diff mercurial/util.py @ 14007:d764463b433e

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.

--- a/mercurial/util.py	Mon Apr 25 18:42:31 2011 +0200
+++ b/mercurial/util.py	Sun Apr 24 19:25:10 2011 -0400
@@ -726,31 +726,31 @@
     name, making the changes visible.
     """
     def __init__(self, name, mode='w+b', createmode=None):
-        self.__name = name
-        self._fp = None
-        self.temp = mktempcopy(name, emptyok=('w' in mode),
-                               createmode=createmode)
-        self._fp = posixfile(self.temp, mode)
+        self.__name = name      # permanent name
+        self._tempname = mktempcopy(name, emptyok=('w' in mode),
+                                    createmode=createmode)
+        self._fp = posixfile(self._tempname, mode)
 
-    def __getattr__(self, name):
-        return getattr(self._fp, name)
+        # delegated methods
+        self.write = self._fp.write
+        self.fileno = self._fp.fileno
 
     def rename(self):
         if not self._fp.closed:
             self._fp.close()
-            rename(self.temp, localpath(self.__name))
+            rename(self._tempname, localpath(self.__name))
 
     def close(self):
-        if not self._fp:
-            return
         if not self._fp.closed:
             try:
-                os.unlink(self.temp)
-            except: pass
+                os.unlink(self._tempname)
+            except OSError:
+                pass
             self._fp.close()
 
     def __del__(self):
-        self.close()
+        if hasattr(self, '_fp'): # constructor actually did something
+            self.close()
 
 def makedirs(name, mode=None):
     """recursive directory creation with parent mode inheritance"""