phabricator: add the DiffChangeType and DiffFileType constants These are used in Phabricator change objects. There are more values but so far as I can tell we don't need them. Differential Revision: https://phab.mercurial-scm.org/D7041

help: adding a help category to narrow and remotefilelog commands Differential Revision: https://phab.mercurial-scm.org/D6998

rust-cpython: drop self.borrow_mut() in favor of PySharedRef wrapper

rust-cpython: drop self.leak_immutable() in favor of PySharedRef wrapper

rust-cpython: add safe wrapper representing shared data borrowed from PyObject PySharedRef is a tempoary wrapper around PySharedRefCell. It provides safe functions for each shared data. $shared_accessor implements a safe method to construct PySharedRefCell. This allows us to add more than once PySharedRefCell to a Python object.

rust-cpython: move $leaked struct out of macro It wasn't easy to hack the $leaked struct since errors in macro would generate lots of compile errors. Let's make it a plain struct so we can easily extend it. PyLeakedRef keeps a more generic PyObject instead of the $name struct since it no longer has to call any specific methods implemented by the $name class. $leaked parameter in py_shared_iterator!() is kept for future change.

rust-cpython: store leaked reference to PySharedState in $leaked struct I want to move it out of the macro, and allow multiple sharable objects per PyObject.

rust-cpython: mark PySharedState as Sync so &'PySharedState can be Send The goal is to store &'static PySharedState in $leaked struct, which allows us to move the $leaked struct out of the macro. Currently, it depends on inner.$data_member(py), which can't be generalized. PySharedState is Sync because any mutation or read operation is synchronized by the Python GIL, py: Python<'a>, which should guarantee that &'PySharedState can be sent to another thread.

rust-cpython: move borrow_mut() to PySharedRefCell PySharedRefCell() will host almost all py_shared public functions. This change is the first step. borrow_mut() can be safely implemented since PySharedRefCell knows its inner object is managed by its own py_shared_state.

rust-cpython: move py_shared_state to PySharedRefCell object The goal of this series is to encapsulate more "py_shared" thingy and reduce the size of the macro, which is hard to debug. Since py_shared_state manages the borrowing state of the object owned by PySharedRefCell, this change makes more sense. If a PyObject has more than one data to be leaked into Python world, each PySharedState should incref the parent PyObject, and keep track of the corresponding borrowing state.