scmutil: use context managers for file handles Now that we dropped support for Python 2.4, we are able to use context managers. Let's replace the try..finally pattern in scmutil.py with context managers, which close files automatically when the context manager is exited. There should be no change in behavior with this patch. Why convert to context managers if nothing is broken? I'm working on closing file handles in background threads to improve performance on Windows. As part of this, I realized there could be some future issues if the background file closing code isn't designed with context managers in mind. So, I'd like to switch some code to context managers so I can design an API that works with context managers.

statichttprepo: implement __enter__ and __exit__ on httprangeheader httprangeheader behaves like a file object. Implement __enter__ and __exit__ so it can be used as a context manager, just like file objects.

osutil: implement __enter__ and __exit__ on posixfile So they can be used as context managers.

util: introduce ctxmanager, to avoid nested try/finally blocks This is similar in spirit to contextlib.nested in Python <= 2.6, but uses an extra level of indirection to avoid its inability to clean up if an __enter__ method raises an exception. Why add this mechanism? It greatly simplifies scoped resource management, and lets us eliminate several hundred lines of try/finally blocks. In many of these cases the "finally" is separated from the "try" by hundreds of lines of code, which makes the connection between resource acquisition and disposal difficult to follow. (The preferred mechanism would be the "multi-with" syntax of 2.7+, but Mercurial can't move to 2.7 for a while.) Intended use: >>> with ctxmanager(lambda: file('foo'), lambda: file('bar')) as c: >>> f1, f2 = c() This will open both foo and bar when c() is invoked, and will close both upon exit from the block. If the attempt to open bar raises an exception, the block will not be entered - but foo will still be closed.

hghave: support HGMODULEPOLICY for pure HGMODULEPOLICY was introduced in 4374d819ccd5

merge with stable

tests: extend check-commit self-tests This now contains both positive and negative tests for almost all the check-commit rules.