~ int(num), lst)
		else:
			raise PreprocError("Invalid op token %r for get_num" % lst)
	elif p == NUM:
		return v, lst[1:]
	elif p == IDENT:
		# all macros should have been replaced, remaining identifiers eval to 0
		return 0, lst[1:]
	else:
		raise PreprocError("Invalid token %r for get_num" % lst)

def get_term(lst):
	"""
	Evaluate an expression recursively, for example::

		1+1+1 -> 2+1 -> 3

	:param lst: list of tokens
	:type lst: list of tuple(token, value)
	:return: the value and the remaining tokens
	:rtype: value, list
	"""

	if not lst: raise PreprocError("empty list for get_term")
	num, lst = get_num(lst)
	if not lst:
		return (num, [])
	(p, v) = lst[0]
	if p == OP:
		if v == ',':
			# skip
			return get_term(lst[1:])
		elif v == '?':
			count_par = 0
			i = 1
			while i < len(lst):
				(p, v) = lst[i]

				if p == OP:
					if v == ')':
						count_par -= 1
					elif v == '(':
						count_par += 1
					elif v == ':':
						if count_par == 0:
							break
				i += 1
			else:
				raise PreprocError("rparen expected %r" % lst)

			if int(num):
				return get_term(lst[1:i])
			else:
				return get_term(lst[i+1:])

		else:
			num2, lst = get_num(lst[1:])

			if not lst:
				# no more tokens to process
				num2 = reduce_nums(num, num2, v)
				return get_term([(NUM, num2)] + lst)

			# operator precedence
			p2, v2 = lst[0]
			if p2 != OP:
				raise PreprocError("op expected %r" % lst)

			if prec[v2] >= prec[v]:
				num2 = reduce_nums(num, num2, v)
				return get_term([(NUM, num2)] + lst)
			else:
				num3, lst = get_num(lst[1:])
				num3 = reduce_nums(num2, num3, v2)
				return get_term([(NUM, num), (p, v), (NUM, num3)] + lst)


	raise PreprocError("cannot reduce %r" % lst)

def reduce_eval(lst):
	"""
	Take a list of tokens and output true or false for #if/#elif conditions.

	:param lst: a list of tokens
	:type lst: list of tuple(token, value)
	:return: a token
	:rtype: tuple(NUM, int)
	"""
	num, lst = get_term(lst)
	return (NUM, num)

def stringize(lst):
	"""
	Merge a list of tokens into a string

	:param lst: a list of tokens
	:type lst: list of tuple(token, value)
	:rtype: string
	"""
	lst = [str(v2) for (p2, v2) in lst]
	return "".join(lst)

def paste_tokens(t1, t2):
	"""
	Token pasting works between identifiers, particular operators, and identifiers and numbers::

		a ## b  ->  ab
		> ## =  ->  >=
		a ## 2  ->  a2

	:param t1: token
	:type t1: tuple(type, value)
	:param t2: token
	:type t2: tuple(type, value)
	"""
	p1 = None
	if t1[0] == OP and t2[0] == OP:
		p1 = OP
	elif t1[0] == IDENT and (t2[0] == IDENT or t2[0] == NUM):
		p1 = IDENT
	elif t1[0] == NUM and t2[0] == NUM:
		p1 = NUM
	if not p1:
		raise PreprocError('tokens do not make a valid paste %r and %r' % (t1, t2))
	return (p1, t1[1] + t2[1])

def reduce_tokens(lst, defs, ban=[]):
	"""
	Replace the tokens in lst, using the macros provided in defs, and a list of macros that cannot be re-applied

	:param lst: list of tokens
	:type lst: list of tuple(token, value)
	:param defs: macro definitions
	:type defs: dict
	:param ban: macros that cannot be substituted (recursion is not allowed)
	:type ban: list of string
	:return: the new list of tokens
	:rtype: value, list
	"""
	i = 0

	while i < len(lst):
		(p, v) = lst[i]

		if p == IDENT and v == "defined":
			del lst[i]
			if i < len(lst):
				(p2, v2) = lst[i]
				if p2 == IDENT:
					if v2 in defs:
						lst[i] = (NUM, 1)
					else:
						lst[i] = (NUM, 0)
				elif p2 == OP and v2 == '(':
					del lst[i]
					(p2, v2) = lst[i]
					del lst[i] # remove the ident, and change the ) for the value
					if v2 in defs:
						lst[i] = (NUM, 1)
					else:
						lst[i] = (NUM, 0)
				else:
					raise PreprocError("Invalid define expression %r" % lst)

