rust-cpython: add stub wrapper that'll prevent leaked data from being mutated
In order to allow mutation of PySharedRefCell value while PyLeaked reference
exists, we need yet another "borrow" scope where mutation is prohibited.
try_borrow<'a> and try_borrow_mut<'a> defines the "borrow" scope <'a>. The
subsequent patches will implement leak counter based on this scope.
PyLeakedRef<T> and PyLeakedRefMut<T> could be unified to PyLeakedRef<&T>
and PyLeakedRef<&mut T> respectively, but I didn't do that since it seemed
a bit weird that deref_mut() would return a mutable reference to an immutable
reference.
rust-cpython: rename PyLeakedRef to PyLeaked
This series will make PyLeaked* behave more like a Python iterator, which
means mutation of the owner object will be allowed and the leaked reference
(i.e. the iterator) will be invalidated instead.
I'll add PyLeakedRef/PyLeakedRefMut structs which will represent a "borrowed"
state, and prevent the underlying value from being mutably borrowed while the
leaked reference is in use:
let shared = self.inner_shared(py);
let leaked = shared.leak_immutable();
{
let leaked_ref: PyLeakedRef<_> = leaked.borrow(py);
shared.borrow_mut(); // panics since the underlying value is borrowed
}
shared.borrow_mut(); // allowed
The relation between PyLeaked* structs is quite similar to RefCell/Ref/RefMut,
but the implementation can't be reused because the borrowing state will have
to be shared across objects having no lifetime relation.
PyLeaked isn't named as PyLeakedCell since it isn't actually a cell in that
leaked.borrow_mut() will require &mut self.
py3: don't use bytes with vars() or __dict__
Inspired by D7227. These were all the remaining instances I could
find.
Differential Revision: https://phab.mercurial-scm.org/D7230
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