Qiskit / qiskit / 35882578663

88%

main: 88%

Build Type

push

github

Committed by web-flow

Commit Message

Add `unsafe` trait  for C/Rust ownership transfer (#17037)

* Add `unsafe` trait  for C/Rust ownership transfer

We currently have ad-hoc cross-function assumptions that all Rust-native
objects exposed directly to C are boxed and leaked.  This works fine in
principle, but will become more complicated when we introduce some types
that expose by `Arc`, which will happen as soon as we have
shared-ownership vtables for custom trait objects (e.g.
`CustomOperation`, `Pass` and `IR`).

Encapsulating this in a trait has two major benefits:

1. In existing code, we can abstract away the FFI boundary layer, making
   it much easier to ensure the `leak`/`steal` sides agree on the base
   type used.

2. In new code, we can use trait bounds on `ExposesOwnedPointers` to
   assert particular behaviour around the ownership shape.  This is
   anticipated to be used in the new pass-manager logic which needs to
   cast between `Box<dyn IR>` and `Box<T>` where `trait IR: Any`, and
   subsequently expose owned downcast objects to C.  This is only safe
   when the owner of the downcast type is exposed via `Box`, but the
   same PR will introduce objects that expose via `Arc`.

* Use leak in circuit-library functions

* Fix typos

Coverage Stats

73 of 77 new or added lines in 11 files covered. (94.81%)

6 existing lines in 3 files now uncovered.

118753 of 135166 relevant lines covered (87.86%)

971121.27 hits per line