		elif p == IDENT and v in defs:

			if isinstance(defs[v], str):
				a, b = extract_macro(defs[v])
				defs[v] = b
			macro_def = defs[v]
			to_add = macro_def[1]

			if isinstance(macro_def[0], list):
				# macro without arguments
				del lst[i]
				accu = to_add[:]
				reduce_tokens(accu, defs, ban+[v])
				for x in range(len(accu)):
					lst.insert(i, accu[x])
					i += 1
			else:
				# collect the arguments for the funcall

				args = []
				del lst[i]

				if i >= len(lst):
					raise PreprocError("expected '(' after %r (got nothing)" % v)

				(p2, v2) = lst[i]
				if p2 != OP or v2 != '(':
					raise PreprocError("expected '(' after %r" % v)

				del lst[i]

				one_param = []
				count_paren = 0
				while i < len(lst):
					p2, v2 = lst[i]

					del lst[i]
					if p2 == OP and count_paren == 0:
						if v2 == '(':
							one_param.append((p2, v2))
							count_paren += 1
						elif v2 == ')':
							if one_param: args.append(one_param)
							break
						elif v2 == ',':
							if not one_param: raise PreprocError("empty param in funcall %s" % p)
							args.append(one_param)
							one_param = []
						else:
							one_param.append((p2, v2))
					else:
						one_param.append((p2, v2))
						if   v2 == '(': count_paren += 1
						elif v2 == ')': count_paren -= 1
				else:
					raise PreprocError('malformed macro')

				# substitute the arguments within the define expression
				accu = []
				arg_table = macro_def[0]
				j = 0
				while j < len(to_add):
					(p2, v2) = to_add[j]

					if p2 == OP and v2 == '#':
						# stringize is for arguments only
						if j+1 < len(to_add) and to_add[j+1][0] == IDENT and to_add[j+1][1] in arg_table:
							toks = args[arg_table[to_add[j+1][1]]]
							accu.append((STR, stringize(toks)))
							j += 1
						else:
							accu.append((p2, v2))
					elif p2 == OP and v2 == '##':
						# token pasting, how can man invent such a complicated system?
						if accu and j+1 < len(to_add):
							# we have at least two tokens

							t1 = accu[-1]

							if to_add[j+1][0] == IDENT and to_add[j+1][1] in arg_table:
								toks = args[arg_table[to_add[j+1][1]]]

								if toks:
									accu[-1] = paste_tokens(t1, toks[0]) #(IDENT, accu[-1][1] + toks[0][1])
									accu.extend(toks[1:])
								else:
									# error, case "a##"
									accu.append((p2, v2))
									accu.extend(toks)
							elif to_add[j+1][0] == IDENT and to_add[j+1][1] == '__VA_ARGS__':
								# TODO not sure
								# first collect the tokens
								va_toks = []
								st = len(macro_def[0])
								pt = len(args)
								for x in args[pt-st+1:]:
									va_toks.extend(x)
									va_toks.append((OP, ','))
								if va_toks: va_toks.pop() # extra comma
								if len(accu)>1:
									(p3, v3) = accu[-1]
									(p4, v4) = accu[-2]
									if v3 == '##':
										# remove the token paste
										accu.pop()
										if v4 == ',' and pt < st:
											# remove the comma
											accu.pop()
								accu += va_toks
							else:
								accu[-1] = paste_tokens(t1, to_add[j+1])

							j += 1
						else:
							# Invalid paste, case    "##a" or "b##"
							accu.append((p2, v2))

					elif p2 == IDENT and v2 in arg_table:
						toks = args[arg_table[v2]]
						reduce_tokens(toks, defs, ban+[v])
						accu.extend(toks)
					else:
						accu.append((p2, v2))

					j += 1


				reduce_tokens(accu, defs, ban+[v])

				for x in range(len(accu)-1, -1, -1):
					lst.insert(i, accu[x])

		i += 1


def eval_macro(lst, defs):
	"""
	Reduce the tokens by :py:func:`waflib.Tools.c_preproc.reduce_tokens` and try to return a 0/1 result by :py:func:`waflib.Tools.c_preproc.reduce_eval`.

