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1#! /usr/bin/env python3
2
3# Selectively preprocess #ifdef / #ifndef statements.
4# Usage:
5# ifdef [-Dname] ... [-Uname] ... [file] ...
6#
7# This scans the file(s), looking for #ifdef and #ifndef preprocessor
8# commands that test for one of the names mentioned in the -D and -U
9# options.  On standard output it writes a copy of the input file(s)
10# minus those code sections that are suppressed by the selected
11# combination of defined/undefined symbols.  The #if(n)def/#else/#else
12# lines themselves (if the #if(n)def tests for one of the mentioned
13# names) are removed as well.
14
15# Features: Arbitrary nesting of recognized and unrecognized
16# preprocessor statements works correctly.  Unrecognized #if* commands
17# are left in place, so it will never remove too much, only too
18# little.  It does accept whitespace around the '#' character.
19
20# Restrictions: There should be no comments or other symbols on the
21# #if(n)def lines.  The effect of #define/#undef commands in the input
22# file or in included files is not taken into account.  Tests using
23# #if and the defined() pseudo function are not recognized.  The #elif
24# command is not recognized.  Improperly nesting is not detected.
25# Lines that look like preprocessor commands but which are actually
26# part of comments or string literals will be mistaken for
27# preprocessor commands.
28
29import sys
30import getopt
31
32defs = []
33undefs = []
34
35def main():
36    opts, args = getopt.getopt(sys.argv[1:], 'D:U:')
37    for o, a in opts:
38        if o == '-D':
39            defs.append(a)
40        if o == '-U':
41            undefs.append(a)
42    if not args:
43        args = ['-']
44    for filename in args:
45        if filename == '-':
46            process(sys.stdin, sys.stdout)
47        else:
48            with open(filename) as f:
49                process(f, sys.stdout)
50
51def process(fpi, fpo):
52    keywords = ('if', 'ifdef', 'ifndef', 'else', 'endif')
53    ok = 1
54    stack = []
55    while 1:
56        line = fpi.readline()
57        if not line: break
58        while line[-2:] == '\\\n':
59            nextline = fpi.readline()
60            if not nextline: break
61            line = line + nextline
62        tmp = line.strip()
63        if tmp[:1] != '#':
64            if ok: fpo.write(line)
65            continue
66        tmp = tmp[1:].strip()
67        words = tmp.split()
68        keyword = words[0]
69        if keyword not in keywords:
70            if ok: fpo.write(line)
71            continue
72        if keyword in ('ifdef', 'ifndef') and len(words) == 2:
73            if keyword == 'ifdef':
74                ko = 1
75            else:
76                ko = 0
77            word = words[1]
78            if word in defs:
79                stack.append((ok, ko, word))
80                if not ko: ok = 0
81            elif word in undefs:
82                stack.append((ok, not ko, word))
83                if ko: ok = 0
84            else:
85                stack.append((ok, -1, word))
86                if ok: fpo.write(line)
87        elif keyword == 'if':
88            stack.append((ok, -1, ''))
89            if ok: fpo.write(line)
90        elif keyword == 'else' and stack:
91            s_ok, s_ko, s_word = stack[-1]
92            if s_ko < 0:
93                if ok: fpo.write(line)
94            else:
95                s_ko = not s_ko
96                ok = s_ok
97                if not s_ko: ok = 0
98                stack[-1] = s_ok, s_ko, s_word
99        elif keyword == 'endif' and stack:
100            s_ok, s_ko, s_word = stack[-1]
101            if s_ko < 0:
102                if ok: fpo.write(line)
103            del stack[-1]
104            ok = s_ok
105        else:
106            sys.stderr.write('Unknown keyword %s\n' % keyword)
107    if stack:
108        sys.stderr.write('stack: %s\n' % stack)
109
110if __name__ == '__main__':
111    main()
112