mercurial/filelog.py

check-code: catch Python 'is' comparing number or string literals

The Python 'is' operator compares object identity, so it should
definitely not be applied to string or number literals, which Python
implementations are free to represent with a temporary object.

This should catch the following kinds of bogus expressions (examples):

  x is 'foo'     x is not 'foo'
  x is "bar"     x is not "bar"
  x is 42        x is not 42
  x is -36       x is not -36

As originally proposed by Martin Geisler, amended with catching
negative numbers.

# filelog.py - file history class for mercurial
#
# Copyright 2005-2007 Matt Mackall <[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.

import revlog

class filelog(revlog.revlog):
    def __init__(self, opener, path):
        revlog.revlog.__init__(self, opener,
                        "/".join(("data", path + ".i")))

    def read(self, node):
        t = self.revision(node)
        if not t.startswith('\1\n'):
            return t
        s = t.index('\1\n', 2)
        return t[s + 2:]

    def _readmeta(self, node):
        t = self.revision(node)
        if not t.startswith('\1\n'):
            return {}
        s = t.index('\1\n', 2)
        mt = t[2:s]
        m = {}
        for l in mt.splitlines():
            k, v = l.split(": ", 1)
            m[k] = v
        return m

    def add(self, text, meta, transaction, link, p1=None, p2=None):
        if meta or text.startswith('\1\n'):
            mt = ["%s: %s\n" % (k, v) for k, v in sorted(meta.iteritems())]
            text = "\1\n%s\1\n%s" % ("".join(mt), text)
        return self.addrevision(text, transaction, link, p1, p2)

    def renamed(self, node):
        if self.parents(node)[0] != revlog.nullid:
            return False
        m = self._readmeta(node)
        if m and "copy" in m:
            return (m["copy"], revlog.bin(m["copyrev"]))
        return False

    def size(self, rev):
        """return the size of a given revision"""

        # for revisions with renames, we have to go the slow way
        node = self.node(rev)
        if self.renamed(node):
            return len(self.read(node))

        # XXX if self.read(node).startswith("\1\n"), this returns (size+4)
        return revlog.revlog.size(self, rev)

    def cmp(self, node, text):
        """compare text with a given file revision

        returns True if text is different than what is stored.
        """

        t = text
        if text.startswith('\1\n'):
            t = '\1\n\1\n' + text

        samehashes = not revlog.revlog.cmp(self, node, t)
        if samehashes:
            return False

        # renaming a file produces a different hash, even if the data
        # remains unchanged. Check if it's the case (slow):
        if self.renamed(node):
            t2 = self.read(node)
            return t2 != text

        return True