	:param lst: list of tokens
	:type lst: list of tuple(token, value)
	:param defs: macro definitions
	:type defs: dict
	:rtype: int
	"""
	reduce_tokens(lst, defs, [])
	if not lst: raise PreprocError("missing tokens to evaluate")
	(p, v) = reduce_eval(lst)
	return int(v) != 0

def extract_macro(txt):
	"""
	Process a macro definition of the form::
		 #define f(x, y) x * y

	into a function or a simple macro without arguments

	:param txt: expression to exact a macro definition from
	:type txt: string
	:return: a tuple containing the name, the list of arguments and the replacement
	:rtype: tuple(string, [list, list])
	"""
	t = tokenize(txt)
	if re_fun.search(txt):
		p, name = t[0]

		p, v = t[1]
		if p != OP: raise PreprocError("expected open parenthesis")

		i = 1
		pindex = 0
		params = {}
		prev = '('

		while 1:
			i += 1
			p, v = t[i]

			if prev == '(':
				if p == IDENT:
					params[v] = pindex
					pindex += 1
					prev = p
				elif p == OP and v == ')':
					break
				else:
					raise PreprocError("unexpected token (3)")
			elif prev == IDENT:
				if p == OP and v == ',':
					prev = v
				elif p == OP and v == ')':
					break
				else:
					raise PreprocError("comma or ... expected")
			elif prev == ',':
				if p == IDENT:
					params[v] = pindex
					pindex += 1
					prev = p
				elif p == OP and v == '...':
					raise PreprocError("not implemented (1)")
				else:
					raise PreprocError("comma or ... expected (2)")
			elif prev == '...':
				raise PreprocError("not implemented (2)")
			else:
				raise PreprocError("unexpected else")

		#~ print (name, [params, t[i+1:]])
		return (name, [params, t[i+1:]])
	else:
		(p, v) = t[0]
		return (v, [[], t[1:]])

re_include = re.compile('^\s*(<(?P<a>.*)>|"(?P<b>.*)")')
def extract_include(txt, defs):
	"""
	Process a line in the form::

		#include foo

	:param txt: include line to process
	:type txt: string
	:param defs: macro definitions
	:type defs: dict
	:return: the file name
	:rtype: string
	"""
	m = re_include.search(txt)
	if m:
		if m.group('a'): return '<', m.group('a')
		if m.group('b'): return '"', m.group('b')

	# perform preprocessing and look at the result, it must match an include
	toks = tokenize(txt)
	reduce_tokens(toks, defs, ['waf_include'])

	if not toks:
		raise PreprocError("could not parse include %s" % txt)

	if len(toks) == 1:
		if toks[0][0] == STR:
			return '"', toks[0][1]
	else:
		if toks[0][1] == '<' and toks[-1][1] == '>':
			return stringize(toks).lstrip('<').rstrip('>')

	raise PreprocError("could not parse include %s." % txt)

def parse_char(txt):
	"""
	Parse a c character

	:param txt: character to parse
	:type txt: string
	:return: a character literal
	:rtype: string
	"""

	if not txt: raise PreprocError("attempted to parse a null char")
	if txt[0] != '\\':
		return ord(txt)
	c = txt[1]
	if c == 'x':
		if len(txt) == 4 and txt[3] in string.hexdigits: return int(txt[2:], 16)
		return int(txt[2:], 16)
	elif c.isdigit():
		if c == '0' and len(txt)==2: return 0
		for i in 3, 2, 1:
			if len(txt) > i and txt[1:1+i].isdigit():
				return (1+i, int(txt[1:1+i], 8))
	else:
		try: return chr_esc[c]
		except KeyError: raise PreprocError("could not parse char literal '%s'" % txt)

def tokenize(s):
	"""
	Convert a string into a list of tokens (shlex.split does not apply to c/c++/d)

	:param s: input to tokenize
	:type s: string
	:return: a list of tokens
	:rtype: list of tuple(token, value)
	"""
	return tokenize_private(s)[:] # force a copy of the results

@Utils.run_once
def tokenize_private(s):
	ret = []
	for match in re_clexer.finditer(s):
		m = match.group
		for name in tok_types:
			v = m(name)
			if v:
				if name == IDENT:
					try: v = g_optrans[v]; name = OP
					except KeyError:
						# c++ specific
						if v.lower() == "true":
							v = 1
							name = NUM
						elif v.lower() == "false":
							v = 0
							name = NUM
				elif name == NUM:
					if m('oct'): v = int(v, 8)
					elif m('hex'): v = int(m('hex'), 16)
					elif m('n0'): v = m('n0')
					else:
						v = m('char')
						if v: v = parse_char(v)
						else: v = m('n2') or m('n4')
				elif name == OP:
					if v == '%:': v = '#'
					elif v == '%:%:': v = '##'
				elif name == STR:
					# remove the quotes around the string
					v = v[1:-1]
				ret.append((name, v))
				break
	return ret

