byteify-strings: add helpers to check for item access or method call

These helpers will be used in a future patch, split for ease of review.

contrib/byteify-strings.py

@@ -1,262 +1,292 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
 
+    def _isitemaccess(j):
+        """Assert the next tokens form an item access on `tokens[j]` and that
+        `tokens[j]` is a name.
+        """
+        try:
+            return (
+                tokens[j].type == token.NAME
+                and _isop(j + 1, '[')
+                and tokens[j + 2].type == token.STRING
+                and _isop(j + 3, ']')
+            )
+        except IndexError:
+            return False
+
+    def _ismethodcall(j, *methodnames):
+        """Assert the next tokens form a call to `methodname` with a string
+        as first argument on `tokens[j]` and that `tokens[j]` is a name.
+        """
+        try:
+            return (
+                tokens[j].type == token.NAME
+                and _isop(j + 1, '.')
+                and tokens[j + 2].type == token.NAME
+                and tokens[j + 2].string in methodnames
+                and _isop(j + 3, '(')
+                and tokens[j + 4].type == token.STRING
+            )
+        except IndexError:
+            return False
+
     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()