byteify-strings: add support for ignore comments

Our simple token analysis is sometimes not clever enough, we need to be able
to turn off our script for parts of the code.

This change introduces three special comments:

    - `#no-py3-transform` to tell `byteify-strings` ignore the next line
    - `#py3-transform: off` to ignore everything until the end of the file
    - `#py3-transform: on` to stop ignoring

The last two can be particularly useful within Python 2/3 compatibility files.

contrib/byteify-strings.py

@@ -1,245 +1,262 b''
 #!/usr/bin/env python3
 #
 # byteify-strings.py - transform string literals to be Python 3 safe
 #
 # Copyright 2015 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import, print_function
 
 import argparse
 import contextlib
 import errno
 import os
 import sys
 import tempfile
 import token
 import tokenize
 
 def adjusttokenpos(t, ofs):
     """Adjust start/end column of the given token"""
     return t._replace(start=(t.start[0], t.start[1] + ofs),
                       end=(t.end[0], t.end[1] + ofs))
 
 def replacetokens(tokens, opts):
     """Transform a stream of tokens from raw to Python 3.
 
     Returns a generator of possibly rewritten tokens.
 
     The input token list may be mutated as part of processing. However,
     its changes do not necessarily match the output token stream.
     """
     sysstrtokens = set()
 
     # The following utility functions access the tokens list and i index of
     # the for i, t enumerate(tokens) loop below
     def _isop(j, *o):
         """Assert that tokens[j] is an OP with one of the given values"""
         try:
             return tokens[j].type == token.OP and tokens[j].string in o
         except IndexError:
             return False
 
     def _findargnofcall(n):
         """Find arg n of a call expression (start at 0)
 
         Returns index of the first token of that argument, or None if
         there is not that many arguments.
 
         Assumes that token[i + 1] is '('.
 
         """
         nested = 0
         for j in range(i + 2, len(tokens)):
             if _isop(j, ')', ']', '}'):
                 # end of call, tuple, subscription or dict / set
                 nested -= 1
                 if nested < 0:
                     return None
             elif n == 0:
                 # this is the starting position of arg
                 return j
             elif _isop(j, '(', '[', '{'):
                 nested += 1
             elif _isop(j, ',') and nested == 0:
                 n -= 1
 
         return None
 
     def _ensuresysstr(j):
         """Make sure the token at j is a system string
 
         Remember the given token so the string transformer won't add
         the byte prefix.
 
         Ignores tokens that are not strings. Assumes bounds checking has
         already been done.
 
         """
         k = j
         currtoken = tokens[k]
         while currtoken.type in (token.STRING, token.NEWLINE, tokenize.NL):
             k += 1
             if (
                 currtoken.type == token.STRING
                 and currtoken.string.startswith(("'", '"'))
             ):
                 sysstrtokens.add(currtoken)
             try:
                 currtoken = tokens[k]
             except IndexError:
                 break
 
     coldelta = 0  # column increment for new opening parens
     coloffset = -1  # column offset for the current line (-1: TBD)
     parens = [(0, 0, 0)]  # stack of (line, end-column, column-offset)
+    ignorenextline = False  # don't transform the next line
+    insideignoreblock = False # don't transform until turned off
     for i, t in enumerate(tokens):
         # Compute the column offset for the current line, such that
         # the current line will be aligned to the last opening paren
         # as before.
         if coloffset < 0:
             if t.start[1] == parens[-1][1]:
                 coloffset = parens[-1][2]
             elif t.start[1] + 1 == parens[-1][1]:
                 # fix misaligned indent of s/util.Abort/error.Abort/
                 coloffset = parens[-1][2] + (parens[-1][1] - t.start[1])
             else:
                 coloffset = 0
 
         # Reset per-line attributes at EOL.
         if t.type in (token.NEWLINE, tokenize.NL):
             yield adjusttokenpos(t, coloffset)
             coldelta = 0
             coloffset = -1
+            if not insideignoreblock:
+                ignorenextline = (
+                    tokens[i - 1].type == token.COMMENT
+                    and tokens[i - 1].string == "#no-py3-transform"
+                )
+            continue
+
+        if t.type == token.COMMENT:
+            if t.string == "#py3-transform: off":
+                insideignoreblock = True
+            if t.string == "#py3-transform: on":
+                insideignoreblock = False
+
+        if ignorenextline or insideignoreblock:
+            yield adjusttokenpos(t, coloffset)
             continue
 
         # Remember the last paren position.
         if _isop(i, '(', '[', '{'):
             parens.append(t.end + (coloffset + coldelta,))
         elif _isop(i, ')', ']', '}'):
             parens.pop()
 