@Utils.run_once
def define_name(line):
	"""
	:param line: define line
	:type line: string
	:rtype: string
	:return: the define name
	"""
	return re_mac.match(line).group(0)

class c_parser(object):
	"""
	Used by :py:func:`waflib.Tools.c_preproc.scan` to parse c/h files. Note that by default,
	only project headers are parsed.
	"""
	def __init__(self, nodepaths=None, defines=None):
		self.lines = []
		"""list of lines read"""

		if defines is None:
			self.defs  = {}
		else:
			self.defs  = dict(defines) # make a copy
		self.state = []

		self.count_files = 0
		self.currentnode_stack = []

		self.nodepaths = nodepaths or []
		"""Include paths"""

		self.nodes = []
		"""List of :py:class:`waflib.Node.Node` found so far"""

		self.names = []
		"""List of file names that could not be matched by any file"""

		self.curfile = ''
		"""Current file"""

		self.ban_includes = set([])
		"""Includes that must not be read (#pragma once)"""

	def cached_find_resource(self, node, filename):
		"""
		Find a file from the input directory

		:param node: directory
		:type node: :py:class:`waflib.Node.Node`
		:param filename: header to find
		:type filename: string
		:return: the node if found, or None
		:rtype: :py:class:`waflib.Node.Node`
		"""
		try:
			nd = node.ctx.cache_nd
		except AttributeError:
			nd = node.ctx.cache_nd = {}

		tup = (node, filename)
		try:
			return nd[tup]
		except KeyError:
			ret = node.find_resource(filename)
			if ret:
				if getattr(ret, 'children', None):
					ret = None
				elif ret.is_child_of(node.ctx.bldnode):
					tmp = node.ctx.srcnode.search_node(ret.path_from(node.ctx.bldnode))
					if tmp and getattr(tmp, 'children', None):
						ret = None
			nd[tup] = ret
			return ret

	def tryfind(self, filename):
		"""
		Try to obtain a node from the filename based from the include paths. Will add
		the node found to :py:attr:`waflib.Tools.c_preproc.c_parser.nodes` or the file name to
		:py:attr:`waflib.Tools.c_preproc.c_parser.names` if no corresponding file is found. Called by
		:py:attr:`waflib.Tools.c_preproc.c_parser.start`.

		:param filename: header to find
		:type filename: string
		:return: the node if found
		:rtype: :py:class:`waflib.Node.Node`
		"""
		self.curfile = filename

		# for msvc it should be a for loop on the whole stack
		found = self.cached_find_resource(self.currentnode_stack[-1], filename)

		for n in self.nodepaths:
			if found:
				break
			found = self.cached_find_resource(n, filename)

		if found:
			# TODO the duplicates do not increase the no-op build times too much, but they may be worth removing
			self.nodes.append(found)
			if filename[-4:] != '.moc':
				self.addlines(found)
		else:
			if not filename in self.names:
				self.names.append(filename)
		return found

	def addlines(self, node):
		"""
		Add the lines from a header in the list of preprocessor lines to parse

		:param node: header
		:type node: :py:class:`waflib.Node.Node`
		"""

		self.currentnode_stack.append(node.parent)
		filepath = node.abspath()

		self.count_files += 1
		if self.count_files > recursion_limit:
			# issue #812
			raise PreprocError("recursion limit exceeded")
		pc = self.parse_cache
		debug('preproc: reading file %r', filepath)
		try:
			lns = pc[filepath]
		except KeyError:
			pass
		else:
			self.lines.extend(lns)
			return

		try:
			lines = filter_comments(filepath)
			lines.append((POPFILE, ''))
			lines.reverse()
			pc[filepath] = lines # cache the lines filtered
			self.lines.extend(lines)
		except IOError:
			raise PreprocError("could not read the file %s" % filepath)
		except Exception:
			if Logs.verbose > 0:
				error("parsing %s failed" % filepath)
				traceback.print_exc()

	def start(self, node, env):
		"""
		Preprocess a source file to obtain the dependencies, which are accumulated to :py:attr:`waflib.Tools.c_preproc.c_parser.nodes`
		and :py:attr:`waflib.Tools.c_preproc.c_parser.names`.

