atomictempfile: avoid infinite recursion in __del__(). The problem is that a programmer using atomictempfile directly can make an innocent everyday mistake -- not enough args to the constructor -- which escalates badly. You would expect a simple TypeError crash in that case, but you actually get an infinite recursion that is surprisingly difficult to kill: it happens between __del__() and __getattr__(), and Python does not handle infinite recursion from __del__() well. The fix is to not implement __getattr__(), but instead assign instance attributes for the methods we wish to delegate to the builtin file type: write() and fileno(). I've audited mercurial.* and hgext.* and found no users of atomictempfile using methods other than write() and rename(). I audited third-party extensions and found one (snap) passing an atomictempfile to util.fstat(), so I also threw in fileno(). The last time I submitted a similar patch, Matt proposed that we make atomictempfile a subclass of file instead of wrapping it. Rejected on grounds of unnecessary complexity: for one thing, it would make the Windows implementation of posixfile quite a bit more complex. It would have to become a subclass of file rather than a simple function -- but since it's written in C, this is non-obvious and non-trivial. Furthermore, there's nothing wrong with wrapping objects and delegating methods: it's a well-established pattern that works just fine in many cases. Subclassing is not the answer to all of life's problems.

import os
import glob
from mercurial.util import atomictempfile

# basic usage
def test1_simple():
    if os.path.exists('foo'):
        os.remove('foo')
    file = atomictempfile('foo')
    (dir, basename) = os.path.split(file._tempname)
    assert not os.path.isfile('foo')
    assert basename in glob.glob('.foo-*')

    file.write('argh\n')
    file.rename()

    assert os.path.isfile('foo')
    assert basename not in glob.glob('.foo-*')
    print 'OK'

# close() removes the temp file but does not make the write
# permanent -- essentially discards your work (WTF?!)
def test2_close():
    if os.path.exists('foo'):
        os.remove('foo')
    file = atomictempfile('foo')
    (dir, basename) = os.path.split(file._tempname)

    file.write('yo\n')
    file.close()

    assert not os.path.isfile('foo')
    assert basename not in os.listdir('.')
    print 'OK'

# if a programmer screws up and passes bad args to atomictempfile, they
# get a plain ordinary TypeError, not infinite recursion
def test3_oops():
    try:
        file = atomictempfile()
    except TypeError:
        print "OK"
    else:
        print "expected TypeError"

if __name__ == '__main__':
    test1_simple()
    test2_close()
    test3_oops()