rust: module policy with importrust...
rust: module policy with importrust
We introduce two rust+c module policies and a new
`policy.importrust()` that makes use of them.
This simple approach provides runtime switching of
implementations, which is crucial for the performance
measurements such as those Octobus does with ASV.
It can also be useful for bug analysis.
It also has the advantage of making conditionals in
Rust callers more uniform, in particular
abstracting over specifics like `demandimport`
At this point, the build stays unchanged, with the rust-cpython based
`rustext` module being built if HGWITHRUSTEXT=cpython.
More transparency for the callers, i.e., just using
`policy.importmod` would be a much longer term and riskier
effort for the following reasons:
1. It would require to define common module boundaries
for the three or four cases (pure, c, rust+ext, cffi) and that
is premature with the Rust extension currently under heavy
development in areas that are outside the scope of the C extensions.
2. It would imply internal API changes that are not currently wished,
as the case of ancestors demonstrates.
3. The lack of data or property-like attributes (tp_member
and tp_getset) in current `rust-cpython` makes it impossible to
achieve direct transparent replacement of pure Python classes by
Rust extension code, meaning that the caller sometimes has to be able
to make adjustments or provide additional wrapping.