         # Convert most string literals to byte literals. String literals
         # in Python 2 are bytes. String literals in Python 3 are unicode.
         # Most strings in Mercurial are bytes and unicode strings are rare.
         # Rather than rewrite all string literals to use ``b''`` to indicate
         # byte strings, we apply this token transformer to insert the ``b``
         # prefix nearly everywhere.
         if t.type == token.STRING and t not in sysstrtokens:
             s = t.string
 
             # Preserve docstrings as string literals. This is inconsistent
             # with regular unprefixed strings. However, the
             # "from __future__" parsing (which allows a module docstring to
             # exist before it) doesn't properly handle the docstring if it
             # is b''' prefixed, leading to a SyntaxError. We leave all
             # docstrings as unprefixed to avoid this. This means Mercurial
             # components touching docstrings need to handle unicode,
             # unfortunately.
             if s[0:3] in ("'''", '"""'):
                 # If it's assigned to something, it's not a docstring
                 if not _isop(i - 1, '='):
                     yield adjusttokenpos(t, coloffset)
                     continue
 
             # If the first character isn't a quote, it is likely a string
             # prefixing character (such as 'b', 'u', or 'r'. Ignore.
             if s[0] not in ("'", '"'):
                 yield adjusttokenpos(t, coloffset)
                 continue
 
             # String literal. Prefix to make a b'' string.
             yield adjusttokenpos(t._replace(string='b%s' % t.string),
                                  coloffset)
             coldelta += 1
             continue
 
         # This looks like a function call.
         if t.type == token.NAME and _isop(i + 1, '('):
             fn = t.string
 
             # *attr() builtins don't accept byte strings to 2nd argument.
             if (fn in ('getattr', 'setattr', 'hasattr', 'safehasattr') and
                     not _isop(i - 1, '.')):
                 arg1idx = _findargnofcall(1)
                 if arg1idx is not None:
                     _ensuresysstr(arg1idx)
 
             # .encode() and .decode() on str/bytes/unicode don't accept
             # byte strings on Python 3.
             elif fn in ('encode', 'decode') and _isop(i - 1, '.'):
                 for argn in range(2):
                     argidx = _findargnofcall(argn)
                     if argidx is not None:
                         _ensuresysstr(argidx)
 
             # It changes iteritems/values to items/values as they are not
             # present in Python 3 world.
             elif opts['dictiter'] and fn in ('iteritems', 'itervalues'):
                 yield adjusttokenpos(t._replace(string=fn[4:]), coloffset)
                 continue
 
         # Looks like "if __name__ == '__main__'".
         if (t.type == token.NAME and t.string == '__name__'
             and _isop(i + 1, '==')):
             _ensuresysstr(i + 2)
 
         # Emit unmodified token.
         yield adjusttokenpos(t, coloffset)
 
 def process(fin, fout, opts):
     tokens = tokenize.tokenize(fin.readline)
     tokens = replacetokens(list(tokens), opts)
     fout.write(tokenize.untokenize(tokens))
 
 def tryunlink(fname):
     try:
         os.unlink(fname)
     except OSError as err:
         if err.errno != errno.ENOENT:
             raise
 
 @contextlib.contextmanager
 def editinplace(fname):
     n = os.path.basename(fname)
     d = os.path.dirname(fname)
     fp = tempfile.NamedTemporaryFile(prefix='.%s-' % n, suffix='~', dir=d,
                                      delete=False)
     try:
         yield fp
         fp.close()
         if os.name == 'nt':
             tryunlink(fname)
         os.rename(fp.name, fname)
     finally:
         fp.close()
         tryunlink(fp.name)
 
 def main():
     ap = argparse.ArgumentParser()
     ap.add_argument('-i', '--inplace', action='store_true', default=False,
                     help='edit files in place')
     ap.add_argument('--dictiter', action='store_true', default=False,
                     help='rewrite iteritems() and itervalues()'),
     ap.add_argument('files', metavar='FILE', nargs='+', help='source file')
     args = ap.parse_args()
     opts = {
         'dictiter': args.dictiter,
     }
     for fname in args.files:
         if args.inplace:
             with editinplace(fname) as fout:
                 with open(fname, 'rb') as fin:
                     process(fin, fout, opts)
         else:
             with open(fname, 'rb') as fin:
                 fout = sys.stdout.buffer
                 process(fin, fout, opts)
 
 if __name__ == '__main__':
     if sys.version_info.major < 3:
         print('This script must be run under Python 3.')
         sys.exit(3)
     main()