		:param node: source file
		:type node: :py:class:`waflib.Node.Node`
		:param env: config set containing additional defines to take into account
		:type env: :py:class:`waflib.ConfigSet.ConfigSet`
		"""

		debug('preproc: scanning %s (in %s)', node.name, node.parent.name)

		bld = node.ctx
		try:
			self.parse_cache = bld.parse_cache
		except AttributeError:
			bld.parse_cache = {}
			self.parse_cache = bld.parse_cache

		self.addlines(node)

		# macros may be defined on the command-line, so they must be parsed as if they were part of the file
		if env['DEFINES']:
			try:
				lst = ['%s %s' % (x[0], trimquotes('='.join(x[1:]))) for x in [y.split('=') for y in env['DEFINES']]]
				lst.reverse()
				self.lines.extend([('define', x) for x in lst])
			except AttributeError:
				# if the defines are invalid the compiler will tell the user
				pass

		while self.lines:
			(token, line) = self.lines.pop()
			if token == POPFILE:
				self.count_files -= 1
				self.currentnode_stack.pop()
				continue

			try:
				ve = Logs.verbose
				if ve: debug('preproc: line is %s - %s state is %s', token, line, self.state)
				state = self.state

				# make certain we define the state if we are about to enter in an if block
				if token[:2] == 'if':
					state.append(undefined)
				elif token == 'endif':
					state.pop()

				# skip lines when in a dead 'if' branch, wait for the endif
				if token[0] != 'e':
					if skipped in self.state or ignored in self.state:
						continue

				if token == 'if':
					ret = eval_macro(tokenize(line), self.defs)
					if ret: state[-1] = accepted
					else: state[-1] = ignored
				elif token == 'ifdef':
					m = re_mac.match(line)
					if m and m.group(0) in self.defs: state[-1] = accepted
					else: state[-1] = ignored
				elif token == 'ifndef':
					m = re_mac.match(line)
					if m and m.group(0) in self.defs: state[-1] = ignored
					else: state[-1] = accepted
				elif token == 'include' or token == 'import':
					(kind, inc) = extract_include(line, self.defs)
					if inc in self.ban_includes:
						continue
					if token == 'import': self.ban_includes.add(inc)
					if ve: debug('preproc: include found %s    (%s) ', inc, kind)
					if kind == '"' or not strict_quotes:
						self.tryfind(inc)
				elif token == 'elif':
					if state[-1] == accepted:
						state[-1] = skipped
					elif state[-1] == ignored:
						if eval_macro(tokenize(line), self.defs):
							state[-1] = accepted
				elif token == 'else':
					if state[-1] == accepted: state[-1] = skipped
					elif state[-1] == ignored: state[-1] = accepted
				elif token == 'define':
					try:
						self.defs[define_name(line)] = line
					except Exception:
						raise PreprocError("Invalid define line %s" % line)
				elif token == 'undef':
					m = re_mac.match(line)
					if m and m.group(0) in self.defs:
						self.defs.__delitem__(m.group(0))
						#print "undef %s" % name
				elif token == 'pragma':
					if re_pragma_once.match(line.lower()):
						self.ban_includes.add(self.curfile)
			except Exception as e:
				if Logs.verbose:
					debug('preproc: line parsing failed (%s): %s %s', e, line, Utils.ex_stack())

def scan(task):
	"""
	Get the dependencies using a c/c++ preprocessor, this is required for finding dependencies of the kind::

		#include some_macro()

	This function is bound as a task method on :py:class:`waflib.Tools.c.c` and :py:class:`waflib.Tools.cxx.cxx` for example
	"""

	global go_absolute

	try:
		incn = task.generator.includes_nodes
	except AttributeError:
		raise Errors.WafError('%r is missing a feature such as "c", "cxx" or "includes": ' % task.generator)

	if go_absolute:
		nodepaths = incn + [task.generator.bld.root.find_dir(x) for x in standard_includes]
	else:
		nodepaths = [x for x in incn if x.is_child_of(x.ctx.srcnode) or x.is_child_of(x.ctx.bldnode)]

	tmp = c_parser(nodepaths)
	tmp.start(task.inputs[0], task.env)
	if Logs.verbose:
		debug('deps: deps for %r: %r; unresolved %r' % (task.inputs, tmp.nodes, tmp.names))
	return (tmp.nodes, tmp.names)